N400 sensitivity to inhibitory load during ambiguous word processing.

Semantic comprehension requires not only accessing word meanings but also suppressing contextually inappropriate meanings. Recent accounts suggest that the N400 component is sensitive to such suppression demands, yet few studies have examined suppression using dedicated paradigms. The present study introduced a suppression-based context verification paradigm with 3 graded levels of semantic processing difficulty. Forty participants performed a context verification task involving sentences ending with homophonic (eg "bank") or heterophonic (eg "tear") homographs that biased readers toward the subordinate meaning (eg "The tailor repaired the → tear"). After a short interval, a target word related to the dominant but contextually inappropriate meaning (eg "CRYING") was presented. If the dominant meaning was not yet suppressed, the target was expected to interfere with suppression of the contextually inappropriate meaning, making its rejection more difficult. The findings revealed a graded pattern of behavioral and N400 responses, with amplitudes increasing gradually with semantic processing difficulty: smallest for unambiguous control trials involving semantic incongruency, larger for ambiguous trials, and largest for heterophonic relative to homophonic homographs in left anterior electrodes. This pattern is consistent with the meaning-suppression framework suggesting that 500 ms following heterophonic homograph presentation the irrelevant dominant meaning is still activated.