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Highlights • We investigated how tactile roughness modulates bilateral representation of touch. • Tactile stimuli with varying roughness were slid under subjects' fingertip. • Theta and alpha overlap and long latency SEPs were invariant to stimulus roughness. • The temporal lag between N140 and P240 was modulated by roughness. • SEP modulation by roughness suggests a bilateral processing of tactile information. Abstract Roughness is the most important feature for texture discrimination. Here we investigate how the bilateral cortical representation of touch is modulated by tactile roughness by analyzing the neural responses elicited by stimuli with various coarseness levels ranging from fine to medium. A prolonged stimulation was delivered to 10 healthy subjects by passively sliding tactile stimuli under the fingertip while recording the EEG to study the modulation of Somatosensory Evoked Potentials (SEPs) as well as activity in the theta and alpha bands. Elicited long-latency SEPs, namely bilateral P100-N140 and frontal P240 were consistent across stimuli. On the contrary, the temporal lag N140 – P240 was nonlinearly modulated both in contralateral and ipsilateral sides, in agreement with literature. Using a time-frequency analysis approach, we identified a theta band power increase in the [0 0.5]s interval and a partially overlapped power decrease in the alpha band which lasted throughout the stimulation. The estimated time these two phenomena were overlapped was comparable across stimuli, whereas a linear decrease in alpha band amplitude was reported when increasing the stimulus roughness in both contralateral and ipsilateral sides. This study showed that the selected tactile stimuli generated physiological bilateral responses that were modulated in a diversified way according to the stimulus roughness and side. Specifically, we identified sensory processing features (i.e., theta and alpha time overlap) invariant to the stimulus roughness (i.e., associated to a basic cortical mechanism of touch) and roughness-dependent cortical outputs comparable in the contralateral and ipsilateral sides that confirm a bilateral processing of tactile information. [ABSTRACT FROM AUTHOR]

Intracortical electrical micro-stimulation has been applied widely for the attempts on reconstruction of sensory functions. More recently, thalamic electrical stimulation has been proposed as a promising target for somatosensory stimulation. However, the cortical activations and mechanisms evoked by VPM stimulation remained unclear. In this report, the cortical neural responses to electrical stimulations were recorded by optical imaging of intrinsic signals. The impact of stimulation parameters was characterized to illustrate how the VPM stimulation alter cortical activities. Significant increases were found in cortical responses with increased stimulation amplitude or pulse width. However, frequency modulation exhibited significant inhibition with higher frequency stimulation. Our results suggest that optical imaging of intrinsic signals is sensitive and reliable to deep brain stimulations. These results may not only help to understand the modulation effects through thalamocortical pathway, but also show the possibility to use VPM stimulation to evoke frequency-tuned tactile sensations in rats. [ABSTRACT FROM AUTHOR]

To investigate whether tactile spatial attention is modulated by perceptual load, behavioural and electrophysiological measures were recorded during two spatial cuing tasks in which the difficulty of the target/non-target discrimination was varied (High and Low load tasks). Moreover, to study whether attentional modulations by load are sensitive to the availability of visual information, the High and Low load tasks were carried out under both illuminated and darkness conditions. ERPs to cued and uncued non-targets were compared as a function of task (High vs. Low load) and illumination condition (Light vs. Darkness). Results revealed that the locus of tactile spatial attention was determined by a complex interaction between perceptual load and illumination conditions during sensory-specific stages of processing. In the Darkness, earlier effects of attention were present in the High load than in the Low load task, while no difference between tasks emerged in the Light. By contrast, increased load was associated with stronger attention effects during later post-perceptual processing stages regardless of illumination conditions. These findings demonstrate that ERP correlates of tactile spatial attention are strongly affected by the perceptual load of the target/non-target discrimination. However, differences between illumination conditions show that the impact of load on tactile attention depends on the presence of visual information. Perceptual load is one of the many factors that contribute to determine the effects of spatial selectivity in touch. [ABSTRACT FROM AUTHOR]

Objective: To study whether a temporary block of the tactile afferents from the fingers causes altered activity in the neural network for dexterous manipulation. Methods: Whole-brain functional Magnetic Resonance Imaging (fMRI) was conducted in 18 healthy subjects, while they compressed an unstable spring between the thumb and index finger of the right hand. Two sensory conditions – with and without tactile input from the fingers – were employed. In the latter condition the digital nerves were blocked by local anesthesia. Results: Compression of the unstable spring was associated with activity in an earlier described network for object manipulation. We found that this entire network remained active after a nerve block, and the activity was increased in the dorsal premotor cortex. Conclusions: The neural network for dexterous manipulation is robust with only minor alterations after acute loss of tactile information from the fingers. There was no loss of activity, but, unexpectedly, an increased activity in some parts of the network. Significance : This study gives new insights to possible neural compensatory mechanisms that make fine motor control possible after acute disruption of tactile information in natural situations like cold weather or wearing surgical gloves. [ABSTRACT FROM AUTHOR]

