in the middle temporal visual area (MT) of anesthetized, paralyzed macaque monkeys. A computer-driven stimulator was used to make quantitative tests of selectivity for stimulus direction, speed, and orientation. The data were taken from 168 units that were histologically identified as being in MT. 2. The results confirm previous reports of a high degree of direction selectivity in MT. The response above background to stimuli moving in a unit’s preferred direction was, on average, 10.9 times that to stimuli moving in the opposite direction. There was a marked tendency for nearby units to have similar preferred directions. 3. Most units were also sharply tuned for the speed of stimulus motion. For some cells the response fell to less than half-maximal at speeds only a factor of two from the optimum; on average, responses were greater than half-maximal only over a 7.7-fold range of speed. The distribution of preferred speeds for different units was unimodal, with a peak near 32”/s; the total range of preferred speeds extended from 2 to 256”/s. Nearby units generally responded best to similar speeds of motion. 4. Most units in MT showed selectivity for stimulus orientation when tested with stationary, flashed bars. However, stationary stimuli generally elicited only brief responses; when averaged over the duration of the stimulus, the responses were much less than those to moving stimuli. The preferred orientation was usually, but not always, perpendicular to the preferred direction of movement. 5. A comparison of the results of the present study with a previous quantitative investigation in the owl monkey shows a striking similarity in response properties in MT of the two species. 6. The presence of both direction and speed selectivity in MT of the macaque suggests that this area is more specialized for the analysis of visual motion than has been previously recognized.

Abstract-Inspecting a target whose size oscillates about a constant mean value selectively depresses visual sensitivity to oscillating size. The effect transfers from positive to negative contrast and vice versa. This depression cannot be attributed to fatigued movement detectors. We propose that there are, in the human visual system, channels in which information as to changing size is selectively processed. This notion is consistent with the existence of two neural organizations (e.g., two classes of single neurons) selectively sensitive to increasing and to decreasing size, respectively. Key Words-Vision; tation.

A global shape judgement task was used to investigate the combination of stereopsis and kinetic depth. With botb cues present, there were no distortions of shape perception, even under conditions where either cue alone did show such distortions. We suggest that the addition of motion information overcomes the stereo distance scaling problem. However, when incongruent combinations of disparity and motion were used, the results did not match predictions of a number of combination theories. These data could be described by a model which used weighted linear combination afier correctly scaling disparities for viewing distance. When the motion cue was weakened by presenting only two frames of each motion sequence, stereo was weighted more heavily. Stereopsis Structure-from-motion Three-dimensional shape perception Integration of depth cues

Most models of disparity selectivity consider only the spatial properties of binocular cells. However, the temporal response is an integral component of real neurons ’ activities, and time-varying stimuli are often used in the experiments of disparity tuning. To understand the temporal dimension of V1 disparity representation, we incorporate a specific temporal response function into the disparity energy model and demonstrate that the binocular interaction of complex cells is separable into a Gabor disparity function and a positive time function. We then investigate how the model simple and complex cells respond to widely used time-varying stimuli, including motion-in-depth patterns, drifting gratings, moving bars, moving random-dot stereograms, and dynamic random-dot stereograms. It is found that both model simple and complex cells show more reliable disparity tuning to time-varying stimuli than to static stimuli, but similarities in the disparity tuning between simple and complex cells depend on the stimulus. Specifically, the disparity tuning curves of the two cell types are similar to each other for either drifting sinusoidal gratings or moving bars. In contrast, when the stimuli are dynamic random-dot stereograms, the disparity tuning of simple cells is highly variable, whereas the tuning of complex cells remains reliable. Moreover, cells with similar motion preferences in the two eyes cannot be truly tuned to motion in depth regardless of the stimulus types. These simulation results are consistent with a large body of extant physiological data, and provide some specific, testable predictions.

Abstract-After adapting to changing size by viewing a square whose dimensions increased with a ramp waveform. a subsequently-viewed test square appeared to move continuously away in depth. Adapting to decreasing sire produced the opposite aftereffect. This depth movement aftereffect could be measured by cancelling it by some unique rate of change of size. The direction of the aftereffect and the direction of the cancelling stimulus were independent of whether the adapting square or test square was of positive or negative contrast. The aftereffect built up over 10min adaptation and decayed exponentially (r = 52 se+ It cannot be explained in terms of the classical movement aftereffect. We propose that neural filters sensitive to unidirectionally changing size drive the neural mechanism that underlies the perception of motion in depth. Key Words--motion; aftereffect; size; stereoscopic depth movement. We have reported psychophysical evidence for the existence of information-processing channels sensitive to the relative velocities of the left and right retinal images, and thereby tuned to different directions of

Stereo-motion cooperation and the use ofmotion

Motion as a fundamental visual dimension Functional aspects of image motion processing (I) Encoding of the third dimension (2) Time to collision (TTC) (3) Image segmentation (4) Motion as a proprioceptive sense (5) Motion as a stimulus to drive eye movements (6) Motion as required for pattern vision (7) Image motion processing as useful for perceiving real moving objects Multiplicity of functional roles Motion blindness? Parallel and serial processing within an early motion system: a skeletal model Random dot stimuli D ImAX Dm, Intermediate values of velocity Experiments using sinusoidal gratings Common space-time framework to account for random dot and grating data Motion hyperacuity Metrical encoding of velocity Fourier domain description of moving images Chromatic input to the motion system? Computational theories of motion processing Early models Recent models Beyond the simple pair? Single cell analysis of image motion Definitional issues Movement, nonmovement and pre-movement units Motion processing at the extrastriate level Orientation tuning in the motion system An oblique effect for motion? The aperture problem Temporal integration of velocity signals Higher-order computations on the optical flow field Derivatives of velocity Interocular comparison of motion signals: motion in depth