Random-dot Cinematograms Research Articles

Performance monitoring in obsessive–compulsive undergraduates: Effects of task difficulty

Both obsessive–compulsive disorder and subclinical obsessive–compulsive (OC) symptoms seem to be associated with hyperactive error-related brain activity. The current study examined performance monitoring in subjects with subclinical OC symptoms using a new task with different levels of difficulty. Nineteen subjects with high and 18 subjects with low OC characteristics performed a random dot cinematogram (RDC) task with three levels of difficulty. The high and low OC groups did not differ in error-related negativity (ERN), correct-related negativity (CRN) and performance irrespective of task difficulty. The amplitude of the ERN decreased with increasing difficulty whereas the magnitude of CRN did not vary. ERN and CRN approached in size and topography with increasing difficulty, which suggests that errors and correct responses are processed more similarly. These results add to a growing number of studies that fail to replicate hyperactive performance monitoring in individuals with OC symptoms in task with higher difficulty or requiring learning. Together with these findings our results suggest that the relationship between OC symptoms and performance monitoring may be sensitive to type of task and task characteristics and cannot be observed in a RDC that differs from typically used tasks in difficulty and the amount of response-conflict.

The detection of counterchange, not motion energy, accounts for coherent motion perception in random-dot cinematograms

The detection of counterchange, not motion energy, accounts for coherent motion perception in random-dot cinematograms

Shared attention for smooth pursuit and saccades.

Identification of brief luminance decrements on parafoveal stimuli presented during smooth pursuit improves when a spot pursuit target is surrounded by a larger random dot cinematogram (RDC) that moves with it (Heinen, Jin, & Watamaniuk, 2011). This was hypothesized to occur because the RDC provided an alternative, less attention-demanding pursuit drive, and therefore released attentional resources for visual perception tasks that are shared with those used to pursue the spot. Here, we used the RDC as a tool to probe whether spot pursuit also shares attentional resources with the saccadic system. To this end, we set out to determine if the RDC could release attention from pursuit of the spot to perform a saccade task. Observers made a saccade to one of four parafoveal targets that moved with the spot pursuit stimulus. The targets either moved alone or were surrounded by an RDC (100% coherence). Saccade latency decreased with the RDC, suggesting that the RDC released attention needed to pursue the spot, which was then used for the saccade task. Additional evidence that attention was released by the RDC was obtained in an experiment in which attention was anchored to the fovea by requiring observers to detect a brief color change applied 130 ms before the saccade target appeared. This manipulation eliminated the RDC advantage. The results imply that attentional resources used by the pursuit and saccadic eye movement control systems are shared.

The Recovery of Shape from 3rd-order Counter-change Specified Motion vs. 1st-order Motion Energy

Visual information is often noisy and ambiguous. To overcome this, the visual system exploits multiple sources of information to resolve ambiguity. Here we investigate the use of different kinds of motion information to recover the shape of a displaced object from the noisy background of a random dot cinematogram (RDC). The ability to perceive shape-from-motion in an RDC depends on the ability to segregate the coherent motion of the object from incoherent background motion. The stimuli in Experiment 1 were two-frame RDCs; a rectangular figure is displaced and the background updated randomly. For half the trials, the contrast is reversed during the second frame, creating reverse-phi motion. Subjects indicated the perceived motion direction (left or right) and shape (tall or wide). Judgments could be based on either 3rd-order counterchange-specified motion or 1st-order motion energy when contrast was not reversed, but only on motion energy when it was reversed. Experiment 2 was identical except that triangular figures were displaced; shape discrimination was based on the triangles’ orientation. Following Sato (1989), shape was easily discernible for small displacements in the non-reverse condition, but not in the reverse-contrast condition, for which reverse-phi motion is perceived in the direction opposite to the displacement. Differences in shape were weakly inferred from differences in reverse-phi motion strength between the flat and upright rectangles; this was eliminated when reverse-phi motion strength was balanced for the triangular shapes in Experiment 2. The results suggest that motion energy provides information that can inferentially aid simple shape discrimination, but is distinct from the non-reverse condition, for which a segregated figure can be perceived. We conclude that 3rd-order, counterchange-specified motion is the basis for perceiving shape-from-motion in the RDC. Its absence for motion in the reverse-phi direction is consistent with the "objectless" quality of 1st-order motion energy. Meeting abstract presented at VSS 2012

Effects of retinal eccentricity and acuity on global-motion processing

The present study assessed direction discrimination with moving random-dot cinematograms at retinal eccentricities of 0, 8, 22, and 40 deg. In addition, Landolt-C acuity was assessed at these eccentricities to determine whether changes in motion discrimination performance covaried with acuity in the retinal periphery. The results of the experiment indicated that discrimination thresholds increased with retinal eccentricity and directional variance (noise), independent of acuity. Psychophysical modeling indicated that the results for eccentricity and noise could be explained by an increase in channel bandwidth and an increase in internal multiplicative noise.

