Performance Characterization of Watson Ahumada Motion Detector Using Random Dot Rotary Motion Stimuli

Abstract

The performance of Watson & Ahumada's model of human visual motion sensing is compared against human psychophysical performance. The stimulus consists of random dots undergoing rotary motion, displayed in a circular annulus. The model matches psychophysical observer performance with respect to most parameters. It is able to replicate some key psychophysical findings such as invariance of observer performance to dot density in the display, and decrease of observer performance with frame duration of the display.Associated with the concept of rotary motion is the notion of a center about which rotation occurs. One might think that for accurate estimation of rotary motion in the display, this center must be accurately known. A simple vector analysis reveals that this need not be the case. Numerical simulations confirm this result, and may explain the position invariance of MST(d) cells. Position invariance is the experimental finding that rotary motion sensitive cells are insensitive to where in their receptive field rotation occurs.When all the dots in the display are randomly drawn from a uniform distribution, illusory rotary motion is perceived. This case was investigated by Rose & Blake previously, who termed the illusory rotary motion the omega effect. Two important experimental findings are reported concerning this effect. First, although the display of random dots evokes perception of rotary motion, the direction of motion perceived does not depend on what dot pattern is shown. Second, the time interval between spontaneous flips in perceived direction is lognormally distributed (mode≈2 s). These findings suggest the omega effect fits in the category of a typical bistable illusion, and therefore the processes that give rise to this illusion may be the same processes that underlie much of other bistable phenomenon.

Intrinsic timescales of sensory integration for motion perception

“…4a). Consistent with previous studies, most subjects reported illusory rotational motion in this condition and the direction of perceived motion was periodically altered, spontaneously 23 . To quantify temporal features of this bistable perception, we measured the phase duration, τ, of illusory motion in one direction.…”

“…We further examined the notion that the observed intrinsic kernel may predict subjects’ behavior for illusory motion perception. Previous studies have shown that random dots scattered in an annulus induce an illusory rotational motion 23,24 and that the perceived motion direction varies spontaneously between clockwise and counterclockwise, showing a typical bistable perception dynamic 23,25,26 . We hypothesized that this periodic alternation in bistable perception might be also governed by the intrinsic decision kernel of subjects.…”

“…A black cross appeared at the center of the screen and each subject was asked to fix his or her eyes on the cross during the experiment. Stimulus conditions were optimized based on the results from preliminary trials and previous references 23 . All visual stimuli were generated with MATLAB Psychtoolbox 3.0.…”

Differential brain activity states during the perception and nonperception of illusory motion as revealed by magnetoencephalography

“…These results show that brain activity varies as a function of perceptual awareness of motion, even in the case that the stimulus carries no motion signals (and does not elicit reproducible responses to repeated viewings of the same stimulus) (4). Most sensors showing differential activity were located above the left parietal cortex.…”

“…Interestingly, the direction of perceived motion does not depend on the specific dot patterns shown. For example, on separate viewings of the same stimulus, a subject's time courses of the direction of perceived motion (which flip between clockwise and counter clockwise) are uncorrelated (4). In other words, a sequence of frames showing random dots may elicit clockwise perception in one viewing, but counter clockwise in another viewing.…”