Ross A Pinder
email: ross.pinder@qut.edu.au

Ian Renshaw

Keith Davids

Information-movement coupling in developing cricketers under changing ecological practice constraints

Keywords: PsychINFO classification: 2330 Dynamic interceptive actions, ecological constraints, information-movement coupling, movement coordination, skill development

Changing informational constraints of practice, such as when using ball projection machines, has been shown to significantly affect movement coordination of skilled cricketers.

To date, there has been no similar research on movement responses of developing batters, an important issue since ball projection machines are used heavily in cricket development programmes. Timing and coordination of young cricketers (n = 12, age = 15.6 ± 0.7 years) were analyzed during the forward defensive and forward drive strokes when facing a bowling machine and bowler (both with a delivery velocity of 28.14 ± 0.56 m s -1 ). Significant group performance differences were observed between the practice task constraints, with earlier initiation of the backswing, front foot movement, downswing and front foot placement when facing the bowler compared to the bowling machine. Peak height of the backswing was higher when facing the bowler, along with a significantly larger step length. Altering the informational constraints of practice caused major changes to the information-movement couplings of developing cricketers. Data from this study were interpreted to emanate from differences in available specifying variables under the distinct practice task constraints.

Considered with previous findings, results confirmed the need to ensure representative batting task constraints in practice, cautioning against an over-reliance on ball projection machines in cricket development programmes.

Introduction

Batting in cricket is a quintessential example of a dynamic interceptive action in sport, and an ideal vehicle for studying interactions between perception and action [START_REF] Stretch | A review of batting in men's cricket[END_REF]. Ecological psychologists have attempted to describe the control mechanisms involved in regulating movement to satisfy specific task constraints in interceptive actions (e.g., [START_REF] Davids | Movement models from sport reveal fundamental insights into the coordination process[END_REF][START_REF] Montagne | Perspective control in sport[END_REF][START_REF] Montagne | A perception-action coupling type of control in long jumping[END_REF]. James Gibson's theory of direct perception proposes how movement is shaped using information constantly available in the surrounding environment (e.g., [START_REF] Gibson | The ecological approach to visual perception[END_REF]. It has become clear how performers can exploit information to regulate action from movements of other players (see [START_REF] Renshaw | Cricket bowling deliveries and the discrimination ability of professional and amateur batters[END_REF][START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF] or moving objects (see [START_REF] Regan | Visual factors in hitting and catching[END_REF][START_REF] Williams | Visual perception and action in Sport[END_REF].

From this viewpoint the process of practice involves becoming better attuned to specifying variables available in different performance contexts [START_REF] Davids | Dynamics of skill Acquisition: A constraints-led approach[END_REF], and calibrating movement responses to those variables. Since the perception of environmental information is specific and constrained by each individual performance setting, it is important that learners improve their capacity to detect specifying from nonspecifying variables (see [START_REF] Jacobs | On the paradox of learning and realism[END_REF]; see also [START_REF] Dicks | Ecological psychology and task representativeness: Implications for the design of perceptual-motor training programmes in sport[END_REF].

In particular performance contexts, specifying variables provide more functional information to constrain performers' actions than non-specifying variables [START_REF] Araújo | Ecological validity, representative design and correspondence between experimental task constraints and behavioural settings[END_REF].

Learners pick up specifying variables to support action in specific performance environments through the education of attention, or perceptual attunement [START_REF] Jacobs | On the paradox of learning and realism[END_REF][START_REF] Fajen | Information, affordances and the control of action in sport[END_REF]. [START_REF] Jacobs | On the paradox of learning and realism[END_REF] suggested that the two stages of constructing information-movement couplings are: a) the education of attention to key informational sources, and b) the fine tuning of movements to a "critical information source" [START_REF] Davids | Movement models from sport reveal fundamental insights into the coordination process[END_REF]. Clearly, the removal of critical information sources at specific developmental stages could impede learning, resulting in unintended changes to coordination of actions. Therefore, while practice task constraints might contain some specifying variables which are available to support learners' actions during practice tasks (i.e., batting against a bowling machine), learners should also be provided with opportunities to pick up specifying variables available to support performance in competitive contexts. It is important that practice task constraints should not lead learners to pick up non-specifying variables for competitive performance environments.

Batting against a bowling machine affords learners to become perceptually attuned to ball flight information during practice. Clearly, while specifying variables may be available from ball flight characteristics when batting against bowling machines, these variables may be non-specifying in competitive performance environments due to the time constraints on action. In cricket batting the time constraints are often severe with ball velocities typically ranging from 19-40 m s -1 [START_REF] Bartlett | The science and medicine of cricket: An overview and update[END_REF]. Thus, when facing medium to fast deliveries from a bowler, batters have to decide on an appropriate shot and initiate it within about 0.7 s [START_REF] Mcleod | Timing accuracy and decision time in high speed ball games[END_REF]. These findings highlight that, due to ball velocities generated by bowlers, batters need to attune to specifying variables that exist in bowlers' actions prior to ball release which are available in competitive performance environments [START_REF] Abernethy | Advanced cue utilisation by skilled cricket batsmen[END_REF]Weissensteiner, Abernethy, Farrow, & Müller, in press).

Specifying variables for action need to be constantly available for perception in the practice and performance environment [START_REF] Dicks | Ecological psychology and task representativeness: Implications for the design of perceptual-motor training programmes in sport[END_REF]. Practice task constraints that provide specifying variables for pick up by learners during competitive performance can be considered to be high in representative task design (see [START_REF] Araújo | Ecological validity, representative design and correspondence between experimental task constraints and behavioural settings[END_REF]. Changing the informational constraints in practice environments might lead to the design of less representative practice tasks by altering availability of specifying variables, resulting in changes to a learner's acquisition of functional movement patterns [START_REF] Beek | Expert performance in sport: Views from the joint perspectives of ecological psychology and dynamical systems theory[END_REF]. The pick-up of non-specifying variables might result in performance success under specific task constraints, but perceivers may become too dependent on these variables even when performance task constraints change [START_REF] Beek | Expert performance in sport: Views from the joint perspectives of ecological psychology and dynamical systems theory[END_REF]. Dependent on the specific performance context, this unintended reliance may not be a problem. As Withagen (2004, p. 242) highlighted "a human being who intercepts 70% of the balls thrown at him or her because she exploits a non-specifying, moderately informative variable will not die because of it". However, [START_REF] Withagen | The pickup of nonspecifying variables does not entail indirect perception[END_REF] noted the significance of becoming better attuned to specifying variables by arguing that "the animals that do survive are the ones that do better than their competitors". In sports performance, as levels of competition increase, those athletes that continue to rely on non-specifying variables will eventually become less competitive than their counterparts who have learned to pick up specifying variables to regulate actions.

The use of ball projection machines

Based on these ideas, an important question is: How does altering the informational constraints in specific practice environments affect the coordination of dynamic interceptive actions, such as cricket batting? Some previous work has demonstrated how ball projection machines (e.g., cricket bowling machines) influence the movement patterns of skilled cricketers [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF]. Bowling machines in cricket are considered to be useful equipment to allow performers to practice batting movements away from the performance environment. They are considered to provide consistent, accurate and specific conditions for practice (e.g., bowling pace or length) to enable batters to acquire individual shot types. One clear advantage of bowling machines is that they alleviate the workload required of developing bowlers, with overuse injuries being a major concern [START_REF] Dennis | Is bowling workload a risk factor for injury to Australian junior cricket fast bowlers[END_REF]. Nevertheless, a key issue is whether practising with a bowling machine may actually impede the pick-up of specifying information variables from the performance environment for batting [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF].

The role of anticipation is firmly established as a key component of expert performance in dynamic fast ball sports, with the use of pre-ball flight information viewed as essential to skilled cricket batting (Müller & Abernethy, 2006). Research in cricket batting has demonstrated a relationship between skill level and anticipation, consistent with those seen in other sports [START_REF] Müller | How do world-class cricket batsmen anticipate a bowler's intention[END_REF]. Current evidence from expertise research suggests that only skilled batters have an ability to utilize information from the prerelease actions of a bowler (Weissensteiner et al., in press). They can gain an advantage, under severe time constraints, by picking up information from limb and body orientations of the bowler during the run-up, bound and moment of release [START_REF] Davids | Movement models from sport reveal fundamental insights into the coordination process[END_REF]. Skilled performers use this information to predict 'line and length' of deliveries from both fast (e.g., [START_REF] Abernethy | Advanced cue utilisation by skilled cricket batsmen[END_REF]McRobert & Taylor, 2005;[START_REF] Penrose | Decision making and advanced cue utilisation by cricket batsmen[END_REF] and slow bowlers (e.g., [START_REF] Renshaw | Cricket bowling deliveries and the discrimination ability of professional and amateur batters[END_REF], in addition to specifying the point of ball release [START_REF] Gibson | Batting stroke timing with a bowler and a bowling machine: A case study[END_REF]. In contrast, less-skilled players appear to gain little information from pre-release sources, relying primarily on ball flight characteristics [START_REF] Renshaw | Cricket bowling deliveries and the discrimination ability of professional and amateur batters[END_REF]. A number of reasons have been proposed to explain why developmental level performers may not be able to pick up information from a bowler's actions. First, it is felt that the lower bowling speeds faced by batsmen in junior competition may not necessarily require them to anticipate for success. This is because the time from ball release to bat contact is long enough to make the need to attune to pre-flight information redundant. A second related suggestion is that anticipation makes a less significant contribution to successful performance in developing athletes, compared to factors such as relative age, strength, and maturity in determining success in junior cricket batting (Weissensteiner et al., in press).

