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Biomedical subjects

G M Gauthier

Publications and source records attributed to G M Gauthier.

66 records · Page 4Linked to original sources
PubMed1978

A film projecting system as a diagnostic and training technique for eye movements of cerebral palsied children.

Films are presented for tracking on a translucent screen after reflection from a galvanometer driven mirror. A wave function generator produces picture displacements of amplitude and velocity capable of stimulating selectively (or simultaneously) the saccadic and smooth pursuit systems. This audiovisual signal permits prolonged eye movement recording and training sessions because of increased motivation and alertness. Optokinetic and vestibulo-ocular reflexes can also be tested. An infra-red photoelectric device monitors the horizontal component of eye movement. Records provide the necessary information for syndrome definition and training progress evaluation. Preliminary results show the technique to be perfectly suitable for the diagnosis of functional disorders and sensory-motor training of the cerebral palsied child's oculomotor system.

Attention↗
PubMed1976

Eye tracking of self-moved targets in the absence of vision.

Smooth pursuit eye movements have been described as resulting from the tracking of self-moved targets in total darkness. This study investigated the nature of the signal responsible for the release of smooth pursuit in this particular situation. Simultaneous monitoring of eye and hand positions shows that in total darkness smooth pursuit can only be released if the imagined target is either passively or actively moved by the subject's hand. An ischaemic block applied at the level of the biceps allowed us to selectively remove the afferent signal preferentially to the efferent copy in tasks involving eye tracking of an imaginary target actively or passively moved. The results show that an afferent signal was necessary and sufficient to release smooth pursuit, whereas the efferent copy alone could not trigger smooth pursuit. However, the efferent copy could play an important role in the phase relationship (prediction) between eye and finger events and in the activation of the concomitantly active saccadic system. Analysis of the eye movement characteristics, in various non-visually guided, load-affected situations, suggested that the main input to the smooth pursuit system was derived, in a non-graded way, from the position detector activation of the target-moving structure.

Darkness↗
PubMed1976

Eye movements in response to real and apparent motions of acoustic targets.

Monitoring of eye movements resulting from the tracking of sound displacements in total darkness confirmed the generally accepted idea that smooth pursuit cannot be induced in the absence of a real visible target. Exclusively saccadic movements were obtained with real and apparent displacements of a constant frequency source and with frequency variations associated to spatially calibrated positions through training for 5 Ss. Smooth pursuit eye movements were only observed if S was allowed to point and follow with his hand the perceived position of acoustic targets.

Acoustic Stimulation↗
PubMed1976

Alterations of the human vestibulo-ocular reflex in a simulated dive at 62 ATA.

In an attempt to investigate some aspects of the high pressure nervous syndrome, the vestibulo-ocular reflex (VOR) gain was measured in two professional divers undergoing a simulated dive at 62 ATA. The aquanauts in a seated position were rotated sinusoidally around the vertical axis at a frequency of about 0.3 Hz over a 20 degrees range. Tests were performed at regular intervals prior to, during, and after the compression/decompression period. The rotations were applied either in total darkness or with a visual target rotating with the chair or with a target fixed to the chair-supporting frame. An infrared photoelectric system monitored eye movements. The results showed no spontaneous nystagmus, but two definite changes in VOR gain: (1) a slight but significant increase related to pressure increase, which may be due to an increase of the vestibular system excitability or a decrease of the cerebellar inhibition exerted upon the vestibular nuclei, and (2) an intermittently appearing increase (VOR gain between 1 and 1.3) during brief periods. The latter finding, not related to pressure, was interpreted as the expression of an underwater-adapted mode that may developed in professional divers submitted to the intensive use of magnifying diving-optical systems.

Diving↗
PubMed1975

Two-dimensional eye movement monitor for clinical and laboratory recordings.

A photo-electric device designed to monitor simultaneously vertical and horizontal eye movements within a 20 degrees range is presented with illustrating experimental data. Four small infrared detecting cells are mounted on a light spectacle-like frame together with a miniature true infrared (9000 A) emitting diode. This original design which eliminates separate source illumination artifacts is extremely light, preserves maximum vision field size, and has particularly straightforward operation. The instrument resolution is less than 1 minute of arc with a 1000 c/sec bandwidth and a 5% linearity over the maximum operating range.