Response adaptation is associated with attenuation of neural responses as the result of different mechanisms. However, the main function of adaptation may be to enhance the flow of relevant information transmission in sensory pathways. To study tactile response adaptation in the somatosensory pathway, unit recordings were performed in the principal trigeminal nucleus, ventro postero-medial thalamic nucleus and barrel cortex by means of tungsten microelectrodes in urethane anesthetized rats. Tactile stimuli consisted in 20 ms duration whisker deflections at different frequencies (0.5–10 Hz). Presumably pyramidal cortical neurons showed response adaptation at frequencies >2 Hz while putative inhibitory cortical neurons did not show response adaptation at 0.5, 5 or 10 Hz. Inhibitory activity was increased by muscimol application into the cortex (8 mM, 0.1 µl); in this condition cortical adaptation was not affected, suggesting that adaptation was not due to an increase of inhibitory mechanisms. Adaptation was also observed in subcortical structures although the response attenuation was lesser than in the barrel cortex. Adaptation remained in subcortical structures after reversible cortical inactivation by cooling the barrel cortex. Acetylcholine application (10 μM; 0.1 μl) into the barrel cortex reduced response adaptation through the activation of muscarinic receptors because the effect was blocked by intraperitoneal injection of atropine (1 mg/kg), suggesting that adaptation may change according to the cortical Ach level. Results indicate that response adaptation increases along the somatosensory pathway probably to alter the sensitivity of neurons in order to encode sensory stimuli more efficiently and to enhance the detectability of rare stimuli. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the neural mechanisms implicated in tactile perception using a discrimination task. We also investigated the influence of the type of presentation on the subject׳s uncertainty. The stimuli varied across four levels of roughness and were presented using a pure/mixed block design. We used an oddball paradigm with three target stimuli varying in the level of roughness, and a smooth surface as the non-target. Stimuli were presented using a specific-purpose device. We analyzed the modulation of the P300 amplitude elicited by targets and non-targets in both presentation conditions. The results showed that the P300 waveform was modulated by roughness, as well as by the order of stimuli presentation. The P300 amplitude was more sensitive to roughness when stimuli were presented in mixed blocks (higher uncertainty). The results are discussed in the context of the attention resources allocation theory applied to tactile modality. [Copyright &y& Elsevier]

Abstract: Magnetoencephalography (MEG) recordings were collected to investigate the effect of the number of mechanical pins and inter-pin distance on somatosensory evoked magnetic fields (SEFs) following mechanical stimulation (MS). We used a 306-ch whole-head MEG system. SEFs were elicited through tactile stimuli with 1-, 2-, 3-, 4- and 8-pins using healthy participants. Tactile stimuli were applied to the tip of the right index finger. SEF following electrical stimulation of the index finger was recorded in order to compare the activity in the primary somatosensory cortex (S1) following MS. Prominent SEFs were recorded from the contralateral hemisphere approximately 54ms (P50m) and 125ms (P100m) after MS regardless of the number of pins. Equivalent current dipoles were located in the S1. The source activities for P50m and P100m significantly increased in tandem with the number of pins for MS. However, the increased ratios for the source activities according to the increase in the number of pins were significantly smaller than that induced by electrical stimulation, and when the number of the pins doubled from 1-pin to 2-pins, from 2-pins to 4-pins, and from 4-pins to 8-pins, S1 activities increased by only 130%. Additionally, source activities significantly increased when the inter-pin distance increased from 2.4 to 7.2mm. The number of stimulated receptors was considered to have increased with an increase in the inter-pin distance as well as an increase in the number of pins. These findings clarified the effect of the number of pins and inter-pin distance for MS on SEFs. [Copyright &y& Elsevier]

Abstract: We examined whether somatosensory activity could be modulated by the observation of bodily experiences. For this purpose, somatosensory-evoked potentials elicited by non-painful stimulation were recorded when subjects were viewing a hand penetrated by a needle, touched by a cotton swab or at resting without stimulation. Participants were instructed to adopt an egocentric perspective when viewing the videos and to rate pain intensity and unpleasantness supposedly experienced by the model, as well as the unpleasantness induced by the video clips. Results indicated that pain videos were rated as more unpleasant than touch videos, and that observation of both pain and touch video clips led to a significant enhancement of P50 amplitudes as compared to viewing a hand without stimulation. Moreover, enhanced P50 amplitudes during observation of both pain and touch in others were associated with increased unpleasant ratings induced by the video clips, as well as with high scores in a perspective taking scale (IRI). These findings provide support for the involvement of an attentional bottom-up mechanism which could be responsible to enhance sensory processing of somatic information when observing bodily experiences in others irrespective of whether they are painful or not. [Copyright &y& Elsevier]

Abstract: The present fMRI study examined cortical activity to repeated vibrotactile sequences in 11 early blind and 11 sighted participants. All participants performed with >90% accuracy and showed practice induced improvement with faster reaction times in identifying matched and unmatched vibrotactile sequences. In blind only, occipital/temporal and parietal/somatosensory cortices showed practice induced reductions in positive BOLD amplitudes that possibly reflected repetition induced learning effects. The significant findings in occipital cortex of the blind indicated that perceptual processing of tactile inputs in visually deprived cortex is dynamic as response amplitudes changed with practice. Thus, stimulus processing became more efficient. It was hypothesized that the changes in occipital cortex of the blind reflected life-long skill in processing somatosensory inputs. Both groups showed activity reductions with practice in mid/posterior ventrolateral prefrontal cortex. These activity reductions suggested common stimulus–response learning associations for vibrotactile sequences in mid/posterior ventrolateral prefrontal cortex. [Copyright &y& Elsevier]

