Is lexical access autonomous? Evidence from combining overlapping tasks with recording event-related brain potentials

In order to test the frequent assumption that lexical access in visual word recognition would proceed independent of central attention, the overlapping task paradigm has recently been employed with somewhat contradictory results. Here we combined overlapping tasks with the recording of event-related brain potentials to assess task load dependent modulations of lexical access in more detail. The study was carried out in Spanish with native Spanish speaking participants. They performed a high-priority pitch discrimination task followed by a visual lexical decision task, in which the difficulty of lexical access was manipulated by means of word frequency. Increasing task load by reducing the stimulus onset asynchrony between both tasks from 700 to 100 ms resulted in considerable slowing of lexical decisions. Word frequency effects were underadditive with the slowing induced by task overlap, indicating lexical access to take place although central attention was dedicated to the high-priority task. The effect of word frequency on the event-related potentials, used as electrophysiological indicator of lexical access, was much less delayed than the lexical decision responses in conditions of high task overlap, providing converging evidence for the independence of lexical access from central attention. On the other hand, this slight delay and an amplitude reduction of the effect with high task load show that lexical access may not be completely autonomous, but subject to some additional early source of interference.