Aging, perceptual learning, and changes in efficiency of motion processing

In the present study we examined the use of perceptual learning to improve motion processing in older and younger individuals. Using the Perceptual Template Model (Lu & Dosher, 1998, 1999), age-related differences in baseline perceptual inefficiencies and changes due to training were assessed for additive internal noise, tolerance to external noise, and internal multiplicative noise. In Experiments 1 and 2 we trained participants by manipulating contrast in noise embedded sine-wave gratings and Random Dot Cinematograms (RDCs). The results indicate that older observers have higher additive internal noise and lower tolerance to external noise compared to younger observers. The rate of perceptual learning in older observers was found to be similar to that of younger observers suggesting that plasticity of motion processing mechanisms is well preserved in advancing age. Transfer of learning between sine-wave gratings and RDCs for both older and younger observers was examined in an analysis of pre/post-test measurements. The results indicate that transfer of learning occurred for both age groups. This suggests that older individuals maintain a sufficient degree of plasticity to allow generalization between sine-wave gratings and RDCs. In addition, training with RDCs was found to produce greater perceptual learning than training with sine-wave gratings. These experiments provide important findings regarding changes in perceptual efficiency for motion perception in older adults and suggest that perceptual learning is an effective approach for recovering from age-related declines in visual processing.

Perceived global flow direction reveals local vector weighting by luminance

Global flow occurs when random dots, each selecting their direction of motion randomly each frame from a distribution of directions spanning up to 180°, appear to move as a whole in the mean direction of the components. This percept arises because the visual system integrates the many independent local motion signals over space and time. Through a series of direction discrimination experiments with random-dot cinematograms (RDCs), we show that varying the luminance of dots over a suprathreshold range profoundly affects perceived direction; the brightest dots appear to be weighted more and dimmer dots weighted less when determining perceived global direction. This effect is not observable if all dots in the display have the same luminance but only when the display contains dots with different luminance values. The results are consistent with energy models of motion detectors whose responses are contrast dependent. A Monte Carlo simulation of global direction discrimination employing a 12-mechanism line-element model that weighted the local motion vectors by the normalized squared contrast of the component dots (a proxy for contrast energy) captured well the features of the experimental data.

A linear cue combination framework for understanding selective attention

We can base visual judgements on selected parts of a scene, and ignore other parts. This ability is called selective visual attention. Sometimes selective attention is imperfect, which raises the question of how attended and unattended stimulus elements together determine observers' responses, and the related question of how to measure intermediate degrees of selective attention. Using a linear cue combination framework, we develop a measure of selective attention, *attentional weight*, that describes the relative weight observers assign to attended and unattended stimulus elements. We describe a method for measuring attentional weight by measuring the correlation between the strength of attended and unattended elements and observers' responses. We use this method to test whether observers can direct selective attention according to contrast polarity when judging global direction of motion or global orientation. We find that when observers try to judge the global direction or orientation of black or white stimulus elements, their responses are influenced by elements of the opposite contrast polarity. The attentional weight assigned to opposite-polarity distractors is typically 65% of the weight assigned to targets in the motion task, and 25% in the orientation task. Thus observers have only a limited ability to direct attention according to contrast polarity. Finally, we test a key assumption of the cue combination approach, namely that selectivity is the same for attended and unattended elements, and that observers simply assign less weight to unattended elements. We do this by using reverse correlation to measure directional selectivity for attended and unattended motion signals in random dot cinematograms. We find that selectivity is the same for both, namely a sinusoidal function of direction. We conclude that selective attention operates by modulating the weight assigned to unattended stimulus elements, without changing selectivity for unattended elements.

