Lateralised covert attention in word identification

Abstract

The right visual field superiority in word recognition has been attributed to an attentional advantage by the left brain hemisphere. We investigated whether such advantage involves lateralised covert attention, in the absence of overt fixations on prime words. In a lexical decision task target words were preceded by an identical or an unrelated prime word. Eye movements were monitored. In Experiment 1 lateralised (to the left or right of fixation) prime words were parafoveally visible but foveally masked, thus allowing for covert attention but preventing overt attention. In Experiment 2 prime words were presented at fixation, thus allowing for both overt and covert attention. Results revealed positive priming in the absence of fixations on the primes when these were presented in the right visual field. The effects of covertly attended primes were nevertheless significantly reduced in comparison with those of overtly attended primes. It is concluded that word identification can be accomplished to a significant extent by lateralised covert attention alone, with right visual field advantage.

Keywords:

• Parafoveal
• Attention
• Eye movements
• Word priming
• Lexical access
• Lateralisation

Acknowledgements

This research was supported by Grant SEJ2004-420/PSIC, from the Spanish Ministry of Education and Science, and grant #119088 from the Academy of Finland. We are grateful to M. Dolores Castillo for her assistance in conducting the experiments.

Notes

¹We used a repetition-priming paradigm. Although repetition priming can be affected by processing of the word form (i.e., orthographic and phonological codes), it is also sensitive to word meaning. The finding that repetition priming effects are much stronger for words than for nonwords implies that the priming effect is not occurring merely at the letter level; if priming was determined only by the verbal stimulus form, it should occur similarly for words and nonwords (see Lachter et al., 2004). In addition, Pesciarelli et al. (2007) found that both repetition and semantic priming effects are modulated by at least partially overlapping neural mechanisms. Furthermore, repetition priming is less affected by attentional manipulations than semantic priming (Fabre, Lemaire, & Grainger, 2007). This implies that, if an RVF word recognition advantage appears under covert attention conditions in (the less sensitive) repetition priming, then such lateralised covert attention is expected be involved—even more strongly—also in semantic priming.

²The similarity between the current study and the Hyönä and Koivisto (2006), Marzouki and Grainger (2008), and Pernet et al. (2007) studies deserves some additional comments. Hyönä and Koivisto did not use any prime masking, Pernet et al. used forward masking, and Marzouki and Grainger used forward and backward masking (i.e., immediately before and after the prime). In contrast, we used on-line masking that was contingent on, i.e., during, eye movements (and thus did not have to remove any trials with fixations on—or visibility of—the prime). This allowed us to demonstrate priming in the RVF—but not in the LVF—in spite of a tendency of more eye movements to the LVF than to the RVF prime. Interestingly, the different methodological approaches yielded lateralised priming effects in all four studies. This supports the robustness of the asymmetric word processing outside the focus of overt attention.