When we perceive speech, our goal is to extract the meaning of the verbal message which includes semantic processing. However, how deeply do we process speech in different situations? In two experiments, native Dutch participants heard spoken sentences describing simultaneously presented pictures. Sentences either correctly described the pictures or contained an anomalous final word (i.e. a semantically or phonologically incongruent word). In the first experiment, spoken sentences were task-irrelevant and both anomalous conditions elicited similar centro-parietal N400s that were larger in amplitude than the N400 for the correct condition. In the second experiment, we ensured that participants processed the same stimuli semantically. In an early time window, we found similar phonological mismatch negativities for both anomalous conditions compared to the correct condition. These negativities were followed by an N400 that was larger for semantic than phonological errors. Together, these data suggest that we process speech semantically, even if the speech is task-irrelevant. Once listeners allocate more cognitive resources to the processing of speech, we suggest that they make predictions for upcoming words, presumably by means of the production system and an internal monitoring loop, to facilitate lexical processing of the perceived speech.
Bibliographical noteFunding Information:
The work presented in this manuscript was supported by NWO grant no. 453-02-006 to Niels O. Schiller. The authors would like to thank Ingrid Christoffels (Leiden Institute for Brain and Cognition), as well as Heidi Koppenhagen and Bernadette Jansma (both Maastricht University) for their helpful comments. The manuscript benefited from discussions following talks at the Psycholinguistics in Flanders workshop in Leuven (Belgium), May 2005 and the 14th conference of the European Society for Cognitive Psychology in Leiden (The Netherlands), September 2005, as well as poster presentations at the Endo-Neuro-Psycho Meeting in Doorwerth (The Netherlands), June 2005 and the Annual Meeting of the Cognitive Neuroscience Society in San Francisco (USA), April 2008.