Interactions between language and attention systems: early automatic lexical processing?

An ongoing debate is whether and to what extent access to cortical representations is automatic or dependent on attentional processes. To address this, we modulated the level of attention on auditory input and recorded ERPs elicited by syllables completing acoustically matched words and pseudowords. Under nonattend conditions, the word-elicited response (peaking at approximately 120 msec) was larger than that to pseudowords, confirming early activation of lexical memory traces. However, when attention was directed toward the auditory input, such word-pseudoword difference disappeared. Whereas responses to words seemed unchanged by attentional variation, early pseudoword responses were modulated significantly by attention. Later on, attention modulated a positive deflection at approximately 230 msec and a second negativity at approximately 370 msec for all stimuli. The data indicate that the earliest stages of word processing are not affected by attentional demands and may thus possess certain automaticity, with attention effects on lexical processing accumulating after 150-200 msec. We explain this by robustness of preexisting memory networks for words whose strong internal connections guarantee rapid full-scale activation irrespective of the attentional resources available. Conversely, the processing of pseudowords, which do not have such stimulus-specific cortical representations, appears to be strongly modulated by the availability of attentional resources, even at its earliest stages. Topography analysis and source reconstruction indicated that left peri-sylvian cortices mediate attention effects on memory trace activation.