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PubMed1996

Object motion perception during ego-motion: patients with a complete loss of vestibular function vs. normals.

Object motion perception was assessed in avestibular patients and normal controls. Two experiments were conducted, in which subjects were required to assess the motion of a visual stimulus with respect to earth. In the first experiment, we measured the velocity at which a briefly presented (200 ms) grating was perceived as earth fixed, while the subject maintained fixation on a visual target fixed relative to the body, during whole-body yaw rotation (VOR suppression). In this experimental setup, the influence of the semicircular canal signals on object motion perception was evaluated. The avestibular patients judged the grating to be stationary with respect to earth, when it was moving at the same velocity as their body, whereas for normal controls, the grating was perceived as stationary when it moved at a velocity slower than their body motion, but greater than zero. The difference between the two subject groups was significant, and showed the strong contribution of the vestibular system to object motion perception. Similarly, a measurement of the velocity at which a grating was perceived as stationary was obtained during smooth pursuit eye movements. In this experiment the contribution of the efference copy of the oculomotor signal and proprioceptive signals to object motion perception were assessed. As with the first experiment, the normal controls displayed a more veridical sense of object motion perception than the patients, although the difference was only just significant. We suggest that the difference could be an adaptive change in the patients perception of motion, which allows them to reduce the effects of oscillopsia.

Humans↗
PubMed2006

Auditory motion perception activates visual motion areas in early blind subjects.

We have previously shown that some visual motion areas can be specifically recruited by auditory motion processing in blindfolded sighted subjects [Poirier, C., Collignon, O., De Volder, A.G., Renier, L., Vanlierde, A., Tranduy, D., Scheiber, C., 2005. Specific activation of V5 brain area by auditory motion processing: an fMRI study. Brain Res. Cogn. Brain Res. 25, 650-658]. The present fMRI study investigated whether auditory motion processing may recruit the same brain areas in early blind subjects. The task consisted of simultaneously determining both the nature of a sound stimulus (pure tone or complex sound) and the presence or absence of its movement. When a movement was present, blind subjects had to identify its direction. Auditory motion processing, as compared to static sound processing, activated the brain network of auditory and visual motion processing classically observed in sighted subjects. Accordingly, brain areas previously considered as specific to visual motion processing could be specifically recruited in blind people by motion stimuli presented through the auditory modality. This indicates that the occipital cortex of blind people could be organized in a modular way, as in sighted people. The similarity of these results with those we previously observed in sighted subjects suggests that occipital recruitment in blind people could be mediated by the same anatomical connections as in sighted subjects.

Adolescent↗
PubMed2004

Long range interactions between object-motion and self-motion in the perception of movement in depth.

Self-motion through a three-dimensional array of objects creates a radial flow pattern on the retina. We superimposed a simulated object moving in depth on such a flow pattern to investigate the effect of the flow pattern on judgments of both the time to collision (TTC) with an approaching object and the trajectory of that object. Our procedure allowed us to decouple the direction and speed of simulated self motion-in-depth (MID) from the direction and speed of simulated object MID. In Experiment 1 we found that objects with the same closing speed were perceived to have a higher closing speed when self-motion and object-motion were in the same direction and a lower closing speed when they were in the opposite direction. This effect saturated rapidly as the ratio between the speeds of self-motion and object-motion was increased. In Experiment 2 we found that the perceived direction of object-MID was shifted towards the focus of expansion of the flow pattern. In Experiments 3 and 4 we found that the erroneous biases in perceived speed and direction produced by simulated self-motion were significantly reduced when binocular information about MID was added. These findings suggest that the large body of research that has studied motion perception using stationary observers has limited applicability to situations in which both the observer and the object are moving.

Depth Perception↗
PubMed2005

Asymmetry of perceived motion smear during head and eye movements: evidence for a dichotomous neural categorization of retinal image motion.