Different mechanisms for the learning of motion detection vs. the learning of motion direction discrimination

[Purpose] We examined whether different mechanisms are involved in the learning of coherent motion detection and motion direction discrimination. [Methods] The experiment consisted of two test and one training phases. In the pre-training test, all subjects were shown a random-dot cinematogram and were asked to judge whether the stimulus contained coherently moving dots or whether all dots moved randomly. Coherent motion detection thresholds were measured for each of 9 directions within 90 degrees. Subjects were divided into 2 groups for training. One group (n=6) participated in the same motion coherence detection task as in the pre-test except that only 2 of 9 directions were used (difference of the 2 directions = 20 deg) and the signal/noise ratio was fixed at 18%. The other group of subjects (n=6) participated in the motion direction discrimination task, where they were asked to judge whether the global motion flow directions in two successively presented displays matched. The same stimuli (i.e., the same directions and the same S/N ratio) were presented an equal number of times as in the detection task. After training, all the subjects participated in the post-training test, with the same procedure as in the pre-training test. [Results] In the post-training test, the subjects trained on coherent motion detection showed significantly greater improvement for trained directions than for untrained directions. However, to our surprise, in the post-training test the group trained on motion direction discrimination showed significantly less improvement for trained directions than for untrained directions. [Conclusions] Despite the fact that both groups viewed the same stimuli equally often, they showed opposite patterns of improvement in their detection of presented motion directions. Thus, we conclude that the learning of motion detection may involve different mechanisms than the learning of motion direction discrimination.

A counterchange mechanism for the perception of motion

A computational model for the perception of counterchange-specified motion is examined in detail and compared with various versions of the Reichardt motion detection model [Reichardt, W. (1961). Autocorrelation, a principle for the evaluation of sensory information by the central nervous system. In W. A. Rosenblith (Ed.), Sensory communication (pp. 303-317). New York: Wiley]. The counterchange model is composed of a pair of temporally biphasic subunits at two retinal locations, one detecting decreases and the other increases in input activation. Motion is signaled when both subunits are simultaneously excited, as determined by the multiplicative combination of their transient responses. In contrast with the Reichardt detector, which effectively tracks motion energy and accounts solely for results obtained with standard apparent motion stimuli (a surface is visible at one location, then at another), the counterchange model also accounts for the generalized apparent motion perceived between pairs of simultaneously visible surfaces. This indicates that standard apparent motion can be perceived via the same non-sequential, non-motion-energy mechanism as generalized apparent motion. There is no need for either an explicit delay mechanism to account for optimal motion perception at non-zero inter-stimulus intervals, or for inhibitory interaction between subunits to account for the absence of motion in the detector's null direction (Barlow, H. B., & Levick, W. R., 1965). Both are emergent properties that result from the inhibitory states of the counterchange detector's biphasic subunits. In addition to apparent motion, the counterchange principle potentially accounts for the perception of motion for drifting gratings, the short range motion perceived for random-dot cinematograms, and the motion perceived for continuously moving objects.

Biological Motion Alters Coherent Motion Perception

When a movie presents a person walking, the background appears to move in the direction opposite to the person's gait. This study verified this backscroll illusion by presenting a point-light walker against a background of a random-dot cinematogram (RDC). The RDC consisted of some signal dots moving coherently either leftward or rightward among other noise dots moving randomly. The method of constant stimuli was used to vary the RDC in motion coherence from trial to trial by manipulating the direction and percentage of the signal dots. Six observers judged the perceived direction of coherent motion in a two-alternative forced-choice procedure. Response rates for coherent motion perception in the direction opposite to walking were evaluated as a function of motion coherence. The results showed that the psychometric function shifted toward the direction determined by a bias in the opposite direction to the walker. The mean threshold was about half as high as that in a control condition in which the positions of the point-lights were scrambled to impair the recognition of the walker. The results demonstrate that biological motion noticeably affects the appearance of motion coherence in the background.

Selective impairment in visual perception of biological motion in obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is associated with a variety of well-documented cognitive deficits such as deficits in memory and executive functioning, but little is known about basic perceptual concomitants of OCD. This study investigated global, configural processing in OCD using dynamic (moving) and static stimuli with minimal demands on cognitive function. Twenty OCD patients and 16 age- and education-matched healthy control subjects were tested on four perceptual tasks: two motion tasks involved detection and discrimination of human activity portrayed by point-light animations ("biological" motion). The other two tasks involved detection of coherent, translational motion defined by random-dot cinematograms and detection of static global shape defined by spatially distributed contours. OCD patients exhibited impaired performance on biological motion tasks; in contrast, their performance on tasks of coherent motion detection and global form perception were comparable to those of healthy controls. These results indicate that OCD patients have a specific deficit in perceiving biological motion signals, whereas their perception of non-biological coherent motion and static global shape is intact. Because efficient social interactions depend on accurate and rapid perception of subtle socially relevant cues, deficits in biological motion perception may compromise social functioning in people with OCD.

