Ilanit Hochmitz¹, Yaffa Yeshurun¹; ¹University of Haifa

Temporal crowding refers to impaired target identification when it is preceded and/or succeeded by other irrelevant items. Critically, this temporal interference occurs with stimulus onset asynchronies (SOAs) that exceed the typical limits of visual masking (i.e., SOA>150ms), and was even found with an SOA of almost half a second. Recently, we have directly compared temporal crowding and visual masking demonstrating that temporal crowding is not merely ‘particularly long’ masking, but rather the two phenomena rely on different perceptual processes. Furthermore, unlike suggested by common models for its spatial counterpart —spatial crowding—the interference brought about by temporal crowding cannot be accounted for by simple pooling (i.e., averaging) of information across time. In the current study, we examined whether temporal crowding primarily arises from forward interference or backward interference. Across three experiments, participants performed an orientation estimation task. A sequence of three randomly oriented stimuli was presented to the periphery. SOAs ranged from 175 to 475ms. Depending on the experiment, the target was either the first, second, or third item in the sequence. Participants had to reproduce the target orientation by rotating a probe line, and the measure of performance was the angular difference between the target’s true orientation and the reported orientation. Mixture modeling analysis revealed that temporal crowding was strongest for the second item, showing significant effects of SOA on target encoding precision and the rate of reporting the orientation of a non-target item, but not on the guessing rate. A similar, yet weaker, pattern of effects was found for the first item, while minimal interference was observed when the target was the third item. These findings suggest that crowding reflects a combination of strong backward interference and weaker forward interference.