Tactual perception: a review of experimental variables and procedures <s> Passive and active touch <s> Two experiments investigated characteristics of Immediate recall for brief tactile stimuli applied to the 24 interjoint regions of the fingers of both hands (thumbs excluded) The obtained Immediate-memory span varied from 35 to 7,5 stimulus positions correct after correction for guessing, similar to the results In analogous visual studies, Properties of any hypothetical tactile short-term memory were studied by requiring subjects to report only a specified portion of the stimuli presented, and by varying the time of occurrence of the marker specifying which portion of the stimuli to report, In this partial-report condition, subjects had more stimulus information available at the time of reporting than their immediate memory spans indicated, provided that the stimulus marker occurred within 0.8 sec after stimulus termination, The data suggest that at least for the amount of training employed here, any tactile short-term memory has much less capacity than an analogous visual short-term memory. <s> BIB001 </s> Tactual perception: a review of experimental variables and procedures <s> Passive and active touch <s> Summary In a study of the effect of self-produced movement on tactual form recognition 30 male and 30 female college students actively or passively touched cooky-cutter forms with the preferred index finger to identify the shapes. In a static passive condition, the forms were pressed on the fingers. Ss were limited to either 5 or 30 sec of stimulus exposure time. Results indicate that active touch was superior to either passive static or passive sequential touch. Adding stimulus change failed to improve performance. Recognition accuracy was greater with 30 sec of exposure, but 5 sec of active touch produced accuracy equivalent to that produced by longer periods of passive stimulation. <s> BIB002 </s> Tactual perception: a review of experimental variables and procedures <s> Passive and active touch <s> Haptic identification of real objects is superior to that of raised two-dimensional (2-D) depic­ tions. Three explanations of real-object superiority were investigated: contribution of material information, contribution of 3-D shape and size, and greater potential for integration across the fingers. In Experiment 1, subjects, while wearing gloves that gently attenuated material infor­ mation, haptically identified real objects that provided reduced cues to compliance, mass, and part motion. The gloves permitted exploration with free hand movement, a single outstretched finger, or five outstretched fingers. Performance decreased over these three conditions but was superior to identification of pictures of the same objects in all cases, indicating the contribution of 3-D structure and integration across the fingers. Picture performance was also better with five fingers than with one. In Experiment 2, the subjects wore open-fingered gloves, which provided them with material information. Consequently, the effect of type of exploration was substantially reduced but not eliminated. Material compensates somewhat for limited access to object struc­ ture but is not the primary basis for haptic object identification. It has been amply demonstrated that people's ability to identify raised line drawings of common objects, using touch alone, is quite poor (Ikeda & Uchikawa, 1978; Kennedy & Fox, 1977; Lederman, Klatzky, Chataway, & Summers, 1990; Loomis, Klatzky, & Lederman, 1991; Magee & Kennedy, 1980). Subjects may spend several minutes on a single picture, and accuracy is generally be­ low 50%-sometimes well below. This is especially strik­ ing when one considers that haptic identification of real, common objects is both fast and accurate, with modal re­ sponse latency observed to be under 2 sec and accuracy near 100% (Klatzky, Lederman, & Metzger, 1985). The purpose of the present study is to evaluate potential ex­ planations of these differences in performance with real objects and two-dimensional (2-D) depictions. We con­ sider three explanations, which are not meant to be mutu­ ally exclusive. The first account of picture/object differences focuses on a salient aspect of haptic perception-namely, that the <s> BIB003 </s> Tactual perception: a review of experimental variables and procedures <s> Passive and active touch <s> Active and passive touch, respectively with and without voluntary movement on the part of the subject, are frequently reported to be equivalent in terms of the resultant perceptual abilities. This ... <s> BIB004 </s> Tactual perception: a review of experimental variables and procedures <s> Passive and active touch <s> Subjects identified common objects under conditions of a “haptic glance,” a brief haptic exposure that placed severe spatial and temporal constraints on stimulus processing. They received no advance cue, a superordinate-level name as cue, or a superordinate and basic-level name as cue. The objects varied in size relative to the fingertip and in the most diagnostic attribute, either texture or shape. The data suggest that object recognition can occur when global volumetric primitives cannot directly be extracted. Even with no cue, confusion errors resembled the target object and indicated