Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2006 Sep;96(3):1625-37.
doi: 10.1152/jn.00192.2006. Epub 2006 May 24.

Influence of Visual Motion on Tactile Motion Perception

Affiliations
Free PMC article

Influence of Visual Motion on Tactile Motion Perception

S J Bensmaïa et al. J Neurophysiol. .
Free PMC article

Abstract

Subjects were presented with pairs of tactile drifting sinusoids and made speed discrimination judgments. On some trials, a visual drifting sinusoid, which subjects were instructed to ignore, was presented simultaneously with one of the two tactile stimuli. When the visual and tactile gratings drifted in the same direction (i.e., from left to right), the visual distractors were found to increase the perceived speed of the tactile gratings. The effect of the visual distractors was proportional to their temporal frequency but not to their perceived speed. When the visual and tactile gratings drifted in opposite directions, the distracting effect of the visual distractors was either substantially reduced or, in some cases, reversed (i.e., the distractors slowed the perceived speed of the tactile gratings). This result suggests that the observed visual-tactile interaction is dependent on motion and not simply on the oscillations inherent in drifting sinusoids. Finally, we find that disrupting the temporal synchrony between the visual and tactile stimuli eliminates the distracting effect of the visual stimulus. We interpret this latter finding as evidence that the observed visual-tactile interaction operates at the sensory level and does not simply reflect a response bias.

Figures

FIG. 1
FIG. 1
Experimental set-up. The distal finger pad of the subject’s left index finger was pressed against the 400-probe array with a force of 100 g using a counter-weight. The computer monitor was interposed between the subject’s finger and his head. The distance between the monitor screen and the subject’s face was 20 cm, and the distance between the probe array and the screen was 30 cm.
FIG. 2
FIG. 2
Experiment 1: effect of a visual distractor on tactile speed discrimination. Each plot shows the proportion of times the comparison (λt = 8 mm) was judged to be faster than the standard (λt = 8 mm, Vt = 40 mm/s) as a function of the drift speed of the comparison. The blue trace shows the subjects’ performance in the presence of a visual distractor, the parameters of which are indicated in the bottom right of each subplot, presented at the same time as the comparison stimulus. The green trace shows baseline performance in the absence of a distractor. Plots shaded in blue show conditions in which the visual distractor significantly increased the perceived speed of the tactile comparison stimulus. Error bars represent ±1 SE.
FIG. 3
FIG. 3
Experiment 2: proportion of times subjects judged the visual comparison to be faster than the tactile standard (λt = 8 mm, Vt = 40 mm/s). Error bars represent ±1 SE.
FIG. 4
FIG. 4
Experiment 3. Effect of the temporal frequency of the visual distractors on tactile speed discrimination (TSD). The effect of the distractor increases as the temporal frequency of the visual distractor increases. TSD performance can be predicted from the temporal frequency and comparison speed; the effect of spatial period is nonsignificant. Error bars represent ±1 SE.
FIG. 5
FIG. 5
Effect of visual distractor on TSD plotted against temporal frequency. The parameters of the psychometric functions fit to individual subjects’ data: μ (○) denotes a biasing effect, σ (□) an effect on discriminability (see text). —, parameters fitted to data obtained with a 5-mm visual distractor; · · · , data obtained with a 20-mm distractor. The magnitude of the effect of the visual distractor is a function of its temporal frequency. Error bars represent ±1 SE.
FIG. 6
FIG. 6
Effect of visual distractor on TSD plotted as a function of temporal frequency (data replotted from experiment 1). The parameters of the psychometric functions fit to individual subjects’ data: μ (○) denotes a biasing effect, σ (□) an effect on discriminability (see text). Left: results with 3 different wavelength (λv = 20, 10 and 5 mm) when drift speed is constant (Vv = 40 mm/s). Right: results with 6 different drift speeds (Vv = 5, 10, 20, 40, 60, and 80 mm/s) when wavelength is constant (λv = 10 mm). Data points plotted at temporal frequency = 0 Hz denote the baseline values for the psychometric parameters. Data from the constant-speed and constant-wavelength conditions are plotted separately as they were run in separate blocks (see DISCUSSION). Error bars represent ±1 SE.
FIG. 7
FIG. 7
Magnitude estimation of the drift speed of visual distractors identical to those presented in experiments 1 and 3. Each trace corresponds to the ratings (normalized within subject, averaged over 6 subjects) obtained for visual gratings at a given spatial period. Perceived speed was not solely a function of temporal frequency as evidenced by the fact that the 3 traces do not overlap. Error bars represent ±1 SE.
FIG. 8
FIG. 8
Experiment 4: effect of a visual distractor on TSD when the visual and tactile stimuli are drifting in opposite directions. Plots shaded in blue show conditions in which the visual distractor significantly increased the perceived speed of the tactile comparison stimulus; the red shading indicates conditions in which the distractor significantly decreased the perceived speed. Error bars represent ±1 SE.
FIG. 9
FIG. 9
Experiment 5: effect of the 3 most effective visual distractors in experiment 1 when the synchrony between tactile and visual stimuli is removed, along with that of a distractor (10 mm, 40 mm/s) that did not produce an effect in experiment 1; the latter distractor still has no effect on TSD; for the former, the effect disappears almost completely and is nonsignificant except for the [5 mm, 40 mm/s] distractor. Error bars represent ±1 SE.
FIG. 10
FIG. 10
Psychometric functions obtained from individual subjects in experiment 1. Left: baseline TSD performance; right: performance in the presence of a 10-mm, 80-mm/s visual distractor. The dark traces show the baseline condition averaged across subjects. Most of the functions in the experimental condition fall to the left of the mean baseline performance, suggesting some degree of bias in most subjects. For some subjects, the bias was much larger in magnitude than for others.
FIG. 11
FIG. 11
Summary of the effects of the visual distractors on TSD in experiments 1, 4, and 5. The ‘effect index’ denotes the value of the psychometric parameter—σ or μ— obtained in the experimental condition minus that obtained in the control condition. Changes in μ suggest a perceptual bias, changes in σ point to a change in the discriminability of the stimuli. The parameters of the visual distractors are shown beneath each plot: [spatial period (mm) drift speed (mm/s)]. The box plots show the median (interior line) and upper and lower quartiles. The whiskers show the range of the data without outliers (>1 interquartile range from median). An outlier is denoted by a plus. The effect of the visual distractors varied considerably across subjects: Some subjects showed no effect whereas, for other subjects, TSD judgments were almost completely “captured” by the visual distractor.

Similar articles

See all similar articles

Cited by 23 articles

See all "Cited by" articles

Publication types

LinkOut - more resources

Feedback