Visual and phonetic codes and the process of generation in letter matching.

Physically identical letter pairs are matched more quickly than are nominally identical or nonidentical pairs, which is an effect usually interpreted as resulting from the use of a visual memory code versus a phonetic or name code. However, prior manipulations of phonetic confusion and visual-field lateralization have provided little evidence consistent with this notion. Here, three reaction time experiments suggest through converging confusion and visual-field manipulations that a phonetic code is not used in either simultaneous or successive letter matching. Two additional experiments yield confusion evidence consistent with a rapid visual generation process underlying nominally identical and nonidentical matches, emphasizing the role of visual memory processes in all of the commonly used same-different letter-matching tasks. Implications for coding and hemispheric theories are discussed.