Limited effects of action on ensemble processing.

Previous research has shown that production of an action toward a visual stimulus may prioritize features of that stimulus for a brief period of time. One recent report has suggested that such an action effect specifically influences ensemble processing - the extraction of summary statistics from a display of multiple items. In the present study we replicate the results that led to that conclusion by having participants assess the mean size of elements in an ensemble after having made an action to either a small or large object. The size of the acted-on object biased the ensemble judgment, but merely viewing the same object produced no such bias. In two subsequent experiments we found the same pattern of results when participants were asked to judge the size of an individual object - not an ensemble. Because the same pattern occurred even when ensemble processing was not required, the action appears to affect some aspect of the task other than ensemble processing (such as perception of visual stimuli in general, or processes related to memory, decision making or response selection), limiting the conclusions that are possible about ensemble processing, but revealing an important new effect of action.