We measured perceived motion smear when retinal image motion was created either by a physically moving object or by movement of the eyes or head. Consistent with previous reports, the extent of perceived motion smear during an eye or head movement is less than that produced by physical object motion when the eyes are stationary. Moreover, perceived smear is substantially smaller when the motion of the retinal image is in the same direction as the eye or head movement compared to when image motion is in the opposite direction. These results imply that extra-retinal signals associated with eye and head movements contribute to a reduction of perceived motion smear, thereby fostering perceptual clarity. We hypothesize that the visual system uses a simple dichotomous strategy in applying these extra-retinal signals, based only on the direction of retinal image motion with respect to the ongoing eye or head movement.

Brain↗
PubMed2005

Is the direction of second-order, contrast-defined motion patterns visible to standard motion-energy detectors: a model answer?

Previous psychophysical studies (e.g., Smith & Ledgeway, 1997) have provided evidence that under some conditions, the detection of a particular class of stimuli (contrast-modulated static noise) widely employed to study second-order motion processing may be inadvertently based on encoding local imbalances in luminance motion energy. In particular when static noise composed of relatively large noise elements is used, direction-identification performance at threshold may actually be mediated by the same mechanisms that respond to first-order motion, due to the presence of persistent spatial clusters of noise elements of the same polarity. However, Benton and Johnson (1997) modeled the responses of conventional motion-energy detectors to contrast-modulated static noise patterns and found no evidence of any systematic directional biases in such stimuli when the mean opponent motion energy was used to quantify performance. In the present paper we sought to resolve this discrepancy and show that the precise manner in which computational models are implemented is crucial in determining their response to contrast-modulated, second-order motion patterns. In particular we demonstrate that by considering the information encapsulated by the peak (rather than the mean) opponent motion energy and the predominantly local nature of imbalances in motion energy that can arise in contrast-modulated static noise, it is possible to readily model the patterns of empirical results found.

Computer Simulation↗
PubMed2005

An extension of the transparent-motion detection limit using speed-tuned global-motion systems.

When transparent motion is defined purely by direction differences, no more than two signal directions can be detected simultaneously. This limit appears to occur because higher signal intensities are required to detect transparent motion compared with uni-directional motion (Edwards, M., & Greenwood, J. A. (2005). The perception of motion transparency: A signal-to-noise limit. Vision Research, 45, 1877-1884). Increasing the effective signal intensities should therefore increase the number of signals that can be detected. We achieved this by adding speed differences, dividing transparent-motion signals between two speed-tuned global-motion systems. When some signals moved at appropriate low speeds and others at high speeds, up to three signals were detected. This is consistent, at least in part, with the signal-to-noise processing basis of the transparency limit. Differences in contrast polarity were also used to assess whether the limit could be extended using stimulus features without independent global-motion systems. A modest improvement in performance was obtained, suggesting that there may be multiple routes to extending the transparent-motion limit.

Computer Graphics↗
PubMed2006

A single motion system suffices for global-motion perception.

Global-motion perception is the perception of coherent motion in a noisy motion stimulus. Thresholds for coherent motion perception were measured for different combinations of signal and noise speeds. Previous research [Edwards, M., Badcock, D. R., & Smith, A. T. (1998). Independent speed-tuned global-motion systems. Vision Research, 38 (11), 1573-1580; Khuu, S. K., & Badcock, D. R. (2002). Global speed processing: evidence for local averaging within, but not across two speed ranges. Vision Research, 42 (28), 3031-3042.] showed that thresholds were elevated when signal and noise speeds were similar, but not when they were different. The regions of increased threshold values for low and high signal speeds showed little overlap. On the basis of this evidence two independent speed-tuned systems were proposed: one for slow and one for fast-motion. However, in those studies only two signal speeds were used. We expanded the results by measuring threshold-curves for four different signal speeds. Considerable overlap of the threshold-curves was found between conditions. These results speak against a bipartite global-motion system. Model simulations indicate that present and previous experimental results can be produced by a single motion system providing that the mechanisms within it are speed-tuned.

Humans↗
PubMed2002

Self-organized pattern formation: experimental dissection of motion detection and motion integration by variation of attentional spread.

