Perceiving object motion using vision and touch

In a previous experiment, we showed that bistable visual object motion was partially disambiguated by tactile input. Here, we investigated this effect further by employing a more potent visuotactile stimulus. Monocular viewing of a tangible wire-frame sphere (TS) rotating about its vertical axis produced bistable alternations of direction. Touching the TS biased simultaneous and subsequent visual perception of motion. Both of these biases were in the direction of the tactile stimulation and, therefore, constituted facilitation or priming, as opposed to interference or adaptation. Although touching the TS biased visual perception, tactile stimulation was not able to override the ambiguous visual percept. This led to periods of sensory conflict, during which visual and tactile motion percepts were incongruent. Visual and tactile inputs can sometimes be fused to form a coherent percept of object motion but, when they are in extreme conflict, can also remain independent.     

Factor Analysis,Differential Bio-Process,and Mental Organization

This study was designed to show that variation in stimulation has an influence on tactile perception similar to that in the visual modality. Thirty-two subjects were required to identify Hebrew letters by the tactile sense. Identification time was found to be significantly (p < .01) shorter when subjects could feel the letters both with temporal variation (i.e., vibrations) and spatial variation (i.e., allowing the subjects to move their fingers over the letters) than when the letters were stable. The longest identification time was found when both temporal and spatial variation were absent. The effects of the two types of tactile variation were found to be compensatory, and a possible explanation for that is offered. Possible implications of these results regarding the use of tactile perception in man-machine systems are discussed.     

The influence of temporal and spatial variation on tactile identification of letters

This study was designed to show that variation in stimulation has an influence on tactile perception similar to that in the visual modality. Thirty-two subjects were required to identify Hebrew letters by the tactile sense. Identification time was found to be significantly (p less than .01) shorter when subjects could feel the letters both with temporal variation (i.e., vibrations) and spatial variation (i.e., allowing the subjects to move their fingers over the letters) than when the letters were stable. The longest identification time was found when both temporal and spatial variation were absent. The effects of the two types of tactile variation were found to be compensatory, and a possible explanation for that is offered. Possible implications of these results regarding the use of tactile perception in man-machine systems are discussed.     

Emotional modulation of visual remapping of touch

The perception of tactile stimuli on the face is modulated if subjects concurrently observe a face being touched; this effect is termed "visual remapping of touch" or the VRT effect. Given the high social value of this mechanism, we investigated whether it might be modulated by specific key information processed in face-to-face interactions: facial emotional expression. In two separate experiments, participants received tactile stimuli, near the perceptual threshold, either on their right, left, or both cheeks. Concurrently, they watched several blocks of movies depicting a face with a neutral, happy, or fearful expression that was touched or just approached by human fingers (Experiment 1). Participants were asked to distinguish between unilateral and bilateral felt tactile stimulation. Tactile perception was enhanced when viewing touch toward a fearful face compared with viewing touch toward the other two expressions. In order to test whether this result can be generalized to other negative emotions or whether it is a fear-specific effect, we ran a second experiment, where participants watched movies of faces-touched or approached by fingers-with either a fearful or an angry expression (Experiment 2). In line with the first experiment, tactile perception was enhanced when subjects viewed touch toward a fearful face and not toward an angry face. Results of the present experiments are interpreted in light of different mechanisms underlying different emotions recognition, with a specific involvement of the somatosensory system when viewing a fearful expression and a resulting fear-specific modulation of the VRT effect. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Human spatial navigation via a visuo-tactile sensory substitution system

Spatial navigation within a real 3-D maze was investigated to study space perception on the sole basis of tactile information transmitted by means of a 'tactile vision substitution system' (TVSS) allowing the conversion of optical images-collected by a micro camera-into 'tactile images' via a matrix in contact with the skin. The development of such a device is based on concepts of cerebral and functional plasticity, enabling subjective reproduction of visual images from tactile data processing. Blindfolded sighted subjects had to remotely control the movements of a robot on which the TVSS camera was mounted. Once familiarised with the cues in the maze, the subjects were given two exploration sessions. Performance was analysed according to an objective point of view (exploration time, discrimination capacity), as well as a subjective one (speech). The task was successfully carried out from the very first session. As the subjects took a different path during each navigation, a gradual improvement in performance (discrimination and exploration time) was noted, generating a phenomenon of learning. Moreover, subjective analysis revealed an evolution of the spatialisation process towards distal attribution. Finally, some emotional expressions seemed to reflect the genesis of 'qualia' (emotional qualities of stimulation).     