Abstract: The tactile sense comprises pathways for both discriminative and affective touch. Low threshold unmyelinated mechanoafferents (C tactile, CT) in the human hairy skin have recently been linked to pleasant touch sensation. Here, we investigated how perception of the hedonic aspect of tactile stimulation differs between the hairy skin of the arm, and the glabrous skin of the palm, which is not innervated by CT afferents. Three groups of naïve, healthy subjects (total n=28) rated pleasantness on a visual analogue scale (VAS) when we stroked with a soft brush with speeds from 0.1 to 30cm/s on the palm or forearm. We used two different experimental approaches: in experiments 1 and 2, stimuli were delivered successively on the palm and arm (or arm and palm) in temporally separate sequential blocks. In experiment 3, stimuli were delivered alternately on arm and palm. We found that the order of stimulus presentation, palm/arm or arm/palm, has an effect on pleasantness ratings of gentle brush stroking with varying velocity. Notably, the perception of pleasantness for palm stimulation was affected by previous stimulation of the arm, but not vice versa. Thus, assessment of valence of touch may be influenced by affective reactions elicited by activation of the CT afferent pathway. [Copyright &y& Elsevier]

Abstract: Here we investigated how the tactile modality is used along with muscle proprioception in hand movement perception, whether these two sensory inputs are centrally integrated and whether they work complementarily or concurrently. The illusory right hand rotations induced in eleven volunteers by a textured disk scrolling under their hand in two directions at three velocities and/or by mechanical vibration applied to their wrist muscles at three frequencies were compared. The kinesthetic illusions were copied by the subjects on-line with their left hand. Results: 1) in all the subjects, tactile stimulation alone induced an illusory hand rotation in the opposite direction to that of the disk, and the velocity of the illusion increased non-linearly with the disk velocity: the highest gain (the illusion velocity to disk velocity ratio) occurred at the slowest disk rotation; 2) adding a consistent proprioceptive stimulus increased the perceptual effects, whereas adding a conflicting proprioceptive stimulus of increasing frequency gradually decreased the tactile illusions and reversed their initial direction; 3) under both consistent and conflicting conditions, only strong proprioceptive stimulation significantly affected the gain of the resulting illusions, whereas the largest gain always occurred at low tactile stimulation levels when the illusory movements were in the same direction as the tactile-induced illusion. Tactile information may equal or even override muscle proprioceptive information in the perception of relatively small, slow hand movements. These two somatosensory inputs may be integrated complementarily, depending on their respective relevance to the task of accurately perceiving one''s own hand movements. [Copyright &y& Elsevier]

Abstract: The present study using near-infrared spectroscopy (NIRS) examined prefrontal activation associated with maze-solving performance in adult humans. The participants were required to solve a plus-shaped maze, comparable to the one used for pigeons and human children to behaviorally assess planning processes, by moving a target square to a goal square presented on a touch-sensitive screen. The participants made incorrect responses toward a previous goal immediately after the goal jumped to the end of another arm, in parallel with but less frequently than previous participants, with shorter reaction times than when they correctly adjusted their responses. In these incorrect trials, relatively larger hemodynamic changes having two peaks were observed, especially in channels near the right inferior frontal cortex (IFC), suggesting use of additional cognitive resources for adjustment of responses after making errors. In addition to showing human adults’ better behavioral inhibition than previous participants, the present NIRS data suggest a difference in prefrontal activation patterns according to whether inhibition of the forward plan was working well or not. The results also testify to the effective NIRS recording, while the participants were moving a computer-generated stimulus by actually making finger touches to the monitor. [Copyright &y& Elsevier]

Abstract: Vision tends to dominate over touch in the majority of experimental situations, particularly when visual information is presented on, or near to, the body. We combined two visual dominance paradigms in order to investigate crossmodal interactions between vision and touch for stimuli on versus off the body: 1) The Colavita visual dominance effect, which has recently been extended to vision and touch, and 2) The rubber hand illusion, which has often been used to probe visuotactile interactions. Specifically, we investigated whether moving a visual stimulus off the participant''s body would affect visual dominance, and how this dominance would be mediated by the presence/absence of a rubber hand (given the rubber hand illusion provides a way of extending the representation of one''s own body in space). Participants made speeded detection/discrimination responses to a random sequence of visual-only, tactile-only, and visuotactile targets. While participants responded near-perfectly on the unimodal target trials, their performance on the visuotactile target trials was deleteriously affected by the simultaneous presentation of a visual stimulus on (as opposed to away from) their body. In particular, when the visual stimulus was presented to their fingertip, participants failed to respond to far more of the tactile than visual stimuli on bimodal trials. The magnitude of this visual dominance effect decreased significantly when the visual stimulus was moved off the body. When a rubber hand was placed at the off-body location, a similar (albeit reduced) visual dominance effect was observed in both positions. These results therefore suggest that visuotactile interactions are strongest when visual stimuli are presented on a body (no matter whom that body, or body-part, belongs to). [Copyright &y& Elsevier]

