An ERP investigation of perceptual vs motoric iconicity in sign production

The type of form-meaning mapping for iconic signs can vary. For perceptually-iconic signs there is a correspondence between visual features of a referent (e.g., the beak of a bird) and the form of the sign (e.g., extended thumb and index finger at the mouth for the American Sign Language (ASL) sign BIRD). For motorically-iconic signs there is a correspondence between how an object is held/manipulated and the form of the sign (e.g., the ASL sign FLUTE depicts how a flute is played). Previous studies have found that iconic signs are retrieved faster in picture-naming tasks, but type of iconicity has not been manipulated. We conducted an ERP study in which deaf signers and a control group of English speakers named pictures that targeted perceptually-iconic, motorically-iconic, or non-iconic ASL signs. For signers (unlike the control group), naming latencies varied by iconicity type: perceptually-iconic < motorically-iconic < non-iconic signs. A reduction in the N400 amplitude was only found for the perceptually-iconic signs, compared to both non-iconic and motorically-iconic signs. No modulations of N400 amplitudes were observed for the control group. We suggest that this pattern of results arises because pictures eliciting perceptually-iconic signs can more effectively prime lexical access due to greater alignment between features of the picture and the semantic and phonological features of the sign. We speculate that naming latencies are facilitated for motorically-iconic signs due to later processes (e.g., faster phonological encoding via cascading activation from semantic features). Overall, the results indicate that type of iconicity plays role in sign production when elicited by picture-naming tasks.