Search PubMed⌕ Search

Biomedical subjects

K Prazdny

Publications and source records attributed to K Prazdny.

At least 19 recordsLinked to original sources
PubMed1987

Vertical disparity nulling in random-dot stereograms.

Vertical alignment of monocularly visible structures has profound influence on a binocular system's ability to fuse high spatial frequencies of a random-dot stereogram. We show that monocular objects "capture" the vertical alignment: often less than 5% of the total stereogram area determines the state of the vertical alignment and can prevent fusion of the fine scale detail. This suggests that the human binocular system uses a heuristic in which, when monocularly salient information is available, stereomatching is attempted only at vertical alignment settings determined by the monocular structures.

Eye Movements↗
PubMed1986

Some new phenomena in the perception of glass patterns.

Glass patterns are dot pattern displays producing percepts of local orientation and global organization. Our observations suggest that the organizational principles involved in our perception of such patterns may be more consistent with a cortical simple-cell-like mechanisms (i.e., a king of neural summation within various feature maps) than with symbolic processing based on feature similarity.

Humans↗
PubMed1986

What variables control (long-range) apparent motion?

A solid (ie filled-in) two-dimensional form is seen in motion toward another solid object of different shape and not towards an outline object of the same shape. The interpretation of these findings in terms of luminance-domain spatial frequency filtering is challenged by experiments in which the same results were obtained with kinetic and cyclopean forms.

Depth Perception↗
PubMed1986

Three-dimensional structure from long-range apparent motion.

Experiments are reported which show that three-dimensional structure can be perceived from two-dimensional image motions carried by objects defined solely by the differences in binocular and/or temporal correlation (ie disparity or motion discontinuities). This demonstrates that the kinetic depth effect is independent of motion detection in the luminance domain and that its relevant input comes from detectors based on some form of identity preservation of objects or features over time, ie the long-range processes of apparent motion.

Depth Perception↗
PubMed1986

Psychophysical and computational studies of random-dot Moire patterns.

Random-dot Moire dot patterns epitomize the local/global gap, the problem of perceiving global structures when only physical local information is available to the perceptual system. At present, no single theory appears to be able to account for all the phenomena these physically simple patterns generate.

Humans↗
PubMed1985

Studies of some new phenomena of motion perception.

Contrast modulation of a set of features in a Glass pattern invokes, under certain circumstances, the perception of motion in the absence of any physical displacements. The illusion is spatially limited to within about 10' and is governed by contrast relationships. We find that the detected motion in these situations is due to local computations the results of which can be integrated over retinal areas of more than 1 degree. The possible motion detection mechanisms are discussed within the framework of the Reichardt/Hassenstein and Marr/Ullman type of motion detectors.

Animals↗
PubMed1985

Detection of binocular disparities.

A stereo correspondence algorithm designed to perform matching on figurally similar images (arising in normal human binocular vision) is described. It is based on the observation that the operational principles underlying biological stereo disparity detection seem to be extremely general and few in number instead of an extended set of specific "constraints". We identify one general characteristic of objects in the three dimensional world and use it to formulate a simple noniterative, parallel and local algorithm that successfully detects disparities generated by opaque as well as transparent surfaces.

Humans↗
PubMed1984

On the perception of Glass patterns.

Recent findings about our perception of Glass patterns suggest that the processes responsible for the perception of a global pattern composed of random features may be mechanisms performing measurements in the spatial and energy domain rather than logical operations on symbolic descriptions. These mechanisms may be based on principles derivable from spatial regularity and coherence of objects in the three-dimensional world.

Form Perception↗
PubMed1983

Stereoscopic matching, eye position, and absolute depth.

The viewing system parameters (in particular the mutual orientation of the coordinate frames fixed respectively to the left and right projection surface) probably have to be explicitly incorporated into solutions to the stereoscopic-matching problem in binocular vision. An algorithm for computing the relative orientation of the two directions of gaze from purely visual information without a prior solution to the correspondence problem is outlined. The availability of an algorithm of this sort seems to be a precondition for any stereoscopic-matching process that uses the epipolar constraint. It is further argued that fixation of objects in the near space requires integration of the results of stereoscopic matching over eye movements, and that this requirement puts rather tight restrictions on the possible form of representing the results of stereoscopic processing.

Depth Perception↗
PubMed1981

A note on "Optical motions as information for unsigned depth".

Farber and McConkie have questioned whether optical (or retinal) flows provide a basis for the accurate perception of relative distance (or filled depth, in Gibson, Gibson, Smith, & Flock's terms). Some of the analysis Farber and McConkie present is incorrect. In this article I identity some of the fallacies and discuss issues relevant to these fallacies. The critique does not concern the experiments presented by Farber and McConkie but rather the underlying analysis that culminated in the experiments.

Depth Perception↗