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At least 1,783 records · Page 99Linked to original sources
PubMed2003

Perception of shape-from-motion in macaque monkeys and humans.

Motion is one of the most efficient cues for shape perception. We conducted behavioral experiments to examine how monkeys perceive shapes defined by motion cues and whether they perceive them as humans do. We trained monkeys to perform a shape discrimination task in which shapes were defined by the motion of random dots. Effects of dot density and dot speed on the shape perception of monkeys were examined. Human subjects were also tested using the same paradigm and the test results were compared with those of monkeys. In both monkeys and humans, correct performance rates declined when density or speed of random dots was reduced. Both of them tended to confuse the same combinations of shapes frequently. These results suggest that monkeys and humans perceive shapes defined by motion cues in a similar manner and probably have common neural mechanisms to perceive them.

Adult↗
PubMed1999

Motion contrast: a new metric for direction discrimination.

The Adelson-Bergen energy model (Adelson, E. H., & Bergen, J. R. (1985). Spatiotemporal energy models for the perception of motion. Journal of the Optical Society of America A, 2, 284-299) is a standard framework for understanding first-order motion processing. The opponent energy for a given input is calculated by subtracting one directional energy measure (EL) from its opposite (ER), and its sign indicates the direction of motion of the input. Our observers viewed a dynamic sequence of gratings (1 c/deg) equivalent to the sum of two gratings moving in opposite directions with different contrasts. The ratio of contrasts was varied across trials. We found that opponent energy was a very poor predictor of direction discrimination performance. Heeger (1992). Normalization of cell responses in cat striate cortex. Visual Neuroscience, 9, 181-197) has suggested that divisive inhibition amongst striate cells requires a contrast gain control in the energy model. A new metric can be formulated in the spirit of Heeger's model by normalising the opponent energy (EL - ER) with flicker energy, the sum of the directional motion energies (EL + ER). This new measure, motion contrast (EL - ER)/(EL + ER), was found to be a good predictor of direction discrimination performance over a wide range of contrast levels, but opponent energy was not. Discrimination thresholds expressed as motion contrast were around 0.5 +/- 0.1 for the sampled drifting gratings used in our experiments. We show that the dependence on motion contrast, and the threshold of about 0.5, can be predicted by a modified opponent energy model based on current knowledge of the response functions and response variance of cortical cells.

Discrimination, Psychological↗
PubMed2000

Extraretinal and retinal amplitude and phase errors during Filehne illusion and path perception.

Pursuit eye movements give rise to retinal motion. To judge stimulus motion relative to the head, the visual system must correct for the eye movement by using an extraretinal, eye-velocity signal. Such correction is important in a variety of motion estimation tasks including judgments of object motion relative to the head and judgments of self-motion direction from optic flow. The Filehne illusion (where a stationary object appears to move opposite to the pursuit) results from a mismatch between retinal and extraretinal speed estimates. A mismatch in timing could also exist. Speed and timing errors were investigated using sinusoidal pursuit eye movements. We describe a new illusion--the slalom illusion--in which the perceived direction of self-motion oscillates left and right when the eyes move sinusoidally. A linear model is presented that determines the gain ratio and phase difference of extraretinal and retinal signals accompanying the Filehne and slalom illusions. The speed mismatch and timing differences were measured in the Filehne and self-motion situations using a motion-nulling procedure. Timing errors were very small for the Filehne and slalom illusions. However, the ratios of extraretinal to retinal gain were consistently less than 1, so both illusions are the consequence of a mismatch between estimates of retinal and extraretinal speed. The relevance of the results for recovering the direction of self-motion during pursuit eye movements is discussed.

Acceleration↗
PubMed1995

Discrete cortical regions associated with knowledge of color and knowledge of action.

The areas of the brain that mediate knowledge about objects were investigated by measuring changes in regional cerebral blood flow (rCBF) using positron emission tomography (PET). Subjects generated words denoting colors and actions associated with static, achromatic line drawings of objects in one experiment, and with the written names of objects in a second experiment. In both studies, generation of color words selectively activated a region in the ventral temporal lobe just anterior to the area involved in the perception of color, whereas generation of action words activated a region in the middle temporal gyrus just anterior to the area involved in the perception of motion. These data suggest that object knowledge is organized as a distributed system in which the attributes of an object are stored close to the regions of the cortex that mediate perception of those attributes.

Adult↗
PubMed2004

Motion mechanisms in macaque MT.

The macaque middle temporal area (MT) is exquisitely sensitive to visual motion and there is a large amount of evidence that neural activity in MT is tightly correlated with the perception of motion. The mechanisms by which MT neurons achieve their directional selectivity, however, have received considerably less attention. We investigated the motion-energy model as a description of motion mechanisms in macaque MT. We first confirmed one of the predictions of the motion-energy model; macaques-just like humans-perceive a reversed direction of motion when a stimulus reverses contrast with every displacement (reverse-phi). This reversal of perceived direction had a clear correlate in the neural responses of MT cells, which were predictive of the monkey's behavioral decisions. Second, we investigated how multiple motion-energy components are combined. Psychophysical data have been used to argue that motion-energy components representing opposite directions are subtracted from each other. Our data show, however, that the interactions among motion-energy components are more complex. In particular, we found that the influence of a given component on the response to a stimulus consisting of multiple components depends on factors other than the response to that component alone. This suggests that there are subthreshold nonlinear interactions among multiple motion-energy components; these could take place within MT or in earlier stages of the motion network such as V1. We propose a model that captures the complexity of these component interactions by means of a competitive interaction among the components. This provides a better description of the MT responses than the subtractive motion opponency envisaged in the motion-energy model, even when the latter is combined with a gain-control mechanism. The competitive interaction extends the dynamic range of the cells and allows them to provide information on more subtle changes in motion patterns, including changes that are not purely directional.