extraction of material and local shape information, which was sufficient to provide accuracy above 20%. Performance improved with cuing, and the effect of exposure duration was observed primarily with minimal cuing, indicating compensatory effects of top-down processing. <s> BIB005 </s> Tactual perception: a review of experimental variables and procedures <s> Passive and active touch <s> In the present article, we will consider how well people can haptically identify common objects when manual exploration is constrained. The constraints imposed in this study were produced by imposing a rigid link between the skin and the object, in the form of a sheath over the finger or a probe held in the hand. Any constraint that forms an intermediate barrier between skin and objects can be described as producing remote (or indirect) perception. Such intermediaries serve to constrain haptic exploration by reducing the cutaneous and/or kinesthetic inputs available. In earlier work (Klatzky, Loomis, Lederman, Wake, & Fujita, 1993), manual exploration has been constrained in several other ways that did not involve using a rigid link. In this article, we integrate the results of the earlier Klatzky et al. (1993) study with those of the present study to further our understanding of haptic object identification by direct and remote touch. In addition, we relate the result to the design of haptic interfaces for teleoperation and virtual environments, which share some of the same cue reductions that we have produced experimentally. Our article arises from two separate but related themes in previous research on haptic perception. <s> BIB006 </s> Tactual perception: a review of experimental variables and procedures <s> Passive and active touch <s> Active touch involves tactile and proprioceptive sensory inputs, activation of the motor system and executive functions. It has been shown by the previous literature that active touch facilitates shape recognition. Since both active and passive exploration requires sequential presentation of the tactile inputs, this facilitation may be due to the improvement of the sequential-processing mechanism. The effects of active and passive touch on the sequential processing of tactile inputs were tested at different stimulus-presentation rates in a counting task. Active touch did not improve the performance, which shows that the additional sensory and motor information conveyed by active exploration are not utilized by the sequential-processing mechanism. Therefore, the results cannot be explained by the feature-specific theory of sequential processing. On the other hand, the counting errors were higher than those predicted by the limitation of the minimal inter-stimulus interval, which is suggested by the central-timing theory. Consequently, it is proposed that a mechanism based on the central-timing theory may contribute to tactile sequential processing, but the bottleneck at high presentation rates is probably due to short-term memory. <s> BIB007 </s> Tactual perception: a review of experimental variables and procedures <s> Passive and active touch <s> The neural mechanisms behind active and passive touch are not yet fully understood. Using fMRI we investigated the brain correlates of these exploratory procedures using a roughness categorization task. Participants either actively explored a surface (active touch) or the surface was moved under the participant's stationary finger (passive touch). The stimuli consisted of three different grades of sandpaper which participants were required to categorize as either coarse, medium, or fine. Exploratory procedure did not affect performance although the coarse and fine surfaces were more easily categorized than the medium surface. An initial whole brain analysis revealed activation of sensory and cognitive areas, including post-central gyrus and prefrontal cortical areas, in line with areas reported in previous studies. Our main analysis revealed greater activation during active than passive touch in the contralateral primary somatosensory region but no effect of stimulus roughness. In contrast, activation in the parietal operculum (OP) was significantly affected by stimulus roughness but not by exploration procedure. Active touch also elicited greater and more distributed brain activity compared with passive touch in areas outside the somatosensory region, possibly due to the motor component of the task. Our results reveal that different cortical areas may be involved in the processing of surface exploration and surface texture, with exploration procedures affecting activations in the primary somatosensory cortex and stimulus properties affecting relatively higher cortical areas within the somatosensory system. Hum Brain Mapp, 2011. © 2010 Wiley-Liss, Inc. <s> BIB008
