Letter identification processes in reading: Distractor interference reveals an automatically engaged, domain-specific mechanism

Abstract

Recent neuroimaging studies have revealed that letters activate both the left and the right fusiform areas, but that only the left fusiform responds to letters more than to control stimuli (Cohen et al., 2003). Though these findings suggest that the left fusiform is specialized in its function of identifying letters, it does not rule out the possibility that the right fusiform contributes critically to letter identification processes. We used a behavioural word identification task in which we compared bilateral and unilateral displays to determine the cost of engaging the right hemisphere with a distractor stimulus. We found that while engaging the left hemisphere led to a robust interference effect, engaging the right hemisphere had no effect at all. We were able to rule out an attentional bias to the right visual field as a possible explanation of the asymmetrical interference effect. We conclude that while the right hemisphere may be able to assume letter identification processing responsibilities in some patients with brain damage, the right hemisphere does not contribute critically to abstract letter identification processes in healthy right-handed individuals.

Notes

¹ In this article, we use the terms “abstract letter identity” (ALI) and “grapheme” interchangeably.

² It should be noted that the name of this region, “visual word form area”, is somewhat misleading. The so called VWFA responds to a wide range of visual stimuli, not just words (Price & Devlin, 2003). With respect to alphabetic stimuli, consonant strings produce more activation in the VWFA than checkerboards, and real words produce more activation than consonant strings (Cohen et al., 2002). However, words do not produce more activation than pseudowords (Dehaene, Le Clec'H, Poline, Le Bihan, & Cohen, 2002).

³ On this account, it is unclear why patient G.V. (Miozzo & Caramazza, 1998) or C.N. (Chanoine et al., 1998) did not exhibit any RH reading. It may be that the degree to which letter identification processes are lateralized premorbidly affects the likelihood of RH reading mechanisms from becoming engaged following LH damage (cf. Knecht et al., 2002).