A lateral masking effect in tactile and blurred visual letter recognition

In a letter recognition task in which the letters were presented temporally across two columns of a vibrotactile array, the masking effects of added columns of steady vibrotactile stimulation were investigated. The primary variable studied was the spatial separation between the masking columns and the letter-carrying columns. The results indicate a spatially dependent masking effect which is independent of the tactile masking associated with mask onset. A comparable masking effect was obtained with visual letter recognition using the same relative stimulus configurations viewed under conditions of optical blurring. An interpretation of the tactile masking is offered in terms of the limited spatial resolution of the cutaneous sense.     

Sensitivity to shifts of a point stimulus: An instance of tactile hyperacuity

The sensitivity of the tactile sense to shifts in the position of a point stimulus was determined at four body loci: the index finger, forehead, belly, and back. Water-jet stimulation was used, a method which allows frictionless travel of a point stimulus over the skin. Three subjects were tested by means of the method of forced choice, with the task being to say whether the stimulus moved to the right or to the left. The shift threshold was defined as that shift excursion which gave rise to 75% correct responding. The basic finding was that shift thresholds were on the order of 10 to 30 times smaller than the corresponding two-point limens obtained by Weinstein (1968) for the same body loci. These unexpectedly small shift thresholds indicate an exquisite sensitivity of the cutaneous sense to rapid changes in position of a point stimulus. A physiological model is presented which accounts for the difference between localization and spatial resolution. nt]mis|This research was supported by Department of Health~ Education, and Welfare Grant 14-P-SS282/9 from the Social and Rehabilitation Services, NIH Research Grant R01-EY-00686 from the National Eye Institute, and the Smith-Kettlewell Eye Research Foundation.     

Laterality differences and shifts as a function of tactile temporal pattern complexity: Implications for differential processing strategies of the cerebral hemispheres

Summary The ability of subjects with a right-hand or left-hand preference to report accurately the number of tactile pulses in temporal sequences presented to preferred and nonpreferred hands was investigated as a function of temporal pattern complexity which varied in terms of intrinsic temporal relations among successive pulses and ranged from slow regular (periodic) sequences of small numbers of pulses to fast irregular (aperiodic) sequences of large numbers of pulses. As the complexity of the pattern increased in terms of pulse number, presentation rate, pulse density, and pulse aperiodicity, all subjects, for both preferred- and nonpreferred-hand stimulation, were increasingly less accurate in reporting the number of pulses in a temporal pattern. Most interesting was the finding that although hand-preference groups did not differ reliably in overall report accuracy, both groups showed a consistent shift in report accuracy from preferred- to nonpreferred-hand stimulation when patterns had more than seven pulses; furthermore, these shifts occurred for all presentation rates and pulse periodicities. A possible relationship between hand preference and cerebral psychological organization is suggested and the data are discussed in terms of the laterality differences reflecting basic underlying cerebral asymmetries in stimulus processing.These investigations were supported by Grant A8621 from the National Research Council of Canada. This paper was prepared while the author was a Visiting Researcher at the Department of Psychology, University of Stockholm, and supported, in part, by a Leave Fellowship awarded by the Social Sciences and Humanities Research Council of Canada. I would like to thank Gordon Tanne for his assistance in data collection and analysis. Requests for offprints should be sent to E.C. Lechelt, Department of Psychology, University of Alberta, Edmonton, Alberta, Canada T6G 2E9.     

Implicit processing of tactile information: evidence from the tactile change detection paradigm

People can maintain accurate representations of visual changes without necessarily being aware of them. Here, we investigate whether a similar phenomenon (implicit change detection) also exists in touch. In Experiments 1 and 2, participants detected the presence of a change between two consecutively-presented tactile displays. Tactile change blindness was observed, with participants failing to report the presence of tactile change. Critically, however, when participants had to make a forced choice response regarding the number of stimuli presented in the two displays, their performance was significantly better than chance (i.e., implicit change detection was observed). Experiment 3 demonstrated that tactile change detection does not necessarily involve a shift of spatial attention toward the location of change, regardless of whether the change is explicitly detected. We conclude that tactile change detection likely results from comparing representations of the two displays, rather than by directing spatial attention to the location of the change.     