LIGHT INTENSITY AND PERCEPTION OF THE VERTICAL

N yborg H. Light intensity and perception of the vertical: Two experiments with the Rod-and-Frame Test. Scand. J. Psychol ., 1972, 13 , 314–326.—Radical changes in light intensity of the visual field did not influence perception of the vertical appreciably as tested by means of a modified Rod-and-Frame Test apparatus in which the illumination of the rod and frame or of the frame alone was changed. Large individual differences in response to the Rod-and-Frame Test were found but little effect of changes in light intensity. A hypothesis that field dependent subjects would be more influenced than field independent by changes in light intensity of the rod and/or the frame was rejected.     

The Fabric of Thought: Priming Tactile Properties During Reading Influences Direct Tactile Perception

The present studies examined whether implied tactile properties during language comprehension influence subsequent direct tactile perception, and the specificity of any such effects. Participants read sentences that implicitly conveyed information regarding tactile properties (e.g., Grace tried on a pair of thick corduroy pants while shopping) that were either related or unrelated to fabrics and varied in implied texture (smooth, medium, rough). After reading each sentence, participants then performed an unrelated rating task during which they felt and rated the texture of a presented fabric. Results demonstrated that the texture properties implied in sentences influence direct tactile perception. Specifically, after reading about a smooth or rough texture, subsequent fabric ratings became notably smoother or rougher, respectively. However, we also show that there was some specificity to these effects: Fabric‐related sentences elicited more specific and interactive effects on subsequent ratings. Together, we demonstrate that under certain circumstances, language comprehension can prime tactile representations and affect direct tactile perception. Results are discussed with regard to the nature and scope of multimodal mental simulation during reading.     

An analysis of tactile letter confusions

A confusion matrix of the whole block capital letters of the alphabet was obtained so as to examine the nature of tactile letter recognition, using a 17 by 17 matrix of tactile stimulators placed against blind subjects’ backs. A hierarchical cluster analysis and a nonmetric multidimensional scaling technique were applied to the matrix. The results of the two analyses were consistent with each other and indicated that at least three independent basic letter features—enclosing shapes, vertical parallel lines, andangle of lines—play important parts in tactile letter recognition. Most confusion may be attributable to displacement of the apparent loci, omission or fusion of loci of stimulation, and failure to detect gaps in the tactile letters.     

Reorganization of tactile perception following the simulated amputation of one finger.

The tactile counterpart of diplopia has recently been described: tactile diplopia or diplesthesia. The human fingers show a rather precise organization of the cutaneous areas eliciting diplesthesia. In particular, these areas are very extensive between nonadjacent fingers (second and fourth, second and fifth, and third and fifth), suggesting that the illusory doubling depends on the lack of reciprocal interaction between cutaneous zones during manipulation. In the present study, four subjects agreed to explore and manipulate objects only through nonadjacent fingers for a period of up to six months. The amputation of the third finger was simulated by excluding it from active exploration by means of a bandage. After six months, the diplesthetic areas of the nonadjacent fingers decreased in size or completely disappeared. It is suggested that this reorganization of tactile perception is due to the increase in temporal correlation of the sensory inputs between nonadjacent fingers.     

A comparison of tactile and blurred visual form perception

Two experiments were performed to assess the similarity of tactile form perception and visual form perception under conditions of extreme visual blurring. In the first experiment, resolution and relative localization tasks were performed by five subjects under both tactile and blurred visual presentation. The results obtained here were the same for the two modalities. In the second experiment, all 26 block letters were presented to each of four subjects in two distinct methods of presentation, using both tactile and blurred visual displays. In one method, the full-field letter was flashed for 1.0 sec; in the other, a vertical slit scanned the letter from left to right. For all method comparisons, a strong similarity was found between the patterns of correct responses as a function of letter. In addition, there was a definite similarity between the two modalities in terms of which letters improved in recognizability in the change from the full-field to the slit mode of presentation. However, the overall superiority of the slit method found for tactile recognition was not obtained visually. The two experiments indicate that recognition with blurred vision is similar to recognition using the intact cutaneous sense, although some differences remain.     

Referred sensations induced by a mirror box in healthy subjects

Twenty-one healthy subjects were instructed to observe the mirror image of the tactile stimulation of their own hand (control condition) or an assistant’s hand (experimental condition) while being queried about the referred sensation (RS) in their own masked hand behind the mirror. The rated intensity of the RS under the experimental condition was significantly stronger than that under the control condition. In a second experiment, the experimental condition was replaced with the tactile stimulation of a prosthetic (rubber) hand, and was compared with the tactile stimulation of the subject’s own hand (control condition). In both of the experiments, the rated intensity of RS was significantly stronger under the experimental condition than under the control condition. The qualitative characteristics of the induced RS on the mirror image hand—including the location, sense of ownership, and various subjective feelings—were also found to vary among subjects. In conclusion, an RS could be induced in healthy subjects on the mirror image of the hand by tactile stimulations, although this effect differed substantially among individuals.     

