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Biomedical subjects

A Roucoux

Publications and source records attributed to A Roucoux.

At least 37 records · Page 2Linked to original sources
PubMed1983

Development of fixation and pursuit eye movements in human infants.

Visual fixation and pursuit abilities of human infants were tested during their first year of life. Eye as well as head position was measured. Results show that the fixation of visual targets is accomplished by a head rotation accompanied by a series of small eye saccades. The number of these saccades increases with target eccentricity but progressively decreases with age. Pursuit of a moving visual target is performed by a smooth eye and head movement only if the target velocity is low. The maximum speed of pursuit progressively increases with age. The results are compatible with the relatively late development of the fovea.

Eye Movements↗
PubMed1980

Stimulation of the superior colliculus in the alert cat. I. Eye movements and neck EMG activity evoked when the head is restrained.

Electrical stimulation of the cat superior colliculus (SC), in conjunction with the accurate measurement of elicited eye movements and histologically verified electrode positions, has revealed a striking antero-posterior variation in collicular organization. Three zones could be defined in the SC on the basis of eye movement patterns and associated neck muscle EMG activity evoked from the deeper layers. The Anterior zone was coextensive with the central 25 degrees of the visual retinotopically coded map contained in the superficial layers. Saccades evoked from this zone were also retinotopically coded, and the latency of EMG activity depended on the position of the eye in the orbit. A similar observation applies to the entire monkey SC. The Intermediate zone was coextensive with the 25 degrees--70 degrees of visual projections. Saccades evoked from this region were "goal-directed" and were associated with invariant, short latency EMG responses. The Posterior zone was found in the extreme caudo-lateral portion of the SC. Eye movements evoked from this zone were centering saccades associated with constant latency EMG activity. The present results in conjunction with previously demonstrated antero-posterior variations in projections to the SC, suggest that the motor strategies controlling gaze shifts toward visual targets vary depending on the location of the target in the visual field.

Animals↗
PubMed1980

Stimulation of the superior colliculus in the alert cat. II. Eye and head movements evoked when the head is unrestrained.

Electrical stimulation of the superior colliculus (SC) in alert cats free to move their head, evoked coordinate eye and head movements. The characteristics of these movements as well as their mode of coordination differed according to the collicular region being explored. Three zones were distinguished. In the anterior zone, evoked eye saccades were retinotopic and the accompanying head movements were slow and small in amplitude. The vestibular slow phase velocity signal was continuously added to the eye saccadic command so that the evoked gaze shift was identical, with the head fixed or free. In the intermediate zone, evoked eye saccades were goal-directed and the synchronous head movements fast and of large amplitude. The vestibular slow phase signal was cancelled during the eye saccade so that the evoked gaze shift was the result of the eye plus head angular displacement. In the posterior zone, the evoked head movements were goal-directed. The pattern of eye movements was similar to a vestibular nystagmus. This zone probably directly commands body orienting movements. A model of SC function in gaze orienting behavior is proposed, calling upon at least two different modes of eye-head coordination.

Animals↗
PubMed1976

Eye movements evoked by superior colliculus stimulation in the alert cat.

(1) The electrical stimulation of the superior colliculus (SC) in the cat evokes exclusively conjugate and contraversive eye saccades. (2) Their maximum velocity is markedly higher than that of spontaneous saccades. (3) The stimulus parameters (intensity, frequency, pulse width) have but little effect on the characteristics of the saccades. (4) In the anterior half of the SC, corresponding to the projection of the 12-15 central degrees of the retina, amplitude and direction of saccades depend exclusively on the position of the electrode. (5) In the posterior half, corresponding to the projection of the peripheral retina, saccades are 'goal directed' and the position of the goal is determined by the location of the electrode. (6) An increase in stimulus train length produces, in the anterior part, a succession of identical saccades and, in the posterior part, a goal fixation. (7) Taking all these data into consideration, a model of the foveation process in the cat is proposed.

Animals↗