Saccadic adaptation induced by a perceptual task
21.14, Saturday, May 11, 8:15 - 9:45 am, Royal Ballroom 1-3
Alexander C Schütz1, Dirk Kerzel2, David Souto2; 1Abteilung Allgemeine Psychologie, Justus-Liebig-Universität Gießen, 2Faculté de Psychologie et des Sciences de l'Education, Université de Genève
Saccadic adaptation allows for the gradual compensation of systematic position errors and is traditionally thought to maintain saccadic accuracy despite peripheral changes such as muscle weakness or growth. In the lab it is commonly induced by shifting the target during the saccade. Here we asked whether adaptation can be similarly driven by a mismatch between the requirements of a post-saccadic perceptual task and the saccade landing position. Observers were asked to saccade towards a peripheral letter array. At one particular location in the array they had to perform a letter-discrimination task. In pre- and post-adaptation trials, the central letter in the array had to be discriminated. In adaptation trials, the letter at a fixed eccentric location in the array had to be discriminated, such that saccades had to be shortened or prolonged. In contrast to previous research, only the position of the discrimination-letter within the array changed, while the position of the array itself remained identical. There was a strategic adjustment of saccade amplitudes towards the discrimination-letter within few trials at the beginning of the adaptation and the post-adaptation phase. However there was also a slower, gradual adaptation of saccade amplitudes towards the discrimination-letter over 100 trials during the adaptation and the post-adaptation phase. The magnitude of this adaptation was similar to a classic adaptation paradigm, in which the whole array was shifted during the saccade. Further, we found no adaptation with the same stimulus when observers did not perform the discrimination task, confirming that the requirements of the perceptual task were actually driving the adaptation. We suggest that a perceptual task can modify oculomotor commands by generating a top-down error signal in saccade maps just like a bottom-up visual position error. Hence saccadic adaptation not only maintains saccadic accuracy, but also optimizes gaze behavior for the behavioral goal.