Directional sensitivity to a tactile point stimulus moving across the fingerpad

The ability of subjects to discriminate between directions of a point contact moving across the fingerpad was examined. Subjects were required to report, using an adaptive two-interval, two-alternative forced-choice procedure, whether in two sequential stimuli the direction of motion changed in a clockwise or counterclockwise direction. The overall mean orientation-change threshold across eight stimulus orientations was approximately 14°, with the lowest threshold for the point motion toward the wrist. This observed lower threshold in the distal-to-proximal direction is thought to be due to stretching of the skin at the tip of the fingernail, to which one may be particularly sensitive. For all orientations, thresholds were generally more uniform and higher than those reported on vibrotactile linear contactor arrays for horizontal and vertical orientations.     

Short-term memory for spatial configurations in the tactile modality: A comparison with vision

This study investigates the role of acquisition constraints on the short-term retention of spatial configurations in the tactile modality in comparison with vision. It tests whether the sequential processing of information inherent to the tactile modality could account for limitation in short-term memory span for tactual-spatial information. In addition, this study investigates developmental aspects of short-term memory for tactual- and visual-spatial configurations. A total of 144 child and adult participants were assessed for their memory span in three different conditions: tactual, visual, and visual with a limited field of view. The results showed lower tactual-spatial memory span than visual-spatial, regardless of age. However, differences in memory span observed between the tactile and visual modalities vanished when the visual processing of information occurred within a limited field. These results provide evidence for an impact of acquisition constraints on the retention of spatial information in the tactile modality in both childhood and adulthood.     

Lateral asymmetry and tactile sensitivity

Weinstein found in 1963 that the left female breast is more sensitive to tactile stimulation than the right breast. Saling and Cooke in 1984 hypothesized that this asymmetry in breast sensitivity underlies the well-documented leftward bias in maternal cradling behaviour, which is independent of manual specialization. Our interest in the Saling and Cooke hypothesis led to an attempt to replicate Weinstein's 1963 study. His findings were not supported. Further, a review of the literature on the lateral distribution of cutaneous thresholds showed that there is little experimental support for the widely held belief that the left side of the body is uniformly more sensitive than the right.     

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.     

Relative roles of spatial and intensive cues in the discrimination of spatial tactile stimuli

Two psychophysical measures of tactile sensitivity--grating-orientation (GO) and smooth-grooved (SG) discrimination--were used to determine tactile spatial acuity with and without an intermediate surface (latex glove) interposed between the contactor and the skin. Measures were made at three locations that varied in sensitivity and in density of innervation of the primary afferent fibers: the index fingerpad (fingertip), palmar surface of the proximal phalanx (fingerbase), and the thenar eminence (palm). Neurophysiological studies have suggested that the density of innervation of SAI fibers is a limiting factor in spatial acuity. In the present study, without a glove, the GO thresholds varied as a function of location. With the glove, increases in the GO thresholds were relatively uniform and modest. Without a glove, however, the SG thresholds were well below the GO thresholds, and changing the site of stimulation had little effect on the threshold. With a glove, the SG thresholds increased by 100% to more than 300% as in comparison with those in the no-glove condition. The largest increases occurred at the less sensitive locations. The results of the GO task are consistent with the view that GO is a valid measure of spatial acuity. The results of the SG task, however, are inconsistent with previous results and suggest that both spatial and intensive factors are involved in this task.     

The effect of spatial orientation on the perception of moving tactile stimuli

Previous studies have shown that the perception of spatial patterns, such as letters, presented to the hand is affected by the spatial orientation of the hand. The present study investigated how the perception of direction of motion across the fingerpads changes with the position of the hand in space. The moving stimuli were generated on two displays. In one condition, the displays were placed horizontally in front of the subject, with the subject’s thumb (target site) and index finger (nontarget site) placed flat on the displays. In a second condition, the displays were vertically oriented and gripped between the thumb and index finger. Using a selective-attention paradigm in which subjects are instructed to respond only to the direction of motion at the target site, performance was still affected by the direction of motion at the nontarget site. Changing the orientation of the displays changed the effectiveness of the nontarget in interfering with the identification of the target movement. Nontarget stimuli that produced no interference in the horizontal orientation did so in the vertical, and vice versa. It appears that subjects are not using the local direction of movement across the fingerpads to judge the relative direction of movement at the two sites; rather, they are using the external direction of movement.     

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.     

Processing of tactile spatial information with crossed fingers

The erroneous perception of two objects when one object is touched with crossed fingers has been explained as an inability of the brain to correctly perceive the crossed fingers' positions. This account is examined in Experiment 1, in which the perceived position of stimuli touching the crossed fingers is mapped. Crossing the third finger over the fourth displaced the perceived stimulus position counter-clockwise; crossing the third under the fourth displaced perceptions clockwise. In Experiment 2, perceived positions were found to fit a model of tactile saturation past the point of the functional range of action of the fingers. Two major conclusions are drawn: (a) Tactile stimuli are always perceived as if fingers were uncrossed, and (b) spatial mapping is present only within the functional range of finger excursion.     