Eye Movements↗
PubMedDate not supplied

Egocentric visual target position and velocity coding: role of ocular muscle proprioception.

Limited knowledge is available regarding the processes by which the brain codes the velocity of visual targets with respect to the observer. Two models have been previously proposed to describe the visual target localization mechanism. Both assume that the necessary information is derived from the coding of the position of the eye in the orbit, either through a copy of the muscular activation (out flow model) or through eye muscle proprioception (in flow model). Eye velocity coding might be derived from velocity sensitive ocular muscle proprioceptors or from position coding signals through differentiation. We used techniques based on manual pointing and manual tracking of visual target, combined with passive deviation of one covered eye, to demonstrate that ocular muscle proprioception is involved in (i) eye-in-head position coding, hence in target localization function; (ii) long-term maintenance of ocular alignment (phoria); and (iii) sensing of visual target velocity with respect to the head. These observations support other data now available, describing the processes by which the brain codes position and velocity of visual targets. Such findings might interest engineers in the field of robotics who are facing the problem of providing robots with the ability to sense object position and velocity in order to create an internal model of their working environment.

Humans↗
PubMedDate not supplied

Eye-head movement coordination: vestibulo-ocular reflex suppression with head-fixed target fixation.

To maintain clear vision, the images on the retina must remain reasonably stable. Head movements are generally dealt with successfully by counter-rotation of the eyes induced by the combined actions of the vestibulo-ocular reflex (VOR) and the optokinetic reflex. A problem of importance relates to the value of the so-called intrinsic gain of the VOR (VORG) in man, and how this gain is modulated to provide appropriate eye movements. We have studied these problems in two situations: 1. fixation of a stationary object of the visual space while the head moves; 2. fixation of an object moving with the head. These two situations were compared to a basic condition in which no visual target was allowed in order to induce "pure" VOR. Eye movements were recorded in seated subjects during stationary sinusoidal and transient rotations around the vertical axis. Subjects were in total darkness (DARK condition) and involved in mental arithmetic. Alternatively, they were provided with a small foveal target, either fixed with respect to earth (earth-fixed target: EFT condition), or moving with them (chair-fixed-target: CFT condition). The stationary rotation experiment was used as baseline for the ensuing experiment and yielded control data in agreement with the literature. In all 3 visual conditions, typical responses to transient rotations were rigorously identical during the first 200 ms. They showed, sequentially, a 16-ms delay of the eye behind the head and a rapid increase in eye velocity during 75 to 80 ms, after which the average VORG was 0.9 +/- 0.15. During the following 50 to 100 ms, the gain remained around 0.9 in all three conditions. Beyond 200 ms, the VORG remained around 0.9 in DARK and increased slowly towards 1 or decreased towards zero in the EFT and CFT conditions, respectively. The time-course of the later events suggests that visual tracking mechanisms came into play to reduce retinal slip through smooth pursuit, and position error through saccades. Our data also show that in total darkness VORG is set to 0.9 in man. Lower values reported in the literature essentially reflect predictive properties of the vestibulo-ocular mechanism, particularly evident when the input signal is a sinewave.

Dark Adaptation↗
PubMedDate not supplied

Visual object localization through vestibular and neck inputs. 2: Updating off-mid-sagittal-plane target positions.

The vestibular signal plays a significant role in sensing changes in head orientation during rotations and in determining the magnitude of the rotations, but has only minor contributions in updating the internal representation of object positions with respect to the body after body rotations. The small contribution of the vestibular signal in egocentric object localization was evidenced in experiments in which the subjects reported the remembered position of eccentric earth-fixed targets after passive body rotations. The experiment reported here tested whether motor systems, such as the oculomotor system, make use of vestibular signals to generate accurate goal-directed motor responses toward a target whose position needs to be updated with respect to the body during and after whole-body rotations. The results showed that although subjects can produce saccadic eye movements of about the same magnitude as passive whole-body rotations (as previously reported by a number of researchers), they failed to generate accurate saccades toward the position of an extinguished peripheral visual target after the rotation. Overall, these results combined with those found in the literature suggest different central processes for determining changes in body orientation in complete darkness and for updating a target position with respect to the body during and after body rotations.

Adult↗