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Biomedical subjects

B Julesz

Publications and source records attributed to B Julesz.

At least 73 records · Page 4Linked to original sources
PubMed1978

Binocular utilization of monocular cues that are undetectable monocularly.

The latency time of tracking dynamic random-dot stereograms can be shortened by as much as 100 ms when monocular cues are added by introducing a difference in dot density between target and surround. It has been tacitly assumed that perception time will be reduced only if the added monocular cues are above the detection threshold for each eye. However, the experiments reported here clearly show that stereoscopic performance as measured by an eye tracking task can be greatly enhanced by added monocular cues that cannot be detected. Observers were instructed to track a suddenly displaced vertical bar (portrayed as a dynamic random-dot stereogram) while their eye movements were recorded by EOG. The bar had either a given binocular disparity or zero binocular disparity with respect to its surround. For the target with a disparity (in a wide range), the latency time of tracking decreased by more than 30 ms (10%) as density difference increased from 0 to 4%, whereas in the control conditions with no stereoscopic cues (zero disparity) subjects were unable to track the bar at all within that range of density difference. Thus stereopsis is greatly aided by minimal monocular cues that by themselves elude monocular detection.

Cues↗
PubMed1976

Binocular-disparity-dependent upper-lower hemifield anisotropy and left-right hemifield isotropy as revealed by dynamic random-dot stereograms.

Dynamic random-dot stereograms devoid of all monocular depth cues were used to measure the limits of temporal and spatial resolution in the center of the visual field. The temporal durations for detecting a small, briefly presented test square of different binocular disparity than the surround varied as a function of its location and binocular disparity. The test squares presented in the upper hemifield were detectable at consistently shorter durations than those presented in the lower hemifield for a surround disparity which was uncrossed relative to the fixation marker. For crossed surround disparity this preference reversed, resulting in a superiority of the lower hemifield. The anisotropy diminished for zero surround disparity. No such anisotropy was found when left and right visual hemifields were compared. It was also shown that this upper-lower temporal anisotropy (and left-right isotropy) is paralleled by a similar disparity-dependent upper-lower anistropy (and left-right isotropy) in spatial resolution. Introduction of monocular clues into the stereograms tended to eliminate the anisotropies. This implies that the anisotropies reflect the spatiotemporal properties and distribution of binocular disparity detectors in the human cortex and result in a tilted surface that pivots around the horizontal midline in the space of binocular depth perception.

Depth Perception↗
PubMed1975

Dynamic random-dot stereograms reveal up-down anisotropy and left-right isotropy between cortical hemifields.

With the use of dynamic random-dot sterograms (which are devoid of all monocular depth cues), the temporal duration for detecting a small, briefly presented test square of different depth than the surround varied as a function of its location in the central portion of the visual field. Test squares presented in the upper hemifield were detectable at consistently shorter durations than those in the lower hemifield when the fixation marker was in front of the surround, and vice versa when the marker was behind. No such anisotropy was found for left and right hemifield. Esploratory studies suggested a similar up-down anisotropy and left-right isotropy in spatial resolution. Thus, the upper hemifield representation at the cortex shows a general superiority over the lower one for vinocular detectors tuned to uncrossed disparitites, and the lower hemifield shows superiority for those tuned to crossed disparities.

Brain Mapping↗
PubMed1973

Masking in visual recognition: effects of two-dimensional filtered noise.

It is difficult to recognize portraits that have been coarsely sampled and quantized. Blurring such images improves recognition. A simple, straightforward explanation is that high-frequency noise introduced by the sampling and quantizing must be removed by low-pass filtering to improve the signal-to-noise ratio and hence signal detectability or recognition. Experiments reported here, suggested on the basis of a different model, show instead that noise bands that are spectrally adjacent to the picture's spectrum are considerably more effective in suppressing recognition.

Computers↗
PubMed1971

Stereoscopic depth aftereffect produced without monocular cues.

Random-dot stereograms when used as adaptation stimuli can influence the perceived depth of similar test stimuli. Adaptation for 1 minute is sufficient to evoke this three-dimensional aftereffect for several seconds. This aftereffect must occur after stereopsis because prior to stereopsis no relevant monocular cues exist in these adaptation and test stimuli.

Adaptation, Ocular↗