Abstract: Previous studies of dynamic crossmodal integration have revealed that the direction of apparent motion in a target modality can be influenced by a spatially incongruent motion stream in another, distractor modality. Yet, it remains to be examined whether non-motion intra- and crossmodal perceptual grouping can affect apparent motion in a given target modality. To address this question, we employed Ternus apparent-motion displays, which consist of three horizontal aligned visual (or tactile) stimuli that can alternately be seen as either ‘element motion’ or ‘group motion’. We manipulated intra- and crossmodal grouping by cueing the middle stimulus with different cue-target onset asynchronies (CTOAs). In unimodal conditions, we found Ternus apparent motion to be readily biased towards ‘element motion’ by precues with short or intermediate CTOAs in the visual modality and by precues with short CTOAs in the tactile modality. By contrast, crossmodal precues with short or intermediate CTOAs had no influence on Ternus apparent motion. However, crossmodal synchronous tactile cues led to dominant ‘group motion’ percepts. And for unimodal visual apparent motion, precues with long CTOAs shifted apparent motion towards ‘group motion’ in general. The results suggest that intra- and crossmodal interactions on visual and tactile apparent motion take place in different temporal ranges, but both are subject to attentional modulations at long CTOAs. [Copyright &y& Elsevier]

Abstract: It has often been shown that people experience difficulty restricting their tactile attention to one hand when both hands are touched simultaneously, especially if the hands are in close spatial proximity. Taken in conjunction with a growing body of evidence that the sensations arising from stimulation of the skin are referred to locations in external space rather than their positions on the body, these tactile attention findings provide evidence for the spatial distribution of attention in touch. However, the effect of spatial distance between the arms on the distribution of attention has been shown in only a limited number of studies and in single testing sessions. In a set of experiments we examined the stability of the arm separation effect by measuring performance over two sessions and with varying visual information about arm location. Tactile selection was more efficient when the stimulated hands were placed far apart compared with when they were adjacent but the effect was short lived (session 1 only) and only occurred when participants were tested with their eyes open. These findings suggest that somatosensory attention is a flexible, dynamic process, based on coordinates that can vary over time. [ABSTRACT FROM AUTHOR]

Abstract: A significant number of studies that evaluated tactile–pain interactions employed heat to evoke nociceptive responses. However, relatively few studies have examined the effects of non-noxious thermal stimulation on tactile discriminative capacity. In this study, the impact that non-noxious heat had on three features of tactile information processing capacity was evaluated: vibrotactile threshold, amplitude discriminative capacity, and adaptation. It was found that warming the skin made a significant improvement on a subject''s ability to detect a vibrotactile stimulus, and although the subjects'' capacities for discriminating between two amplitudes of vibrotactile stimulation did not change with skin heating, the impact that adapting or conditioning stimulation normally had on amplitude discrimination capacity was significantly attenuated by the change in temperature. These results suggested that although the improvements in tactile sensitivity that were observed could have been a result of enhanced peripheral activity, the changes in measures that reflect a decrease in the sensitization to repetitive stimulation are most likely centrally mediated. The authors speculate that these centrally mediated changes could be a reflection of a change in the balance of cortical excitation and inhibition. [Copyright &y& Elsevier]

Abstract: This study quantitatively investigates the actual movements that observers make when exploring a shape. It addresses the question of how the kinematics of these movements relate to and may affect perceived shape. It is one of the first studies to do so for real stimuli and for relatively unconstrained exploration. Observers discriminated the curvature of circularly shaped strips. We identify a kinematic cue for a single finger stroking across circular strips under conditions of slip. This cue consists of two terms that are related to the shift of the skin contact surface across the fingertip and the rotation angle of the finger. The rotation angle of the finger is found to increase linearly with the curvature of the stimulus. Observers rotated their finger less on a concave curvature by a constant amount, while at the same time they overestimated the radius of the concave strips compared to the convex ones. We show that responses were related to kinematic properties of the actual movements and we consider several mechanisms that could explain this finding. [Copyright &y& Elsevier]

Abstract: The spatio-temporal scalp distribution of multisensory auditory–somatosensory integration was investigated in typically developing children ages 6–13. Event-related potentials were recorded from 32 scalp electrodes while participants watched a silent cartoon. Three types of sensory stimulation were presented pseudo-randomly: auditory clicks, somatosensory median nerve electrical pulses, or simultaneous auditory and somatosensory stimuli. No behavioral responses were required of the participant. To examine integration, responses to simultaneous auditory and somatosensory stimulation were compared to the sum of unisensory auditory plus unisensory somatosensory responses for four time-windows: (60–80 ms, 80–110 ms, 110–150 ms and 180–220 ms). Results indicated significant multisensory integration occurred in central/post-central scalp regions between 60–80 ms in the hemisphere contralateral to the side of somatosensory stimulation and between 110–150 ms in the hemisphere ipsilateral to the side of somatosensory stimulation. Between 180–220 ms, significant multisensory integration was evident in central/post-central regions in both hemispheres as well as midline scalp regions. This study suggests that children exhibit differential processing of multisensory compared to unisensory stimuli, as has previously been reported in adults. [Copyright &y& Elsevier]

Abstract: The present research addressed the question of the influence of visual contextual cues on the manual discrimination of spatial orientations in 5-month-old infants. Different types of visual contextual cues were proposed during the haptic discrimination task: congruent–informative, non congruent–informative or noninformative. A familiarisation (with a 60-s fixed-duration)/reaction to novelty procedure was used in three experiments. In Experiment 1, a congruent–informative visual context (a visual context composed of alternate black and white stripes tilted to 20°-left) was present and a haptic discrimination between a 20°-left rod and a 30°-left rod was observed (this discrimination was absent without visual context in Gentaz and Streri''s study, 2004). In Experiment 2, the visual context cues (composed of black dots) were noninformative, and infants could not discriminate these two oblique rods. In Experiment 3, the presence of a non congruent visual context (a visual context composed of alternate black and white stripes tilted to 20°-left, as in Experiment 1) disturbed the gravitational vertical perception usually observed: infants could not discriminate the vertical rod from the 10°-left rod. These results showed that only the informative (congruent and non congruent) visual contextual cues influenced the haptic discrimination of spatial orientations in 5-month-old infants. These results are discussed in relation with data observed in adults and with the current models of the multisensorial integration and attentional level. [Copyright &y& Elsevier]

