On the relation between crowding and ensemble perception: Examining the role of attention.

Ensemble perception of a crowd of stimuli is very accurate, even when individual stimuli are invisible due to crowding. The ability of high-precision ensemble perception can be an evolved compensatory mechanism for the limited attentional resolution caused by crowding. Thus the relationship of crowding and ensemble coding is like two sides of the same coin wherein attention may play a critical factor for their coexistence. The present study investigated whether crowding and ensemble coding were similarly modulated by attention, which can promote our understanding of their relation. Experiment 1 showed that diverting attention away from the target harmed the performance in both crowding and ensemble perception tasks regardless of stimulus density, but crowding was more severely harmed. Experiment 2 showed that directing attention toward the target bar enhanced the performance of crowding regardless of stimulus density. Ensemble perception of high-density bars was also enhanced but to a lesser extent, while ensemble perception of low-density bars was harmed. Together, our results indicate that crowding is strongly modulated by attention, whereas ensemble perception is only moderately modulated by attention, which conforms to the adaptive view.