However, recently van der Kamp, Rivas, [START_REF] Van Der Kamp | Ventral and dorsal contributions in visual anticipation in fast ball sports[END_REF] have criticized the occlusion paradigm on which these assumptions are based. Typically, occlusion studies have tended to examine perception in isolation from action, suggesting that the actual performance of experts in these tests may not be truly 'expert'. For example, these authors collated results from a number of key occlusion studies noting significant spatial errors in predicting landing location of an object even under full vision conditions for both novices and experts (e.g., in badminton 1.4-1.8 m, Abernethy & Russell, 1987;in cricket wicket-keeping 45-55 inches, Houlston & Lowes, 1993;in soccer, 3.3 m, McMorris & Colenso, 1996;in squash, 0.6-1.8 m, Abernethy, Gill, Parks, & Packer, 2001[START_REF] Van Der Kamp | Ventral and dorsal contributions in visual anticipation in fast ball sports[END_REF]. Reevaluation of these data suggested that the occlusion paradigm has significant limitations and highlights the need to analyze anticipation in tasks such as cricket batting by examining perception and action in unison.

Adaptations to practice constraints in cricket batting

The most common stroke in cricket is the forward defensive which also forms the basis of the drive (Stretch, Buys, Dutoit, & Viljeon, 1998), and consequently, it is often the starting point for many coaches when teaching novices. A previous two-dimensional analysis of the forward defensive stroke in cricket batting [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF] examined the movement coordination and timing of four 'high intermediate' standard batsmen during the forward defensive stroke, against a medium pace bowler and bowling machine (26.76 m s -1 ). Significant adaptations were observed under the two different informational constraints and central to these changes was the organization of the two phases of bat swing. The backswing in the bowling machine condition varied greatly, but was coupled to ball release (0.02 ± 0.10 s after ball release), whereas against the bowler, initiation of the backswing occurred later (0.12 ± 0.04 s). Similarly, initiation and speed of the downswing occurred earlier and more quickly when facing the bowling machine (0.32 ± 0.04 s; bowler: 0.41 ± 0.03 s), resulting in different ratios of backswing-downswing between conditions.

The findings of [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF] are somewhat different to other data on cricket batting by [START_REF] Gibson | Batting stroke timing with a bowler and a bowling machine: A case study[END_REF]. Utilizing a case study approach, [START_REF] Gibson | Batting stroke timing with a bowler and a bowling machine: A case study[END_REF] observed how one international cricketer initiated the backswing before ball release, with front foot movement occurring much earlier when facing the bowling machine compared with the bowler. This observation was rather surprising, and could be attributed to the experimental task constraints (i.e., the batsman knew in advance the landing position of the ball) or the previous experience of the participant facing the bowling machine. [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF] observed no differences in front foot initiation time under both practice task constraints, noting that it was more closely coupled with the backswing when facing the bowler (r = .88; bowling machine, r = .65), and occurred after ball release in both conditions, Additionally, it was observed that a higher peak bat height was reached against the bowler (1.56 ± 0.20 m vs. 1.72 ± 0.10 m), as well as a longer front foot stride (0.55 ± 0.07 m vs. 0.59 ± 0.06).

Differences in co-ordination patterns observed in these two studies when facing both the ball machine and bowlers highlighted the importance of ecological task constraints.

Practice under the two distinctive ecological task constraints led to variations in functional movement solutions which might be attributed to differences in the practice task constraints (i.e., not knowing in advance versus knowing in advance where the ball would land) as well as to the absence of advanced information from the bowler. To explain their findings, [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF] proposed that the previous experiences of these relatively skilled batsman against a bowling machine might have led participants to rely on non-specifying variables provided by the machine [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF]. This strategy may have been employed by the skilled participants because of the removal of important information sources from the bowler. These explanations signalled the need for further empirical research to examine the movement responses of developing players under similar practice task constraints. This is a significant practical issue because bowling machines are used extensively in the development of young cricketers. In this regard, an important point to note is that ball projection machines prevent the use of advanced information sources available prior to ball release (e.g., the run-up, bound and delivery stride of a bowler's approach).

Currently it is not clear whether the pick up of kinematic and early ball flight information can be utilized by children.

Therefore, the aim of this study was to extend understanding of informationmovement coupling in cricket batting by assessing the timing and kinematic responses of developing batters under two practice task constraints, when performing an attacking (forward drive) and defensive (forward defence) stroke. It was anticipated that less-skilled individuals would demonstrate differences in the temporal and spatial movement responses, leading to shorter strides and lower peak bat heights when facing the bowling machine. It was also predicted that observation of a bowlers' movements might afford advanced information sources that allowed developing players to initiate movements earlier than against a bowling machine, providing them with more time to organize their responses.

Method

Participants

Eight right-handed and four left-handed junior batsmen (n = 12, age = 15.6 ± 0.7 years), with 6.6 ± 0.6 years playing experience, provided informed consent and took part in the study. Ethical clearance was completed through a local university ethics committee. The batters were adjudged by skill acquisition specialists (who were also qualified Level II ECB cricket coaches) to be representative of individuals at the control stage in [START_REF] Newell | Coordination, control and skill[END_REF] model of skill acquisition, and were considered to have received similar amounts of taskspecific practice. Using this assessment, participants were classified as "less-skilled" than those studied in previous work (see [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF]. Four left-arm bowlers (age = 15.0 ± 0.8 years) with similar, representative actions for medium-fast bowlers of the same developmental status were asked to participate in the study.

Apparatus and experimental set-up

The study took place at an indoor cricket school which was the regular practice facility of the participants. Mean bowling speed (28.14 ± 0.56 m s -1 ) was assessed for the four bowlers using a sports radar gun (Stalker Radar, Texas), and mean height of release (2.06 ± 0.07 m) was calculated. This information was next used to set up a bowling machine (Jugs Inc., Tualatin, Oregon) to mirror the release height and bowling speeds of the bowlers. All batters had some limited experience of practising with the bowling machine as part of their training programme. The machine was operated by an experienced Australian level 3 coach.

The same balls ("Oz" bowling machine balls) were used to maintain consistency of bounce across conditions. A video camera (Sony HVR-V1P) was positioned 10 m from the plane of action perpendicular to the batting crease following standard set-up procedure (see [START_REF] Bartlett | Introduction to sports biomechanics: Analysing human movement patterns[END_REF]. A second synchronized camera was used to simultaneously capture the point of release from the bowler or the emergence of the ball from the bowling machine. Both cameras were set to a frame rate of 100 Hz, and a shutter speed of 1/300 s. The image of the batters was maximized in the field of view in front of a plain uncluttered background, and calibration was attained using horizontal and vertical references (metre rules). Participants wore full protective equipment, including batting helmets. Markers were placed on specific body locations before filming as in previous research [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF], allowing for comparisons. Contrasting markers were placed on the foot (proximal phalanx of the big toe), ankle (malleolus), knee (estimated axis of rotation), hip (greater trochanter), shoulder (greater tubercle of the humerus), elbow (lateral epicondyle of the humerus), and wrist (head of the ulna). For the knee and ankle, markers were placed on the pads covering the joint/location, and remained in the same places between trials. Additionally, one marker was placed on the helmet and two on the edge of the bat facing the camera. This marker set was chosen to replicate previous research and enable recording of segment angles of the knee and elbows, in addition to initiation timings at key phases, bat heights, and step lengths [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF].

