Category-related brain activity to natural categories is associated with the retrieval of visual features: Evidence from repetition effects during visual and functional judgments.

It is debated whether category-related brain activation reflects a modality-specific (e.g., visual, functional representation systems) or a domain-specific (e.g., natural vs. artifactual categories) semantic memory organization. The present event-related potentials (ERPs) study is aimed at elucidating the nature of semantic representations of objects from natural (e.g., animal) and artifactual (e.g., tool) categories. Within a repetition priming paradigm, we tested the assumption that modality-specific semantic systems are differentially involved in representing artifacts and natural kinds by probing either visual or functional knowledge in a test task. In the exposure phase, subjects performed a classification task on object names for artifacts and natural objects. In the test phase, these previously presented (old) names were presented together with new names, and subjects had to perform either a visual (shape) or a functional (use) judgment. As in previous ERP studies, words from natural categories were associated with a more positive potential at occipito-parietal electrodes than words from artifactual categories. This effect was only obtained during the visual judgment task. This category-related ERP effect was diminished for words that had been previously presented. In the functional judgment task, category-related ERP effects were not obtained at all, probably due to the heterogeneity of the probed features. The observed interaction between task, category and repetition provides direct evidence that visual features play a more important role for the representations of natural compared to artifactual categories. Our data are therefore compatible with the notion of modality-specific semantic systems.