Animals↗
PubMed2002

[Synthesis of binocular disparity with motion parallax in depth slant perception: statistical efficiency approach].

Statistical efficiency approach is used in order to investigate sampling properties of both binocular disparity and motion parallax processes in depth slant perception and to examine the independent decisions model (Mulligan & Shaw, 1980) consisting of these processes. We carried out two experiments in which each cue was displayed solely (i.e., single condition) and both cues were displayed simultaneously (i.e., multiple condition). A two-alternative forced-choice (2AFC) task was used under the situation where a Gaussian noise was added to the stimulus value of depth slant. Statistical efficiencies were calculated in each experiment. The results showed that sampling size from binocular disparity was at least comparable or larger by a factor of 2.5-3.5 with that from motion parallax and that efficiencies of the multiple condition considerably exceeded those of the single condition. This suggests invalidity of the independent decisions model.

Cues↗
PubMed1996

Motion transparency arises from perceptual grouping: evidence from luminance and contrast modulation motion displays.

What circumstance lead to the perception of global motion transparency? it has been shown that, in paired random dot displays, motion transparency can be abolished if the separation of the dot pairs is sufficiently small. Motion transparency has also been shown to be influenced by high level cognitive cues. Here, we report that the combination of two moving dot stimuli, which separately invoke a percept of transparent motion, gives rise to a non-transparent percept of local rotation. These stimuli were constructed using various different pattern elements, including luminance defined elements and contrast modulations. The results extend and support the view that high-level grouping of local measures of the velocity field can determine whether a motion transparency is perceived or not.

Humans↗
PubMed1979

Perception of wheel-generated motions.

Data are presented on an old and familiar Gestalt demonstration--perceiving wheel-generated motions--in which the perceived motions of a rolling wheel are shown not to be obviously derived from the motions of the parts. The history of study of this phenomenon is presented, and contradictions in the literature are noted. The focus for experimentation is on the contrasting approaches found in Johansson's perceptual vector analysis and Wallach's arguments for the priority of object-relative displacement in the extraction of invariants. Johansson's approach asserts that common vectors are extracted from moving events first, whereas Wallach asserts that the motion of objects relative to each other is first. These two approaches yield different predictions about what ought to be seen when different configurations are viewed in rotation. In five experiments viewers rated how wheellike the movement of various point-light systems attached to a rolling wheel appeared to be. Results support Wallach's views over Johansson's. Viewer judgments of goodness in wheellike motion correspond highly with a mathematical description of the parameters of cycloidal motion for the geometric center of any system of lights on a rolling wheel. This specification can be made only after the extraction of object-relative displacement information. Number of lights and order of symmetry influence viewer judgments to a much lesser degree, and placement of a light at the wheel's center matters not at all.

Form Perception↗
PubMed2006

Cerebrocerebellar circuits for the perceptual cancellation of eye-movement-induced retinal image motion.

Despite smooth pursuit eye movements, we are unaware of resultant retinal image motion. This example of perceptual invariance is achieved by comparing retinal image slip with an internal reference signal predicting the sensory consequences of the eye movement. This prediction can be manipulated experimentally, allowing one to vary the amount of self-induced image motion for which the reference signal compensates and, accordingly, the resulting percept of motion. Here we were able to map regions in CRUS I within the lateral cerebellar hemispheres that exhibited a significant correlation between functional magnetic resonance imaging signal amplitudes and the amount of motion predicted by the reference signal. The fact that these cerebellar regions were found to be functionally coupled with the left parieto-insular cortex and the supplementary eye fields points to these cortical areas as the sites of interaction between predicted and experienced sensory events, ultimately giving rise to the perception of a stable world despite self-induced retinal motion.

Brain Mapping↗
PubMed1988

Influence of stationary and moving textured backgrounds on the response of visual neurons in toads (Bufo bufo L.).

Previous studies have shown that configurational prey recognition in common toads is performed by feature-analyzing functional units consisting of assemblies of connected neurons such as retinal (classes R2, R3), tectal [classes T5(1), T5(2), T5(3)], and pretectal (class TH3) cells. In the present paper, effects of textured backgrounds on the response of these neurons to a configurational moving stimulus have been tested quantitatively. (1) In all investigated neurons, neither the overall activation nor the respective stimulus-response relationships were significantly influenced by a stationary black/white-textured background as far as black stimulus objects are concerned. (2) The neuronal activity in response to a moving object (signal) could be inhibited (masked) if a black/white-textured background (noise) was moving simultaneously at the same speed. The strength (I) of this 'surround inhibition' (signal masking by the background) was different in the various classes of neurons, i.e. strongest for T5(2) and weakest for R3: IT5(2) greater than IT5(1) greater than IT5(3) greater than IR2 greater than ITH3 greater than IR3. These inhibitory effects were not correlated with the size of the neuronal excitatory receptive field (ERF), since T4 neurons (ERF = 180 degrees) in this context displayed response properties similar to T5(2) neurons (ERF less than 30 degrees). (3) It is suggested that the signal (prey)-masking effect of a moving textured background is brought about by pretecto (TH3)-tectal [T5(1), T5(2)] inhibitory connectivity which allows toads: (a) to select prey from nonprey; (b) to discriminate between prey and a textured background, and (c) to determine the origin of moving retinal images caused either by object movement or by self-induced motion.

Animals↗