The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform

D I Mccloskey - One of the best experts on this subject based on the ideXlab platform.

Alain Berthoz - One of the best experts on this subject based on the ideXlab platform.

  • eye and head coupled and dissociated movements during orientation to a double step visual Target Displacement
    Experimental Brain Research, 1991
    Co-Authors: Alain Berthoz
    Abstract:

    Tight coupling between eye and head movements has been observed in response to a single visual Target offset. On this basis, when the visual stimulus consists of two successive steps in the same (horizontal) direction, either increasing in eccentricity (staircase) or decreasing in eccentricity (pulse-step) gaze should be due to concomitant eye and head angular Displacement. That is, the eyes and head should aim at each Target Displacement so that their combined movement matches Target offset. We have tested this hypothesis in five healthy subjects. The measured variables were head and gaze offset, the interval between two consecutive saccades from onset to onset (I) and the response delay between onset of the second step and onset of the first gaze saccade (D). With both staircase and pulse-step stimuli, the eye saccade preceded the head movement, and the gaze response either had the stimulus profile pattern or consisted of one gaze saccade to the final Target offset. In response to staircase stimuli, I decreased concomitantly with an increase in D; with pulse-step stimuli, as D increased, I decreased slightly in three subjects and decreased markedly in two subjects. Dissociation between the eye and head movements could clearly be demonstrated with pulse-step stimuli: the first gaze saccade to the Target pulse Displacement was accompanied by a head movement to the Target step offset. We also observed cases in which the gaze saccade to the Target step Displacement was made simultaneously with the head movement to the Target pulse offset. Our study extends previous observations in head fixed condition and illustrates that in the majority of cases, when the head is free and a visual pulse step stimulus is presented, both the saccadic and head systems have the ability to modify or cancel the initial neural command to move to the first Target Displacement. When this modification takes place in only one system, eye and head movements are dissociated.

Janet L Taylor - One of the best experts on this subject based on the ideXlab platform.

Kirk G Thompson - One of the best experts on this subject based on the ideXlab platform.

  • neural control of visual search by frontal eye field effects of unexpected Target Displacement on visual selection and saccade preparation
    Journal of Neurophysiology, 2009
    Co-Authors: Aditya Murthy, Stephanie M Shorter, Jeffrey D Schall, Kirk G Thompson
    Abstract:

    The dynamics of visual selection and saccade preparation by the frontal eye field was investigated in macaque monkeys performing a search-step task combining the classic double-step saccade task with visual search. Reward was earned for producing a saccade to a color singleton. On random trials the Target and one distractor swapped locations before the saccade and monkeys were rewarded for shifting gaze to the new singleton location. A race model accounts for the probabilities and latencies of saccades to the initial and final singleton locations and provides a measure of the duration of a covert compensation process—Target-step reaction time. When the Target stepped out of a movement field, noncompensated saccades to the original location were produced when movement-related activity grew rapidly to a threshold. Compensated saccades to the final location were produced when the growth of the original movement-related activity was interrupted within Target-step reaction time and was replaced by activation of other neurons producing the compensated saccade. When the Target stepped into a receptive field, visual neurons selected the new Target location regardless of the monkeys’ response. When the Target stepped out of a receptive field most visual neurons maintained the representation of the original Target location, but a minority of visual neurons showed reduced activity. Chronometric analyses of the neural responses to the Target step revealed that the modulation of visually responsive neurons and movement-related neurons occurred early enough to shift attention and saccade preparation from the old to the new Target location. These findings indicate that visual activity in the frontal eye field signals the location of Targets for orienting, whereas movement-related activity instantiates saccade preparation.

Luis Augusto Teixeira - One of the best experts on this subject based on the ideXlab platform.

  • Intercepting moving Targets: does memory from practice in a specific condition of Target Displacement affect movement timing?
    Experimental Brain Research, 2011
    Co-Authors: Raymundo Machado Azevedo Neto, Luis Augusto Teixeira
    Abstract:

    This investigation aimed at assessing the extent to which memory from practice in a specific condition of Target Displacement modulates temporal errors and movement timing of interceptive movements. We compared two groups practicing with certainty of future Target velocity either in unchanged Target velocity or in Target velocity decrease. Following practice, both experimental groups were probed in the situations of unchanged Target velocity and Target velocity decrease either under the context of certainty or uncertainty about Target velocity. Results from practice showed similar improvement of temporal accuracy between groups, revealing that Target velocity decrease did not disturb temporal movement organization when fully predictable. Analysis of temporal errors in the probing trials indicated that both groups had higher timing accuracy in velocity decrease in comparison with unchanged velocity. Effect of practice was detected by increased temporal accuracy of the velocity decrease group in situations of decreased velocity; a trend consistent with the expected effect of practice was observed for temporal errors in the unchanged velocity group and in movement initiation at a descriptive level. An additional point of theoretical interest was the fast adaptation in both groups to a Target velocity pattern different from that practiced. These points are discussed under the perspective of integration of vision and motor control by means of an internal forward model of external motion.

  • Use of visual information in the correction of interceptive actions
    Experimental Brain Research, 2006
    Co-Authors: Luis Augusto Teixeira, Romeo Chua, Paul Nagelkerke, Ian M. Franks
    Abstract:

    Use of visual information in interceptive actions requiring large-scale changes to movement timing was investigated. The task consisted of intercepting a moving Target on a monitor screen through an angular arm movement. In half of the trials, the initial Target velocity of 8 cm/s was unexpectedly decreased to 4 cm/s or increased to 12 cm/s, leaving 800 ms to Target arrival after velocity change. Visual information about Target Displacement was manipulated by interpolating full vision with occlusion of the last 200, 400, or 600 ms before the due time of interception. The results revealed that reduction of visual exposure of Target Displacement affected movement variability, but not arm velocity or directional trend of temporal errors. This finding supports the concept that motor control in interception is based on an internal representation of Target Displacement, formed during the initial portion of visual exposure following velocity change, which is updated by further visual information of Target Displacement.