Asymmetries in a unilateral flanker task depend on the direction of the response: The role of attentional shift and perceptual grouping

Four experiments were conducted using a flanker task with 1 distracter appe aring either on the left or right side of a central target. Responses were made on a keyboard aligned parallel to the displays. A larger flanker effec t was obtained when the distracter was on the same side as the response. Tw o factors account for this asymmetry. First, when the flanker and target ar e identical, the 2 form a group that is assigned a spatial tag, creating a form of the Simon effect on the basis of the compatibility between the resp onse keys and the group. Second, preparation of a lateralized response appe ars to entail a shift of visual attention in the corresponding direction, t hus enhancing processing of the flanker on the response side. Consistent wi th the 2nd hypothesis, participants were more likely to correctly recognize letters that were briefly presented at the distracter position on the same side as the response.