Speed Discrimination in Luminance and Colour Stimuli as a Function of Contrast

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 49-49
Author(s):  
S M Wuerger ◽  
A H Morgan
Keyword(s):  
Carrier Frequency ◽  
Standard Stimulus ◽  
Consistent Difference ◽  
Adaptive Procedure ◽  
Gabor Function ◽  
Moving Stimulus ◽  
Measured Speed ◽  
Speed Discrimination ◽  
Luminance Stimulus ◽  
Perceived Speed

We measured speed discrimination for isoluminant red - green and luminance-defined moving stimuli. The horizontal profile of the stimuli was a Gabor function with a carrier frequency of 2 cycles deg−1. The standard stimulus was a luminance stimulus with a fixed speed of 2 deg s−1 and a fixed contrast of 0.1. The comparison stimuli were either luminance stimuli (cone contrasts: 0.05, 0.1, 0.2, 0.4) or chromatic stimuli (cone contrasts: 0.025, 0.05, 0.1). The speed of the comparison stimuli was varied by an adaptive procedure. After each trial the observer indicated which of the 2 intervals contained the slower moving stimulus. The stimuli always moved horizontally and the direction was chosen randomly at each trial. The main findings were: (i) For luminance stimuli, the perceived speed was independent of contrast (ranging from 0.1 to 0.4). For colour stimuli, the perceived speed increased with contrast for two out of four observers. (ii) The sensitivity for speed discrimination was independent of contrast for luminance and for colour stimuli. (iii) There was no consistent difference in speed discrimination sensitivity between colour and luminance stimuli when the stimuli were equated in cone contrast.

Adaptation in Macaque MT Reduces Perceived Speed and Improves Speed Discrimination

2006 ◽  
Vol 95 (1) ◽  
pp. 255-270 ◽  
Author(s):  
Bart Krekelberg ◽  
Richard J. A. van Wezel ◽  
Thomas D. Albright
Keyword(s):  
Speed Discrimination ◽  
Perceived Speed

Terminator Position Affects the Perceived Speed of Line Segments Tilted with Respect to Direction of Motion

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 141-141 ◽  
Author(s):  
K C Scott-Brown ◽  
D W Heeley
Keyword(s):  
Random Perturbation ◽  
Critical Factor ◽  
Vertical Line ◽  
Vertical Position ◽  
Stimulus Uncertainty ◽  
Line Segments ◽  
Tilted Line ◽  
Motion Measurements ◽  
Speed Discrimination ◽  
Perceived Speed

We investigated factors producing bias in the perceived speed of tilted lines in horizontal translation. The effects of grouping, collinearity, eccentricity, terminator proximity, and stimulus uncertainty on perceived speed were studied. The matched speed of vertical line compared to an inclined line was estimated with the use of a double random interleaved staircase for speed discrimination with a two-alternative forced choice. The speed of the tilted stimulus was held constant while the speed of the vertical stimulus was modified by the subject's response. Stimuli were single lines and groups of lines. The groups of short lines were arranged either in a collinear or in a randomly scattered fashion. The length of the line stimuli ranged from 0.33 deg to 7.0 deg of visual angle. Speed estimates were obtained for angles of tilt ranging from 0° to 90°. For line segments, collinearity was found to be the critical factor in determining perceived speed. Collinear segments showed a similar bias in perceived speed to single lines of the same overall length. However, randomly scattered segments were not subject to a bias in perceived speed. Random perturbation of the length or vertical position of a single line abolished the bias in perceived speed of a tilted line compared to a vertical line. Current models of the integration of motion measurements should be changed to account for the effects of topological arrangement and terminator position on the perceived speed of inclined lines.