An fMRI investigation on image generation in different sensory modalities: The influence of vividness

In the present fMRI study the issue of the specific cortices activation during imagery generation in different sensory modalities is addressed. In particular, we tested whether the vividness variability of imagery was reflected in the BOLD signal within specific sensory cortices. Subjects were asked to generate a mental image for each auditory presented sentence. Each imagery modality was contrasted with an abstract sentence condition. In addition, subjects were asked to fill the Italian version of the Questionnaire Upon Mental Imagery (QMI) prior to each neuroimaging session. In general, greater involvement of sensory specific cortices in high-vivid versus low-vivid subjects was found for visual (occipital), gustatory (anterior insula), kinaesthetic (pre-motor), and tactile and for somatic (post-central parietal) imagery modalities. These results support the hypothesis that vividness is related to image format: high-vivid subjects would create more analogical representations relying on the same specific neural substrates active during perception with respect to low-vivid subjects. Results are also discussed according to the simulation perspective.     

A test of the sensorimotor account of vision and visual perception

Two theories define the relationship between sensory experience and perception of location. The doctrine of specific nerve energies relies on hard-wired, genetically specified relationships between stimulation and perception, modifiable only within limits by adaptation. In a newer sensorimotor account, experience tunes the relationship between stimulation and perception. The perception of pressure phosphenes can differentiate the two theories, because the phosphene appears at a location predicted by physiological optics and in a modality predicted by specific nerve energies. Moving a finger vertically along the outer orbit of the eye while pressing gently on it through the lid during nasally directed gaze results in apparent motion of the phosphene out of phase with the finger, therefore in contradiction to information from motor efference to the finger, tactile sense at the fingertip, eyelid and bulb, joint receptors, and proprioception from muscles driving the finger. A test of the sensorimotor theory giving it every advantage had six observers in darkness moving their fingers along the eye and observing phosphenes for 1 h and 2400 motion cycles; the phosphene always obeyed the doctrine of specific nerve energies, never adapting or changing modality as the sensorimotor theory predicts.     

Attention and suppression affect tactile perception in reach-to-grasp movements

Reaching with the hand is characterized by a decrease in sensitivity to tactile stimuli presented to the moving hand. Here, we investigated whether tactile suppression can be canceled by attentional orienting. In a first experiment, participants performed a dual-task involving a goal-directed movement paired with the speeded detection of a tactile pulse. The pulse was either delivered to the moving or stationary hand, during movement preparation, execution, or the post-movement phase. Furthermore, stimulation was delivered with equal probability to either hand, or with a higher probability to either the moving or resting hand. The results highlighted faster RTs under conditions of higher probability of stimulation delivery to both moving and resting hands, thus indicating an attentional effect. For the motor preparation period, RTs were faster only at the resting hand under conditions where tactile stimulation was more likely to be delivered there. In a second experiment, a non-speeded perceptual task was used as a secondary task and tactile discrimination thresholds were recorded. Tactile stimulation was delivered concomitantly at both index fingers either in the movement preparation period (both before and after the selection of the movement effector had taken place), in the motor execution period, or, in a control condition, in the time-window of motor execution, but the movement of the hand was restrained. In the preparation period, tactile thresholds were comparable for the two timings of stimulation delivery; i.e., before and after the selection of the movement effector had taken place. These results therefore suggest that shortly prior to, and during, the execution of goal-directed movements, a combined facilitatory and inhibitory influence acts on tactile perception.     

Spatial patterns in tactile perception: is there a tactile field?

Previous studies of tactile spatial perception focussed either on a single point of stimulation, on local patterns within a single skin region such as the fingertip, on tactile motion, or on active touch. It remains unclear whether we should speak of a tactile field, analogous to the visual field, and supporting spatial relations between stimulus locations. Here we investigate this question by studying perception of large-scale tactile spatial patterns on the hand, arm and back. Experiment 1 investigated the relation between perception of tactile patterns and the identification of subsets of those patterns. The results suggest that perception of tactile spatial patterns is based on representing the spatial relations between locations of individual stimuli. Experiment 2 investigated the spatial and temporal organising principles underlying these relations. Experiment 3 showed that tactile pattern perception makes reference to structural representations of the body, such as body parts separated by joints. Experiment 4 found that precision of pattern perception is poorer for tactile patterns that extend across the midline, compared to unilateral patterns. Overall, the results suggest that the human sense of touch involves a tactile field, analogous to the visual field. The tactile field supports computation of spatial relations between individual stimulus locations, and thus underlies tactile pattern perception.     

