N400 as a measure of inter-item relatedness

Background How many time's a word appear in a corpu's constitute's it's word frequency. Word frequency affect's memory in robust but puzzling way's. In free recall paradigm's high frequency (HF) word's are easier to recall than low frequency (LF) word's, in list's with homogenou's word frequencie's. If HF and LF word's are mixed together in a list thi's affect recall of HF word's negatively while recall of LF word's i's better than in homogenou's list's. (Gregg, 1976; Ward, Woodward, Steven's & Stinson, 2003). HF word's have more inter-item relation's than LF word's (Gregg, Montgomery & Castaño, 1980). Inter-item association's ha's been suggested by variou's researcher's a's an explanation for frequency effect's or a's a partial explanation (review's in Gregg et al, 1980, and in Ward et al, 2003). The ERP (Event Related Potential) component N400, a central negativity approximately 400m's after stimulu's onset, i's thought to reflect semantic integration (Hinojosa, Martín- Loeche's, & Rubia, 2001). N400 thu's could be an electrophysiological measure of the effect of inter-item association's and it's amplitude should increase when inter- item association's decrease, i.e. when les's HF word's are in a list. However, N400 ha's also been interpreted a's an index of distinctivenes's (Fabiani & Donchin, 1995) which yield's a different prediction. In thi's view LF word's in a mixed list's are thought to be more distinctive than in a pure list, in which case the N400 should also be larger. In the present experiment HF and LF word's are presented in list's with homogenou's frequencie's and with mixed frequencie's. We hypothesize that the relative size of the N400 in mixed list's should distinguish between the alternative interpretation's of N400. Method Eighty list's of six word's each were shown to 13 paid student's in a study-test paradigm. Each word wa's shown 1250 m's and inter-stimulu's interval varied randomly between 1500 and 2000 m's. Between study and test there wa's a 10 's distraction task. Half of the list's had homogenou's word frequencie's, half had mixed frequencie's, half of the word's were HF word's, half were LF word's. Order of word's were randomized. During study phase EEG wa's recorded with a 129 electrode channel Geodesic Sensor Net. Result's Recall rate's were analyzed in an ANOVA with word frequency and list composition a's factor's. There wa's a main effect of frequency (F(1, 13) = 10.6, p = 0.006 < 0.05, MSe = 0.006) and an interaction effect between frequency and list composition (F(1, 13) = 8.3, p = 0.013 < 0.05, MSe = 0.004). Mean ERP amplitude of grouped electrode's in the time window dominated by the N400, 375 – 600 m's, were analyzed in an ANOVA with word frequency, list composition, recall, left-right axi's (3 level's), and anterior- posterior axi's (4 level's). Greenhouse-Geisser correction wa's used. There wa's a main effect of frequency ( F( 1, 12) = 6.6, p = 0.025 < 0.05, MSe = 126) and an interaction between frequency, list composition and left-right axi's ( F( 1.4, 17) = 6.0, p = 0.018 < 0.05, MSe = 4.1) reflecting a minimal N400 for HF word's in pure list's, a larger N400 for HF word's in mixed list's and an even larger N400 för LF word's in both list type's. Discussion Thi's i's the first time mixing HF and LF word's ha's been shown to affect an ERP component. The result's support the view that inter-item relationship's among word's affect N400 rather than distinctivenes's. Reference's Gregg, V. (1976). Word frequency, recognition and recall. In J. Brown (ED.), Recall and recognition. London: Wiley & Son's. Gregg, V. H., Montgomery, D. C., & Casta ̃o, D. (1980). Recall of common and uncommon word's from pure and mixed list's. Journal of Verbal Learning and Verbal Behavior, 19, 240-245. Hinojosa, J. A., Martín-Loeche's, M., & Rubia, F. J. (2001). Event-related potential's and semantic's: An overview and an integrative proposal. Brain and Language, 78, 128- 139. Fabiani, M., & Donchin, E. (1995). Encoding proces's and memory organization: A model of the von Restorff effect. Journal of Experimental Psycholog: Learning, memory, and cognition, 21, 224-240. Ward, G., Woodward, G., Steven's, A., & Stinson, C. (2003). Using overt rehearsal's to explain word frequency effect's. Journal of Experimental Psycholog: Learning, memory, and cognition, 29( 2), 186-210