Influence of Temporal Frequency on Perceived Speed

1977 ◽  
Vol 45 (1) ◽  
pp. 39-50 ◽  
Author(s):  
André Delorme ◽  
Jean-Yves Frigon
Keyword(s):  
Visual Perception ◽  
Spatial Frequency ◽  
Temporal Frequency ◽  
Stable Fixation ◽  
Ocular Pursuit ◽  
The Third ◽  
Contextual Elements ◽  
Moving Stimulus ◽  
Perceived Speed ◽  
Moving Line

The visual perception of velocity was studied in three experiments. The stimulus used in the first experiment was an endless striped belt moving behind a stable fixation line. In the second experiment a vertical moving line was presented in front of a stable striped background. In the third experiment the same moving line was pursued by the eye but the background was stable or moving either with the moving stimulus or in the opposite direction. The variables studied were the speed of the moving stimulus, the speed of the background, and the density (spatial frequency) of the stripes. Two theoretical explanations of the perceptual effects obtained are compared. The first explains variations of perceptual velocity in terms of density. The second asserts effects of perceptual velocity are contingent upon temporal frequency of encounters between the moving stimulus and the stable or moving contextual elements. The results favor the latter interpretation in the three experiments, but part of the results of Exp. 3 could be explained by the influence of ocular pursuit.

scholarly journals Influence of Visual Motion on Tactile Motion Perception

2006 ◽  
Vol 96 (3) ◽  
pp. 1625-1637 ◽  
Author(s):  
S. J. Bensmaïa ◽  
J. H. Killebrew ◽  
J. C. Craig
Keyword(s):  
Visual Stimulus ◽  
Visual Motion ◽  
Temporal Frequency ◽  
Sensory Level ◽  
Temporal Synchrony ◽  
Tactile Stimuli ◽  
Tactile Interaction ◽  
Visual Distractors ◽  
Speed Discrimination ◽  
Perceived Speed

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.

scholarly journals Illusory changes in the perceived speed of motion derived from proprioception and touch

2019 ◽  
Vol 122 (4) ◽  
pp. 1555-1565 ◽  
Author(s):  
Alessandro Moscatelli ◽  
Cecile R. Scotto ◽  
Marc O. Ernst
Keyword(s):  
Arm Movement ◽  
Motion Processing ◽  
Stimulus Velocity ◽  
Retinal Motion ◽  
Visual Phenomenon ◽  
Moving Stimulus ◽  
Finger Motion ◽  
Perceived Speed ◽  
Perceived Velocity

In vision, the perceived velocity of a moving stimulus differs depending on whether we pursue it with the eyes or not: A stimulus moving across the retina with the eyes stationary is perceived as being faster compared with a stimulus of the same physical speed that the observer pursues with the eyes, while its retinal motion is zero. This effect is known as the Aubert–Fleischl phenomenon. Here, we describe an analog phenomenon in touch. We asked participants to estimate the speed of a moving stimulus either from tactile motion only (i.e., motion across the skin), while keeping the hand world stationary, or from kinesthesia only by tracking the stimulus with a guided arm movement, such that the tactile motion on the finger was zero (i.e., only finger motion but no movement across the skin). Participants overestimated the velocity of the stimulus determined from tactile motion compared with kinesthesia in analogy with the visual Aubert–Fleischl phenomenon. In two follow-up experiments, we manipulated the stimulus noise by changing the texture of the touched surface. Similarly to the visual phenomenon, this significantly affected the strength of the illusion. This study supports the hypothesis of shared computations for motion processing between vision and touch. NEW & NOTEWORTHY In vision, the perceived velocity of a moving stimulus is different depending on whether we pursue it with the eyes or not, an effect known as the Aubert–Fleischl phenomenon. We describe an analog phenomenon in touch. We asked participants to estimate the speed of a moving stimulus either from tactile motion or by pursuing it with the hand. Participants overestimated the stimulus velocity measured from tactile motion compared with kinesthesia, in analogy with the visual Aubert–Fleischl phenomenon.