The formation of global motion patterns depends on the stimulus activation of local motion detectors as well as integrative excitatory and/or inhibitory interactions among the activated detectors. The counterphase row-of-elements [Vis. Res. 34 (1994) 1843] is an ideal stimulus for examining the relationship between the activational/energizing effect of the stimulus and interaction among the activated detectors. This is because the formation of the alternative unidirectional and oscillatory motion patterns for this stimulus requires the stimulation of local motion detectors, but there is no information in the stimulus that specifies either of the patterns. Their formation depends instead on the relative contributions of excitatory and inhibitory interactions to detector activation; the temporal patterns are self-organized. Broadly spread attention affects motion integration by changing the balance of excitatory versus inhibitory interactions, increasing the perception of unidirectional compared with oscillatory motion. (It likewise increases the perception of group compared with element motion for the Ternus stimulus.) There is, however, little if any effect of attentional spread on the luminance contrast required for the perception of single-element motion. The results indicate that the balance of integrative excitatory and/or inhibitory detector interactions can be modified by the perceiver's spread of attention, and further, that such changes need not be mediated by changes in the local, stimulus activation of the detectors.

Adult↗
PubMed2002

Can spatio-temporal energy models of motion predict feature motion?

Current "spatio-temporal energy" models of how we perceive pattern motion have been very successful in helping us to understand the mechanisms of motion perception. Although they have been supported by a large number of physiological and psychological studies, they have so far not provided a complete explanation for a number of results. These results emerge from experiments concerned with predicting perceived motion direction from patterns comprising two or more components. It has been suggested that these results are more consistent with an earlier type of model based on the motion of two-dimensional features. This paper briefly describes how three generic spatio-temporal energy models have been extended to predict motion derived from two-component stimuli. A new model is then presented that utilises similar architecture to the two-stage spatial-temporal energy model proposed by Adelson and Movshon (Nature 300 (1982) 523). The first stage is a spatial temporal filtering stage and the second stage computes the intersection of constraints (IOC), an important constraint used in combining motion information across two or more components. In the model presented here the second stage is different. A directional spatial second derivative is used to extract zero-crossings at the component level, i.e. gratings. If any zero-crossing falls in the same spatial position for two or more components its displacement is tracked using a nearest neighbour match. Tracking these 'intersecting zero-crossings' essentially computes the IOC but also provides other properties that predict non-IOC motion, and second-order component motion. Surprising new insights are described into how current spatio-temporal energy models may also account for these results. However, unlike the model presented here, they rely on operations carried out on the two-dimensional pattern.

Contrast Sensitivity↗
PubMed1997

Motion processing for saccadic eye movements during the visually induced sensation of ego-motion in humans.

During ego-motion an observer is often faced with the task of controlling his heading direction while simultaneously registering the movement of objects in order to avoid possible obstacles. Psychophysical experiments have shown that the detection of moving objects is impaired by concurrent ego-motion. We investigated the interaction between ego-motion and object-motion by examining the latencies of saccades executed to moving targets under a visually induced sensation of ego-motion. Saccadic latencies increased during this sensation, with a global or non-retinotopic effect of optic flow on motion detection. Furthermore, separating stereoscopically the moving target and the optic flow into foreground and background, respectively, still resulted in increased latencies. We propose that an inhibitory influence of the perception of self-motion exists on the perception of object-motion. These results support a model of space constancy which strives to create a stable world during locomotion.

Adult↗
PubMed1998

Motion detection on flashed, stationary pedestal gratings: evidence for an opponent-motion mechanism.

Contrast thresholds were measured for discriminating left vs right motion of a vertical, 1 c/deg luminance grating lasting for one cycle of motion. This test was presented on a 1 c/deg stationary grating (pedestal) of twice-threshold, flashed for the duration of the test motion. Lu and Sperling [(1995). Vision Research, 35, 2697-2722] argue that the visual system detects the underlying, first-order motion of the test and is immune to the presence of the stationary pedestal (and the 'feature wobble' which it induces). On the contrary, we observe that the stationary pedestal has large effects on motion detection at 7 and 15 Hz, and smaller effects at 0.9-3.7 Hz, evidenced by a spatial phase dependency between the stationary pedestal and moving test. At 15 Hz the motion threshold drops as much as five-fold, with the stationary pedestal in the optimal spatial phase (i.e., pedestal and test spatially in phase at middle of motion), and the perceived direction of the test motion reverses with the pedestal in the opposite phase. Phase dependency was also explored using a very brief (approximately 1 msec) static pedestal presented with the moving test. The pedestal of Lu and Sperling (flashed for the duration of the test) has a broad spectrum of left and right moving components which interact with the moving test. The pedestal effects can be explained by the visual system's much higher sensitivity to the difference of the contrast of right vs left moving components than to either component alone.