Abstract: Humans rely heavily on vision to identify objects in the world and can create mental representations of the objects they encounter. Objects can also be identified and mentally represented through haptic exploration. However, it is unclear whether prior visual experience is necessary to generate these internal representations. Subject EA, an early blind artist, provides insight into this question. Like other blind individuals, EA captures the external world by touch. However, he is also able to reveal his internal representations through highly detailed drawings that are unequivocally understandable by a sighted person. We employed fMRI to investigate the neural correlates associated with EA''s ability to transform tactilely explored three-dimensional objects into drawings and contrasted these findings with a series of control conditions (e.g. nonsensical scribbling as a sensory-motor control). Activation during drawing (compared to scribbling) occurred in brain areas normally associated with vision, including the striate cortex along with frontal and parietal cortical regions. Some of these areas showed overlap when EA was asked to mentally imagine the pictures he had to draw (albeit to a lesser anatomical extent and signal magnitude). These results have important implications as regards our understanding of the ways in which tactile information can generate mental representations of shapes and scenes in the absence of normal visual development. Furthermore, these findings suggest the occipital cortex plays a key role in supporting mental representations even without prior visual experience. [Copyright &y& Elsevier]

Abstract: Do physical tilt and tilt of the visual environment affect perception of allocentric and egocentric space? We addressed this question using two perceptual-motor tasks: alignment of a tactile rod (ROD) and saccadic eye movements (EM). Nine participants indicated the vertical axis of their heads (egocentric task), as well as the direction of gravity (allocentric task). Head orientation (±60° and 0°) and visual environment orientation (±120°, ±60° and 0°) were independently manipulated in the fronto-planar roll plane. ROD and EM estimates of both allocentric and egocentric reference directions varied with head and room orientation. Physical tilt dominated allocentric estimates in the dark where overestimates of physical tilt were noted up to 11° using both measures. Allocentric ROD and EM estimates were significantly correlated across all head orientations (r =.70, p <.01) but only when upright for egocentric estimates (r =.38, p <.01). The relative contributions of the visual environment, gravity''s direction and long-body axis to the estimation of allocentric and egocentric directions were determined by vector modeling. This modeling found that vision determined about 14% of the allocentric ROD and EM estimates, that the long-axis body reference played no discernible role, and that the largest factor was gravity, the effective direction of which was non-veridical. For egocentric estimates, vision contributed about 3% with the largest factor being the body reference. We conclude that perception of allocentric and egocentric space is likely influenced by multiple senses that define common egocentric and allocentric frames of reference accessible for saccadic and tactile estimates of perceived self-orientation. [Copyright &y& Elsevier]

Abstract: In temporal numerosity judgment, observers systematically underestimate the number of pulses. The strongest underestimations occur when stimuli are presented with a short interstimulus interval (ISI) and are stronger for vision than for audition and touch. We investigated if multisensory presentation leads to a reduction of underestimation. Participants were presented with 2 to 10 (combinations of) auditory beeps, tactile taps to the index finger and visual flashes at different ISIs (20 to 320 ms). For all presentation modes, we found underestimation, except for small number of pulses. A control experiment showed that the latter is due to a (cognitive) range effect. Averaged over conditions, the order of performance of sensory modalities is touch, audition and last vision. Generally, multisensory presentation improves performance over the unisensory presentations. For larger ISIs (160 and 320 ms), we found a tendency toward a reduction in variance for the multisensory presentation modes. For smaller ISIs (20 and 40 ms), we found a reduction in underestimation, but an increase in variance for the multisensory presentation modes. In the discussion, we relate these two findings to Maximum Likelihood Estimation (MLE) models predicting that multisensory integration reduces variance. [Copyright &y& Elsevier]

Abstract: A large body of work now exists that demonstrates the interaction between different sensory modalities when they are integrated into a single coherent percept. Yet, it is not yet clear whether attention plays a critical role in such crossmodal interactions. We investigated the effect of attention on the crossmodal integration of apparent motion signals using the crossmodal dynamic capture paradigm. The stimuli were bimodal apparent motion streams consisting of audio–visual, visual–tactile, or audio–tactile signals. The task was to indicate the direction of motion in one of the modalities, called the target modality, that could be congruent or incongruent with the direction of the second motion stream, called the distractor modality. The influence of the distractor modality on participants'' response accuracy, called crossmodal capture, was assessed across three conditions of attentional manipulation. We found that attention does have an effect on how the motion signals are combined across modalities, but only when the susceptibility for capture between the two signals are comparable. [Copyright &y& Elsevier]

