Adaptation of Saccadic Sequences with and without Remapping

Saccadic adaptation in the presence of artificial central scotomas

Saccadic adaptation can occur over a short period of time through a constant adjustment of the saccade target during the saccade, resulting in saccadic re-referencing, which directs the saccade to a location different from the target that elicited the saccade. Saccade re-referencing could be used to help patients with age-related macular degeneration to optimally use their residual visual function. However, it remains unknown whether saccade adaptation can take place in the presence of central scotomas (i.e., without central vision). We tested participants in two experiments in a conventional double-step paradigm with a central gaze-contingent artificial scotoma. Experiment 1 (N = 12) comprised a backward adaptation paradigm with no scotoma control, visible, and invisible 3° diameter scotoma conditions. Experiment 2 (N = 13) comprised a forward adaptation paradigm with no scotoma control, invisible 2°, and 4° diameter scotoma conditions. In Experiment 1, we observed significant adaptation in both the visible and invisible scotoma conditions comparable to the control condition with no scotoma. This was the case even when the saccade landed such that the target was occluded by the scotoma. We observed that adaptation occurred based on peripheral viewing of the stepped target during the deceleration period. In Experiment 2, we found that both scotoma conditions showed adaptation again comparable to the control condition with no scotoma. We conclude that saccadic adaptation can occur with central scotomas, showing that it does not require central vision and can be driven primarily by peripheral retinal error.

Signals driving the adaptation of saccades that require spatial updating

Saccades adapt to persistent natural or artificially imposed dysmetrias. The characteristics and circuitry of saccade adaptation have been revealed using a visually guided task (VGT) where the vectors of the target step and the intended saccade command are the same. However, in real life, another saccade occasionally intervenes before the saccade to the target occurs. This necessitates an updating of the intended saccade to account for the intervening saccadic displacement, which dissociates the visual target signal and the intended saccade command. We determined whether the adaptation process is similar for VGT and updated saccades by studying the transfer of adaptation between them. The ultimate visual target was dissociated from the intended saccade command with double-step saccade tasks (DSTs) in which two targets are flashed sequentially at different locations while the monkey maintains fixation. The resulting saccades toward the first and second targets occur in the dark. The transfer of visually guided saccade adaptation to the second saccades of a DST and vice versa depended on the eccentricity of the second visual target, and not the second saccade command. If a target with the same eccentricity as the adapted target appears briefly during the intersaccadic interval of a DST, more adaptation transfers. Because a brief appearance of the visual target either before the first saccade or during the intersaccadic interval influences how much adaptation transfer the second saccade will express, the processing of adaptation and DST updating may overlap. NEW & NOTEWORTHY Adaptation and the spatial updating of saccades are thought to be independent processes. When we dissociate the visual target and the intended saccade command, the transfer of visually guided saccade adaptation to the saccades of the double-step saccade tasks (DST) and vice versa is driven by a visual not motor error. The visual target has an effect until the second saccade of a DST occurs. Therefore, the processing of adaptation and the spatial updating of saccades may overlap.