An Event-Related Potential Study of Cross-modal Morphological and Phonological Priming

Abstract

The current work investigated whether differences in phonological overlap between the past- and present-tense forms of regular and irregular verbs can account for the graded neurophysiological effects of verb regularity observed in past-tense priming designs. Event-related potentials were recorded from sixteen healthy participants who performed a lexical-decision task in which past-tense primes immediately preceded present-tense targets. To minimize intra-modal phonological priming effects, cross-modal presentation between auditory primes and visual targets was employed, and results were compared to a companion intra-modal auditory study (Justus, Larsen, de Mornay Davies, & Swick, 2008). For both regular and irregular verbs, faster response times and reduced N400 components were observed for present-tense forms when primed by the corresponding past-tense forms. Although behavioral facilitation was observed with a pseudopast phonological control condition, neither this condition nor an orthographic-phonological control produced significant N400 priming effects. Instead, these two types of priming were associated with a post-lexical anterior negativity (PLAN). Results are discussed with regard to dual- and single-system theories of inflectional morphology, as well as intra- and cross-modal prelexical priming.

Figure 1

Behavioral data. Mean response times (RTs) for correct lexical decisions (A) as a function of Word Type (regular verbs, irregular verbs, pseudopast, and orthophono) and Priming, and (B) for the irregular verbs alone, separated into weak irregular verbs and strong verbs. Error bars represent standard errors.

Figure 2

ERPs to target words within the nine-electrode region of interest, demonstrating the N400 and LPC (A) as a function of Word Type (regular verbs, irregular verbs, pseudopast, and orthophono) and Priming, and (B) for the irregular verbs alone, separated into weak irregular verbs and strong verbs.

Figure 3

Topographic maps of the scalp distributions displaying the N400/LPC priming effects (difference between primed and unprimed waveforms) between 200–400 msec and 400–600 msec for (A) each of the four Word Types (regular verbs, irregular verbs, pseudopast, and orthophono), and (B) weak irregular verbs and strong verbs.

Figure 4

Difference waves (unprimed minus primed) within the nine-electrode region of interest, combining the results of an auditory intra-modal study (Justus et al., 2008; solid lines) with the present auditory-to-visual cross-modal study (dashed lines). Results are shown for (A) each of the four Word Types (regular verbs, irregular verbs, pseudopast, and orthophono), and (B) weak irregular verbs and strong verbs.

Figure 5

Difference waves (unprimed minus primed) at electrode Cz, illustrating the verb conditions of both the auditory intra-modal study (Justus et al., 2008; upper row) and the present auditory-to-visual cross-modal study (lower row). The left column displays the verb priming effects as a function of the categorical division of regular and irregular verbs, with arrows indicating the moment of largest numeric difference between the two at approximately 600 msec (intra-modal) and 500 msec (cross-modal). The right column represents the same data as a function of a continuous division of regular, weak irregular, and strong verbs, with arrows indicating the graded and continuous data pattern suggested by the use of three verb classes rather than two.