Data collection procedure

Participants faced the bowlers and bowling machine in a counterbalanced design to control for order effects, and none had previously faced any of the four bowlers but had faced bowlers of similar speed and ability in practice. Bowlers were asked to bowl as they would in a game, ensuring that the batters were unsure of the upcoming delivery due to variations in length. The length was equally varied in the bowling machine condition without the batters being aware of subtle changes to the angle of the machine, ensuring similarity between both conditions. This was important, as previous research has described how bowling machines may allow for more certainty, therefore enabling a batter to initiate front foot movement earlier than against bowlers [START_REF] Gibson | Batting stroke timing with a bowler and a bowling machine: A case study[END_REF]. Batters, therefore, were required to play both forward and back with little certainty over upcoming deliveries. A series of lines on the floor in front of the batters enabled consistency of shots chosen for analysis. Due to individual constraints (e.g., height and segment lengths), coaches' assessments were used to determine the correct lengths (bounce point) for the defence and drive of individual batsmen. These areas in line with the stumps, measured 0.23 m in width and 1 m in length, and were used to determine which shots constituted a forward defence and a forward drive in both the bowler and bowling machine conditions. Bowlers ensured that the batters were ready before beginning their approach, and a standard "feeding" routine (see [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF] was used in the bowling machine to enable consistency and safety.

Data analysis

A total of 288 shots were used for temporal analysis, 72 forward defensive strokes and 72 forward drives in both the bowler and machine conditions (six for each batsman in each condition), based on the explained criteria. The forward defensive shots were used for kinematic analysis, to provide comparisons with previous research. Data were analyzed using SIMI motion software, with key phases selected for analysis. Means and standard deviations of the relative timing between phases were calculated. These data included the point of release, backswing initiation, initiation of front foot movement, initiation of downswing, front foot placement, and at the ball's impact with the bat. As in previous research [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF], the protocol employed was to consider the first video frame of a specific event, for example, the initiation of the front foot movement to show when the foot was first lifted off the ground. Parametric assumptions were met, and each dependent variable (event initiation, bat height, step length, or angle) was compared between the bowler and machine condition using paired-samples t-tests, for both defence and drive shots. Additionally, effect size (r) was calculated to observe if significant effects were substantive, and to judge the relative magnitude and importance of each dependent variable [START_REF] Mullineaux | Research design and statistics in biomechanics and motor control[END_REF]. Finally, Pearson's correlation coefficient was used to assess the relationship between backswing initiation and front foot movement.

Results

****Insert Fig. 1 about here**** 3.1. Temporal and spatial differences Significant differences were observed in the timing and initiation of key phases of the forward defence and forward drive strokes (see Fig. 1). Results are represented in seconds before the impact of bat and ball, with ball release in both conditions occurring 0.64 s before impact. Initiation of the backswing occurred earlier against the bowler than against the bowling machine for the defence (B: 0.58 ± 0.07 s; BM: 0.49 ± 0.08 s, t(65) = 8.27, p < .001, r = .72) and the drive (B: 0.58 ± 0.07s vs. BM: 0.50 ± 0.07s, t(65) = 8.82, p < .001, r = .74).

Similarly, the developing batters initiated the downswing of the bat earlier when facing bowlers compared with the bowling machine, for both defence (B: 0.22 ± 0.06 s; BM: 0.20 ± 0.05 s, t(71) = 2.59, p < .05, r = .29) and drive strokes (B: 0.19 ± 0.05 s; BM: 0.17 ± 0.04 s, t(71) = 3.38, p < .005, r = .37) , t(71) = 3.38, p < .005, r = .37). Peak height of the backswing was measured (see Fig. 2), with batters swinging higher against the bowler during the defence (B: 1.34 ± 0.29 m; BM: 1.27 ± 0.31 m, t(65) = 2.48, p < .05, r = .29) and drive (B: 1.52 ± 0.25 m: BM: 1.41 ± 0.26 m, t(65) = -4.71, p < .001, r = .50). These differences amounted to slightly longer backswings when facing the bowler (defence: 0.36 s; drive: 0.39 s) compared with the bowling machine (defence: 0.29 s; drive: 0.33 s). Initiation of the downswing occurred earlier and lasted longer against the bowler compared to the bowling machine. This combination of reduced bat height and shorter backswing and downswing periods when facing the bowling machine resulted in very little difference in the ratio of backswingdownswing timings (B -defence: 63-37%, drive: 69-31%; BM -defence: 61-39%, drive: 67-33%).

Front foot movement initiation occurred earlier against the bowler compared with the bowling machine for the forward defence (B: 0.47 ± 0.11 s; BM: 0.39 ± 0.09 s, t(71) = 7.35, p < .001, r = .66) and the forward drive (B: 0.48 ± 0.08 s; BM: 0.41 ± 0.08 s, t(71) = 10.22, p < .001, r = .77). Correspondingly, front foot placement occurred significantly earlier in the bowler condition, for both defence (B: 0.10 ± 0.05 s; BM: 0.06 ± 0.04 s, t(71) = 4.58, p < .001, r = .48) and drive strokes (B: 0.09 ± 0.03 s; BM: 0.05 ± 0.03 s, t(71) = 8.00, p < .001, r = .69). These timings resulted in a shorter total time to complete the front foot stride when facing the bowling machine (defence: 0.33 s; drive: 0.36 s) compared to a bowler (defence: 0.37 s; drive: 0.39). Additionally, we measured the length of the stride at front foot placement (see Fig. 3). Significant differences were found between the bowler and bowling machine conditions, with larger strides when facing a bowler for the forward defence (B: 0.76 ± 0.17 m; BM: 0.71 ± 0.16 m, t(65) = 2.14, p < .05, r = .25) and forward drive (B: 0.89 ± 0.13 m; BM: 0.84 ± 0.15, t(65) = 3.80, p < .001, r = .41). ****Insert Fig. 2 and Fig. 3 about here****

Backswing and front foot movement coupling

The relationships between the initiation of the backswing and the front foot movement were marginally stronger in the bowling machine condition for both the defence (B: r = .38, p < .01; BM: r = .47, p < .01) and the drive (B: r = .42, p < .01; BM: r = .48, p < .01). It is clear that despite the changing ecological constraints and delayed initiations, developing players were able to coordinate the initial movements of the upper and lower extremities to a similar degree. 1 about here****

****Insert Table

Kinematic differences

Knee and elbow angles were recorded throughout the key phases of the forward defensive stroke (see Table 1), with significant changes observed corresponding to the temporal findings previously described. Changes in knee and elbow joint segment angles demonstrated differences in backswing-downswing coordination and movement on the front foot. Smaller angles of the front (r = .40) and back elbows (r = .37) at the point of front foot initiation when facing the bowlers corresponded to the earlier initiation of the backswing.

Similarly, at the initiation of the downswing, smaller elbow angles (front: r = .48; back: r = .42) were observed due to higher bat swings in the bowler condition. At front foot placement, front and back elbow angles were significantly larger in the bowling machine condition (with moderate effects), demonstrating that the arms were more extended and further forward.

Additionally, a key difference at impact was the larger knee angle during the bowling machine condition, suggesting players stood in a more upright position (possibly as a result of the shorter stride), as observed in Fig. 4. ****Insert Fig. 4 about here****

Individual analysis

To support the group analysis, we checked the performance trends in individual batsmen to ascertain whether group results were consistent across all participants. Bat heights and step lengths were highly consistent throughout the group, with 90% of individual findings matching those observed in the group analysis. The few instances where they did not follow the trend were characterized by only small differences (0.03-0.09 m) and larger variances in the bowling machine condition. Further analysis of the temporal responses demonstrated almost complete consistency across all 12 participants; with only one batter showing a tendency to initiate later movement (i.e., downswing and front foot placement) against the bowling machine when playing a forward defence.

Discussion

This study sought to manipulate practice task constraints to evaluate effects on movement control and coordination of developing cricket batters. The aim was to investigate whether the information-movement couplings used during batting by developing players changed when facing a bowler and bowling machine. Based on previous work, if the developing players were not attuned to advanced information sources from bowlers, then relatively smaller changes in movement responses between the conditions would be expected, compared with data from more skilled batters [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF].

Data showed that batting against a medium-fast bowler and a bowling machine produced significant adaptations to movement timing and coordination of both a defensive and an attacking stroke. The major differences observed appear to have been a result of the delayed initiation of the backswing and front foot movements during the bowling machine condition. Under bowling machine and bowler conditions developing players demonstrated a similar level of coupling between these two components of batting actions. However, when batting against a machine the developing players did not initiate these sub-components at the same time, compared to when they batted against a bowler. At this stage of learning it seems that batters have the required coordinative relationships between movement components, but

are not yet able to finely adapt them in different performance contexts, showing less independence between the upper and lower extremities. Initiation of the backswing against the bowler occurred after ball release (drive: 0.06 s; defence: 0.06 s), and significantly later against the bowling machine (drive: 0.15 s; defence: 0.14 s). These data contradicted outcomes of studies from more skilled batsmen [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF]. Although against the bowler backswing initiation occurred after ball release (0.12 s), when skilled batters faced the bowling machine backswing initiation occurred around the point of ball release, suggesting that they had picked up non-specifying variables to regulate their batting actions. It was concluded that the batters may have used other information sources specific to practice task constraints involving use of ball projection machines to couple and initiate movement responses. This is a key difference between skilled and developing batters, which suggests that extended experience of practising against a bowling machine resulted in a major shift in information-movement coupling, as players searched for and relied on a non-specifying variable in a competitive performance environment.

