Eye Position Effects in Oculomotor Plasticity and Visual Localization

Abstract

For visual localization to remain accurate across changes of gaze, a signal representing the position of the eye in the orbita is needed to code spatial locations in a reference frame that is independent of retinal displacements. Here we report evidence that the localization of visual objects in space is coded in an extraretinal reference frame. In human subjects, we used outward saccadic adaptation, which can be induced artificially by a systematic displacement of the saccade target. This form of oculomotor plasticity is accompanied by changes in spatial perception, thus highlighting the relevance of saccade metrics for visual localization. We tested the reference frame of outward adaptation for reactive and scanning saccades and visual localization. For scanning saccades, adaptation magnitude was drastically reduced at positions distant from the adapted eye position. Changes in visual localization showed a very similar modulation of eye position. These results suggest that scanning saccade adaptation is encoded in a nonretinotopic reference frame. Eye position effects for reactive saccade adaptation were smaller, and the induced mislocalization did not vary significantly between eye positions. The different modulation of reactive and scanning saccade adaptation supports the idea that oculomotor plasticity can occur at multiple sites in the brain. The findings are also consistent with previous evidence for a stronger influence of scanning saccade adaptation on the visual localization of objects in space.

Eye position effects in saccadic adaptation

“…Several recent observations have suggested that inward and outward adaptation rely on partly different mechanisms (Alahyane et al 2007;Catz et al 2008;Ethier et al 2008;Panouilleres et al 2009;Zimmermann and Lappe 2009). Eye position modulation occurs also for outward adaptation, but it is smaller for reactive than for scanning saccades (Zimmermann and Lappe 2011).…”

Visual cues that are effective for contextual saccade adaptation

“…There seems little difference, in principle, between vector specificity and motor contexts defined by orbital position. The orbital dependency of eye muscle strength (Collins et al 1975) requires different sets of saccadic commands for different orbital starting positions, making strong orbital-specific adaptation readily explicable (Alahyane and Pelisson 2004;Shelhamer and Clendaniel 2002;Tian and Zee 2010;Zimmermann and Lappe 2011;Havermann et al 2011;Wulff et al 2012). Similarly, we redirect our gaze in combined eye and head movements, and hence motor states incorporating head position signals such as head tilt (Shelhamer and Clendaniel 2002) would also be expected to show context specificity.…”

“…The simple act of looking upward vs. downward involves different sets of muscle commands, whose independent motor states provide sufficient contexts to allow independent adaptation. For example, shifting a target onward during 10°rightward saccades can induce lengthening of saccades in the upper visual field, while on interleaved trials, backward shifts in the lower visual field can simultaneously shorten the same vector saccades in the lower visual field (Alahyane and Pelisson 2004;Shelhamer and Clendaniel 2002;Tian and Zee 2010;Zimmermann and Lappe 2011;Havermann et al 2011;Wulff et al 2012). Similarly, saccade gain (saccade amplitude/ initial target amplitude) can be adapted separately depending on orbital eccentricity or vergence command contexts (Chaturvedi and van Gisbergen 1997).…”

Mislocalization of stationary and flashed bars after saccadic inward and outward adaptation of reactive saccades

“…Saccadic adaptation is specific to the direction and amplitude of the saccade (Albano and King 1989;Collins et al 2007;Deubel 1987;Deubel et al 1986;Frens and Van Opstal 1994;Schnier et al 2010), to the initial eye position (Havermann et al 2011;Zimmermann and Lappe 2011), and to the particular saccade type.…”