Abstract: We report two psychophysical experiments designed to investigate the effects of non touch-produced sounds on the tactile perception of roughness and length. Previous studies have demonstrated that the tactile roughness perception of object surfaces is modified by sounds elicited by rubbing the surfaces. In this study, we examined the crossmodal effects of non touch-produced sounds such as white noise (Experiment 1) and pure tones (Experiment 2). Participants touched abrasive paper, synchronizing their touch with changes in the intensity of sounds or with the onset of beeps (control condition), and judged the tactile roughness or length of the stimuli, using the magnitude estimation method. Although the white noise (complex sound) significantly decreased the slope of the roughness estimation function, it did not affect that of the length estimation function. Pure tones had no effect on roughness or length perception. The results revealed that complex sounds selectively affected tactile roughness perception, even when they were seemingly irrelevant to the exploration of the surfaces. We suggest that the processing of complex sounds may be related to the processing of tactile roughness, whereas it is independent of tactile length processing. [Copyright &y& Elsevier]

Abstract: Humans rely on the integration of information from multiple sensory modalities to interact successfully with their environment. In the present series of studies, we investigated how the visuomotor system integrates congruent and incongruent visual and tactile sensory inputs for goal-directed action comprehension and execution. Specifically, we investigated whether orienting of attention towards vision, touch, or both vision and touch enhances the impact of one modality over another. In Experiment 1 participants were presented with visual (on a computer monitor) and/or tactile (in unseen left hand) sensory inputs of an action, and made button-press responses to categorise it as ‘wide’ or ‘narrow’. Responses were significantly faster when attending to vision compared with touch, and faster in fully congruent compared with grasp congruent and incongruent conditions. Thus, both vision and touch are significant in action comprehension, but visual inputs are in general more influential than tactile inputs. Moreover, responses to wide grasp actions were significantly faster than to narrow-grasp actions. In the same task was performed but the participants made reach-to-grasp movements, recorded with ProReflex motion capture system. Although actions to wide objects produced wider peak grasp overall than to a narrow object, in contrast to action comprehension, there was no systematic effect of attended modality or tactile input in action execution. We speculate that action comprehension and execution utilize visual and tactile inputs differentially. [Copyright &y& Elsevier]

Abstract: In the following review, we discuss the evidence for the role of vision and touch in the perception of texture with the particular aim of evaluating whether these systems contribute information to texture perception in either an independent or integrated manner. Although texture is perceived by both vision and touch, several behavioural and neuroimaging studies have suggested that texture information is processed in qualitatively different ways, such that the type of information encoded and the manner in which it is encoded differs across these sensory systems. Furthermore, vision and touch perceive different aspects of texture information with vision the more appropriate modality for discriminating texture boundaries and touch the more appropriate modality for discriminating stimulus roughness and compliance. Differences also exist in the neural structures and functions which underlie these systems, further suggesting independence of these modalities in the perception of texture. Accordingly, recent evidence suggests that behavioural tasks involving texture perception do not benefit from integration across the senses, suggesting that qualitatively different information is represented across vision and touch which cannot be combined to enhance perceptual performance. Research using more familiar objects, however, does suggest a role for sensory integration on texture perception, although these effects may be due to more cognitive influences rather than basic sensory encoding. In sum, we suggest that unlike shape perception, vision and touch contribute information to the perception of texture in an independent but complementary manner. [Copyright &y& Elsevier]

Abstract: Tactile stimulation usually occurs as a combination of an active movement (reaching out to touch a surface) and a sensation (actually feeling the surface against the skin). The brain has information about the active component (the motor command) before it occurs because of efference copy, while the passive component must be transduced before it can be processed. Since the active and passive tactile components are available to the brain at different times, determining the time of touch requires calculation worked backwards from the passive sensation, and/or worked forward from the active motor command. In order to determine which touch process is perceived more quickly, we varied the relative delay between an active and a passive touch signal and determined the relative time percieved as simultaneous. A passive touch needed to be presented before an active key was pressed in order for the two touches to be perceived as simultaneous, but this timing difference was not significant. In order to test the plasticity of the active and passive touch systems, we exploited the fact that the point of subjective simultaneity between two stimuli can sometimes be altered by repeated exposure to asynchronous presentation. We exposed subjects to an active key press/ passive touch pair delayed by 250 ms. This exposure increased the range of relative delays between active and passive touches at which the pairs were judged as simultaneous. This is consistent with an adaptive change in the processing of active touch. [Copyright &y& Elsevier]

Abstract: Humans can easily tap in synchrony with an auditory beat but not with an equivalent visual rhythmic sequence, suggesting that the sensation of meter (i.e. of an underlying regular pulse) may be inherently auditory. We assessed whether the perception of meter could also be felt with tactile sensory inputs. We found that, when participants were presented with identical rhythmic sequences filled with either short tones or hand stimulations, they could more efficiently tap in synchrony with strongly rather than weakly metric sequences. These observations suggest that non-musician adults can extract the metric structure of purely tactile rhythms and use it to tap regularly with the beat induced by such sequences. This finding represents a challenge for present models of rhythm processing. [Copyright &y& Elsevier]

Abstract: Recent studies of change detection have revealed that people are surprisingly poor at detecting changes between two consecutively-presented scenes, when they are separated by a distractor that masks the transients typically associated with change. This failure, known as ‘change blindness’, has been reported within vision, audition, and touch. In the three experiments reported here, we investigated people''s ability to detect the change between two patterns of tactile stimuli presented to their fingertips. The two to-be-compared patterns were presented either consecutively, separated by an empty interval or else by a tactile, visual, or auditory mask. Participants'' performance was impaired when an empty interval was inserted between the two consecutively-presented patterns as compared with the consecutive stimulus presentation. Participants'' performance was further impaired not only when a tactile mask was introduced between the two to-be-compared displays, but also when a visual mask was used instead. Interestingly, however, the addition of an auditory mask to an empty interval did not have any effect on participants'' performance. These results are discussed in relation to the multisensory/amodal nature of spatial attention. [Copyright &y& Elsevier]