Previous research has highlighted the importance of the organization of the twophases of bat swing, with skilled players being able to alter the ratio of backswingdownswing in the forward defensive stroke across different ecological task constraints [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF]. For developing batsmen there were practically no differences between the ratios, with both shorter backswings and downswings when facing a bowling machine. Batters controlled this bi-phase action by significantly limiting the height of the bat swing when facing the bowling machine when attacking and defending. Due to the reduction in the advanced information afforded by the bowling machine condition, developing batters tended to rely on a prospective control strategy during ball flight to adapt movement timings and responses. This strategy resulted in a reduction in the height of the backswing, to enable successful task performance. Similarly, due to the late initiation of the front foot movement, the step length during the bowling machine condition was significantly shorter. As [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF] observed this movement strategy resulted in the player being further away from the pitch of the delivery and more susceptible to late swing or deviation [START_REF] Woolmer | Bob Woolmer's art and science of cricket[END_REF]. Analysis of the position of the head over the front foot in each condition revealed no significant differences between practice task constraints due to wide variations. However, it was evident that the batters tended to play in a more upright stance against the machine. Observation of larger elbow and front knee angles at impact complimented the qualitative video and coaches' analysis, suggesting that the added temporal constraint when batting against the bowling machine resulted in significant spatial changes to the movement pattern. Under this condition batters played further away from their body (e.g., forward of the front pad, see Fig. 4), suggesting that they were attempting to reduce the distance between the bat and bounce point. As a result of these changes, there was a reduction in shot quality and batsmen were evidently not as balanced during the impact and follow-through.

Temporal and kinematic differences observed for the defensive and drive shots in the two different ecological conditions raised some issues about the perceptual abilities of nonexpert batters. Previous research in fast ball sports using visual occlusion paradigms has shown that only experts are able to pick up pre-ball flight information from opponents' movement patterns (e.g., Müller & Abernethy, 2006;Müller et al., 2006). However, findings from our study suggested that batters at lower levels of skill development may be able to use the bowler's movements to guide their actions. First, the different backswing heights for the two shots suggested that batters were able to distinguish between a ball of good length that afforded a defensive shot, and a half volley which could be driven, very early in the delivery.

Interestingly, when facing the bowling machine, although initiation began later due to the need to assimilate ball flight information, similar differences were observed in backswing height for both shots, although they were evidently shorter due to their later initiation. This interpretation is tentative, given that in temporal terms bat swing times were similar in the two conditions, but were longer in the bowler condition. This finding could be interpreted as batters adjusting their movements in a prospective manner and taking the bat higher as a result of picking up more ball flight information. Second, given that batters had no certainty over the length of the upcoming delivery, their foot movements could be interpreted as identifying the point at which they made a decision about the length of the delivery (whether to advance forward for a forward defence or forward drive or to move backwards due to a shorter pitched delivery). In the bowler condition initiation took place 0.06 s after ball release. It is noteworthy that laboratory-based tasks on young football players have demonstrated eye-foot reaction times that were much larger than this value (e.g., 0.3-0.4 s, see [START_REF] Montes-Mico | Eye-hand and eye-foot visual reaction times of young soccer players[END_REF], and visual reaction times in fast ball sports are considered to be in the region of 0.2 s (see [START_REF] Mcleod | Visual reaction time and high speed ball games[END_REF]. These findings could be interpreted to suggest that the batters made up their minds on the eventual bounce point of the ball at a point in time either prior to or very close to ball release, proposing that non-experts could use information from a bowler's actions to guide movement. Conversely, the constraints of batting against the bowling machine meant that batters had to delay the initiation of the front foot movement until early ball flight information could be assimilated to determine ball length.

Changing the ecological constraints of practice and making it more representative in task design, by enhancing the availability of specific advanced information from a bowler's movements, resulted in major changes to the information-movement couplings of the batters.

The results of this study are comparable with data reported by [START_REF] Renshaw | Changing ecological constraints of practice alters coordination of dynamic interceptive actions[END_REF] and help to extend our understanding of how movements are coupled to information in interceptive actions. The findings support previous suggestions of avoiding an over-reliance on bowling machines in practice at a developmental stage. Less-skilled batsmen displayed stable patterns of movement coordination, exemplified by the maintenance of the backswing and front foot movement coupling in both conditions. It is important at the control stage of learning that batsmen are able to identify the critical information sources and continue the process of perceptual attunement with specifying variables [START_REF] Jacobs | On the paradox of learning and realism[END_REF][START_REF] Dicks | Ecological psychology and task representativeness: Implications for the design of perceptual-motor training programmes in sport[END_REF]. This practice strategy requires specifying variables to be available for pick up by learners at all times. Batting against a bowler permits established coordination patterns to be calibrated and finely tuned by the pick-up of specifying variables. This calibration process relies on the availability of representative task designs that accurately reflect performance environments [START_REF] Dicks | Ecological psychology and task representativeness: Implications for the design of perceptual-motor training programmes in sport[END_REF]. The results of the present study are aligned with proposals of [START_REF] Beek | Expert performance in sport: Views from the joint perspectives of ecological psychology and dynamical systems theory[END_REF], highlighting the importance of specificity of practice task constraints, particularly during specific developmental stages. The use of a bowling machine resulted in batters converging on nonspecifying variables, delaying the development and attunement to specifying variables [START_REF] Araújo | Ecological validity, representative design and correspondence between experimental task constraints and behavioural settings[END_REF].

Our results suggested that use of a bowling machine not only changes available informational variables up until ball release [START_REF] Bartlett | The science and medicine of cricket: An overview and update[END_REF], but also changes the nature of the delivery after ball release. We are not suggesting the complete removal of bowling machines from practice. Further research is needed to develop innovative methods to allow batters to undertake the volume of task specific practice required to develop perceptual skills (Weissensteiner et al., in press), while maintaining representative task designs. Batting against real bowlers supports the detection of specifying variables. However, as bowlers are limited to specific workloads (see Stretch & Gray, 1998, cited in Woolmer et al., 2008) research into representative video-based simulations may be more beneficial than using bowling machines. Research is required to assess the information-movement couplings established when using video-based simulation training. A representative video-based training system would allow batsmen to practice in a safe environment, and could be used to speed up the development of perceptual and movement capabilities of players against fast bowling. We have demonstrated that due to changes in the information movement couplings, developing players are more attuned to advanced information sources than previously believed. Future research is required to discover the exact sources of information that can be picked up to regulate actions at different stages of the skill pathway in cricket batting. Step length (m) Bowler Bowling Machine

Release

Fig. 1 .

 1 Fig. 1. Differences in the timing of key phases of the forward defensive and forward drive strokes in bowler and bowling machine conditions (BS: Initiation of backswing; FFM: Initiation of front foot movement; DS: Initiation of downswing; FFP: Front foot placement).

Fig. 2 .

 2 Fig. 2. Peak height of the backswing for batsmen (n = 12) facing a bowler and bowling machine for the forward defence and forward drive.

Fig. 3 .

 3 Fig. 3. Step lengths at front foot placement of the forward drive and forward defence, with batsman (n = 12) facing a bowler and a bowling machine.

Table 1 .

 1 Joint segment angles (degrees) of the forward defensive stroke in both bowler and bowling machine conditions (means ± s).

		Front Elbow	Back Elbow	Front Knee
	Backswing initiation
	Bowler	135 ± 20	108 ± 20	166 ± 8
	Bowling Machine	140 ± 14	113 ± 18	167 ± 7
		p < .05	p < .001
		r	r	r
		= .36	= .47	= .03
	Front foot initiation
	Bowler	124 ± 23	92 ± 23	156 ± 6
	Bowling Machine	130 ± 15	98 ± 21	160 ± 6
		p < .001	p < .05	p < .001
		r	r	r
		= .40	= .37	= .44
	Downswing initiation
	Bowler	110 ± 13	71 ± 13	163 ± 9
	Bowling Machine	117 ± 13	75 ± 15	161 ± 7
		p < .001	p < .001
		r	r	r
		= .48	= .42	= .19
	Front foot placement
	Bowler	110 ± 18	87 ± 20	166 ± 8
	Bowling Machine	120 ± 19	94 ± 18	168 ± 6
		p < .001	p < .05
		r	r	r
		= .46	= .29	= .20
	Impact
	Bowler	127 ± 20	112 ± 20	163 ± 10
	Bowling Machine	131 ± 23	120 ± 18	167 ± 7
			p < .05	p < .05
		r	r	r
		= .22	= .37	= .25

Note:

effect size, r; .10 = small effect, .30 = moderate effect, .50 = large effect

Fig. 4. Video stills highlighting the major differences in the batters' responses to a bowling machine (left) and a bowler (right).


