Biomedical subjects

D Pélisson

Publications and source records attributed to D Pélisson.

24 records · Page 2Linked to original sources

PubMed1992

A non-contact system for 2-dimensional trajectory recording.

A new non-contact, real-time, 2-dimensional recording technique is described. This technique used in a cat training procedure, permits on-line monitoring of the position of a hand-held food target displaced at variable speeds, directions and amplitudes in front of the animal. Due to the optical constraints imposed by this training procedure, 2 orthogonally located 1-dimensional position-sensitive detectors (PSDs) are used in the near infrared bandwidth in association with a pair of pulsing infrared emitting diodes (IREDs) orthogonally mounted on the monitored object. This geometrical configuration and the wide infrared emission angle insure the visibility of each IRED from its associated PSD, whatever the position of the IRED pair in the working area. A computer program controls the sequence of both IREDs pulses and sampling of the corresponding PSDs outputs and provides the x and y coordinates of the IREDs pair at a 80-Hz rate. This non-contact linear technique can be duplicated at a very low cost for use in a variety of contexts, even under extreme luminance conditions.

Animals↗

PubMed1991

Movement of neural activity on the superior colliculus motor map during gaze shifts.

The superior colliculus contains neurons that cause displacements of the visual axis (gaze shifts). These cells are arranged topographically in a motor map on which the vector (amplitude and direction) of the coded movement varies continuously with location. How this spatial representation becomes a temporal code (frequency and duration) in the motoneurons is unknown. During a gaze shift, a zone of neural activity moved continuously on the map from an initial location, defining the vector of the desired gaze shift, to a final "zero" position containing neurons that were active during fixation. Thus, the spatial-temporal transformation may be accomplished by control of gaze throughout the spatial trajectory of activity on the motor map.

Animals↗

PubMed1991

Control of orienting gaze shifts by the tectoreticulospinal system in the head-free cat. III. Spatiotemporal characteristics of phasic motor discharges.

1. In this paper we describe the movement-related discharges of tectoreticular and tectoreticulospinal neurons [together called TR (S) Ns] that were recorded in the superior colliculus (SC) of alert cats trained to generate orienting movements in various behavioral situations; the cats' heads were either completely unrestrained (head free) or immobilized (head fixed). TR (S) Ns are organized into a retinotopically coded motor map. These cells can be divided into two groups, fixation TR (S) Ns [f TR (S) Ns] and orientation TR (S) Ns [oTR(S)Ns], depending on whether they are located, respectively, within or outside the zero (or area centralis) representation of the motor map in the rostral SC. 2. oTR(S)Ns discharged phasic motor bursts immediately before the onset of gaze shifts in both the head-free and head-fixed conditions. Ninety-five percent of the oTR(S)Ns tested (62/65) increased their rate of discharge before a visually triggered gaze shift, the amplitude and direction of which matched the cell's preferred movement vector. For movements along the optimal direction, each cell produced a burst discharge for gaze shifts of all amplitudes equal to or greater than the optimum. Hence, oTR(S)Ns had no distal limit to their movement fields. The timing of the burst relative to the onset of the gaze shift, however, depended on gaze shift amplitude: each TR(S)N reached its peak discharge when the instantaneous position of the visual axis relative to the target (i.e., instantaneous gaze motor error) matched the cell's optimal vector, regardless of the overall amplitude of the movement. 3. The intensity of the movement-related burst discharge depended on the behavioral context. For the same vector, the movement-related increase in firing was greatest for visually triggered movements and less pronounced when the cat oriented to a predicted target, a condition in which only 76% of the cells tested (35/46) increased their discharge rate. The weakest movement-related discharges were associated with spontaneous gaze shifts. 4. For some oTR(S)Ns, the average firing frequency in the movement-related burst was correlated to the peak velocity of the movement trajectory in both head-fixed and head-free conditions. Typically, when the head was unrestrained, the correlation to peak gaze velocity was better than that to either peak eye or head velocity alone. 5. Gaze shifts triggered by a high-frequency train of collicular microstimulation had greater peak velocities than comparable amplitude movements elicited by a low-frequency train of stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1989

Compensatory eye and head movements generated by the cat following stimulation-induced perturbations in gaze position.

It is thought that saccades are controlled by signals representing target and instantaneous eye positions coded with respect to the head. To determine the frame of reference relevant to gaze (= eye + head) control, we extended to the cat whose head is unrestrained the original study of Mays and Sparks (Mays and Sparks 1980). We stimulated the superior colliculus (SC) to perturb initial gaze position before the onset of a gaze shift made in the dark to a flashed target. Gaze shifts compensated for this perturbation and reached the target with normal accuracy, despite the absence of visual feedback. This result indicates that gaze shifts were coded in either a body-centered or spatial frame but we could not distinguish between these two alternatives because the cat's body was fixed.

Animals↗

PubMed1986

Visual control of reaching movements without vision of the limb. I. Role of retinal feedback of target position in guiding the hand.

The spatial and temporal organization of hand and eye movements were studied in normal human subjects as they pointed toward small visual targets. The experiment was designed to assess the role of information about target position in correcting the trajectory of the hand when view of the hand was not available. To accomplish this, the duration of target presentation was systematically varied across blocks of trials. The results of this experiment showed that pointing movements were about 3 times more accurate when the target was present throughout the entire pointing movement, than when the target disappeared shortly after the hand movement had begun. These data indicate that pointing movements made without view of the limb are not purely preprogrammed but instead, are corrected during their execution. These modifications to the motor program are smoothly integrated into the ongoing movement and must depend upon comparing visual information about the position of the target with nonvisual information about the position of the limb. The source of this non-visual information was not directly established in the present experiment but presumably must be derived from kinesthetic reafferences and/or efference copy.

Biofeedback, Psychology↗

PubMed1986

Visual control of reaching movements without vision of the limb. II. Evidence of fast unconscious processes correcting the trajectory of the hand to the final position of a double-step stimulus.

In this study, a visual target was localized by both limb and eye. The experimental procedure provided an opportunity to analyze the limb movement trajectories to the target whose location was displaced during saccades. Absence of visual information about position of the moving limb did not interfere with correction of the trajectory of pointing movements. These corrections reflect the new information about target position that becomes available at the end of the first saccade. Mean localization errors to stationary and to displaced targets were not significantly different. This result suggests that subjects were able to compare visual (retinal + eye position) information about the position of the target with information about the position of their moving limb derived from kinesthesis and/or efference copies of the motor commands. An analysis of velocity profiles indicates that the observed corrections of hand movement to target displacement could not be identified by an inflexion point in the trajectory. None of the subjects reported seeing the target change location. In other words, the motor command was adjustable despite the failure of changes in visual locus to reach consciousness.

Adult↗