Tactual perception: a review of experimental variables and procedures <s> Faces <s> Is face perception carried out by modules specialized only for processing faces? Or are faces perceived by domain-general mechanisms that can also operate on non-face stimuli? Considerable evidence supports the domain-specific view. <s> BIB001 </s> Tactual perception: a review of experimental variables and procedures <s> Faces <s> We investigated participants’ ability to identify and represent faces by hand. In Experiment 1, participants proved surprisingly capable of identifying unfamiliar live human faces using only their sense of touch. To evaluate the contribution of geometric and material information more directly, we biased participants toward encoding faces more in terms of geometric than material properties, by varying the exploration condition. When participants explored the faces both visually and tactually, identification accuracy did not improve relative to touch alone. When participants explored masks of the faces, thereby eliminating material cues, matching accuracy declined substantially relative to tactual identification of live faces. In Experiment 2, we explored intersensory transfer of face information between vision and touch. The findings are discussed in terms of their relevance to haptic object processing and to the faceprocessing literature in general. <s> BIB002 </s> Tactual perception: a review of experimental variables and procedures <s> Faces <s> Recent studies have suggested that the familiarity of a face leads to more robust recognition, at least within the visual domain. The aim of our study was to investigate whether face familiarity resulted in a representation of faces that was easily shared across the sensory modalities. In Experiment 1, we tested whether haptic recognition of a highly familiar face (one’s own face) was as efficient as visual recognition. Our observers were unable to recognise their own face models from tactile memory alone but were able to recognise their faces visually. However, haptic recognition improved when participants were primed by their own live face. In Experiment 2, we found that short-term familiarisation with a set of previously unfamiliar face stimuli improved crossmodal recognition relative to the recognition of unfamiliar faces. Our findings suggest that familiarisation provides a strong representation of faces but that the nature of the information encoded during learning is critical for efficient crossmodal recognition. <s> BIB003 </s> Tactual perception: a review of experimental variables and procedures <s> Faces <s> Abstract Although the perception of our world is experienced as effortless, the processes that underlie object recognition in the brain are often difficult to determine. In this chapter, we review the effects of familiarity on the recognition of moving or static objects. In particular, we concentrate on exemplar-level stimuli such as walking humans, unfamiliar objects and faces. We found that the perception of these objects can be affected by their familiarity; for example the learned view of an object or the learned dynamic pattern can influence object perception. Deviations in the viewpoint from the familiar viewpoint, or changes in the temporal pattern of the objects can result in some reduction of efficiency in the perception of the object. Furthermore, more efficient sex categorization and crossmodal matching were found for familiar than for unfamiliar faces. In sum, we find that our perceptual system is organized around familiar events and that perception is most efficient with these learned events. <s> BIB004 </s> Tactual perception: a review of experimental variables and procedures <s> Faces <s> It is well documented that both featural and configural information are important in visual face recognition. Less is known, however, about the nature of the information underlying haptic face recognition and whether or not this information is the same as in vision. In our experiments we found better within modal than crossmodal face recognition performance suggesting that face representations are largely specific to each modality. Moreover, this cost in crossmodal performance was found to be independent of differences in exploratory procedures across the modalities during encoding. We found that crossmodal face perception was most efficient when configural information of the facial features was preserved suggesting that configural information is shared across modalities. Our findings suggest that face information is processed in a similar manner across vision and touch but that qualitative differences in the nature of the information encoded underlies efficient within modal relative to crossmodal recognition. <s> BIB005 </s> Tactual perception: a review of experimental variables and procedures <s> Faces <s> The well-known ventriloquist illusion arises when sounds are mislocalized towards a synchronous but spatially discrepant visual stimulus, and a similar effect of touch on audition has also been reported. By manipulating hand position, we recently demonstrated that this audiotactile ventriloquism effect predominantly operates in an external coordinate system. Using event-related potentials, the present study investigated the neural correlates of this audiotactile ventriloquism effect. Participants reported the perceived location of brief auditory stimuli that were presented either alone or with concurrent tactile stimuli to the fingertips, which were situated at the left and right side of the speaker array. Concurrent electroencephalogram recordings suggested a biasing of cortical activity by the tactile stimuli, which was only observed for trials in which a ventriloquist illusion was elicited. Irrespective of the physical location of the sound source in the bimodal trials, centrally perceived sounds elicited an enhanced centrally distributed negativity, compared to laterally perceived sounds, between 260 and 400 ms following stimulus onset, similar to unimodal auditory stimuli that were actually presented from central and lateral positions, respectively. Moreover, this effect was modulated by hand posture. When external and anatomically centred reference frames were in conflict, the event-related potential effect was reduced for small audiotactile spatial discrepancies, which corresponded to the behavioural finding of a reduced audiotactile ventriloquism effect compared to a parallel hand posture. The present data suggest that the cortical representation of auditory space is adjusted to coincide with spatially disparate tactile input. <s> BIB006
The representation of faces has been considered distinct from the representation of other stimuli BIB001 . Most studies on face perception and recognition have been conducted within the visual modality (e.g., BIB006 , but in recent years, the study of haptic facial recognition has produced interesting results. BIB002 reported a study with three conditions: haptic study and recognition of live faces, haptic study and recognition of facial masks, and visuo-haptic study of live faces with haptic recognition. Results showed that participants were able to correctly identify unfamiliar faces by touch only with rates of about 80 % for the first condition, about 70 % in the second and about 60 % in the last. The last two conditions with haptic recognition of facemasks implied a loss of material cues of the stimuli and participants had to perform their evaluations based on geometrical cues only. Since material cues are central in haptic recognition , this is an expected result. Also, people can recognise facial emotional expressions by touch only, whether touching facemasks or people interpreting the emotional expression  ). In the same study, haptic recognition of emotional facial expressions was analysed comparing dynamic (expressions made by actors) and static (masks representing emotions) emotional faces. The hypothesis was that if participants can recognise the haptic and tactile inputs of an emotional face, they should be able to correctly identify the six universal expressions of emotion  . Results revealed that participants were better at recognising dynamic than static emotional expressions and that happiness, sadness and surprise were easier to recognise by touch than anger, disgust and fear. BIB003 studied familiarity in haptic recognition of faces and concluded that participants were not able to haptically recognise their own face, although visual priming of their live face facilitated the task. In a second experiment, the authors reported that familiarisation with a group of unknown faces improved crossmodal recognition BIB003 . In a later study BIB005 , the authors concluded that face representations were modality-specific, although configurational properties of the faces seemed to be shared between vision and touch (in opposition to feature information). The relevance of familiarity in face perception has also been pointed out by BIB004 , arguing that familiarity is a central process in human perception and that familiar stimuli always present better learning and recognition performance. The haptic system appears to be a valuable perceptual resource, yielding surprisingly good performance even in tasks that are not familiar or recurrent in everyday experience, such as recognising a face or identifying an emotional expression through touch only. Object familiarity is a crucial dimension for touch as well as for other sensory modalities, confirming the familiarity advantage as a general principle of cognitive processing. As shown, familiarity produces enhanced performances, even in unfamiliar tasks, as the haptic recognition of a face or a facial expression of emotion. The distinction between tasks with familiar and unfamiliar stimuli also translates this tendency to find patterns and to organise and process stimuli according to previous cognitive rules and schemas in touch as well as in other sensory modalities.