Markus Janczyk
email: janczyk@fk14.uni-dortmund.de

Stefanie Skirde

Matthias Weigelt

Wilfried Kunde

Visual and tactile action effects determine bimanual coordination performance

Keywords: Motor coordination, intention, reaction time PsycINFO classification: 2300 Human Experimental Psychology, 2330 Motor Processes

Effect-based models of motor control assign a crucial role to anticipated perceptual feedback in action planning. Two experiments were conducted to test the validity of this proposal for discrete bimanual key press responses. The results revealed that the normally observed performance advantage for the preparation of two responses with homologous rather than non-homologous fingers becomes inverted when homologous fingers produce non-identical visual effects, and non-homologous fingers produce identical visual effects. In Experiment 2 the finger homology effect was strongly reduced when homologous fingers produced nonidentical tactile feedback. The results show that representations of to-be-produced visual and tactile action effects both contribute to action planning, though possibly to a varying degree.

Implications of these results for effect-based models of motor control are considered.

Introduction

The human body is to a large extent characterized by symmetry. This applies to the outer appearance as reflected in the existence of two pairs of limbs, fingers, or toes, but also to the anatomical and functional symmetry of neuronal control structures in the central nervous system. To master many of our everyday tasks, such as when lifting a heavy object, tying a tie, playing piano, or rowing a boat, these body parts have to be used in a coordinated fashion.

Experimental research on bimanual coordination has often demonstrated a bias towards symmetric movements or movements involving similar parameter values for amplitude or direction (e.g., [START_REF] Cohen | Synchronous bimanual movements performed by homologous and nonhomologous muscles[END_REF][START_REF] Kelso | Phase transition and critical behavior in human bimanual coordination[END_REF][START_REF] Spijkers | Preparation of bimanual movements with same and different amplitudes: specification interference as revealed by reaction time[END_REF].

For example, symmetric index-finger oscillations (i.e., simultaneous inward and outward movements of the left and right index finger) are more stable than asymmetric index-finger oscillations (i.e., one index finger moves inward while the other moves outward): While performing these movements at low speed, both patterns are stable. However, with increasing movement speed, distinct switches from asymmetric to symmetric oscillation patterns occur, but not vice versa [START_REF] Kelso | Phase transition and critical behavior in human bimanual coordination[END_REF].

Traditionally this superiority of symmetric movements was attributed to a tendency towards the activation of homologous muscles, which are more strongly involved in symmetric than in asymmetric body movements [START_REF] Carson | Neuromuscular-skeletal constraints upon the dynamics of unimanual and bimanual coordination[END_REF][START_REF] Cohen | Synchronous bimanual movements performed by homologous and nonhomologous muscles[END_REF][START_REF] Swinnen | Exploring interlimb constraints during bimanual graphic performance: Effects of muscle grouping and direction[END_REF]. However, recently this view was challenged by experiments demonstrating that performance in such tasks appears to be dependent on the symmetry of the perceptual movement effects rather than on the homology of the involved effectors [START_REF] Mechsner | Perceptual basis of bimanual coordination[END_REF][START_REF] Mechsner | Do muscles matter for coordinated action?[END_REF]. For example, in the study by [START_REF] Mechsner | Do muscles matter for coordinated action?[END_REF] different fingers from both hands (e.g., index-and middle-finger of the left hand, and middle-and ring-finger of the right hand) were combined to a bimanual tapping task. Still, the spatially symmetrical pattern (i.e., left index-finger and right middle-finger vs. left middle-finger and right ring-finger in alternation) was more stable than the parallel pattern (i.e., left and right middle-fingers vs. left index-finger and right ring-finger in alternation). When considering the traditional account, this is most surprising, since in this case parallel patterns involve relatively more homologous muscle activations compared to symmetric patterns.

An explanation of these findings has been derived from ideomotor theories of action control (e.g., [START_REF] Hommel | The theory of event coding (TEC): A framework for perception and action[END_REF]; for a historical overview see [START_REF] Stock | A short history of ideo-motor action[END_REF]. The crucial assumption of this approach is that motor actions are cognitively represented by their sensory effects; that is, by codes of the perceptual effects that contingently follow certain motor actions. As a consequence, a motor action can only be accessed by recollecting codes of the sensory consequences that normally accompany this action, and serve to mentally represent it. Stated differently, there is no other way to generate a motor action than by anticipating its sensory consequences. The important implication of this approach is, that all the constraints of motor control we know off, such as complexity effects (Henry & Roger, 1960), stimulus-response compatibility [START_REF] Simon | Reactions toward the source of stimulation[END_REF], limitations in dual-task performance [START_REF] Welford | The 'psychological refractory period' and the timing of high-speed performance -A review and a theory[END_REF], or symmetry tendencies in bimanual coordination [START_REF] Kelso | Phase transition and critical behavior in human bimanual coordination[END_REF], do not arise because of constraints inherent in the "hardware" of the motor system, but because of constraints in the representation of the perceptual re-afferences of tobe-produced motor actions.

By now, there exist a few studies that demonstrate the bearing capacity of this idea.

For example, the initiation of long responses (such as a long key press) takes usually more time than the initiation of short responses (such as a short key press). Yet, these differences can be altered by changing the duration of the contingent sensory effects following such actions. What seems to influence the initiation of the responses most is the duration of the anticipated feedback of the forthcoming action rather than the duration of the action as such [START_REF] Kunde | Temporal response-effect compatibility[END_REF]). To give another example, key presses are executed more quickly if the desired responses match a response-affording stimulus in a certain respect (such as the faster responding to stimuli that match the required response in terms of spatial location). It has been shown that not the spatial correspondence of the stimulus and response per se matters when producing key presses, but the spatial correspondence of the stimulus and the to-beproduced visual feedback of the response [START_REF] Hommel | Inverting the Simon effect by intention: Determinants of direction and extent of effects of irrelevant spatial information[END_REF].

The same basic idea seems to apply to bimanual coordination as well. As already noted above, Mechnser and Knoblich (2004) found that finger tapping was more stable when spatially symmetric rather than asymmetric fingers were involved -independent of finger homology. A similar observation was reported by [START_REF] Kunde | Goal congruency in bimanual object manipulation[END_REF]. They asked participants to turn two wooden blocks from a horizontal starting position into a specific vertical goal position in each trial. Importantly, these blocks were marked with blue on one end and the goal positions were either congruent (i.e., the color marks on both blocks were either upward or downward) or incongruent (i.e., the color mark of one block was upward and of the other one was downward). It turned out that the congruency of the intended goal positions determined the participants' performance, irrespective of whether this required symmetric rotations (i.e., homologous muscle innervations) or asymmetric rotations (i.e., nonhomologous muscle innervations) of the two hands. In both cases responses were initiated and executed faster with congruent goal positions than with incongruent goal positions. Hence, bimanual coordination is facilitated if both actions are carried out to produce similar goal states, rather than by symmetry constraints inherent in the neuromuscular-skeletal system.

Up to now, the impact of action effects in bimanual coordination has been studied with repetitive actions such as finger oscillation or tapping [START_REF] Mechsner | Perceptual basis of bimanual coordination[END_REF][START_REF] Mechsner | Do muscles matter for coordinated action?[END_REF] or non-repetitive but continuous actions such as object manipulations [START_REF] Kunde | Goal congruency in bimanual object manipulation[END_REF]Kunde, Kraus, & Weigelt, 2009;[START_REF] Weigelt | End-state comfort in bimanual object manipulation[END_REF]. The problem with these tasks is that planning and execution aspects of these actions are hard to disentangle. With repetitive actions the planning of the movement normally occurs while another movement is still executed. The problem with continuous actions is that they are temporally extended. For example, the object manipulations used by [START_REF] Kunde | Goal congruency in bimanual object manipulation[END_REF] took about 800 ms to be completed. Therefore, and in accordance with previous observations on deferred programming effects in bimanual coordination [START_REF] Spijkers | Preparation of bimanual movements with same and different amplitudes: specification interference as revealed by reaction time[END_REF], some of the action specification processes are concluded before the start of the action, while others influence action execution. This renders it somewhat ambiguous to which extent programming processes are reflected in reaction times (from stimulus to response onset; RT) or movement times (from start of the movement to its end; MT) or both. To remove this problem of distributed action specification before and after action onset, we used discrete bimanual responses in the present study.

