Compounding matters: Event-related potential evidence for early semantic access to compound words

Reading words in a native language triggers a largely obligatory cognitive process that we accept as leading to comprehension of the word - we cannot suppress our understanding of word meaning. In this study, we investigated the early stages of this comprehension process by means of event-related potentials (ERPs) to identify when this processing of meaning - that is, semantic processing - first occurs. We report that, when processing visually presented compound words, semantic access at some level occurs as early as the P100 and persists through to the N400. Specifically, we focused on the P100 ERP component, and utilized the unique features of compound words (i.e. variation in the transparency of meaning) to investigate the speed with which we gain access to information about meaning (i.e. semantic access). Twenty-two participants performed a lexical decision task including 40 English compounds, which varied with respect to their constituent semantic transparency. Compounds ranged from full constituent semantic transparency (e.g. grapeseed) to partial transparency (e.g. grapefruit) to full opacity (e.g. hogwash). Regression analyses predicted ERP components from compound constituent transparency, adjusting for word frequency. Word frequency and transparency of both the first and second constituents each uniquely predicted P100 amplitude. Transparency of the second constituent, but not word frequency, predicted later component amplitudes, including that of the N400. The findings suggest that some level of semantic access occurs as early as the P100. Overall, these results support models which emphasize simultaneous processing of form and meaning as opposed to serial or hierarchical approaches.