PubMed Health⌕ Search

Biomedical subjects

W Kropfl

Publications and source records attributed to W Kropfl.

8 recordsLinked to original sources
PubMed1981

Development of stereopsis and cortical binocularity in human infants: electrophysiological evidence.

Dynamic random-dot stereograms and correlograms were used to elicit visually evoked brain potentials from human infants, and these potentials were compared with potentials evoked by classical checkerboard pattern reversal. The results indicate that infants begin to produce stereoscopically evoked potentials at the age of 10 to 19 weeks, several weeks after showing classical checkerboard-evoked potentials, and suggest that the onset of cortical binocularity precedes stereopsis.

Age Factors↗
PubMed1981

Binocular stimulation reveals cortical components of the human visual evoked potential.

Dynamic random dot correlograms (RDCs) produced by a rear-projection television system elicited visual evoked potentials (VEPs) in a sample of 10 observers corrected to emmetropia. When the observers viewed the RDCs binocularly through stereo wave length filters, characteristic wave forms were recorded. Four components were reliably recorded at the onset and the offset of the correlated state of the RDCs. These components differ with statistical significance (P less than 0.05) from each other. These RDC VEPs provide a practical technique to evaluate the integrity of binocular and, by inference, cortical processes.

Adult↗
PubMed1980

Cortical binocularity in infants.

The primate visual cortex, including that of man, receives separate input from each eye and these interact in binocular cortical neurones. This organization is known to be vulnerable to disruption in early life. To understand the development of human visual cortex, and to detect and assess disorders of binocular function at the earliest possible age, a robust method is needed for detecting binocular interactions in the infant's visual system. We have done this by recording cortical visual evoked responses (VERs) to the onset and offset of binocular correlation in a large-screen dynamic random dot display. We report here that, in general, the human infant has a functional binocular visual cortex by 3 months of age, with some individuals showing cortical binocularity at an earlier age.

Age Factors↗
PubMed1980

Large evoked potentials to dynamic random-dot correlograms and stereograms permit quick determination of stereopsis.

The combination of three technological innovations permits the fast and objective determination of stereopsis in nonverbal subjects: (i) It is shown that dynamic random-dot correlograms (RDC) are as effective as dynamic random-dot stereograms (RDS) in eliciting large evoked potentials (EP), and that the generation of RDC is simpler than that of RDS. (ii) The presentation of RDC in the form of red-green anaglyphs is insensitive to subjects' head tilt, because alternation of correlation (binocular fusion) with uncorrelation (binocular rivalry) does not depend on the direction of binocular disparity, whereas perception of depth in RDS does. (iii) Projection TV techniques, using backprojected large screens viewed from near distances, permit noncooperative subjects (e.g., human infants or monkeys) to be surrounded with the stimulus, so they cannot look away.

Animals↗
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↗