To this end, participants were asked to press two response buttons simultaneously (with one finger from each hand) according to a response signal (e.g., the left and right index finger, or the left index and right middle finger). Importantly, these responses required almost no time for their execution (the button is either pressed or not) and thus, they could be entirely planned in advance. Therefore, RT is the main dependent variable here, and it entails all the planning processes necessary to execute the action. Consequently, RTs in discrete bimanual tasks presumably reflects a purer measure of action planning than available from repetitive and continuous actions. The first purpose of the present study was thus to test if the impact of action effects, that has been previously observed for repetitive and continuous actions, extends to discrete bimanual responses as well.

The second purpose was to study the impact of action effects of varying remoteness.

Regarding this issue already William James (1890) made an interesting distinction into "resident" and "remote" action effects. By resident effects he denotes those body-related sensory consequences that accompany every physical activity of the body, such as the tactile and proprioceptive changes that we feel in the index finger when bending it. These effects are resident in that they occur whenever we move a part of our body (except in rare pathological cases). In contrast to this, he referred to remote effects as those action consequences that occur outside the body. These are consequences of physical activity taken in through exteroceptive channels, such as the lightening of a lamp after pressing a light switch, or a tone after pressing a piano key. We want to pick up these intuitive plausible terms although on closer inspection it is clear that resident and remote effect differ in several respects, such as their physical distance to the body, the perceptual channel through which they are perceived, and the certainty with which they follow a certain motor output (see below). We also want to make clear that the terms resident and remote should not be confused with the terms 'proximal' and 'distal' as used in the theory of event coding (TEC; [START_REF] Hommel | The theory of event coding (TEC): A framework for perception and action[END_REF].

According to TEC a code is distal irrespective of the sensory channel informing it if it refers to events in the world, where the body is in some sense part of the world as well. In contrast, a code is proximal irrespective of the sensory channel informing it if it refers to the specifics of the sensory transduction, that is, of how our system responds to external events. Accordingly, it simply does not matter whether fingers are perceived visually or proprioceptively, if the code refers to a finger movement as an event in the world this code is distal, it codes for a distal aspect of the event. Hence, resident and remote action effects in James' terminology would be both considered as being distal.1

Ideo-motor inspired research on motor control has mainly focused on remote perceptual effects, presumably because such effects can be easily controlled in the psychological lab. However, one should assume that the findings relative to motor coordination and remote effects generalize to resident effects as well. Yet, there may be good reasons to doubt this assumption. As noted above, resident and remote action effects differ in certain respects and might serve different roles in action planning. Consider, for example, that the same motor output, such as the bending of the right index finger, can be linked to several exchangeable remote effects, such as the lightening of a desk lamp in one context, or the sound of a piano tone in another context. In contrast, resident effects are less exchangeable.

Although the proprioceptive feedback of bending a finger might differ from time to time, such variability has obviously limitations. For example, it is hard to imagine that bending the finger feels like moving the leg. At least the body-related location of proprioceptive feedback from a moving effector is constant. These properties might assign different roles to remote and resident action effects in action generation. The anticipation of remote effects might activate several body movements or classes of body movements that are in principle instrumental to obtain these remote effects, whereas the anticipation of resident effects might activate very specific motor patterns. This speculation is not meant to say that we know already the different roles of resident and remote effects. We do not. It should simply illustrate that we need experimental approaches to clarify potential differences between them, and the present study is a first attempt to do so.

We report two experiments here. In both experiments one group of participants produced identical and non-identical perceptual effects with homologous and nonhomologous finger presses, respectively (congruent response-effect (R-E) mapping), while a second group produced identical effects with non-homologous and non-identical effect with homologous finger presses (incongruent R-E mapping). The crucial question was whether the normally observed advantage in RT with homologous compared to non-homologous fingers is affected (or possibly even reversed) when homologous fingers produce non-identical effects and non-homologous fingers produce identical effects (i.e., with an incongruent R-E mapping). Experiment 1 used remote (visual) effects and Experiment 2 used resident (tactile) effects.

Experiment 1

In Experiment 1 participants were to respond with one finger (either the ring-or the middle finger) of both hands simultaneously to the onset of a visually presented stimulus. In each ACCEPTED MANUSCRIPT 10 trial, pressing a response button produced a visual effect. These visual effects were growing and shrinking columns that were directly located above the associated response buttons, thus representing salient remote effects (cf. Fig. 1). Importantly, these columns grew either high or low and this characteristic was varied in a way that participants in the congruent R-E mapping condition produced columns of the same height when responding with homologous fingers. In contrast, participants in the incongruent R-E condition produced columns of different heights when responding with homologous fingers.

In the congruent R-E condition, we should find faster responses with homologous fingers than with non-homologous fingers. However, as we suspect actions being accessed through their perceptual (in this case visual) effects, we predict that this advantage of homology should be diminished in the incongruent R-E mapping condition, where homologous finger produce non-identical visual effects. Given this basic assumption, two scenarios appear to be possible. First, the action becomes entirely controlled by the codes of the visual effects and finger homology does not matter anymore. If this were true, we should observe faster responses with identical visual effects, independent of whether these effects are produced by homologous or non-homologous fingers. Thus, the advantage of identical over non-identical visual effects should be of the same magnitude in both congruency conditions (which would mean a full reversal of the finger homology effect with incongruent R-E mapping). Second, the actions become controlled by codes of their visual effects, but finger homology might still play a role as well. In this case, we should find that the advantage of identical effects is somewhat smaller with incongruent R-E mapping, where identical effects are produced by non-homologous fingers and non-identical effects are produced by homologous fingers. (Of course, it is still possible that our theoretical assumptions described above are simply wrong. In this case we should see an advantage of homologous fingers over non-homologous fingers, irrespective of the R-E congruency mapping).

Method

Participants

16 students (nine female) from Dortmund University of Technology participated in this experiment and were paid course credit in return. The students' mean age was 24;2 years and all reported normal or corrected-to-normal vision.

Apparatus and stimuli

An IBM-compatible personal computer with a 17-inch VGA display was used for stimulus and effect presentation, as well as for response recording. All stimuli and effects were presented in white color on a black background. Responses were collected via four custommade response buttons (20 × 20 mm), which were connected to the computer via the parallel port. The response buttons were placed on a small black-painted box directly in front of the computer screen in an attempt to facilitate association of the responses with the produced effects (see below for details).

Following an inter-trial interval of 1000 ms, each trial began with the presentation of a central fixation cross (250 ms). After a fixed interval of 250 ms, the imperative stimulus set on, in our case one of the digits 1, 2, 3, or 4. Each digit was associated with one combination of finger presses, where either the middle-or the index finger of each hand was involved.

Pressing a response button initiated the growing of the associated column displayed right above the response button (see Fig. 1 for an illustration). The columns grew either high (the outer columns in Fig. 1a) or low (the inner columns in Fig. 1a), stopped at their maximum for 800 ms, and then shrank back to the starting level. High growing columns grew and shrank faster than low growing columns, thus -when initiated at the same time -all four columns would reach their maximum at the same time. For each hand either the outer column could be high and the inner column low or vice versa, resulting in four different R-E conditions: two congruent R-E conditions where homologous fingers produced identical effects (congruent R-E mapping; see Figs. 1a and1b), and two incongruent R-E conditions where homologous fingers produced non-identical effects (congruent R-E mapping; see Figs. 1c and1d). Four stimulus-response-mappings were constructed according to a latin-square design, and each one was combined once with one of the four possible R-E conditions. ** PLEASE INSERT FIG. 1 ABOUT HERE **

Procedure and design

The participants were tested in a single one-hour session. They were instructed in written form to respond to the stimuli as fast and accurate as possible. The first block of 64 trials was considered practice and no effects were displayed on the computer screen. Instead the stimuli were accompanied by down-pointing arrows indicating the two correct response buttons. The practice block was followed by six experimental blocks of 64 trials each. During each block the four stimuli occurred equally often and in a random order. Fingers' homology was varied within-participants (homologous vs. non-homologous) while congruency of the R-E mapping (congruent vs. incongruent) was a between-participants factor.

Data analyses

Only RTs associated with correct responses were further analyzed. A trial was counted as an error in cases of wrong responses and in cases in which the asynchrony of both fingers was more than 100 ms. RTs below 300 ms were excluded as anticipations, and RTs exceeding an individuals mean by more than 2.5 individual standard deviations (separately calculated for homologous and non-homologous finger combinations) were excluded as outliers. The remaining RTs were then averaged across both hands. Mean RTs and percentages of errors (without distinguishing different types of errors) were submitted to mixed analyses of variance (ANOVA) with finger homology (homologous vs. non-homologous) as a withinparticipants factor, and R-E mapping (congruent vs. incongruent) as a between-participants factor. Additional analyses were carried out by means of (one sample and two independent samples) t-tests.

