The neural response to highly iconic signs in hearing learners and deaf signers

Previous ERP studies have demonstrated that hearing learners of American Sign Language (ASL) show sensitivity to sign iconicity (a resemblance between form and meaning) prior to learning any signs. Highly iconic (transparent) signs elicited greater negativity in the N400 window than non-iconic signs when participants performed a task that did not require semantic processing (detect an occasional grooming gesture). Greater negativity was interpreted as evidence that participants implicitly recognized the meaning of the iconic signs. Here we investigated how this neural response changes after learning. For comparison, we included a group of fluent deaf signers who performed the same task. Results revealed that the N400 to iconic signs became less negative after learning, indicating that these signs had been integrated into an emerging lexicon. In contrast, the N400 to non-iconic signs became more negative after learning, indicating more effortful processing compared to the iconic signs. For deaf signers, iconic signs elicited a larger N400 than non-iconic signs, which we interpret as a task effect whereby the highly iconic signs were seen as similar to the grooming gestures because both are enactments of actions (e.g., drinking from a cup; rubbing the eyes). In order to accurately perform the gesture detection task, deaf signers may have engaged in greater semantic processing of the iconic than non-iconic signs, which led to a larger N400 response. Overall, we conclude that iconicity modulates the neural response to signs in different ways before and after learning and that for deaf signers, iconicity effects are task dependent.