Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Motion Perception”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources
PubMed2001

Optimizing visual motion perception during eye movements.

We usually perceive a stationary, stable world and we are able to correctly estimate the direction of heading from optic flow despite coherent visual motion induced by eye movements. This astonishing example of perceptual invariance results from a comparison of visual information with internal reference signals predicting the visual consequences of an eye movement. Here we demonstrate that the reference signal predicting the consequences of smooth-pursuit eye movements is continuously calibrated on the basis of direction-selective interactions between the pursuit motor command and the rotational flow induced by the eye movement, thereby minimizing imperfections of the reference signal and guaranteeing an ecologically optimal interpretation of visual motion.

Chi-Square Distribution↗
PubMed1988

A selective impairment of motion perception following lesions of the middle temporal visual area (MT).

Physiological experiments indicate that the middle temporal visual area (MT) of primates plays a prominent role in the cortical analysis of visual motion. We investigated the role of MT in visual perception by examining the effect of chemical lesions of MT on psychophysical thresholds. We trained rhesus monkeys on psychophysical tasks that enabled us to assess their sensitivity to motion and to contrast. For motion psychophysics, we employed a dynamic random dot display that permitted us to vary the intensity of a motion signal in the midst of masking motion noise. We measured the threshold intensity for which the monkey could successfully complete a direction discrimination. In the contrast task, we measured the threshold contrast for which the monkeys could successfully discriminate the orientation of stationary gratings. Injections of ibotenic acid into MT caused striking elevations in motion thresholds, but had little or no effect on contrast thresholds. The results indicate that neural activity in MT contributes selectively to the perception of motion.

Animals↗
PubMed1994

Global motion perception: interaction of the ON and OFF pathways.

A number of experiments were conducted to investigate the interaction of the ON and OFF pathways in the processing of global-motion signals. The stimulus employed was a variant of that used by Newsome and Pare [(1988) Journal of Neuroscience, 8, 2201-2211] in which a small subset of dots move in a common (global-motion) direction in a field of randomly moving dots. The threshold measure was the number of dots required to move in the global-motion direction for that direction to be detected. We found that: (1) the extraction of a global-motion signal carried by light dots (luminance above the background) was impaired by the addition of dark dots (luminance below the background) which did not carry the signal (noise dots); (2) sub-threshold summation occurs for global-motion signals carried by light and dark dots; and (3) a signal dot which changed luminance polarity (went from light to dark) did not result in a motion signal--either in the global-motion direction or in the opposite direction (reverse apparent motion). From these findings we conclude that the inputs to the motion sensitive cells have matched spatial opponency (the ON and OFF pathways remain separate at this level) but that they then combine to form a single pathway prior to the extraction of the global-motion signal. These findings are contrary to those predicted by models which advocate squaring or full-wave rectification prior to global motion processing.

Contrast Sensitivity↗
PubMed2006

Fixational eye movements and motion perception.

Small eye movements are necessary for maintained visibility of the static scene, but at the same time they randomly oscillate the retinal image, so the visual system must compensate for such motions to yield the stable visual world. According to the theory of visual stabilization based on retinal motion signals, objects are perceived to move only if their retinal images make spatially differential motions with respect to some baseline movement probably due to eye movements. Motion illusions favoring this theory are demonstrated, and psychophysical as well as brain-imaging studies on the illusions are reviewed. It is argued that perceptual stability is established through interactions between motion-energy detection at an early stage and spatial differentiation of motion at a later stage. As such, image oscillations originating in fixational eye movements go unnoticed perceptually, and it is also shown that image oscillations are, though unnoticed, working as a limiting factor of motion detection. Finally, the functional importance of non-differential, global motion signals are discussed in relation to visual stability during large-scale eye movements as well as heading estimation.

Afterimage↗
PubMed1996

Contrast gain control in first- and second-order motion perception.