The effects of aging on motion detection and direction identification

Random dot cinematograms were used to probe motion perception in human observers ranging from 23 to 81 years of age. Stimuli were either broadband directional Noise, which produces no experience of global motion flow, or a narrower band directional Signal, which tended to produce experiences of coherent, global direction flow. On each trial, subjects rated their certainty that a Signal had been presented, and used a computer mouse to indicate the direction of perceived global flow. At all ages, sensitivity to motion and accuracy of perceived direction improved significantly as stimulus duration increased from 75 to 470 ms. However, older subjects (>70 years of age) were significantly less sensitive to motion, and were significantly less accurate at identifying the direction of movement. A control experiment, which found that older subjects accurately perceived and remembered the orientation of a line, ruled out the possibility that the observed deficits in motion perception were due to an inability on the part of older subjects to manipulate the computer mouse. Those control results also showed that both younger and older observers maintained robust visual representations over durations ranging from .24 to 6.0 s. The motion detection and identification results obtained from subjects less than 70 years of age were well fit by a simple multichannel model of motion, although different levels of additive internal noise were needed to fit detection data and direction-identification data, suggesting that motion direction and identification are constrained by different mechanisms. To fit the data from the oldest subjects, however, the values of model parameters had to be significantly altered, either by increasing the level of additive internal noise substantially, or by a smaller increase in noise coupled with an increase in the bandwidth of the model’s directionally selective channels. These results are qualitatively consistent with recent neurophysiological studies showing weaker directional selectivity and higher spontaneous noise in visual neurons of senescent monkeys and cats.

Storage of an oculomotor motion aftereffect

Adaptation to motion produces a motion aftereffect (MAE), where illusory, oppositely-directed motion is perceived when viewing a stationary image. A common hypothesis for motion adaptation is that it reflects an imbalance of activity caused by neuronal fatigue. However, the perceptual MAE exhibits storage, in that the MAE appears even after a prolonged period of darkness is interposed between the adapting stimulus and the test, suggesting that fatigue cannot explain the perceptual MAE. We asked whether neural fatigue was a viable explanation for the oculomotor MAE (OMAE) by testing if the OMAE exhibits storage. Human observers were adapted with moving, random-dot cinematograms. Following adaptation, they generated an oculomotor MAE (OMAE), with both pursuit and saccadic components. The OMAE occurred in the presence of a visual test stimulus, but not in the dark. When the test stimulus was introduced after the dark period, the OMAE reappeared, analogous to perceptual MAE storage. The results suggest that fatigue cannot explain the OMAE, and that visual stimulation is necessary to elicit it. We propose a model in which adaptation recalibrates the motion-processing network by adjusting the weights of the inputs to neurons in the middle-temporal (MT) area.

Perception of heading without retinal optic flow

How do we determine where we are heading during visually controlled locomotion? Psychophysical research has shown that humans are quite good at judging their travel direction, or heading, from retinal optic flow. Here we show that retinal optic flow is sufficient, but not necessary, for determining heading. By using a purely cyclopean stimulus (random dot cinematogram), we demonstrate heading perception without retinal optic flow. We also show that heading judgments are equally accurate for the cyclopean stimulus and a conventional optic flow stimulus, when the two are matched for motion visibility. The human visual system thus demonstrates flexible, robust use of available visual cues for perceiving heading direction.

Perception of coherent motion, biological motion and form-from-motion under dim-light conditions

Three experiments investigated several aspects of motion perception at high and low luminance levels. Detection of weak coherent motion in random dot cinematograms was unaffected by light level over a range of dot speeds. The ability to judge form from motion was, however, impaired at low light levels, as was the ability to discriminate normal from phase-scrambled biological motion sequences. The difficulty distinguishing differential motions may be explained by increased spatial pooling at low light levels.

Coherence and the judgment of spatial displacements in retinitis pigmentosa.

We used a motion coherence paradigm to test the hypothesis that patients with retinitis pigmentosa (RP) have difficulty discriminating the direction of spatial displacements because of a random loss of motion-sensitive units owing to cone photoreceptor dropout. Minimum (Dmin) and maximum (Dmax) displacement thresholds of patients with typical RP or Usher syndrome were compared with those of age-similar, visually normal subjects. Two-frame random dot cinematograms were used, in which a group of target dots, which comprised 40-100% of the dot array in steps of 20%, were displaced in one of four directions, whereas the non-target dots were randomly repositioned between frames. Reducing the dot coherence in this way increased Dmin and reduced Dmax for both the RP patients and control subjects. Furthermore, the displacement thresholds of the RP patients were displaced laterally from normal along a log coherence axis, consistent with the hypothesis that the patients had a reduced effective (intrinsic) coherence. However, the displacement thresholds of control subjects, when measured at a reduced coherence, did not mimic those of RP patients at full coherence when both groups were tested with a range of dot contrasts and dot areas. These apparently discrepant findings can be reconciled if it is assumed that the patients' effective coherence varies with stimulus visibility.