Contrast Sensitivity↗
PubMed1998

Motion after-effect due to binocular sum of adaptation to linear motion.

The motion after-effect (MAE) can be elicited by adapting observers to global motion of randomly distributed dots before they view a display containing dots moving in random directions, but no global motion. Experiments by others have shown that if the adaptation stimulus contains two directions of motion, the MAE points opposite to the vector sum of the adapting directions. The present study investigated whether such vector addition in the MAE could also occur if the two directions of motion were presented to separate eyes. Observers were adapted to different, but not opposite, directions of motion in the two eyes. Either the left eye, the right eye, or both eyes were tested. Observers reported the direction of perceived motion during the test. When they saw the test stimulus with both eyes, observers reported seeing motion in the direction opposite that of the vector sum of the adaptation directions. In the monocular test conditions observers reported MAE directions opposite to the corresponding monocular adaptation directions. In a second experiment we verified that subjects had interocular transfer of the MAE. Together these results are consistent with a model in which (1) addition of adaptation directions occurs at a binocular site; (2) directional adaptation occurs at a monocular site; and (3) monocular adaptation is able to change the threshold for obtaining an MAE at the binocular site, thus acting like binocular adaptation in interocular transfer of the MAE.

Adaptation, Ocular↗
PubMed2002

Topography of evoked potentials associated with illusory motion perception as a motion aftereffect.

Motion aftereffect (MAE) is a type of motion illusion. After visual focusing on an object moving in one direction, an illusory perception of motion in the opposite direction occurs while the object suddenly stops moving. In this study we explored components and distribution of evoked potentials related to this motion illusion using MAE caused by motion of concentric rings. When a single array of moving rings was placed to straddle right and left visual fields, a significant bilateral increase of a positive component at about 160 ms (P160) was observed in the occipitotemporal region at the time subjects perceived the motion illusion; this increase was most prominent in the right posterior temporal region. Thus, an early positive component P160 occurs in relation to motion illusion, in agreement with previous results concerning perception of actual motion. When stimuli were presented to produce MAE limited to either the right or left visual hemifield, we also observed a P160 distributed mainly in the right temporal and parietal region. A significant increase in this component was observed in the right posterior temporal region with left hemifield stimulation, while no significant increase was observed with right hemifield stimulation. The right hemispheric dominance of P160 seemed to result partly from functional specialization of the right hemisphere, but hemispheric differences in attentional mechanisms also might contribute to the asymmetric distribution of P160.

Adult↗
PubMed1995

Discrimination of coherent motion when local motion varies in speed and direction.

Random-dot cinematograms (RDCs) consist of multiple local motion signals that can vary in direction and speed. These local motion signals can result in coherent motion: the percept of an overall direction and speed of motion in an RDC. Thresholds were obtained for discriminating differences in the strength of coherent motion. Observers were found to easily discriminate the strength of coherent motion on the basis of the elements' direction or speed under optimal conditions. However, a nonreciprocal relation was evident when this discrimination was performed under nonoptimal conditions. Discrimination of coherent motion that was based on the elements' direction was unaffected, but discrimination that was based on speed was impaired. Results indicate that humans are sensitive to small differences in coherent motion strength and suggest that the visual system processes direction and speed information nonreciprocally.

Humans↗
PubMed2004

Detection of counter-changing contrast: second-order apparent motion without postrectification motion-energy analysis or salience mapping/feature tracking.

