Gain Adaptation of Eye and Head Movement Components of Simian Gaze Shifts

Abstract

Gain adaptation of eye and head movement components of simian gaze shifts. J. Neurophysiol. 78: 2817-2821, 1997. To investigate the site of gaze adaptation in primates, we reduced the gain of large head-restrained gaze shifts made to 50 degrees target steps by jumping the target 40% backwards during a targeting saccade and then tested gain transfer to the eye- and head-movement components of head-unrestrained gaze shifts. After several hundred backstep trials, saccadic gain decreased by at least 10% in 8 of 13 experiments, which were then selected for further study. The minimum saccadic gain decrease in these eight experiments was 12.8% (mean = 18.4%). Head-unrestrained gaze shifts to ordinary 50 degrees target steps experienced a gain reduction of at least 9.3% (mean = 14.9%), a mean gain transfer of 81%. Both the eye and head components of the gaze shift also decreased. However, average head movement gain decreased much more (22.1%) than eye movement gain (9.2%). Also, peak head velocity generally decreased significantly (20%), but peak eye velocity either increased or remained constant (average increase of 5.6%). However, the adapted peak eye and head velocities were appropriate for the adapted, smaller gaze amplitudes. Similar dissociations in eye and head metrics occurred when head-unrestrained gaze shifts were adapted directly (n = 2). These results indicated that head-restrained saccadic gain adaptation did not produce adaptation of eye movement alone. Nor did it produce a proportional gain change in both eye and head movement. Rather, normal eye and head amplitude and velocity relations for a given gaze amplitude were preserved. Such a result could be explained most easily if head-restrained adaptation were realized before the eye and head commands had been individualized. Therefore, gaze adaptation is most likely to occur upstream of the creation of separate eye and head movement commands.

Head-Unrestrained Gaze Adaptation in the Rhesus Macaque

“…Although the contributions of the eyes and head were very different when movements were started with the eyes in these novel positions, the amplitudes of gaze shifts remained at the adapted values; gaze adaptation transferred to movements made under unadapted initial conditions. These data are consistent with the hypothesis that head-unrestrained gaze adaptation is mediated by changing gaze shift commands (Cecala and Freedman 2008;Phillips et al 1997).…”

“…Two previous studies involving head-unrestrained primates have concluded that gaze adaptation results from modifying a gaze displacement command signal (Cecala and Freedman 2008;Phillips et al 1997). The study by Phillips et al (1997) emphasized the transfer of head-restrained saccade amplitude adaptation to head-unrestrained gaze shifts produced by rhesus monkeys.…”

“…The study by Phillips et al (1997) emphasized the transfer of head-restrained saccade amplitude adaptation to head-unrestrained gaze shifts produced by rhesus monkeys. Phillips and colleagues were successful in reducing 50°head-restrained saccades by back-stepping a target by 20°.…”

The lateral intraparietal area codes the location of saccade targets and not the dimension of the saccades that will be made to acquire them

“…The locus of saccadic adaptation has been investigated with single-unit recording, stimulation, and lesion approaches. It has been demonstrated that saccadic adaptation occurs at a point where the saccade is represented as a vector (Hopp and Fuchs 2006) and affects gaze before it is separated into its eye and head components (Cecala and Freedman 2009;Phillips et al 1997). Neurons in the superior colliculus, even neurons that do not have visual responses, represent target location and not saccade amplitude in both the head-fixed (Frens and Van Opstal 1997;Quessy et al 2010) and unrestrained (DeSouza et al 2011;Fernandez-Ruiz et al 2007) conditions.…”

Eye position effects in saccadic adaptation

“…Second, saccades larger than a couple of degrees are normally accompanied by head movements (Guitton 1992). In this case, the control signal of the oculomotor system is a gaze shift command, i.e., a command for a combination of eye and head movements to result in a shift of gaze to the target (Freedman and Sparks 1997;Munoz et al 1991), and the intrasaccadic target displacement paradigm shows adaptation of the gaze shift control Freedman 2008a, 2008b;Phillips et al 1997). The gaze shift command must be decomposed into head and eye components to drive the respective effectors, since the relative contributions of eye and head components to a gaze shift depend on initial eye position (Freedman 2008).…”