ERP measures of partial semantic knowledge: left temporal indices of skill differences and lexical quality

Abstract

This study examines the sensitivity of early event-related potentials (ERPs) to degrees of word semantic knowledge. Participants with strong, average, or weak vocabulary skills made speeded lexical decisions to letter strings. To represent the full spectrum of word knowledge among adult native-English speakers, we used rare words that were orthographically matched with more familiar words and with pseudowords. Since the lexical decision could not reliably be made on the basis of word form, subjects were obliged to use semantic knowledge to perform the task. A d' analysis suggested that high-skilled subjects adopted a more conservative strategy in response to rare versus more familiar words. Moreover, the high-skilled participants showed a trend towards an enhanced "N2c" to rare words, and a similar posterior temporal effect reached significance approximately 650 ms. Generators for these effects were localized to left temporal cortex. We discuss implications of these results for word learning and for theories of lexical semantic access.

Fig. 1

Stimulus sequence.

Fig. 2

(A) Mean response times and (B) mean d′ scores on lexical decision task.

Fig. 3

Skill differences in beta criterion on the lexical discrimination task.

Fig. 4

Grand-averaged ERP waveforms for high-skilled subjects (n = 13). Scale, ±4 μV. Averaged over channel groups (Appendix A). Thick black line, low-frequency words (hits). Thin black line, rare words (hits); thin grey line, rare words (misses). Thick grey line, pseudowords (correct rejections).

Fig. 5

Grand-averaged ERP waveforms for average-skilled subjects (n = 10). Scale, ±4 μV. Averaged over channel groups (Appendix A). Thick black line, low-frequency words (hits). Thin black line, rare words (hits); thin grey line, rare words (misses). Thick grey line, pseudowords (correct rejections).

Fig. 6

Grand-averaged ERP waveforms for low-skilled subjects (n = 11). Scale, ±4 μV. Averaged over channel groups (Appendix A). Thick black line, low-frequency words (hits). Thin black line, rare words (hits); thin grey line, rare words (misses). Thick grey line, pseudowords (correct rejections).

Fig. 7

Major ERP effects. Left, time course of each factor. Right, factor topographies (left, familiar words; right, pseudowords). (*) lexicality effects. (+) interactions between lexicality and skill.

Fig. 8

Left: high-skilled, but not average or low-skilled participants, showed trend towards enhanced posterior temporal responses to rare words at around 270 ms. Right: source localization of the F270 factor points to left ventral temporal region.

Fig. 9

Left: high-skilled, but not average or low-skilled participants, showed towards enhanced posterior temporal responses to rare words at around 640 ms. Right: source localization of the F640 factor points to left ventral temporal regions.