Abstract: The present study aimed at investigating the effects of early visual deprivation (bilateral neonatal enucleation) on auditory and somatosensory coding in the polysensory deep layers of the superior colliculus of the rat. The proportion of cells responding to auditory and somatosensory stimulation and the receptive field properties of single neurons were assessed in both normal and enucleated rats. As expected, in enucleated rats there was a drastic increase in the number of unresponsive units and visual responses could no longer be evoked. Most importantly, the proportion of cells that responded to auditory stimulation was drastically reduced. However, the few cells that remained responsive to auditory stimulation were well tuned to noise stimuli presented in both azimuth and elevation, principally in the contralateral hemifield. Enucleation also increased the proportion of cells responding to somatosensory stimulation, particularly to the vibrissae. Implications in terms of neural plasticity and functionality are discussed. [Copyright &y& Elsevier]

Abstract: Research has shown that unreported information stored in rapidly decaying visual representations may be accessed more accurately using partial report than using full report procedures (e.g., [Sperling, G., 1960. The information available in brief visual presentations. Psychological Monographs, 74, 1–29.]). In the 3 experiments reported here, we investigated whether unreported information regarding the actual number of tactile stimuli presented in parallel across the body surface can be accessed using a partial report procedure. In Experiment 1, participants had to report the total number of stimuli in a tactile display composed of up to 6 stimuli presented across their body (numerosity task), or else to detect whether or not a tactile stimulus had previously been presented in a position indicated by a visual probe given at a variable delay after offset of a tactile display (i.e., partial report). The results showed that participants correctly reported up to 3 stimuli in the numerosity judgment task, but their performance was significantly better than chance when up to 5 stimuli were presented in the partial report task. This result shows that short-lasting tactile representations can be accessed using partial report procedures similar to those used previously in visual studies. Experiment 2 showed that the duration of these representations (or the time available to consciously access them) depends on the number of stimuli presented in the display (the greater the number of stimuli that are presented, the faster their representation decays). Finally, the results of a third experiment showed that the differences in performance between the numerosity judgment and partial report tasks could not be explained solely in terms of any difference in task difficulty. [Copyright &y& Elsevier]

Abstract: To study the effects of touch on auditory processing, we examined whether uninformative and irrelevant tactile stimuli presented together with task-relevant sounds can improve auditory detection (Experiment 1), and enhance perceived loudness (Experiment 2). We demonstrated that irrelevant tactile signals facilitate the detection of faint tones, and increase auditory intensity ratings. These crossmodal facilitation effects were found for synchronous when compared to asynchronous auditory–tactile stimulation, and were stronger for weaker than for louder sounds. They are interpreted in terms of a multisensory integration mechanism that increases the strength of auditory signals, and adheres to the rules of inverse effectiveness and temporal (but not spatial) co-occurrence. This integration might be mediated by auditory–tactile multisensory neurons in regions of auditory association cortex that are also involved in auditory detection and loudness discrimination. [Copyright &y& Elsevier]

Abstract: Does the perceived location of tactile stimuli presented on the torso depend on the orientation of our heads with respect to our bodies? An experiment is reported that was designed to assess whether the subjective perception of tactile stimuli on the torso changes as people turn their heads in different directions. Our participants used a scale presented on a computer monitor to indicate the perceived position of vibrotactile stimuli presented to one of eight different positions around the frontal side of their waist while they either looked straight ahead, turned their head to the left, or else turned their head to the right. The results showed that the perceived location of tactile stimuli was systematically influenced by head orientation. In particular, the perceived location of the tactile stimuli shifted away from their actual position in the direction opposite to the direction of the participant''s head turn. Our results also revealed a systematic decline in the accuracy of tactile localization as a function of the physical distance of the tactile stimuli from the participant''s navel. These results echo related findings in the auditory domain where it has been shown that changes in eye position affect auditory lateralization. Our results also have important implications for the design of tactile displays for presenting directional information in a variety of real-world applications. [Copyright &y& Elsevier]

Abstract: To investigate whether superior tactile acuity in the blind is due to alterations of attentional selection mechanisms, event-related brain potentials (ERPs) were measured in a group of early blind and a group of sighted individuals who performed a difficult tactile spatial selection task. We found systematic differences in the attentional processing of tactile events between early blind and sighted individuals. The blind not only responded faster to tactile targets, but also showed attentional modulations of early somatosensory ERP components (P100 and N140). In contrast, ERP effects of spatial attention in the sighted only emerged at longer-latencies (about 200 ms post-stimulus). Our findings suggest that increased use of one sense due to sensory deprivation, such as touch in blind people, leads to alterations of attentional selection mechanism within modality-specific cortex. [Copyright &y& Elsevier]