Perception of movement and shape in Alzheimer's disease.

Alzheimer's disease is the most prevalent cause of abnormal cognitive decline in older adults and commonly affects visual function. Recent evidence suggests that Alzheimer's disease impairs the processing of visual motion, but these conclusions are based on conflicting results in the few cases studied, and the processing of complex motion images has not been investigated. In the present study of motion processing in Alzheimer's disease we assessed visual functions in 63 adults: 41 with mild to moderate Alzheimer's disease (mean age 72.3 years) and 22 without dementia (mean age 71.7 years). Processing of motion cues was tested with computer animation sequences known as random-dot cinematograms, which resemble the stimuli used to define motion processing deficits in primates with lesions of cortical area MT. Results showed that participants with Alzheimer's disease required significantly greater thresholds for perceiving shapes defined by motion cues compared with participants without dementia (P = 0.0005). There were no significant differences between the two groups (P < 0.05) in static visual acuity, static spatial contrast sensitivity and, surprisingly, dynamic visual acuity, which was normal, and motion direction discrimination, which was relatively spared. We conclude that mild to moderate Alzheimer's disease has significant effects on the perception of structure from motion with relative sparing of motion direction discrimination. We cannot exclude a contribution by retinal pathology, but retinal dysfunction alone cannot explain the pattern of defects we observed. The complex motion image processing deficit we identified is likely to have a cerebral basis and has the potential to affect navigation and the recognition of objects in relative motion, as encountered during walking and automobile driving.

Human smooth pursuit direction discrimination.

The smooth pursuit system is usually studied using single moving objects as stimuli. However, the visual motion system can respond to stimuli that must be integrated spatially and temporally (Williams DG, Sekuler R. Vision Res 1984;24:55-62; Watamaniuk SNJ, Sekuler R, Williams DW. Vision Res 1989;29:47-59). For example, when each dot of a random-dot cinematogram (RDC) is assigned a new direction of motion each frame from a narrow distribution of directions, the whole field of dots appears to move in the average direction (Williams and Sekuler, 1984). We measured smooth pursuit eye movements generated in response to small (10 deg diameter) RDCs composed of 250 dynamic random dots. Smooth eye movements were assessed by analyzing only the first 130 ms of eye movements after pursuit initiation (open-loop period). Comparing smooth eye movements to RDCs and single spot targets, we find that both targets generate similar responses confirming that the signal supplied to the smooth pursuit system can result from a spatial integration of motion information. In addition, the change in directional precision of smooth eye movements to RDCs with different amounts of directional noise was similar to that found for psychophysical direction discrimination. These results imply that the motion processing system responsible for psychophysical performance may also provide input to the oculomotor system.

Spatial integration in human smooth pursuit.

When viewing a moving object, details may appear blurred if the object's motion is not compensated for by the eyes. Smooth pursuit is a voluntary eye movement that is used to stabilize a moving object. Most studies of smooth pursuit have used small, foveal targets as stimuli (e.g. Lisberger SG and Westbrook LE. J Neurosci 1985;5:1662-1673.). However, in the laboratory, smooth pursuit is poorer when a small object is tracked across a background, presumably due to a conflict between the primitive optokinetic reflex and smooth pursuit. Functionally, this could occur if the motion signal arising from the target and its surroundings were averaged, resulting in a smaller net motion signal. We asked if the smooth pursuit system could spatially summate coherent motion, i.e. if its response would improve when motion in the peripheral retina was in the same direction as motion in the fovea. Observers tracked random-dot cinematograms (RDC) which were devoid of consistent position cues to isolate the motion response. Either the height or the density of the display was systematically varied. Eye speed at the end of the open-loop period was greater for cinematograms than for a single spot. In addition, eye acceleration increased and latency decreased as the size of the aperture increased. Changes in the density produced similar but smaller effects on both acceleration and latency. The improved pursuit for larger motion stimuli suggests that neuronal mechanisms subserving smooth pursuit spatially average motion information to obtain a stronger motion signal.