Monday, May 25, 2015

Lau, Phillips, and Peoppel: "A cortical network for semantics" (2008)

This paper contrasts two competing hypotheses about what the N400 signals:
  1. an "integration" theory which alleges that "the N400 effect … reflects the process of semantic integration of the critical word with the working context" (p. 921);
  2. a "lexical" theory which alleges that "the difference between the effects of anomalous and predictable endings arises not because of the anomaly but because predictable words in context are easier to access from memory" (p. 921).
The authors eventually decide that the lexical theory is more likely in view of the data. This conclusion is mostly based on a consideration of results from semantic priming experiments, which are supposed to isolate the task of retrieving a word from memory.

They use the following model of the anatomical distribution of linguistic processing (Fig. 2, p. 923):

Their conclusion is thus that the substrate responsible for the absence of an N400 effect is the pinkish rectangle at the top. It's the brain region which sits underneath your left ear, give or take.

In addition to this discussion, the paper contains a number of references to non-linguistic stimuli that can also produce an N400 effect:
  1. Barrett, S. E., Rugg, M. D. & Perrett, D. I. Event-related potentials and the matching of familiar and unfamiliar faces. Neuropsychologia 26, 105–117 (1988).
  2. Barrett, S. E. & Rugg, M. D. Event-related potentials and the semantic matching of faces. Neuropsychologia 27, 913–922 (1989). (Yes, that is a different title.)
  3. Barrett, S. E. & Rugg, M. D. Event-related potentials and the semantic matching of pictures. Brain Cogn. 14, 201–212 (1990).
  4. Holcomb, P. J. & McPherson, W. B. Event-related brain potentials reflect semantic priming in an object decision task. Brain Cogn. 24, 259–276 (1994).
  5. Ganis, G., Kutas, M. & Sereno, M. I. The search for “common sense”: an electrophysiological study of the comprehension of words and pictures in reading. J. Cogn. Neurosci. 8, 89–106 (1996).
  6. Van Petten, C. & Rheinfelder, H. Conceptual relationships between spoken words and environmental sounds: event-related brain potential measures. Neuropsychologia 33, 485–508 (1995)
  7. Ganis, G. & Kutas, M. An electrophysiological study of scene effects on object identification. Cogn. Brain Res. 16, 123–144 (2003).
  8. Sitnikova, T., Kuperberg, G. & Holcomb, P. J. Semantic integration in videos of real-world events: an electrophysiological investigation. Psychophysiology 40, 160–164 (2003).
  9. Sitnikova, T., Holcomb, P. J., Kiyonaga, K. A. & Kuperberg, G. R. Two neurocognitive mechanisms of semantic integration during the comprehension of visual real-world events. J. Cogn. Neurosci. 20, 2037–2057 (2008).
  10. Plante, E., Petten, C. V. & Senkfor, A. J. Electrophysiological dissociation between verbal and nonverbal semantic processing in learning disabled adults. Neuropsychologia 38, 1669–1684 (2000).
  11. Orgs, G., Lange, K., Dombrowski, J. H. & Heil, M. N400-effects to task-irrelevant environmental sounds: further evidence for obligatory conceptual processing. Neurosci. Lett. 436, 133–137 (2008).
That is a lot of reading.

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