Abstract: This article systematically explores cue integration within active touch. Our research builds upon a recently made distinction between position and force cues for haptic shape perception [Robles-de-la-Torre, G., Hayward, V., 2001. Force can overcome object geometry in the perception of shape through active touch, Nature 412, 445–448]: when sliding a finger across a bumpy surface, the finger follows the surface geometry (position cue). At the same time, the finger is exposed to forces related to the slope of the surface (force cue). Experiment 1 independently varied force and position cues to the curvature of 3D arches. Perceived curvature could be well described as a weighted average of the two cues. Experiment 2 found more weight of the position cue for more convex high arches and higher weight of the force cue for less convex shallow arches—probably mediated through a change in relative cue reliability. Both findings are in good agreement with the maximum-likelihood estimation (MLE) model for cue integration and, thus, carry this model over to the domain of active haptic perception. [Copyright &y& Elsevier]

Abstract: Crossing the hands over, whether across the body midline or with respect to each other, leads to measurable changes in spatial compatibility, spatial attention, and frequently to a general decrement in discrimination performance for tactile stimuli. The majority of multisensory crossed hands effects, however, have been demonstrated with explicit or implicit spatial discrimination tasks, raising the question of whether non-spatial discrimination tasks also show spatial effects when the hands are crossed. We designed a novel, non-spatial tactile discrimination task to address this issue. Participants made speeded discriminations of single- versus double-pulse vibrotactile targets, while trying to ignore simultaneous visual distractor stimuli, in both hands uncrossed and hands crossed postures. Tactile discrimination performance was significantly affected by the visual distractors (demonstrating a significant crossmodal congruency effect) and was affected most by visual distractors in the same external location as the tactile target (i.e., spatial modulation), regardless of the posture (uncrossed or crossed) of the hands (i.e., spatial ‘remapping’ of visual–tactile interactions). Finally, crossing the hands led to a general performance decrement with visual distractors, but not in a control task with unimodal visual or tactile judgements. These results demonstrate, for the first time, significant spatial and postural modulations of crossmodal congruency effects in a non-spatial discrimination task. [Copyright &y& Elsevier]

Abstract: The present investigation was aimed to evaluate the influence of emotional valence on brain correlates of non-painful somatosensory processing. For this purpose, we examined changes on the somatosensory-evoked potentials (SEP) elicited by frequent and deviant tactile stimuli (probability 14%) when subjects were viewing affective pictures. Twenty healthy volunteers aged between 19 and 47 years old participated in the study. The P50, N80, and P200 components of the SEP, as well as the P200 component of the visual-evoked potentials (VEP) elicited by the affective pictures were analyzed. Overall, a significant P50 amplitude reduction was observed when subjects were viewing unpleasant pictures, in comparison to pleasant pictures. Furthermore, larger SEP amplitudes were obtained in response to the deviant than to the frequent stimuli. In addition, unpleasant pictures elicited larger P200 amplitudes of the VEP than pleasant. Data suggest that affective stimuli may modulate the early processing of somatosensory information in the brain, probably reflecting the existence of an adaptive perceptual/attentional mechanism to motivationally relevant stimuli. [Copyright &y& Elsevier]

The current study investigated the influence of changes in sensory information related to postural stability on anticipatory postural adjustments (APAs) in standing subjects. Subjects performed fast arm movements and a load release task while standing on a stable force platform or on an unstable board. We manipulated sensory information through vibration of the Achilles tendons and additional finger touch (contact forces under 1 N). Changes in the background activity of leg, trunk, and arm muscles and displacements of the center of pressure (COP) were quantified within time intervals typical for APAs. In the arm movement task, leg and trunk muscles showed a significant drop in the APAs with finger touch, while the vibration and standing on the unstable board each led to an increase in the APA magnitude. In the load release task, ventral muscles decreased their APA activity with touch, while dorsal muscles showed increased inhibition during APAs. During vibration, dorsal and ventral muscles showed increased excitation and inhibition during APAs, respectively. An additional analysis of APAs at a joint level, has shown that in both tasks, an index related to the co-activation of agonist–antagonist muscle pairs (C-index) was modulated with touch, vibration, and stability particularly in leg muscles. Small changes in the other index related to reciprocal activation (R-index) were found only in trunk muscles. Light touch and vibration induced opposing changes in the C-index, suggesting their opposite effects on the stabilization of a reference point or vertical. We conclude that the central nervous system deploys patterns of adjustments in which increased co-contraction of distal muscles and reciprocal adjustments in trunk muscles are modified to ensure equilibrium under postural instability. [Copyright &y& Elsevier]

We tested the hypothesis that the population receptive field representation (a superposition of the excitatory receptive field areas of cells responding to a tactile stimulus) provides spatial information sufficient to mediate one measure of static tactile acuity. In psychophysical tests, two-point discrimination thresholds on the hindlimbs of adult cats varied as a function of stimulus location and orientation, as they do in humans. A statistical model of the excitatory low threshold mechanoreceptive fields of spinocervical, postsynaptic dorsal column and spinothalamic tract neurons was used to simulate the population receptive field representations in this neural population of the one- and two-point stimuli used in the psychophysical experiments. The simulated and observed thresholds were highly correlated. Simulated and observed thresholds'' relations to physiological and anatomical variables such as stimulus location and orientation, receptive field size and shape, map scale, and innervation density were strikingly similar. Simulated and observed threshold variations with receptive field size and map scale obeyed simple relationships predicted by the signal detection model, and were statistically indistinguishable from each other. The population receptive field representation therefore contains information sufficient for this discrimination. [Copyright &y& Elsevier]