Rapid horizontal gaze movement in the monkey

Abstract

1. We studied horizontal eye and head movements in three monkeys that were trained to direct their gaze (eye position in space) toward jumping targets while their heads were both fixed and free to rotate about a vertical axis. We considered all gaze movements that traveled > or = 80% of the distance to the new visual target. 2. The relative contributions and metrics of eye and head movements to the gaze shift varied considerably from animal to animal and even within animals. Head movements could be initiated early or late and could be large or small. The eye movements of some monkeys showed a consistent decrease in velocity as the head accelerated, whereas others did not. Although all gaze shifts were hypometric, they were more hypometric in some monkeys than in others. Nevertheless, certain features of the gaze shift were identifiable in all monkeys. To identify those we analyzed gaze, eye in head position, and head position, and their velocities at three points in time during the gaze shift: 1) when the eye had completed its initial rotation toward the target, 2) when the initial gaze shift had landed, and 3) when the head movement was finished. 3. For small gaze shifts (< 20 degrees) the initial gaze movement consisted entirely of an eye movement because the head did not move. As gaze shifts became larger, the eye movement contribution saturated at approximately 30 degrees and the head movement contributed increasingly to the initial gaze movement. For the largest gaze shifts, the eye usually began counterrolling or remained stable in the orbit before gaze landed. During the interval between eye and gaze end, the head alone carried gaze to completion. Finally, when the head movement landed, it was almost aimed at the target and the eye had returned to within 10 +/- 7 degrees, mean +/- SD, of straight ahead. Between the end of the gaze shift and the end of the head movement, gaze remained stable in space or a small correction saccade occurred. 4. Gaze movements < 20 degrees landed accurately on target whether the head was fixed or free. For larger target movements, both head-free and head-fixed gaze shifts became increasingly hypometric. Head-free gaze shifts were more accurate, on average, but also more variable. This suggests that gaze is controlled in a different way with the head free. For target amplitudes < 60 degrees, head position was hypometric but the error was rather constant at approximately 10 degrees.(ABSTRACT TRUNCATED AT 400 WORDS)

Premotor Correlates of Integrated Feedback Control for Eye–Head Gaze Shifts

“…This has been a controversial issue with respect to eye-head coordination during gaze shifts, and two general classes of models had been proposed to account for the available data: gaze feedback models (Tomlinson 1990;Galiana and Guitton, 1992;Goossens and Van Opstal, 1997) and separate feedback models (Phillips et al, 1995;Freedman, 2001;Sparks et al, 2002). In the first class of models, gaze accuracy is maintained by comparing the desired change in gaze position with the actual gaze displacement, which is calculated from feedback of the ongoing eye and head movements.…”

“…Dynamic gaze feedback models incorporate this experimental result using their single feedback loop. Separate feedback models rely on either neck reflexes (Freedman, 2001;Freedman and Quessy, 2004;Quessy and Freedman, 2004) or, alternatively, the precise titration of the VOR (Phillips et al, 1995) to ensure gaze accuracy. Similarly, the results of single-unit recording experiments (Cullen et al, 1993;Cullen and Guitton, 1997;Phillips et al, 1999) have been used to support either class of model.…”

Human eye-head coordination in two dimensions under different sensorimotor conditions

“…Alternatively, Phillips et al (1995) suggested that the oculomotor system is independently driven by a saturated static gaze displacement command. Either way, since the eye may start at different positions in the orbit, the limitation of an oculocentric gaze displacement command does not, in general, prevent the eye from running against the bound aries o f the oculomotor range, unless the limits are ap propriately adjusted by taking eye position into account as well.…”

Dissociation of Eye and Head Components of Gaze Shifts by Stimulation of the Omnipause Neuron Region

“…In general, the saccadic eye and head components are temporally coupled (Freedman and Sparks 1997b;Phillips et al 1995;Zangemeister and Stark 1982a); the saccadic eye component initiates the gaze shift, and the onset of the head movement lags behind, at least in part, because of its heavier inertial load. When the initial eye-in-head position is deviated in the direction of the gaze shift (Becker and Jürgens 1992;Freedman and Sparks 1997b;Fuller 1996) or when the location and timing of the stimulus are predictable (Bizzi et al 1972;Moschner and Zangemeister 1993;Zangemeister and Stark 1982a,b), however, the lag in the head component can be reduced or it can even lead gaze onset.…”