■Scaling
effects in the perception of higher-order spatial correlations.
■Neural integration of information specifying
structure from stereopsis and motion.
■A neural
network model of kinetic depth.
■Direction perception in complex dynamic
displays: The integration of direction information.
■How stereovision interacts with optic flow perception:
Neural mechanisms.
■Temporal and spatial integration in dynamic random-dot
stimuli.
Scaling effects in the perception of higher-order spatial correlations.
Joseph, Julian S., Victor, Jonathan D., and Optican, Lance
M.
Vision Research，37(22)，3097-3107，1997
Human texture discrimination depends both on spatial-frequency content and on higher-order or multi-point correlations. Spatial-frequency discrimination exhibits a high degree of scale invariance over a range of several octaves, but the scaling behavior of sensitivity to higher-order correlation structure is unknown. We explored the scale dependence of texture discrimination for image ensembles which shared the same power spectrum, but differed in their higher-order correlations. Literally scaling the ensembles so that they occupy larger retinal regions results in discrimination performance that is largely independent of scale over a 3 octave range. Holding the display size constant and scaling the texture being sampled within the display over the same range produces performance that varies with scale appreciably. The ideal observer performance is computed, and the absolute efficiency is seen to be quite small, on the order of 10(-2)-10(-1). As the texture is scaled down, increasing the number of checks within the fixed display size, performance increases while the efficiency decreases. These dependencies remain when the stimulus onset asynchrony is increased from 50 to 500 msec. We created sets of textures which varied both in check number and correlation strength, for which ideal observer performance was equated. For the human observers, efficiency was significantly higher for textures with higher correlation strength, but fewer checks. These results are consistent with a model in which a fixed number of checks is processed in a scale-invariant manner, while the remainder of the display is processed much less efficiently.
Neural
integration of information specifying structure from stereopsis and motion.
Nawrot, Mark; Blake, Randolph
Science，244，716-718，1989
When one views a 2-dimensional parallel projection of dots on the surface of a rotating globe, the direction of rotation is ambiguous, and the perceived direction of rotation of the 2-dimensional figure is unstable over time. Stability can be temporarily induced by adaptation to a 3-dimensional globe with a direction of rotation unambiguously specified by stereo disparity; adaptation causes the 2-dimensional figure to appear to rotate in the direction opposite that experienced during stereoscopic adaptation. This adaptation effect is selective for axis of rotation but is not shape-specific. Evidently information about stereopsis and information about structure from motion are integrated within a common neural site in the brain.
A
neural network model of kinetic depth.
Nawrot, Mark; Blake, Randolph
Visual Neuroscience，6，219-227，1991
Developed a network model that accounts for the kinetic depth in structure from motion phenomena. Using plausible neural mechanisms, the model accounts for (1) fluctuations in perception when viewing a simple kinetic depth stimulus, (2) disambiguation of this stimulus with stereoscopic information, and (3) subsequent bias of the percept of this stimulus following stereoscopic adaptation. The model comprises a layer of monocular directionally selective motion detectors that provide input to a 2nd layer of disparity- and direction-selective binocular mechanisms. Results of a psychophysical experiment, involving 2 observers with normal and corrected-to-normal acuity, are consistent with the nature of the proposed interactions.
Direction
perception in complex dynamic displays: The integration of direction information.
Watamaniuk, Scott N.; Sekuler, Robert; Williams, Douglas
W.
Vision Research，29(1)，47-59，1989
Created random-dot cinematograms in which each dot's successive movements were independently drawn from a Gaussian distribution of directions of some characteristic bandwidth. Using pairs of cinematograms, direction discrimination of global motion was measured in 4 undergraduates and 1 of the present authors under various conditions of direction distribution bandwidth, exposure and duration, and constancy of each dot's path. A line-element model accounted for the results. Over a considerable range, discrimination was unaffected by the cinematogram's direction distribution bandwidth. Only for the briefest presentations did changes in duration have an effect. So long as the overall directional content of the cinematogram remained unchanged, the constancy or randomness of individual dots' paths did not affect discrimination.
How
stereovision interacts with optic flow perception: Neural mechanisms.
Lappe, M.; Grigo, A.
Neural Networks，12，1325-1329，1999
Human perception is based on a multitude of sensory signals that are integrated with each other in the CNS. This paper is concerned with the interaction of 2 specific visual signals, binocular disparity and visual motion in the perception of complex optic flow patterns. Optic flow arises whenever an animal moves in its environment. In order to investigate this interaction, a neurobiological model of optic flow processing in the medial superior temporal area of the macaque monkey is presented. Findings demonstrate that stereoscopic vision and optic flow processing interact and that the visual system lays special emphasis on distant motion signals.
Temporal
and spatial integration in dynamic random-dot stimuli.
Watamaniuk SN, Sekuler R.
Vision Research，32(12)，2341-2347，1992
Random-dot cinematograms comprising many different, spatially intermingled local motion vectors can produce a percept of global coherent motion in a single direction. Thresholds for discriminating the direction of global motion were measured under various conditions. Discrimination thresholds increased with the width of the distribution of directions in the cinematogram. Thresholds decreased as the duration of area of the cinematogram increased. Temporal integration for global direction discrimination extends over about 465 msec (9.3 frames) while the spatial integration limit is at least as large as 63 deg2 (circular aperture diameter = 9 deg). The large spatial integration area is consistent with the physiology of higher visual areas such as MT and MST.