Adaptation of within-object saccades can be induced by changing stimulus size

Saccadic adaptation maintains saccade accuracy and has been studied with the intrasaccadic target displacement procedure: displacing a target backwards (or forwards) during saccade execution gradually decreases (or increases) subsequent saccade amplitude. Adaptation has traditionally been studied with targeting saccades which bring the eyes onto a new object. Within-object saccades take the eye from one position in an object to another position in the same object and have been shown to resist the intrasaccadic target displacement procedure. The amplitude of within-object saccades depends on object size rather than position, and we therefore hypothesized that within-object saccades might adapt in response to an intrasaccadic change in object size. In separate sessions, we increased or decreased object size during within-object saccade execution. Results showed amplitude lengthening or shortening, respectively. Furthermore, within-object saccade adaptation seems to share several characteristics with targeting-saccade adaptation.