Contribution of somesthetic cues to the perception of body orientation and subjective visual vertical

Without relevant visual cues, the subjective visual vertical (SVV) is biased in roll-tilted subjects toward the body axis (Aubert or A-effect). This study focused on the role of the somatosensory system with respect to the SVV and on whether somesthetic cues act through the estimated body tilt. The body cast technology was used to obtain a diffuse tactile stimulation. An increased A-effect was expected because of a greater underestimation of the body position in the body cast. Sixteen subjects placed in a tilt chair were rolled sideways from 0 degrees to 105 degrees. They were asked to verbally indicate their subjective body position and then to adjust a luminous line to the vertical under strapped and body cast conditions. Results showed a greater A-effect (p < .001) but an overestimation of the body orientation (p < .01) in the body cast condition for the higher tilt values (beyond 60 degrees). Since the otolith organs produced the same gravity response in both conditions, errors were due to a change in somesthetic cues. Visual and postural errors were not directly related (no correlation). However, the angular distance between the apparent body position and the SW remained stable, suggesting that the change in somatosensory pattern inputs has a similar impact on the cognitive processes involved in assessing the perception of external space and the sense of self-position.     

Interactions between apparent motion rivalry in vision and touch

In multistable perception, the brain alternates between several perceptual explanations of ambiguous sensory signals. It is unknown whether multistable processes can interact across the senses. In the study reported here, we presented subjects with unisensory (visual or tactile), spatially congruent visuotactile, and spatially incongruent visuotactile apparent motion quartets. Congruent stimulation induced pronounced visuotactile interactions, as indicated by increased dominance times for both vision and touch, and an increased percentage bias for the percept already dominant under unisensory stimulation. Thus, the joint evidence from vision and touch stabilizes the more likely perceptual interpretation and thereby decelerates the rivalry dynamics. Yet the temporal dynamics depended also on subjects' attentional focus and was generally slower for tactile than for visual reports. Our results support Bayesian approaches to perceptual inference, in which the probability of a perceptual interpretation is determined by combining visual, tactile, or visuotactile evidence with modality-specific priors that depend on subjects' attentional focus. Critically, the specificity of visuotactile interactions for spatially congruent stimulation indicates multisensory rather than cognitive-bias mechanisms.     

Tactile sensitivity in Asperger syndrome

People with autism and Asperger syndrome are anecdotally said to be hypersensitive to touch. In two experiments, we measured tactile thresholds and suprathreshold tactile sensitivity in a group of adults with Asperger syndrome. In the first experiment, tactile perceptual thresholds were measured. Two frequencies of vibrotactile stimulation were used: 30 and 200 Hz. The results demonstrated significantly lower tactile perceptual thresholds in the Asperger group at 200 Hz but not at 30 Hz, thus confirming tactile hypersensitivity but only for one class of stimulus. A second experiment investigated whether self-produced movement affected the perception of touch in a group of adults with Asperger syndrome. A suprathreshold tactile stimulus was produced either by the participant (self-produced condition) or by the experimenter (externally produced condition) and participants were asked to rate the perception of the tactile stimulation. The results demonstrated that, while both Asperger and control groups rated self-produced touch as less tickly than external touch, the Asperger group rated both types of tactile stimulus as significantly more tickly and intense than did the control group. This experiment confirms the finding of tactile hypersensitivity, but shows that the perceptual consequences of self-produced touch are attenuated in the normal way in people with Asperger syndrome. An abnormality in this process cannot therefore account for their tactile hypersensitivity.     

Stimulus factors in the isolation-induced aggression of Bobwhite quail and Khaki Campbell ducklings

Two studies examined the relative abilities of conspecific-derived visual and tactile stimulation to modulate the occurrence of isolation-induced aggression in Bobwhite quail and Khaki Campbell ducklings. In Experiment 1, subjects were permitted visual stimulation from conspecifics but were deprived of conspecific tactile stimulation. In both species, these subjects subsequently showed significantly less aggression towards conspecifics than birds that had been deprived of both visual and tactile stimulation from conspecifics. In Experiment 2, one group of subjects was permitted conspecific tactile stimulation but was deprived of conspecific visual stimulation. Again for both species, these subjects subsequently exhibited significantly less aggressive behavior towards conspecifics than did subjects that had been both visually and tactually de-prived. In sum, the present research suggests that both tactile and visual stimulation from a conspecific are individually sufficient to reduce isolation-induced aggression in these precocial buds.