Biomedical subjects

L Rogal

Publications and source records attributed to L Rogal.

4 recordsLinked to original sources

PubMed1989

Macro square wave jerks in a rhesus monkey: physiological and anatomical findings in a case of selective impairment of attentive fixation.

An otherwise normal female rhesus monkey executed large saccadic eye movements (macro square wave jerks) when required to attentively fixate a small visual target (fixation point). The jerks were observed exclusively in this specific testing situation. They occurred periodically at a frequency of 2.04 + - 0.18 Hz to the right side with an amplitude of 23.5 deg. Direction of the jerks was about 3-4 degrees downward from horizontal. These parameters remained constant throughout the several months of daily recording. No jerks were executed during periods when the behaviourally important target was absent or substituted by another, behaviourally non-relevant visual stimulus. The monkey could perform normal visually guided saccades as well as smooth pursuit eye movements, but with the jerks always superimposed, when the monkey paid attention to the visual target. Histologic inspection of the brain revealed the presence of an incapsulated nematode in the cortex of lobulus simplex of the right cerebellar hemisphere, i.e., in a region involved in oculomotor control.

Animals↗

PubMed1986

Eye-hand-coordination in man: a reaction time study.

Reaction time measurements were used to test the possibility that an eye and a reach movement both aimed at the same visual target share a common final motor command. This hypothesis predicts highly correlated pairs of reaction times on a trial by trial basis. The experiments were based on the earlier observation that long saccadic reaction times (above 200 ms) with a large scatter (150-300 ms) are obtained if the central fixation point remained visible through out a trial (overlap paradigm), whereas extremely short saccadic reaction times (around 120 ms) with a small scatter (100-150 ms) occur if the fixation point was turned off some time (200 ms) before the target appeared (gap paradigm). In the overlap paradigm high correlations (coefficients up to 0.95) between saccadic and reach reaction times were obtained and the corresponding linear regression lines had a slope of almost one. In the gap paradigm, however, correlations were almost absent even though the mean reach reaction times were considerably decreased. These observations clearly contradict the "common command" hypothesis, but can be explained by the assumption that the execution of the reach movement depends on the completion of the preparation of the saccade but not vice versa ("one way synchronization" hypothesis).

Dominance, Cerebral↗

PubMed1986

Eye-hand-coordination: a model for computing reaction times in a visually guided reach task.

A model is described which provides a simple algorithm to compute the reaction times of saccadic eye movements and reach movements aimed at a single visual target. It is assumed, that the two movements are prepared in parallel and initiated independently unless the preparation of the saccade for some reason takes longer than the preparation of the reach movement. In the latter case the final command to execute the reach movement is synchronized with that to execute the eye movement and therefore the corresponding reaction times are highly correlated in a one-to-one relationship. Random variables are used to predict sets of data that are directly comparable with the experimental results. The algorithm includes the effects of daily practice (learning). The structure of the model and its computational results will be compared with the physiological data from monkey and man.

Algorithms↗

PubMed1985

Reaction times of the eye and the hand of the monkey in a visual reach task.

Two monkeys were trained to execute saccadic eye movements and reach movements with the hand from a central fixation point to a peripheral target. Reaction times for both movements were compared on a trial-by-trial basis. If the fixation point was extinguished before the target appeared (gap condition), extremely short latency saccades (85 ms) (express saccades) were obtained, that were followed by short latency reach movements (250 ms), but there was no correlation between them on a trial-by-trial basis. If the fixation point remained visible (overlap condition), very short (100 ms) and rather long (220 ms) latency saccades were observed. Long saccadic latencies correlated strongly with the reach reaction times. Short latency saccades were followed by reach movements of reaction times longer than those observed after express saccades in the gap condition; there was no correlation between them. All reaction times varied systematically with practice.

Animals↗