Poster A54, Saturday, March 25, 5:00 – 7:00 pm, Pacific Concourse
Electrophysiological Correlates of Crowding in the Perception of Letters and Symbols
Kurt Winsler1, Phillip Holcomb1, Katherine Midgley1, Jonathan Grainger2; 1San Diego State University, 2CNRS & Aix-Marseille University
Crowding refers to an increased difficulty in processing target stimuli in peripheral vision when accompanied by flanking stimuli. A number of studies have shown that letters are more resilient to this crowding effect than other stimuli like symbols. It has been hypothesized that exposure to horizontal letter strings during years of reading experience might underlie this specific immunity to interference. However, the precise neuro-cognitive mechanism involved is still unclear. The current study aimed to better understand crowding effects using event-related potentials (ERPs). Thirty-two channels of EEG were recorded from 24 monolingual English speakers while completing a 2AFC task with 324 trials which were either letters or symbols, presented 2 degrees to the left or right of a fixation point. Targets were isolated or flanked by two characters either horizontally or vertically. Results showed a left lateralized increase in P1 amplitude as a result of crowding (regardless of orientation) for letters, reflecting additional visual processing. Moreover, larger N1/N170s were observed for crowded letters and this effect was larger in left hemisphere sites for vertically crowded targets compared to horizontally crowded targets. This provides evidence that during early perceptual processing horizontally flanked letters are more efficiently processed than vertically flanked letters. This pattern of effects was not observed for symbols, further emphasizing the optimization of the visual system for dealing with letters, specifically along the horizontal meridian of the visual field.
Topic Area: LANGUAGE: Other