A novel pedestal-plus-test paradigm is used to determine the nonlinear gain-control properties of the first-order (luminance) and the second-order (texture-contrast) motion systems, that is, how these systems' responses to motion stimuli are reduced by pedestals and other masking stimuli. Motion-direction thresholds were measured for test stimuli consisting of drifting luminance and texture-contrast-modulation stimuli superimposed on pedestals of various amplitudes. (A pedestal is a static sine-wave grating of the same type and same spatial frequency as the moving test grating.) It was found that first-order motion-direction thresholds are unaffected by small pedestals, but at pedestal contrasts above 1-2% (5-10 x pedestal threshold), motion thresholds increase proportionally to pedestal amplitude (a Weber law). For first-order stimuli, pedestal masking is specific to the spatial frequency of the test. On the other hand, motion-direction thresholds for texture-contrast stimuli are independent of pedestal amplitude (no gain control whatever) throughout the accessible pedestal amplitude range (from 0 to 40%). However, when baseline carrier contrast increases (with constant pedestal modulation amplitude), motion thresholds increase, showing that gain control in second-order motion is determined not by the modulator (as in first-order motion) but by the carrier. Note that baseline contrast of the carrier is inherently independent of spatial frequency of the modulator. The drastically different gain-control properties of the two motion systems and prior observations of motion masking and motion saturation are all encompassed in a functional theory. The stimulus inputs to both first- and second-order motion process are normalized by feedforward, shunting gain control. The different properties arise because the modulator is used to control the first-order gain and the carrier is used to control the second-order gain.

Contrast Sensitivity↗
PubMed1999

Colour and polarity contributions to global motion perception.

The influence of the image segmentation cues based on colour and polarity on a motion coherence task were examined. In line with previous reports, when the signal and noise were given unique identities thresholds were much lower than when they were the same, suggesting a strong influence of segmentation. In another paradigm extra noise elements that differed in colour or polarity interfered despite this perceptual segmentation. We suggest that the results when signal and noise have unique identities are attributable to the subjects' ability to attend to a particular location(s) in space. When this strategy was eliminated by presenting the stimuli in the near-periphery or very briefly the effect of the colour or polarity information disappears.

Color Perception↗
PubMed2004

Motion perception without explicit activity in areas MT and MST.

It is widely accepted that middle temporal (MT) and middle superior temporal (MST) cortical areas in the brain of rhesus monkeys are essential for processing visual motion. We asked whether this assumption holds true if the moving stimulus consists of a second-order motion stimulus. In addition, we asked whether neurons in area MT and MST code for moving sound sources. To answer these questions, we trained three rhesus monkeys on a direction-discrimination task. Our monkeys were able to correctly report the direction of all motion stimuli used in this study. Firing rates of directionally selective neurons from area MT (n = 38) and MST (n = 68) were recorded during task performance. These neurons coded only for the stimulus movement if the motion stimulus was separated from the background by luminance or flicker (Fourier and drift-balanced motion). If these segregation cues were absent (in the case of theta motion and of the moving sound source), firing rates did not code for the stimulus' direction. Therefore we conclude that although areas MT and MST are undoubtedly involved in processing a moving stimulus, they are not the final cortical stages responsible for perceiving it.

Action Potentials↗
PubMed2001

Optimal smoothing in visual motion perception.

When a flash is aligned with a moving object, subjects perceive the flash to lag behind the moving object. Two different models have been proposed to explain this "flash-lag" effect. In the motion extrapolation model, the visual system extrapolates the location of the moving object to counteract neural propagation delays, whereas in the latency difference model, it is hypothesized that moving objects are processed and perceived more quickly than flashed objects. However, recent psychophysical experiments suggest that neither of these interpretations is feasible (Eagleman & Sejnowski, 2000a, 2000b, 2000c), hypothesizing instead that the visual system uses data from the future of an event before committing to an interpretation. We formalize this idea in terms of the statistical framework of optimal smoothing and show that a model based on smoothing accounts for the shape of psychometric curves from a flash-lag experiment involving random reversals of motion direction. The smoothing model demonstrates how the visual system may enhance perceptual accuracy by relying not only on data from the past but also on data collected from the immediate future of an event.

Humans↗
PubMed2001

A neural model of smooth pursuit control and motion perception by cortical area MST.