A low-cost spatial contrast sensitivity display driver

The circuit described here can provide the line and frame signals to drive anx, y display scope or oscilloscope at high resolution (1,000 lines) and repetition rate (50 Hz). Synchronizing circuitry at the input of the circuit allows the raster scan to be locked to an input signal, such as the square-wave output from a function generator, while another waveform from the same function genera-tor, the sine output, drives the z (intensity) input of the display scope. A stable spatial contrast display results. Spatial contrast depth is a direct function of z input modulation voltage. Spatial frequency is a direct function of the function generator frequency. The circuit can be used with a programmable function generator under computer control.     

A comparison of backward and forward spatial spans

The standard Corsi blocks task is frequently used to measure the capacity of visuospatial working memory, but the implications of the use of both forward and backward recall are still unclear. In the present study, we showed that the backward Corsi task is particularly powerful in discriminating between low- and high-spatial-ability individuals and involves different processes from those involved in the forward task. From a sample of 425 participants we selected one group of 20 high-spatial-ability participants and one of 20 low-spatial-ability participants. The results demonstrated that a backward spatial span offers specific information not available from a forward spatial span, and that there was no facilitation due to a descending format. In particular, in the low-spatial-ability group, performance was generally poorer, but backward Corsi recall was lower than forward recall, and participants did not show any advantage following the descending presentation format—which in some contexts is considered to reduce proactive interference. We conclude that the backward Corsi task has specific value and that the assumption of fully parallel verbal and visuospatial working-memory systems can lead to a variety of misunderstandings.     

A comparison of backward and forward spatial spans

The standard Corsi blocks task is frequently used to measure the capacity of visuospatial working memory, but the implications of the use of both forward and backward recall are still unclear. In the present study, we showed that the backward Corsi task is particularly powerful in discriminating between low- and high-spatial-ability individuals and involves different processes from those involved in the forward task. From a sample of 425 participants we selected one group of 20 high-spatial-ability participants and one of 20 low-spatial-ability participants. The results demonstrated that a backward spatial span offers specific information not available from a forward spatial span, and that there was no facilitation due to a descending format. In particular, in the low-spatial-ability group, performance was generally poorer, but backward Corsi recall was lower than forward recall, and participants did not show any advantage following the descending presentation format—which in some contexts is considered to reduce proactive interference. We conclude that the backward Corsi task has specific value and that the assumption of fully parallel verbal and visuospatial working-memory systems can lead to a variety of misunderstandings.     

Tactile spatial sensitivity and anisotropy

A gap detection task was examined for its usefulness as a measure of tactile spatial sensitivity and as a measure of anisotropy. In Experiment 1, sensitivity was measured with a gap detection task both with and without a latex glove at three locations on the hand: the fingerpad, fingerbase, and palm. Results showed that sensitivity varied as a function of location and was correlated with changes in the density of innervation of the primary afferent fibers. In accord with other measures of spatial sensitivity, the glove had a moderate effect on sensitivity in the gap detection task. The results both with and without the glove were more similar to those obtained using another measure of spatial sensitivity, the grating orientation task, than to those obtained using the smooth-grooved task, which is considered an intensive measure. In Experiments 2-4, anisotropy was examined using the gap detection and grating orientation tasks, as well as the smooth-grooved task. Locations on the index finger, palm, and arm were tested. Results indicated that anisotropy was revealed only by tasks that relied on spatial cues. The differences between spatial sensitivity measured in the proximal-distal orientation as compared with the lateral-medial orientation varied by location and were as much as 2.35/1. The results are discussed in terms of what they may reveal about the underlying mechanisms responsible for tactile anisotropy.     

Integration of hand and finger location in external spatial coordinates for tactile localization

Tactile stimulus location is automatically transformed from somatotopic into external spatial coordinates, rendering information about the location of touch in three-dimensional space. This process is referred to as tactile remapping. Whereas remapping seems to occur automatically for the hands and feet, the fingers may constitute an exception in that some studies have implied purely somatotopic coding of touch to the fingers. When participants judge the order of two tactile stimuli, they often err when the stimulated body parts (usually the two hands) are crossed, presumably because somatotopic and external coordinates are in conflict in crossed postures. Using this task, we investigated, first, whether the fingers are unlike other limbs with regard to spatial coding, by testing whether crossing effects, indicative of external coding, were observable when stimulating two fingers, either on the same or on different hands. Second, we investigated the interaction of hand and finger posture in tactile localization of finger stimuli. Crossing effects emerged when fingers and hands were crossed, suggesting external coding for all body parts. Crossing effects were larger when both hand and finger were located in the hemifield opposite to their body side, and smaller when only hand or finger lay in the opposite hemifield. We suggest that tactile location is estimated by integrating the external location of all relevant body parts, here of a finger and its belonging hand, and that such integrative coding may represent a general principle for body part processing as well as for tool use.     