The perception of 2nd-order, texture-contrast-defined motion was studied for apparent-motion stimuli composed of a pair of spatially displaced, simultaneously visible checkerboards. It was found that background-relative, counter-changing contrast provided the informational basis for the perception of 2nd-order apparent motion; motion began where contrast changed toward the contrast value of the background checkerboard and ended where contrast changed away from the background value. The perceived apparent motion was not attributable to either postrectification motion-energy analysis or salience-mapping/feature-tracking mechanisms. Parallel results for 1st-order, luminance-defined motion (H. S. Hock, L. A. Gilroy, & G. Harnett, 2002) suggest that counter-changing activation provides a common basis for the perception of both luminance- and texture-contrast-defined apparent motion.

Humans↗
PubMed1994

Contribution of colour to the motion aftereffect and motion perception.

The aim in this work was to assess the contribution which colour information makes to the perception of motion. Two dependent variables were measured: the reaction time to a sudden cessation of motion (motion-end RT) and the duration of the motion aftereffect (MAE). In each case, a baseline measure of performance was made with the aid of a monochrome stimulus with a given contrast and added luminance noise. This was compared with performance when red/green colour modulation was added to the luminance display. Any difference between these measures would reveal the extent of chromatic input. For motion-end RT the addition of colour had little effect under conditions where the stimulus had a strong luminance component and little added luminance noise. Increasing departures from these conditions revealed the contribution of a colour-sensitive mechanism. In general, the chromatic contribution to MAE duration was much smaller than was the equivalent contribution to motion-end RT, thus possibly indicating a neurological dissociation between the mechanisms subserving these effects. The results of an experiment in which the effect of different temporal frequencies of the added luminance noise was assessed supported this dissociation between MAE and motion-end RT. The findings are therefore consistent with there being two motion (sub)systems, which differ in the extent of chromatic input. The subsystem revealed by MAE measures is less affected by colour information.

Color Perception↗
PubMed1996

Cooperative interactions and the perception of motion and stationarity for directionally ambiguous apparent-motion stimuli.

Evidence is reported that stationarity rather than motion can be perceived for displaced stimuli, not because of insufficient motion energy for the stimulus to activate individual motion detectors, but because of cooperative interactions that actively suppress the perception of motion. A long row of evenly spaced dots was presented in counterphase; the dots presented during each 180 ms frame were located midway between the dots presented during the previous frame. When either a blank interval as brief as 15 ms was inserted between successive frames or the luminance polarity of the dots was reversed on successive frames, the unidirectional motion pattern perceived for small interdot distances (small displacements) was replaced by the perception of stationarity. However, when under the same conditions a single dot was displaced over the same small distances, motion rather than stationarity was perceived. The contrasting results for the long row of displaced dots and the single displaced dot indicated that when the activation of motion detectors is weakened (by nonzero interframe intervals and/or the reversal of luminance polarity), the perception of motion can be actively suppressed by the collective effects of inhibitory interactions among the large ensemble of detectors that is activated by the long row of dots.

Field Dependence-Independence↗
PubMed1998

Independence of contour and biological-motion cues for motion-defined animal shapes.

The effects of different kinds of cues on the perception of second-order motion-defined animal shapes were assessed. In the first experiment discrimination thresholds for motion-defined animals without biological motion (non-BioM) were compared with motion-defined animals with biological motion (BioM). The results show no significant difference between the two conditions, suggesting that BioM does not interact with simple contour motion. In order to isolate the relative strength and interaction between the motion cues a second experiment was conducted where four conditions were used. The first condition consisted of animal contours with non-BioM, the second condition consisted of animal contours with BioM, the third condition was composed of dots present at the joints of the animals with non-BioM, and the fourth condition was composed of dots with BioM. In all cases the animal shapes traveled across the screen for a given number of frames. As in the first experiment, the results of the second study show no interaction between cues. Furthermore, the data show that the thresholds are similar whether BioM or contour cues are presented. The only condition which is significantly different is the condition without either contour or BioM cues. It is concluded that the form representation generated from these cues in motion-defined animal shapes consists of separate mechanisms which appear equally efficient for discrimination and which do not interact with one another.

Adult↗