Effect of orthographic processes on letter position encoding

We investigate whether orthographic processes influence the identification and encoding of letter position within letter strings. To minimise word-specific effects, we adopt a visual letter search task that requires participants to identify a cued letter target among a random five-letter string. Using this paradigm, previous studies have shown that letter targets to the left are identified faster than those to the right of centre and letter targets in the initial, medial and final positions are identified faster than those in neighbouring positions. While the medial letter advantage is likely to arise from greater visual acuity at the point of fixation, the mechanisms responsible for the left-to-right, and exterior, letter advantage have yet to be determined. We show that: (i) search functions for most letters reflect the directional scanning process required for reading English orthography; (ii) search times are significantly faster for letter targets that appear in the most, compared with the least, frequent position in written words; and (iii) search times correlate significantly with positional letter frequency, especially in the initial and final positions. We propose that a combination of low-level visual, and higher-level orthographic, processes modulate the encoding of letter identities and position in written word recognition.