Touch Perception

Vision plays a central role in how we represent and interact with the world around us. Roughly, one-third of the cortical surface in primates is involved in visual processes. The loss of vision, either at birth or later in life, must therefore have profound consequences on brain organization and on the way the world is perceived and acted upon. In this chapter, we formulate a number of critical questions. Do blind individuals indeed develop supra-normal capacities for the remaining senses in order to compensate for their loss of vision? Do brains from sighted and blind individuals differ, and how? How does the brain of someone who has never had any visual perception form an image of the external world? We discuss findings from animal research as well from recent psychophysical and functional brain imaging studies in sighted and blind individuals that shed some new light on the answers to these questions.

We report two experiments designed to investigate the nature of aesthetic preferences for tactile textures in humans. In Experiment 1, the participants rated their preference for a range of actively and passively explored textures presented on their hands and on their cheeks. The results revealed that those textures that were subjectively-rated as smoother were preferred over those that were rated as rougher. Moreover, certain textures were disliked more during active than during passive stimulation. In Experiment 2, the speed of tactile stimulation was controlled in order to elicit vigorous responses from C-tactile fibers (present only in hairy skin), which are thought to play a central role in pleasant aspects of touch. The results revealed that textures were preferred when presented on the hairy skin of the forearm than on the glabrous palm of the hand. These results provide preliminary evidence regarding people's preferences for different attributes of tactile surface.

The nose is important not only for breathing, filtering air, and perceiving olfactory stimuli. Although the face and hands have been mapped, the representation of the internal and external surface of the nose on the primary somatosensory cortex (SI) is still poorly understood. To fill this gap functional magnetic resonance imaging (fMRI) was used to localize the nose and the nasal mucosa in the Brodman areas (BAs) 3b, 1, and 2 of the human postcentral gyrus (PG). Tactile stimulation during fMRI was applied via a customized pneumatically driven device to six stimulation sites: the alar wing of the nose, the lateral nasal mucosa, and the hand (serving as a reference area) on the left and right side of the body. Individual representations could be discriminated for the left and right hand, for the left nasal mucosa and left alar wing of the nose in BA 3b and BA 1 by comparing mean activation maxima and Euclidean distances. Right-sided nasal conditions and conditions in BA 2 could furth...

Vision plays a central role in how we represent and interact with the world around us. Roughly, one-third of the cortical surface in primates is involved in visual processes. The loss of vision, either at birth or later in life, must therefore have profound consequences on brain organization and on the way the world is perceived and acted upon. In this chapter, we formulate a number of critical questions. Do blind individuals indeed develop supra-normal capacities for the remaining senses in order to compensate for their loss of vision? Do brains from sighted and blind individuals differ, and how? How does the brain of someone who has never had any visual perception form an image of the external world? We discuss findings from animal research as well from recent psychophysical and functional brain imaging studies in sighted and blind individuals that shed some new light on the answers to these questions.

This paper presents an enhanced haptic-enabled master-slave teleoperation system which can be used to provide force feedback to surgeons in minimally invasive surgery (MIS). One of the research goals was to develop a combined-control architecture framework that included both direct force reflection (DFR) and position-error-based (PEB) control strategies. To achieve this goal, it was essential to measure accurately the direct contact forces between deformable bodies and a robotic tool tip. To measure the forces at a surgical tool tip and enhance the performance of the teleoperation system, an optical force sensor was designed, prototyped, and added to a robot manipulator. The enhanced teleoperation architecture was formulated by developing mathematical models for the optical force sensor, the extended slave robot manipulator, and the combined-control strategy. Human factor studies were also conducted to (a) examine experimentally the performance of the enhanced teleoperation system w...

Sensory substitution devices (SSDs) have been developed with the ultimate purpose of supporting sensory deprived individuals in their daily activities. However, more than forty years after their first appearance in the scientific literature, SSDs still remain more common in research laboratories than in the daily life of people with sensory deprivation. Here, we seek to identify the reasons behind the limited diffusion of SSDs among the blind community by discussing the ergonomic, neurocognitive and psychosocial issues potentially associated with the use of these systems. We stress that these issues should be considered together when developing future devices or improving existing ones. We provide some examples of how to achieve this by adopting a multidisciplinary and participatory approach. These efforts would contribute not solely to address fundamental theoretical research questions, but also to better understand the everyday needs of blind people and eventually promote the use ...

Evidence suggests that interoceptive and exteroceptive attention might have different perceptual effects.However, the effects of these different types of body-focused attention have never been directly compared. The current research investigated how interoceptive and exteroceptive attention affect subsequent
performance on the somatic signal detection task (SSDT). In Experiment 1, 37 participants completed the SSDT under usual testing conditions and after prforming an interoceptive heartbeat perception task. This task led to a more liberal response criterion, leading to increased touch reports in the presence
and absence of a target vibration. This finding is consistent with suggestions that attending internally contributes to physical symptom reporting in patients with medically unexplained symptoms (MUS). In Experiment 2, 40 participants completed the SSDT before and after an exteroceptive grating orientation
task. This task led to amore stringent response criterion, leading to decreased touch reports in the presence and absence of the target, possibly via a reduction in sensory noise.Thiswork demonstrates that internal and external body-focused attention can have opposite effects on subsequent somatic perceptual decision making and suggests that attentional training could be useful for patients reporting MUS.

Pain and the conscious mind (or the self) are experienced in our body. Both are intimately linked to the subjective quality of conscious experience. Here, we used virtual reality technology and visuo-tactile conflicts in healthy subjects to test whether experimentally induced changes of bodily self-consciousness (self-location; self-identification) lead to changes in pain perception. We found that visuo-tactile stroking of a virtual body but not of a control object led to increased pressure pain thresholds and self-location. This increase was not modulated by the synchrony of stroking as predicted based on earlier work. This differed for self-identification where we found as predicted that synchrony of stroking increased self-identification with the virtual body (but not a control object), and positively correlated with an increase in pain thresholds. We discuss the functional mechanisms of self-identification, self-location, and the visual perception of human bodies with respect to pain perception.

Cross-modal responses in occipital areas appear to be essential for sensory processing in visually deprived subjects. However, it is yet unclear whether this functional recruitment might be dependent on the sensory channel conveying the information. In order to characterize brain areas showing task-independent, but sensory specific, cross-modal responses in blind individuals, we pooled together distinct brain functional studies in a single based meta-analysis according only to the modality conveying experimental stimuli (auditory or tactile). Our approach revealed a specific functional cortical segregation according to the sensory modality conveying the non-visual information, irrespectively from the cognitive features of the tasks. In particular, dorsal and posterior subregions of occipital and superior parietal cortex showed a higher cross-modal recruitment across tactile tasks in blind as compared to sighted individuals. On the other hand, auditory stimuli activated more medial a...