Response Requirements Shape the Spatial Coding of Location-Specific Adjustments to Conflict Frequency

Humans adjust to the frequency of conflicting stimuli so that the detrimental behavioral effects of frequent conflicts become smaller than those of rare conflicts. These adjustments become contingent on the locations where frequent and infrequent conflicts have been encountered. Experimentally such phenomena are studied by means of conflict tasks, a prominent one being the Simon task of the present experiments. Our Simon task involved four stimulus locations (upper-left, upper-right, lower-left, lower-right). Conflict frequency was manipulated for two diagonally opposite locations. For example, conflict frequency was low at the upper-left location and high at the lower-right location. At the remaining (non-manipulated) locations conflict frequency was intermediate. In Experiment 1 participants responded to stimulus colors by pressing a left or right key, in Experiment 2 by pressing a lower or upper key. We observed larger conflict effects for the low-conflict location than for the high-conflict location. Crucially, these adjustments to conflict frequency transferred to non-manipulated locations depending on the response configuration: transfer regions were the left or right hemifield with left-right responses, but the lower or upper hemifield with lower-upper responses. Assuming that transfer regions around manipulated stimulus locations are defined by identical (or similar) spatial codes, the pattern of transfer suggests a process of weighted two-dimensional location coding. According to this notion, the spatial dimension that is relevant for response discrimination has stronger weight in the coding of stimulus locations than a response-irrelevant dimension, and can therefore produce anisotropic transfer of conflict-frequency effects around manipulated locations.