Tactual perception: a review of experimental variables and procedures <s> Exploratory movements and time <s> Abstract An analysis of matching tasks in terms of memory demands has two advantages: it accounts for some variations in the difficulty of matching by eye and by hand, and it suggests an analysis of “visual” and “tactual” tasks in terms that may cut across modalities. Memory for information gathered by hand appears to be less stable than for information gathered by eye, more likely to show loss when the number of comparison objects is large. As memory demands increase, accuracy declines first on any matching that starts with inspection by hand. <s> BIB001 </s> Tactual perception: a review of experimental variables and procedures <s> Exploratory movements and time <s> Subjects attempted to recognize simple line drawings of common objects using either touch or vision. In the touch condition, subjects explored raised line drawings using the distal pad of the index finger or the distal pads both of the index and of the middle fingers. In the visual condition, a computer-driven display was used to simulate tactual exploration. By moving an electronic pen over a digitizing tablet, the subject could explore a line drawing stored in memory; on the display screen a portion of the drawing appeared to move behind a stationary aperture, in concert with the movement of the pen. This aperture was varied in width, thus simulating the use of one or two fingers. In terms of average recognition accuracy and average response latency, recognition performance was virtually the same in the one-finger touch condition and the simulated one-finger vision condition. Visual recognition performance improved considerably when the visual field size was doubled (simulating two fingers), but tactual... <s> BIB002 </s> Tactual perception: a review of experimental variables and procedures <s> Exploratory movements and time <s> On the whole, people recognize objects best when they see the objects from a familiar view and worse when they see the objects from views that were previously occluded from sight. Unexpectedly, we found haptic object recognition to be viewpoint-specific as well, even though hand movements were unrestricted. This viewpoint dependence was due to the hands preferring the back “view” of the objects. Furthermore, when the sensory modalities (visual vs. haptic) differed between learning an object and recognizing it, recognition performance was best when the objects were rotated back-to-front between learning and recognition. Our data indicate that the visual system recognizes the front view of objects best, whereas the hand recognizes objects best from the back. <s> BIB003 </s> Tactual perception: a review of experimental variables and procedures <s> Exploratory movements and time <s> Two experiments used visual-, verbal-, and haptic-interference tasks during encoding (Experiment 1) and retrieval (Experiment 2) to examine mental representation of familiar and unfamiliar objects in visual/haptic crossmodal memory. Three competing theories are discussed, which variously suggest that these representations are: (a) visual; (b) dual-code—visual for unfamiliar objects but visual and verbal for familiar objects; or (c) amodal. The results suggest that representations of unfamiliar objects are primarily visual but that crossmodal memory for familiar objects may rely on a network of different representations. The pattern of verbal-interference effects suggests that verbal strategies facilitate encoding of unfamiliar objects regardless of modality, but only haptic recognition regardless of familiarity. The results raise further research questions about all three theoretical approaches. <s> BIB004 </s> Tactual perception: a review of experimental variables and procedures <s> Exploratory movements and time <s> The aim of this study was to investigate the extent to which tactile information that is unavailable for full conscious report can be accessed using partial-report procedures. In Experiment 1, participants reported the total number of tactile stimuli (up to six) presented simultaneously to their fingertips (numerosity judgment task). In another condition, after being presented with the tactile display, they had to detect whether or not the position indicated by a (visual or tactile) probe had previously contained a tactile stimulus (partial-report task). Participants correctly reported up to three stimuli in the numerosity judgment task, but their performance was far better in the partial-report task: Up to six stimuli were perceived at the shortest target–probe intervals. A similar pattern of results was observed when the participants performed a concurrent articulatory suppression task (Exp. 2). The results of a final experiment revealed that performance in the partial-report task was overall better for stimuli presented on the fingertips than for stimuli presented across the rest of the body surface. These results demonstrate that tactile information that is unavailable for report in a numerosity task can nevertheless sometimes still be accessed when a partial-report procedure is used instead. <s> BIB005
Haptic processing is sequential BIB002 implying a progressive apprehension of discrete stimulus properties, contrasting to the simultaneous perception of the whole stimulus that occurs in vision. The consequence of this type of processing is that haptic exploration takes longer than vision. Vision, on the other hand, represents parallel processing, that is, being able to collect simultaneously a set of different properties from the stimuli. In an experiment designed to compare visual and haptic processing in sequential processing, BIB002 restricted the visual field of view in object exploration, allowing the participants to look sequentially to a small area in different points of a stimulus. Within these conditions, performance was very similar in haptic and visual perception, revealing that the type of processing significantly affected the participants' ability to recognise stimuli. This distinction is crucial, and when planning haptic experiments, one should allow sufficient time for haptic stimuli exploration. In a review on sensory modality effects, Freides (1974) noted the differences in time resolution between sensory modalities. BIB001 observed that when delays increased, shape-matching in touch was much more affected than in vision. Also,  indicated that vision was capable of processing more information than touch within the same time. BIB004 reported that the ratio in presentation times has to be of 2:1 when comparing haptic to visual presentation, a conclusion they came across during a set of pilot experiments.  described that matching performance levels in a crossmodal paradigm with vision and touch implied that stimuli presentation in touch took twice the time of the visual presentation. Likewise, in a study with three-dimensional complex objects, built with toy construction blocks, it was found that visual presentation required half the time as haptic presentation BIB003 . Time is a crucial variable in perception and memory, and our ability to maintain a certain stimulus in memory actually contributes to the definition of that specific memory storage. For instance, a partial report paradigm in a numerosity task with tactile stimulation showed that in short-term registers, participants can access information that they could not report in a regular tasks requiring a complete recall BIB005 ). As such, in tactual experiments, if the participants are taking longer to perceive the stimuli, they will take longer to perform the task, which can result in a need to establish specific durations of haptic memory stores. Furthermore, the increased presentation times in haptics make comparison with vision and audition very difficult in traditional memory paradigms, such as memory span or even n-back tasks. A direct comparison between performances in all sensory modalities in similar tasks might not be possible, but it is necessary to explore haptic memory attending to its specificity and perhaps comparing haptic performance in optimal haptic conditions in contrast to conditions in which other modalities have already been evaluated (for instance, with shorter time intervals). In this context, analysing visual and auditory tasks with equivalent times to haptic optimal performance might enlighten how haptic information is processed and clarify if haptic memory storages present longer durations than visual or auditory stores. As was mentioned throughout this section, movement cues are essential for touch and they allow the extraction of unique features of the stimuli, determining participants' performance. Enabling an active interaction with the stimuli besides presenting a more natural exploration also implies a higher degree of feature perception, optimising tactual perception. Even though usually a free exploration condition implies a longer interaction with the stimuli and a longer interval between study and test, and the time factor is very relevant in perceptual but specially memory tasks and as such must be considered.