A comparison of the effects of spatial separation on apparent motion in the auditory and visual modalities

In the present investigation, the effects of spatial separation on the interstimulus onset intervals (ISOIs) that produce auditory and visual apparent motion were compared. In Experiment 1, subjects were tested on auditory apparent motion. They listened to 50-msec broadband noise pulses that were presented through two speakers separated by one of six different values between 0 degrees and 160 degrees. On each trial, the sounds were temporally separated by 1 of 12 ISOIs from 0 to 500 msec. The subjects were instructed to categorize their perception of the sounds as "single," "simultaneous," "continuous motion," "broken motion," or "succession." They also indicated the proper temporal sequence of each sound pair. In Experiments 2 and 3, subjects were tested on visual apparent motion. Experiment 2 included a range of spatial separations from 6 degrees to 80 degrees; Experiment 3 included separations from .5 degrees to 10 degrees. The same ISOIs were used as in Experiment 1. When the separations were equal, the ISOIs at which auditory apparent motion was perceived were smaller than the values that produced the same experience in vision. Spatial separation affected only visual apparent motion. For separations less than 2 degrees, the ISOIs that produced visual continuous motion were nearly equal to those which produced auditory continuous motion. For larger separations, the ISOIs that produced visual apparent motion increased.     

Gestalt grouping effects on tactile information processing: when touching hands override spatial proximity

Using a tactile variant of the negative-priming paradigm, we analyzed the influence of Gestalt grouping on the ability of participants to ignore distracting tactile information. The distance between participants’ hands, to which the target and distractor stimuli were simultaneously delivered, was varied (near/touching hands vs. hands far apart). In addition, the influence of touching hands was controlled, as participants wore gloves and their hands were blocked from vision by a cover. The magnitude of the tactile negative-priming effect was modulated by the interaction between hand separation and whether or not gloves were worn. When the hands were touching, negative priming emerged only while wearing gloves that prevented direct skin-to-skin contact. In contrast, when the separation between the participants’ hands was larger, negative priming emerged only when gloves were not worn. This pattern of results is interpreted in terms of the competing influences of two interacting Gestalt principles—namely, connectedness and proximity—on the processing of tactile distractors.     

A comparison of visual and auditory representational momentum in spatial tasks

Similarities have been observed in the localization of the final position of moving visual and moving auditory stimuli: Perceived endpoints that are judged to be farther in the direction of motion in both modalities likely reflect extrapolation of the trajectory, mediated by predictive mechanisms at higher cognitive levels. However, actual comparisons of the magnitudes of displacement between visual tasks and auditory tasks using the same experimental setup are rare. As such, the purpose of the present free-field study was to investigate the influences of the spatial location of motion offset, stimulus velocity, and motion direction on the localization of the final positions of moving auditory stimuli (Experiment 1 and 2) and moving visual stimuli (Experiment 3). To assess whether auditory performance is affected by dynamically changing binaural cues that are used for the localization of moving auditory stimuli (interaural time differences for low-frequency sounds and interaural intensity differences for high-frequency sounds), two distinct noise bands were employed in Experiments 1 and 2. In all three experiments, less precise encoding of spatial coordinates in paralateral space resulted in larger forward displacements, but this effect was drowned out by the underestimation of target eccentricity in the extreme periphery. Furthermore, our results revealed clear differences between visual and auditory tasks. Displacements in the visual task were dependent on velocity and the spatial location of the final position, but an additional influence of motion direction was observed in the auditory tasks. Together, these findings indicate that the modality-specific processing of motion parameters affects the extrapolation of the trajectory.     

The influence of spatial contrast on the frequency-dependent nature of vibration sensitivity

Several stimulus configurations have been described for measuring the threshold for vibration perception. One such configuration, used primarily for screening for peripheral nervous system function, for example, consists of a matrix of 24 rows and 6 columns of tiny pins vibrating at 230 Hz, with the even rows of pins vibrating in opposite phase to the uneven rows. In order to determine which class of mechanoreceptors is being tested with such a stimulus, the frequency dependence of the threshold for vibration perception was measured with a similar stimulus configuration in a group of younger subjects and in a group of older subjects. Moreover, the stimulus configuration could be changed from opposite phase stimulation to equal phase stimulation, wherein all pins vibrated with equal phase. In the range above 160 Hz, it appeared that in younger subjects the threshold of the Pacinian receptor system was evaluated with both modes of stimulation, although the sensitivity for opposite phase stimulation was reduced relative to the sensitivity for equal phase stimulation. In the older subjects, equal phase stimulation also appeared to evaluate the Pacinian receptor system. However, with the opposite phase stimulation, the non-Pacinian receptors tended to be evaluated. Below 100 Hz, sensitivity was greater for opposite phase than for equal phase stimulation in both groups. Moreover, with both modes of stimulation, a sensitivity maximum at 40 Hz could be obtained, which was tentatively ascribed to the rapidly adapting class of mechanoreceptors.     

Effects of body image on tactile sensitivity to a tickle:: a study of pregnancy

A group of 20 middle-class women between 20 and 40 yr. of age and in the third trimester of pregnancy was compared with a control group of 20 non-pregnant women for cutaneous sensitivity (to a tickle) and for modifications of body schema which were hypothesized to occur during pregnancy. Latency and actual duration were considered in the perception of the tickle. Body schema were studied using two of Fisher's tests, Body Prominence and Body Cathexis. Pregnancy leads to modifications in sensitivity to tickle, specifically with regard to the right half of the body and to some extent in body schema.