Results

Error analyses

Mean percentages of errors are depicted in Fig. 2 (dotted lines). With both R-E mappings, participants committed numerically more errors when they aimed at producing non-identical effects with both fingers regardless of whether this was done by homologous or nonhomologous fingers. However, neither finger homology, F(1, 14) = 1.15, p = .30., nor R-E mapping, F(1, 14) < 1, p = .64, reached significance, but the interaction only marginally failed significance, F(1, 14) = 3.86, p = .07. The error rates' difference between identical and nonidentical effects was numerically slightly smaller with an incongruent R-E mapping (1%) than with an congruent R-E mapping (3.3%), t( 14

RT analyses

Mean RTs are displayed in Fig. 2 (solid lines). Participants with an incongruent R-E mapping responded somewhat, though non-significantly, slower than those with a congruent R-E mapping, F(1, 14) = 3.04, p = .10, and, overall, finger homology revealed no effect, F(1, 14) < 1, p = .41. However, with both R-E mappings responses were faster when they produced two identical effects, as compared to when they produced two non-identical effects. This was confirmed by a significant interaction of finger homology and R-E mapping, F(1, 14) = 5.97, p < .05. The advantage of identical effects over non-identical effects was numerically larger with the congruent R-E mapping (71 ms), as compared to the incongruent R-E mapping (34 ms), t(14) = -0.86, p = .41.

Response asynchrony

Bimanual interference can also become evident through increased asynchrony of both required responses. Thus, we determined this asynchrony and computed their means and standard deviations (see Table 1), with negative means indicating faster reactions of the right hand's finger. None of the means differed significantly from zero (one sample t-tests). The absolute mean values of asynchrony were not affected by finger homology, F(1, 14) < 1, p = .50, and R-E mapping, F(1, 14) = 3.11, p = .10, and the interaction was also not significant, F(1, 14) = 2.38, p = .15. In contrast, standard deviations of asynchronies were smaller for homologous fingers, F(1, 14) = 20.93, p < .01, and with the incongruent R-E mapping, F(1, 14) = 9.23, p < .01. The interaction was not significant, F(1, 14) < 1, p = .37.

** INSERT TABLE 1 ABOUT HERE **

Discussion

The results of Experiment 1 are straightforward: When homologous fingers produced identical visual effects (i.e., a congruent R-E mapping) performance was superior with homologous compared to non-homologous fingers. This finding replicates the typical homology advantage in the bimanual-tapping task [START_REF] Rabbitt | Programming sequences of complex responses[END_REF]). Yet, with a congruent R-E mapping homology of the fingers is confounded with the assignment of identical visual effects. To disentangle the impact of finger homology and R-E congruency, the data from the incongruent R-E mapping are crucial, where homologous fingers produce non-identical effects, and non-homologous fingers produce identical effects. Here, performance was better with identical effects (non-homologous fingers) than with nonidentical effects (homologous fingers). This supports the idea that the initiation of bimanual key presses is mainly influenced by the identity of the to-be-produced visual effects rather than by the homology of the fingers that are used for their production. In this respect, the experiment can be taken to show that the impact of perceptual effects on bimanual coordination, which has been reliably observed in repetitive and continuous actions, extends to the production of discrete bimanual responses. In line with an ideo-motor point of view [START_REF] Hommel | The theory of event coding (TEC): A framework for perception and action[END_REF], we suggest that this pattern arises from the fact that motor actions are accessed through their anticipated perceptual consequences. Conceivably retrieving and anticipating two similar or identical effects is faster than retrieving two non-identical effects, thus resulting in faster response initiations (see also [START_REF] Kunde | Goal congruency in bimanual object manipulation[END_REF]. The conclusions derived from the RT analyses are corroborated the fact that the percentages of errors exhibited the same pattern (although the interaction marginally failed significance). It should be noted that non-identical effects differed in two physical features, namely the final height of the columns on the screen and their growing speed. This was done to make the effects phenomenally as different as possible, to the cost that we cannot tell apart which of the two features was most relevant here. This might be addressed by future experiments.

Finally, the advantage of identical over non-identical effects was still numerically (though not significantly) smaller with an incongruent R-E mapping compared to a congruent R-E mapping. This indicates some residual influence of finger homology as well, and the reasons for this are considered in Experiment 2.

Experiment 2

In Experiment 1 we successfully demonstrated the impact of (remote) visual effects in the bimanual-tapping task. Performance was superior when identical rather than non-identical effects were produced, independent of whether homologous or non-homologous fingers produced them. Yet, the advantage of identical over non-identical effects was numerically larger when identical effects were produced by homologous rather than non-homologous fingers. This suggests that finger homology still played a role, and that might appear problematic for a radical model of effect-based action representation. However, we have to remember that motor actions normally produce several perceptual consequences, i.e. visual, tactile, and/or proprioceptive ones. Some of them are more remote (e.g., visual ones) and some of them are more resident (e.g., tactile ones). It seems tenable, that the normally observed finger homology advantage in bimanual coordination that occurs when remote actions effects are not manipulated in a way done in Experiment 1, might be construed as a consequence of effect congruency as well. The tactile and proprioceptive feedback, hence resident effects, which ensue with homologous fingers, might appear as more similar to each other than that with non-homologous This speculation is not easy to test, because one would have to rely on some sort of subjective measure to judge whether the resident effects of homologous fingers (both index fingers) are experienced as more similar to each other than those of non-homologous fingers (index-and ring-finger).

A possible approach to resolve this issue is to try to directly manipulate, rather than measure, the similarity of resident response effects. In Experiment 2, we therefore manipulated the tactile effects that were linked to the effectors. To this end, the response buttons were covered with two different surfaces, a soft and fluffy surface and a surface built from nail points respectively (cf. Fig. 3). The predictions for Experiment 2 were essentially the same as for Experiment 1. Responses with homologous fingers should be faster than responses with non-homologous fingers in the congruent R-E mapping condition, but this advantage should be diminished (and possibly reversed) in the incongruent condition.

Method

Participants

Another 16 students (twelve females) from Dortmund University of Technology participated in this experiment and were paid course credit in return. The students' mean age was 24;2 years and all reported normal or corrected-to-normal vision.

Apparatus and stimuli

The stimuli and apparatus were the same as in Experiment 1, with one important alternation.

The remote visual effects (high and low growing columns; see Fig. 1) were replaced with tactile effects. To this end, two response buttons were covered with a soft and fluffy surface (see Fig. 3, inner responses buttons) and the other two were covered with a surface built from nail points (see Fig. 3, outer response buttons). Similar to Experiment 1, four combinations were possible, with two congruent (homologous fingers produce identical effects; an example is given in Fig. 3) and two being incongruent (homologous fingers produce nonidentical effects). ** INSERT FIG. 3 ABOUT HERE **

Procedure, design, and data analysis

The design, procedure, and data analysis were the same as in Experiment 1, with the exception that during the first (unanalyzed) practice block the tactile effects were already present (In Experiment 1 the visual effects were only introduced after this practice block.).

Results

Error analyses

Mean percentages of errors are shown in Fig. 4 (dotted lines). While R-E mapping did not affect mean error percentages, F(1, 14) = 1.53, p = .24, participants committed more errors when responding with non-homologous fingers than when responding with homologous fingers, F(1, 14) = 10.66, p < .01, and the interaction was also significant, F(1, 14) = 5.73, p < .05. The advantage of homologous fingers over non-homologous fingers was larger with the congruent R-E mapping (5.9%) than with the incongruent R-E mapping (0.9%), t( 14

RT analyses

Mean RTs are depicted in Fig. 4 (solid lines). Participants responded faster with homologous fingers compared to non-homologous fingers, F(1, 14) = 34.00, p < .01, and congruency of R-E mapping did not affect RTs, F(1, 14) < 1, p = .68. The interaction was significant, F(1, 14) = 11.05, p < .01. Similar to the pattern in mean error percentages, the advantage of homology for the congruent R-E mapping (115 ms) diminished (significantly) for the incongruent R-E mapping (31 ms), t(14) = -3.33, p < .01.

Response asynchrony

As in Experiment we determined mean asynchronies of both responses and calculated their mean values and standard deviations (Table 1). None of the means differed significantly from zero (one sample t-tests). The absolute mean values of asynchrony did not differ significantly between congruent and incongruent R-E mapping, F(1, 14) = 1.06, p = .32, but they were smaller for homologous fingers than for non-homologous fingers, F(1, 14) = 12.83, p < .01.

The latter difference was numerically larger in a congruent R-E mapping (5.1 ms) than in an incongruent R-E mapping (1.7 ms), F(1, 14) = 3.46, p = .08. Standard deviations of asynchronies were smaller for homologous fingers, F(1, 14) = 9.01, p < .05, andnumerically, but non-significantly -in the incongruent R-E mapping, F(1, 14) = 1.96, p = .18.

