Semantic processing of natural and artificial entities is modulated by feature-based properties: An EEG study

Journal: 

Neuropsychologia

Date: 

September, 2018

Authors: 

Argiris, G., Crepaldi, D., and Rumiati, R.I.

Category-specific impairments witnessed in patients with semantic deficits have broadly dissociated into natural and artificial kinds. However, how the category of food (more specifically, fruits and vegetables) fits into this distinction has been difficult to interpret, given a pattern of deficit that has inconsistently mapped onto either kind, despite its intuitive membership to the natural domain. The high evolutionary importance of food for survival and its consequent reliance on certain properties for its rapid identification renders it a critical category of investigation. The present study explores the effects of a manipulation of a visual sensory (i.e., color) or functional (i.e., orientation) feature on the consequential semantic processing of fruits and vegetables and tools, by comparison, first at the behavioral and then at the neural level. In experiment one, the categorization of natural (i.e., fruits/vegetables) and artificial (i.e., utensils) entities was investigated via semantic (identity) priming in a lexical decision task. Participants were presented with a picture prime of a natural (e.g., apple) or artificial (e.g., fork) entity modified in color, orientation, or presented normally, followed by a string of letters as target and reaction times to the target string analyzed. Results indicated that color-modified primes yielded less priming than orientation-modified primes preceding a word target depicting a natural entity; the opposite pattern was found for words depicting an artificial entity. In experiment two, participants were presented with the same paradigm and electroencephalography (EEG) recorded. Standard event-related potential (ERP) analysis was performed in addition to principle component analysis (PCA) and linear classification. For natural entities, an N400 effect at central channel sites was observed for the color-modified condition compared with the normal condition, with a difference between conditions confirmed by PCA and classification analysis; for the artificial category, linear classification analysis revealed significantly accurate discrimination between the orientation and normal condition at right posterior channel sites. These findings support a sensory-functional distinction extending to the fruits/vegetables category, whereby feature-based processing guides categorization and that this processing varies as a function of semantic category