but more frontally-distributed N400, similar to that for concrete words (Ganis, Kutas & Sereno 1996). The N400 effects for familiar faces completed by mismatching versus matching internal features had an occipital maximum (Olivares et al 1999). Within-subject comparisons of words and meaningful environmental sounds demonstrated N400 effects for each, similar in all but hemispheric laterality, right dominant for words and left dominant for environmental sounds (Van Petten & Rheinfelder 1995). The weight of these studies pointed to a functional entity that varies systematically with relatedness within and across a wide range of sensory input types, but characterized by topographic differences that implicate an assortment of at least partially non-overlapping neural areas in meaning construction. N400s thus are modality-dependent but not modality-specific (perhaps marking a unimodal to amodal interface; see section on theory) – an electrophysiological marker of processing in a distributed semantic memory system.