Orientation Discrimination for Moving Isoluminant and Luminance Targets

Perception ◽  
1996 ◽  
Vol 25 (1_suppl) ◽  
pp. 182-182
Author(s):  
S M Wuerger ◽  
M J Morgan
Keyword(s):  
Standard Deviation ◽  
Spatial Frequency ◽  
Psychometric Function ◽  
Carrier Frequency ◽  
Spatial Vision ◽  
Orientation Discrimination ◽  
Moving Target ◽  
Binary Decision ◽  
Gabor Function

Last year we presented orientation discrimination thresholds for stationary isoluminant red — green and luminance-defined stimuli as a function of spatial frequency and contrast (Wuerger and Morgan, 1995 Perception24 Supplement, 16). The horizontal profile of the stimuli was a Gabor function with a carrier frequency of either 0, 2, or 4 cycles deg−1. Observers made a binary decision (clockwise versus anticlockwise from vertical) and thresholds were defined as the standard deviation of their psychometric function. One main finding was that for carrier frequencies of 2 and 4 cycles deg−1, when stimuli of equal cone contrast are compared, orientation discrimination thresholds for red — green isoluminant stimuli do not differ significantly from the thresholds for luminance-defined stimuli. To further characterise the chromatic mechanisms involved in spatial vision, we assessed orientation discrimination thresholds for isoluminant red — green and luminance-defined Gabor stimuli as a function of the velocity of the moving target. When velocity is increased, orientation discrimination thresholds for isoluminant targets increase more rapidly than the thresholds for luminance targets of identical cone contrasts. We conclude that orientation discrimination is mediated by different chromatic mechanisms with different spatial and temporal sensitivities.

scholarly journals Enhanced Optic Flow Speed Discrimination While Walking: Contextual Tuning of Visual Coding

Perception ◽  
10.1068/p5845 ◽  
2007 ◽  
Vol 36 (10) ◽  
pp. 1465-1475 ◽  
Author(s):  
Frank H Durgin ◽  
Krista Gigone
Keyword(s):  
Flow Field ◽  
Optic Flow ◽  
Flow Speed ◽  
Visual Coding ◽  
Choice Procedure ◽  
Flow Speeds ◽  
Forced Choice Procedure ◽  
Speed Discrimination ◽  
Self Motion ◽  
Perceived Speed

We tested the hypothesis that long-term adaptation to the normal contingencies between walking and its multisensory consequences (including optic flow) leads to enhanced discrimination of appropriate visual speeds during self-motion. In experiments 1 (task 1) and 2 a two-interval forced-choice procedure was used to compare the perceived speed of a simulated visual flow field viewed while walking with the perceived speed of a flow field viewed while standing. Both experiments demonstrated subtractive reductions in apparent speed. In experiments 1 and 3 discrimination thresholds were measured for optic flow speed while walking and while standing. Consistent with the optimal-coding hypothesis, speed discrimination for visual speeds near walking speed was enhanced during walking. Reduced sensitivity was found for slower visual speeds. The multisensory context of walking alters the coding of optic flow in a way that enhances speed discrimination in the expected range of flow speeds.

Effect of Repetitive Transcranial Magnetic Stimulation on a Target Moving in Front of a Static or Random Dynamic Visual Noise

Perception ◽  
2020 ◽  
Vol 49 (8) ◽  
pp. 882-892
Author(s):  
Luca Battaglini
Keyword(s):  
Transcranial Magnetic Stimulation ◽  
Magnetic Stimulation ◽  
Repetitive Transcranial Magnetic Stimulation ◽  
Control Site ◽  
Visual Noise ◽  
Dynamic Visual Noise ◽  
Temporal Area ◽  
Early Visual Cortex ◽  
Speed Discrimination ◽  
Perceived Speed

Observers report seeing as slower a target disk moving in front of a static visual noise (SVN) background than the same object moving in front of a random dynamic visual noise (rDVN) background when the speed is the same. To investigate in which brain region (lower vs. higher visual areas) the background and the target signals might be combined to elicit this misperception, the transcranial magnetic stimulation (TMS) was delivered over the early visual cortex (V1/V2), middle temporal area (MT) and Cz (control site) while participants performed a speed discrimination task with targets moving in front of an SVN or an rDVN. Results showed that the TMS over MT reduced the perceived speed of the target moving in front of an SVN, but not when the target was moving in front of an rDVN background. Moreover, the TMS do not seem to interfere with encoding processing but more likely affected decoding processing in conditions of high uncertainty (i.e., when targets have similar speed).

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