Temporal crowding and its interplay with spatial crowding

Spatial crowding refers to impaired target identification when the target is surrounded by other stimuli in space. Temporal crowding refers to impaired target identification when the target is surrounded by other stimuli in time. Previously, when spatial and temporal crowding were measured in the fovea they were interrelated with amblyopic observers but almost absent with normal observers (Bonneh, Sagi, & Polat, 2007). In the current study we examined whether reliable temporal crowding can be found for normal observers with peripheral presentation (98 of eccentricity), and whether similar relations between temporal and spatial crowding will emerge. To that end, we presented a sequence of three displays separated by a varying interstimulus interval (ISI). Each display included either one letter (Experiments 1a, 1b, 1c) or three letters separated by a varying interletter spacing (Experiments 2a, 2b). One of these displays included an oriented T. Observers indicated the T's orientation. As expected, we found spatial crowding: accuracy improved as the interletter spacing increased. Critically, we also found temporal crowding: in all experiments accuracy increased as the ISI increased, even when only stimulus-onset asynchronies (SOAs) larger than 150 ms were included, ensuring this effect does not reflect mere ordinary masking. Thus, with peripheral presentation, temporal crowding also emerged for normal observers. However, only a weak interaction between temporal and spatial crowding was found.