Psychophysiology, 39:S45, 2002.

Left or right button press versus silent count in tonal and phonetic oddball tasks: Current Source Density (CSD) ERPs and Principal Components Analysis (PCA)

JÃ¼rgen Kayser, Craig E. Tenke, Carlye B. Griggs, Stewart Shankman, Gerard E. Bruder

Department of Biopsychology, New York State Psychiatric Institute, New York, NY 10032, USA

Abstract

ERPs (30 sites) were recorded from 66 right-handed adults during oddball tasks (20% targets) using syllables or tones. Response mode (left press, right press, silent count) and task was varied within subjects. Reference-free CSD waveforms (spherical splines; Perrin et al 1989) were computed for each ERP to sharpen scalp topographies and eliminate volume-conducted contributions from distant regions. CSDs were submitted to covariance-based, unrestricted temporal PCA (Varimax) to disentangle temporally and spatially overlapping CSD components. The first six factors (84.5% variance) had distinct time courses of factor loadings (100, 155, 210, 360, 560, 910 ms peak latency) and topographies of factor scores, and corresponded to known ERP generators. For example, the dipolar organization of factor 100 (central N1) was evident from anterior sinks and posterior sources encompassing the Sylvian fissure. Factor 210 was characterized by frontolateral (tonal) and parietotemporal (phonetic) sinks for targets. Two P3 sources covered parietal sites for targets, the earlier 360 also including frontotemporal regions, the later 560 a prominent sink sharply localized to Fz. Task asymmetries (tonal: frontotemporal R>L; phonetic: parietotemporal L>R) were evident for CSD factors 210 and 360 for all response modes. Response effects involved a smaller P3 source for silent count compared to button press. Left or right press produced opposite, long-lasting, and region-specific asymmetries originating from central sites. The combined CSD/PCA approach clarified the differentiation of task- and response-related effects.

Keywords: Laplacian, temporal PCA, oddball response mode