Spatiotemporal Letter Processing in Visual Word Recognition Uncovered by Perceptual Oscillations

Abstract

The processing of individual letters and letter combinations in visual word recognition was studied using random temporal sampling. Across the 200 ms five-letter word exposure, the visibility of letters varied randomly and independently, and response accuracy was measured. Classification images were calculated reflecting the processing efficiency of letters or conjunctions thereof through time. Fourier transforms of these classification images were passed to a classifier (support vector machine, leave-one-out cross validation) to assess differences in the result patterns across individual letters or letter conjunctions, the temporal features characteristic of each, and the replicability of result patterns across participants. The results indicate parallel letter processing throughout exposure duration, distinct processing mechanisms for each letter position and letter-position-specific mechanisms for letter conjunctions which are distinct from those for individual letters.

Keywords: Visual word recognition, Parallel processing, Letter processing, Perceptual oscillations, Visual mechanisms, Vision