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Biomedical subjects

Z Kapoula

Publications and source records attributed to Z Kapoula.

7 recordsLinked to original sources
PubMed1992

Scrutinization, spatial attention, and the spatial programming of saccadic eye movements.

Results are presented from an experiment in which subjects' eye movements were recorded while they carried out two visual tasks with similar material. One task was chosen to require close visual scrutiny; the second was less visually demanding. The oculomotor behaviour in the two tasks differed in three ways. (1) When scrutinizing, there was a reduction in the area of visual space over which stimulation influences saccadic eye movements. (2) When moving their eyes to targets requiring scrutiny, subjects were more likely to make a corrective saccade. (3) The duration of fixations on targets requiring scrutiny was increased. The results are discussed in relation to current theories of visual attention and the control of saccadic eye movements.

Adult↗
PubMed1990

Retinal image motion alone does not control disconjugate postsaccadic eye drift.

1. In these experiments, postsaccadic ocular drift was induced by postsaccadic motion of the visual scene. In the most important case, the scene was moved in one eye but not the other. Six human subjects viewed the interior of a full-field hemisphere filled with a random-dot pattern. During training, eye movements were recorded by the electrooculogram. A computer detected the end of every saccade and immediately moved the pattern horizontally in the same or, in different experiments, in the opposite direction as the saccade. The pattern motion was exponential with an amplitude of 25% of the size of the antecedent saccade and a time constant of 50 ms. Before and after 3-4 h of such training, movements of both eyes were measured simultaneously by the eye coil-magnetic field method while subjects looked between stationary targets for calibration, explored the visual pattern with saccades, or made saccades in the dark to measure the effects of adaptation on postsaccadic ocular drift. The amplitude of this drift was expressed as a percentage of the size of the antecedent saccade. 2. In monocular experiments, subjects viewed the random-dot pattern with one eye. The other eye was patched. With two subjects, the pattern drifted backward in the direction opposite to the saccade; with the third, it drifted onward. The induced ocular drift was exponential, always in the direction to reduce retinal image motion, had zero latency, and persisted in the dark. After training, drift in the dark changed by 6.7% in agreement with our prior study with binocular vision, which produced a change of 6.0%. 3. In a dichoptic arrangement, one eye regarded the moveable random-dot pattern; the other, through mirrors, saw a different random-dot pattern (with similar spacing, contrast, and distance) that was stationary. These visual patterns were not fuseable and did not evoke subjective diplopia. In this case, the induced change in postsaccadic drift in the same three subjects was only 4.8%. In all cases the changes in postsaccadic drift were conjugate--they obeyed Hering's law. 4. Normal human saccades are characterized by essentially no postsaccadic drift in the abducting eye and a pronounced onward drift (approximately 4%) in the adducting eye. After training, this abduction-adduction asymmetry was preserved in the light and dark with monocular or dichoptic viewing, indicating again that all adaptive changes were conjugate. 5. When the subjects viewed the adapting stimulus after training, the zero-latency, postsaccadic drift always increased from levels in the dark.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1989

Visually induced plasticity of postsaccadic ocular drift in normal humans.

1. Five human subjects viewed binocularly the interior of a full-field hemisphere filled with a random-dot pattern. During training, eye movements were recorded by the electrooculogram. A computer detected the end of every saccade and immediately moved the pattern horizontally either in the same or, in different experiments, the opposite direction as the saccade. The motion was exponential, its amplitude was 25% of the horizontal component of the antecedent saccade, and its time constant was either 25, 50, or 100 ms in different experiments. Before and after 2-3 h of this experience, movements of both eyes were measured simultaneously by the eye-coil/magnetic-field method while subjects made saccades across the moveable pattern, looked between stationary targets, or made saccades in the dark, to see the effect of such adaptation on postsaccadic eye movements. 2. After 2-3 h (10,000-20,000 saccades) subjects developed a zero-latency, postsaccadic, ocular drift in the dark in the direction of the pattern motion. Three subjects were trained to backward drift, two to onward drift. Drift amplitude in the dark changed by 6% of the saccade size (range: 2-11%). The drift was exponential with an overall time constant of 108 ms. 3. After training, while viewing the adapting pattern motion, the change in the amplitude of the zero-latency drift was approximately 10% (range: 6.5-14%). 4. Increasing the time constant of the pattern motion produced significant increases in the time constant of the ocular drift. 5. The incidence of dynamic overshoot (a tiny, backward saccade immediately following a main saccade) was idiosyncratic and went up in some subjects and down in others with adaptation. These changes did not seem related to modifications of postsaccadic drift. 6. Normal human saccades are characterized by essentially no postsaccadic drift in the abducting eye and a pronounced onward drift (approximately 4%) in the adducting eye. This adduction-adduction asymmetry is largely preserved through adaptation. Thus the changes in drift were conjugate and conformed to Hering's law of equal (change of) innervation. 7. These results agree with those previously demonstrated in the monkey and can similarly be explained by parametric changes in the pulse, slide, and step of normal saccadic innervation.

Acclimatization↗
PubMed1987

Adaptive changes in post-saccadic drift induced by patching one eye.

A prior study showed that after horizontal saccades the abducting eye has little post-saccadic drift (about 0.5 deg/sec) while the abducting eye has considerable onward drift (about 1.7 deg/sec). To investigate this further, five subjects patched one eye for three days. This reduced the drift after adducting saccades in the viewing eye to the level of that after abducting saccades. The changes were a combination of conjugate and disconjugate alterations. Decreases in drift in the viewing eye did not cause increases in drift in the covered eye. These changes appear functional in that retinal image slip is decreased in the viewing eye but why this goal is not attained when both eyes habitually view is not understood. Also, post-saccadic drift could depend on which eye was used to view the target.

Adaptation, Ocular↗
PubMed1986

Saccadic undershoot is not inevitable: saccades can be accurate.

Saccades normally take the eye 90% of the way to a target, followed by a 10% corrective saccade. An exception to this rule occurs with the range effect. When targets appear in a set of positions, saccades overshoot the near positions and undershoot the far. This phenomenon, previously reported, was confirmed with more accurate methods. The range effect increases if a visual discrimination task is added. It is established rapidly in only a few trials. Latencies of corrective saccades from overshoots and undershoots were the same. Centripetal saccades were more accurate than centrifugal. Thus, undershooting is not inevitable.

Eye Movements↗
PubMed1985

Evidence for a range effect in the saccadic system.

There is general belief that saccadic eye movements almost always undershoot by about 10%. It has long been known, however, in manual tracking that there exists a response bias termed the range effect: small distances are overestimated while large distances are underestimated. The present experiments demonstrate that saccades also show a range effect. The use of two different sets of target distances that partially overlap each other showed that saccades can be made to systematically either overshoot or undershoot their targets depending on the locations of the other targets in the set.

Discrimination, Psychological↗