Picking an apple from a tree: Response-selection demands, inhibition requirements, and the functionality of the Quiet Eye in a far-aiming task.

In the study of the mutual coupling between perception and action, the performance-enhancing effect of the last fixation before movement initiation, the Quiet Eye (QE), has been repeatedly shown. To the explanation of this phenomenon, among others, an inhibition hypothesis was formulated which suggests that the parametrisation of the optimal task solution is shielded against non-optimal task solutions. In this study, a prediction of this hypothesis was tested by manipulating response-selection demands over movement preparation in a targeting task which required to throw balls as accurate as possible at virtual target discs. Participants in the group with high response-selection demands always had to select one out of four targets, whereas the selection for the participants in the group with low response-selection demands was yoked to the selection of the other group. The results showed the predicted longer QE durations for the high response-selection demands group that, particularly, emanated from earlier QE onsets. Because of similar throwing demands, these differences cannot merely be explained by differences in the fine-tuning of the motor response but provide evidence for the suggested inhibition function. Particularly, with high response-selection demands, the parametrisation of the non-selected targets over movement preparation had to be inhibited. Descriptively, differences in the QE offset suggest that these shielding requirements persisted over movement control. This study extends earlier work on the theoretical foundation of the QE phenomenon and provides fruitful insights into its underlying mechanisms.