In touch research, three main types of touch are distinguished: passive touch, active touch and dynamic touch. Cogn Process (2012) 13:285-301 291 Passive touch refers to conditions in which participants are not allowed to move, and the stimuli are presented against the skin. This type of touch is used with air jets (e.g., BIB001 , vibration (e.g.,  , or even by pressing still stimuli against the participant's skin (e.g.,  . Active touch implies movement from the participants and can be: 1) free, when the participants are allowed to explore the objects with the whole hand (e.g.,  ; or 2) restricted, when participants can touch the objects: with only one finger (e.g., BIB005 , through gloves (e.g., BIB003 ), or with a specific type of movement (e.g., BIB006 .  , in an analysis of active touch, emphasised the exploratory nature of active touch, in contrast to the receptive nature of passive touch, which is caused by an external agent, and additionally argued that active touch was not equivalent to a simple adding of passive touch and kinaesthesia. Dynamic touch was defined by  as the perception that results from the combination of cutaneous, muscular and joints cues. In such conditions, the stimuli are moved through the participant's skin, allowing the perception of movement cues not present in passive touch, but not requiring the voluntary exploration present in active touch (e.g., Turvey 1996; Sanders and Kappers 2008). Experimentally, dynamic touch is a condition that allows higher experimental control than active touch, since participants are not allowed to move their hands, minimising variations in exploration. This type of touch is sometimes referred to as an option of passive touch, in which the stimuli are moved by the experimenter (e.g.,  or by a mechanical device against the participant's skin allowing the participant to perceive relevant cues that result from movement, without having to actively manipulate the stimuli. Another author analysed the differences between active and passive touch in the identification of geometrical forms  . Comparing participants in the first, third and fifth grade and college students, the author concluded that a developmental advantage existed for active touch (the participants actively touch the object) and dynamic touch (the stimulus is moved against the participant's hand) conditions, but not for passive touch conditions, in which 5-year participants showed differences compared to the college students, but not compared to third-and fifth-year students. The author argued that the equivalence in performance between active and dynamic touch might be explained by the fact that participants had to explore the objects with the palm of the hand, and not the finger, which could have limited the type of information gathered in active touch conditions, making it similar to dynamic touch. Overall, conditions that involved movement resulted in better performance than passive touch, in every age group. In a study comparing the perception of forms in active and passive exploration conditions BIB002 , results also pointed to a clear advantage of active touch, with passive static or sequential presentation resulting in worst identification than active touch. In some conditions, passive touch might present an advantage when compared to active touch. For instance, in a recent study comparing tactile learning of a maze (Richardson et al. 2011) , participants in the passive touch condition were much faster to learn the path than participants in the active touch condition. Nonetheless, the disadvantage in the active conditions was due to the repetition of errors in the chosen paths and was a consequence of the participants' decisions. As such, the authors concluded that the active touch disadvantage translated into a cognitive limitation but not a haptic system limitation (Richardson et al. 2011 ). There can be conditions where active touch shows no advantage in performance. BIB007 published a study comparing active and passive touch in a counting task. Participants had to count the number of bumps presented in sticks that were either actively explored or slid against the participants' hands. Results showed that active touch did not imply a better performance. Active touch and passive touch are distinct processes. While active touch involves proprioception, kinaesthesia and cutaneous senses, passive touch relies only on the latter. Interestingly, electrophysiology studies have reported that active touch generates a suppression of afferent information to the somatosensory cortex, a phenomenon known as movement-related sensory gating (e.g., Chapman 1994). This phenomenon could lead to worst encoding in active than passive touch. Nonetheless, active touch allows the participant to control movement velocity and to select which properties to evaluate at each moment, resulting in a central advantage for active touch BIB004 . Using functional Magnetic Resonance Image (fMRI) in a study that required evaluation of roughness in active (participants moved their fingers through the samples) and passive (the samples were moved beneath the participants' fingers) touch, it was possible to verify that exploratory conditions affected activation in the primary sensory cortex and that active touch resulted in a larger pattern of activation, possibly because of the motor component of this condition BIB008 . Although considering some exceptions to the active touch superiority, it seems that this type of stimuli exploration in touch is ideal to observe optimal performance. Although passive touch allows a great control of manipulation variables, active touch can be studied and explored with controlled experimental paradigms and seems to be able to provide more information about processing in touch  ).