Smooth pursuit eye movements (SPEMs) are eye rotations that are used to maintain fixation on a moving target. Such rotations complicate the interpretation of the retinal image, because they nullify the retinal motion of the target, while generating retinal motion of stationary objects in the background. This poses a problem for the oculomotor system, which must track the stabilized target image while suppressing the optokinetic reflex, which would move the eye in the direction of the retinal background motion (opposite to the direction in which the target is moving). Similarly, the perceptual system must estimate the actual direction and speed of moving objects in spite of the confounding effects of the eye rotation. This paper proposes a neural model to account for the ability of primates to accomplish these tasks. The model simulates the neurophysiological properties of cell types found in the superior temporal sulcus of the macaque monkey, specifically the medial superior temporal (MST) region. These cells process signals related to target motion, background motion, and receive an efference copy of eye velocity during pursuit movements. The model focuses on the interactions between cells in the ventral and dorsal subdivisions of MST, which are hypothesized to process target velocity and background motion, respectively. The model explains how these signals can be combined to explain behavioral data about pursuit maintenance and perceptual data from human studies, including the Aubert--Fleischl phenomenon and the Filehne Illusion, thereby clarifying the functional significance of neurophysiological data about these MST cell properties. It is suggested that the connectivity used in the model may represent a general strategy used by the brain in analyzing the visual world.

Animals↗
PubMed1985

Vector analysis and process combination in motion perception.

Experiments are reported supporting an altered explanation of the vector analysis that occurs in certain motion displays discovered by Johansson (1950). What seemed the result of a perceptual vector analysis is ascribed to the outcome of two different, independent stimulus conditions to which such displays can give rise because of external vector analysis. The different stimulus conditions are configurational change on the one hand and one of the subject-relative stimulus conditions on the other. In two of Johansson's displays, conditions for configurational change were altered by adding stationary reference points in the surround of the displays. Veridical perception of the displays resulted in a majority of instances. We also found that the different motions that result from configurational change and from subject-relative stimulation may combine to form unitary perceived motions and that this happens quite frequently under some conditions.

Humans↗
PubMed1993

Surface segmentation mechanisms and motion perception.

Two studies are presented which explore how depth information is determined from conditions of transparency and whether this information combines with other depth information to determine the segmenting of motion information on the basis of likely surface boundaries. The first study explored how binocular disparity combines with monocular depth cues associated with transparency to determine whether subjects see one or multiple surfaces in depth in static displays. When transparency provided a depth cue that was consistent with binocular disparity, depth discrimination thresholds were at normal levels. However, if transparency was inconsistent with the binocular disparity, depth discrimination thresholds were elevated, indicating that subjects had difficulty seeing distinct surfaces lying in separate depth planes. Moreover, threshold elevations were found to correspond to the reductions in contrast between the intersecting contours of the stimulus, suggesting that the strength of perceived depth from transparency is the result of attenuated responses from competing contrast sensitive T-junction mechanisms responsible for the detection of opaque occlusion. A second experiment explored whether the grouping of local motion signals relied on surface interpretations that result from the interaction of transparency and disparity. Surface interpretations were manipulated in moving plaids by combining transparent layering and binocular disparity to show that the motion arising from contours is grouped together (pattern motion) when these cues support the existence of a single surface, and is segregated (component motion) when they support separate surfaces. When these cues were consistent, only small disparity differences were required for the gratings to appear as separately moving surfaces. However, when they were inconsistent, greater disparities were required (about a factor of 2 greater). Taken together, these studies demonstrate that the grouping of local motion information is not resolved within the motion system alone. Information seemingly unrelated to motion processing, namely surface segmentation cues, is used to determine whether or not motion information arising from various contours is pooled together to determine a single motion.

Cues↗
PubMed1998

Motion perception in global versus local attentional modes.

PURPOSE: Global and local attention are two forms of selective visual attention which activate different areas of the cortex. The purpose of this experiment was to test subjects' motion coherence thresholds under conditions of global or local attention. It was hypothesized that thresholds in global attention would be lower than in local attention. METHODS: Eleven adult subjects participated in this study. Subjects were required to identify direction of motion at variable coherence levels, while simultaneously identifying either the global or local letter. Three velocities were used for coherent motion (3, 6 and 18 degrees/s). RESULTS: The results showed that letter identification (global or local) did not significantly affect motion coherence thresholds; however, thresholds were significantly higher at 18 degrees/s than in the lower velocities. CONCLUSIONS: These results highlight the attentional limitations of visual information shown by increased motion coherence thresholds when two objects must be identified simultaneously in a brief display.

Adolescent↗