The interaction was not significant, F(1, 14) = 1.62, p = .22.

Discussion

In Experiment 2, we tested to which extent the manipulation of tactile response-feedback affects the production of bimanual responses. Most importantly, identical tactile feedback benefited performance across conditions. In congruent R-E mappings, responses with homologous fingers were about 115 ms faster when compared to responses with non-homologous fingers. However, this advantage was reduced to 31 ms in the incongruent R-E mapping, where homologous fingers resulted in the experience of very different tactile feedback. The reason for this, we suggest, is the anticipation of two different effects necessary for planning responses of homologous fingers under this condition. A similar pattern was evident in mean error percentages. Thus, the impact of perceptual effects on response planning and initiation in the bimanual finger-tapping task extends to resident effects, although it appears that their impact was not strong enough to entirely overrun and reverse the finger homology effects, as was observed in Experiment 1 with remote (visual) effects.

There are several possible explanations for this. One reason might be that the resident effects were simply not salient enough. Another reason could be that the participants had their fingers resting on the response buttons' surfaces during the experiment. Hence, they already experienced the resulting effects in parts, and the reduced necessity to mentally anticipate the effects lessened their impact on response planning and initiation. This issue is further addressed in the General Discussion section.

General Discussion

Two experiments investigated the impact of action effects on response planning and execution in the bimanual finger-tapping task. The often observed advantage of symmetrical response patterns has frequently been ascribed to the involvement of homologous muscle portions [START_REF] Carson | Neuromuscular-skeletal constraints upon the dynamics of unimanual and bimanual coordination[END_REF][START_REF] Cohen | Synchronous bimanual movements performed by homologous and nonhomologous muscles[END_REF][START_REF] Swinnen | Exploring interlimb constraints during bimanual graphic performance: Effects of muscle grouping and direction[END_REF]. However, recent experimentation casts doubt on this assertion by demonstrating the impact of perceptual effects rather than homology of involved effectors on the stability of continuous repetitions of movements [START_REF] Mechsner | Perceptual basis of bimanual coordination[END_REF][START_REF] Mechsner | Do muscles matter for coordinated action?[END_REF]. According to the ideo-motor hypothesis (e.g., [START_REF] Hommel | The theory of event coding (TEC): A framework for perception and action[END_REF] motor actions are accessed through an anticipation of their perceptual effects. In the present study, participants produced two identical or non-identical effects with a discrete response of two fingers. This allowed us to investigate whether or not these effects have an impact on the planning of bimanual responses.

Not surprisingly responses were faster and more accurate when two homologous finger presses produced the same effects. However, and in accordance with our reasoning, this familiar result became unstable when responses with homologous fingers resulted in two nonidentical effects: In Experiment 2 the homology advantage was diminished by the resident tactile effects, and the pattern was even reversed by the remote visual effects in Experiment 1.

Importantly, action effects in this striking latter set on only after pressing the response buttons. Hence, these effects must have been cognitively represented before the response was actually carried out.

Note, that the finger homology advantage in bimanual keypressing tasks resembles to some degree the pattern arising from the response-cuing paradigm [START_REF] Miller | Discrete versus continuous models of human information processing: In search of partial output[END_REF] where RTs in the 'finger-cued condition' (here: homologous fingers) are faster than RTs in the 'neithercued condition' (here: non-homologous fingers). It has been suggested that these effects reflect processes of response grouping with Gestalt factors and inter-response dependencies mediating the formation and strength of response subgroups (for a review see [START_REF] Adam | Preparing for perception and action. I: The role of grouping in the response-cuing paradigm[END_REF]. From the perspective of this account identical effects can be construed as a powerful gestalt factor that prompts response grouping and enables a quick response preparation (Wenderoth & Weigelt, in press).

The experimental setup brought about that homologous finger presses required symmetrically located responses and were associated with symmetrically located action effects, as each response location was linked to one effect location. This might be seen as a disadvantage and (for Experiment 1) one might advocate the use of only two columns, each mapped to one hands' responses, to remove this aspect of spatial symmetry. Yet, we used four columns, and this was done in an attempt to keep both experiments reported here as comparable as possible. Trivially, in Experiment 2, each response location required its own effect location. To clarify another related point: It is true that homologous fingers always required responses at symmetrical locations and produced action effects at symmetrical locations whereas the opposite was true for non-homologous fingers. Still, this was true in both mapping conditions (the congruent and the incongruent R-E mapping) with the only difference being the identity or non-identity of the two action effects. Thus, the results show that mere midline-symmetry was not an overly important factor, but rather action effects were.

Any motor sequence is determined by a series of effects and goals that can be located on a continuum from 'very remote' to 'very resident'. If, for example, one of the authors writes a scientific article, the most remote goal might be, to communicate results to colleagues in the field. However, this remote goal can be decomposed into more resident goals or effects, such as starting the word processor, planning the intended content, and so forth. Eventually, typing a specific letter has the effect of producing this letter on the screen [START_REF] Rieger | Automatic keypress activation in skilled typing[END_REF] and experiencing an effect on the finger tip when touching the key on the keyboard. Most likely, the proximity of action effects is linked to the time-point in action planning when anticipatory codes of these effects come into play. Normally, the goal of an action is a remote event, and therefore must be represented in the first place. Only some time later, when it comes to the execution of specific motor patterns, more resident and movement-related effects come into play. Hence it might be that early processes of movement planning are governed by codes of remote effects, whereas later processes of movement planning are governed by more resident ones. Future research is needed to explore this issue. One way to do so would be to combine the task of the present experiments with the precuing technique (Rosenbaum, 1993). Here, it could be speculated that the impact of remote effects disappears with long precuing intervals in which much of the early motor preparation processes are removed from the RT interval, whereas the impact of resident effects might remain.

The benefit of identical visual effects was very pronounced in Experiment 1. After all, identical visual effects were strong enough to reverse the benefit of finger homology, an otherwise very stable effect [START_REF] Kelso | Phase transition and critical behavior in human bimanual coordination[END_REF]. This raises the question of why the impact of tactile effects was less pronounced in Experiment 2. Apart from theoretically less interesting reasons such as differences in saliency and varying needs to retain these effects during the experiment, this might have to do with a common origin of benefits from similar tactile feedback and homologous fingers. Conceivably, homologous effectors produce resident feedback that is more similar to each other than that of two non-homologous effectors. finger-homology benefit might be construed as an influence of similar resident feedback from anatomically homologous effectors. While it appears to be easier to overwrite a resident representation of an action by some remote visual code, it might proof to be impossible or at least much harder to replace it by some other resident tactile code. If true, this may turn out to be an important boundary condition of effect-based action control. Motor output might become represented and controlled by arbitrary remote consequences, such as visual or auditory changes in the environment, but not by arbitrary resident consequences. This issue should be addressed in future research.

In sum, the present study demonstrates the impact of effects upon the production of discrete bimanual responses. The congruency of such action effects strongly influenced the planning of these responses, at least in parts independent of whether homologous muscle portions are involved or not. Future research should investigate the time course of this impact as a function of remoteness of the produced effects, and the reasons for the reduced impact of resident effects.

  ) = -1.07, p = .30. ** INSERT FIG. 2 ABOUT HERE **

  ) = -2.39, p < .05. ** INSERT FIG. 4 ABOUT HERE **

Fig. 1 :

 1 Fig. 1: Experimental setup for Experiment 1. Participants had their fingers resting on four

Fig. 2 :

 2 Fig. 2: Reaction times in milliseconds (solid lines) and percentages of errors (dotted lines) as

Fig. 3 :

 3 Fig.3: Surfaces of the response buttons in Experiment 2. Two buttons were covered with a

Fig. 4 :

 4 Fig. 4: Reaction times in milliseconds (solid lines) and percentages of errors (dotted lines) as

Table 1 :

 1 Mean values (M) and standard deviations (SD) for asynchronies of left and right hand responses in milliseconds.

		Experiment 1	Experiment 2
		congruent	incongruent	congruent	incongruent
	homologous fingers
	M	1.5	3.0	1.5	1.4
	SD	15.7	11.9	14.3	12.6
	non-homologous fingers
	M	-2.4	0.5	-2.1	-1.6
	SD	19.5	14.4	17.4	13.9

We thank Bernhard Hommel for directing our attention to this issue.

Fig.1

Fig.2

Fig.3

Fig.4

The research reported here was supported by a grant from the German Research Foundation (DFG) awarded to WK (Ku 1964/2-1). We thank Bernhard Hommel and an anonymous reviewer for helpful comments on an earlier draft of this manuscript.