Temporal crowding is a unique phenomenon reflecting impaired target encoding over large temporal intervals

Crowding refers to impaired object identification when presented with other objects, and it is well established that spatial crowding-crowding from adjacent objects-affects many aspects of visual perception and cognition. A similar interference also occurs across time-the identification of a target object is impaired when distracting objects precede and succeed it. When such interference is observed with relatively long interitem intervals it is termed temporal crowding. Thus far, little was known about temporal crowding and its underlying processes. Particularly it was unknown which aspects of visual processing are impaired by temporal crowding, and the answer to this question bears critical theoretical implications. To reveal the nature of this impairment we used a continuous-report task and a mixture-model analysis. In three experiments, observers viewed sequences of three oriented items separated by relatively long intervals (170-475ms). The target was the second item in the sequence, and the task was to reproduce its orientation. The findings suggest that temporal crowding impairs target encoding and increases substitution errors, but there was no evidence of a reduced signal-to-noise ratio. This pattern of results was similar regardless of stimuli duration and target-distractor similarity. However, it differed considerably from the pattern found for ordinary masking and spatial crowding, indicating that temporal crowding is a unique phenomenon. Moreover, the finding that temporal crowding affected the precision of target encoding even when the items were separated by almost half a second suggests that visual processing requires a surprisingly long time to complete.