About the time-shrinking illusion in the tactile modality

The aim of this study was to examine the occurrence of a so-called time-shrinking illusion in the tactile modality, while it had been tested so far mainly with auditory and visual stimuli. We examined whether the perception of an empty time interval marked by two brief tactile stimuli, S (240 ms), would be influenced by the presence of a preceding time interval, P (160, 240, or 320 ms). Results showed that S was underestimated when P was shorter than S. This underestimation appeared as a kind of perceptual assimilation between P and S, but S was not overestimated when P was longer. The underestimation was rather interpreted as a manifestation of the time-shrinking illusion.     

Stimulus contrast in tactile resolutlon

This experiment was designed to test the influence of contrast on tactile resolution by the use of different modes of distribution of pressure stimuli, with control of various factors such as intensity, area, rate, and time of application. The experimental task was two-point discrimination. The results showed that the use of annular stimuli result in a significantly higher number of resolutions than the use of circular stimuli, the intensity, total stimulating area, and pressure being controlled. The proposed interpretation of the results is that increase of stimulus contrast increases the resolving power of the somesthetic system.     

Interference in localizing tactile stimuli

A series of experiments investigated the ability of subjects to localize a tactile stimulus in the presence of an additional, extraneous tactile stimulus. The subject's task was to localize a tactile stimulus (target) presented at one of several locations on his or her left index fingerpad. The target stimulus, generated on a 6 x 24 array of stimulators, was presented either by itself or in the presence of an extraneous stimulus (masker) that either preceded or followed the target. The localizability of the target was affected by the temporal separation between the target and masker in much the same way as previous studies have shown identification of tactile patterns to be affected. Unlike previous identification results, presenting the masking stimulus to the same location as the target interfered with localizability, although not as much as did presenting the masker to a different location. The results are discussed in terms of their implications for identification and discrimination of tactile patterns.     

Expertise in tactile pattern recognition

This article explores expertise in tactile object recognition. In one study, participants were trained to differing degrees of accuracy on tactile identification of two-dimensional patterns. Recognition of these patterns, of inverted versions of these patterns, and of subparts of these patterns was then tested. The inversion effect (better recognition of upright than inverted patterns) and the part-whole effect (better recognition of the whole than a part pattern), traditionally considered signatures of visual expertise, were observed for tactile experts but not for novices. In a second study, participants were trained as visual or tactile experts and then tested in the trained and nontrained modalities. Whereas expertise effects were observed in the modality of training, cross-modal transfer was asymmetric; visual experts showed generalization to haptic recognition, but tactile experts did not show generalization to visual recognition. Tactile expertise is not obviously attributable to visual mediation and emerges from domain-general principles that operate independently of modality.     

Detection of tactile pulses

ROC curves were obtained by the rating-scale method for the detection of brief mechanical pulses presented to the finger and dorsal forearm to study differences in detection processes at the two sites. An adaptive psychophysical procedure was successful in equating detectability at the two sites when data were averaged across sessions. Criteria adopted by the Os appeared to depend on locus of stimulation, since fewer false alarms were given at the arm than at the finger. These findings were discussed with respect to continuous and multistate detection models.     

Recent developments in the study of tactile attention.

The last few years have seen a rapid growth of research on the topic of tactile attention. We review the evidence showing that attention can be directed to the tactile modality, or to the region of space where tactile stimuli are presented, in either an endogenous or exogenous (top-down or bottom-up) manner. We highlight the latest findings on the interaction between these two forms of attentional orienting in touch. We also review the latest research on tactile numerosity judgments and change detection highlighting the severe cognitive (attentional) limitations that constrain people's ability to process more complex tactile information displays. These findings are particularly important given that tactile interfaces are currently being developed for a number of different application domains.     

Spatial-frequency specificity in visual masking

Visual masking between nonoverlapping gratings depends on the similarity of their spatial frequencies. In a metacontrast experiment, bar gratings of 6 and 12 cycles/deg were masked by flanking gratings of various spatial frequencies. For three observers, masking was greatest when the masking frequency was approximately equal to the masked frequency. The results are interpreted in terms of a theory of reciprocal inhibition among frequency-specific neural units.     

Current concerns in visual masking

Theories of emotion postulate that emotional input is processed independently from perceptual awareness. Although visual masking has a long tradition in studying whether emotional pictures are processed below a supposed threshold of perceptual awareness (subliminal perception), a consensus has yet to be reached. This article reviews current concerns in the use of visual masking. These include a reliable presentation method, the role of masking pictures, common definitions of awareness and their problems, current models of awareness, and neural mechanisms. A useful strategy may be the study of dose-response relationships between awareness and emotion processing that avoids a dichotomous view of awareness and allows conclusions about the relative independence of emotional processing from awareness.