Masked repetition priming using magnetoencephalography

Abstract

Masked priming is used in psycholinguistic studies to assess questions about lexical access and representation. We present two masked priming experiments using MEG. If the MEG signal elicited by words reflects specific aspects of lexical retrieval, then one expects to identify specific neural correlates of retrieval that are sensitive to priming. To date, the electrophysiological evidence has been equivocal. We report findings from two experiments. Both employed identity priming, where the prime and target are the same lexical item but differ in case (NEWS-news). The first experiment used only forward masking, while the prime in the second experiment was both preceded and followed by a mask (backward masking). In both studies, we find a significant behavioral effect of priming. Using MEG, we identified a component peaking approximately 225 ms post-onset of the target, whose latency was sensitive to repetition. These findings support the notion that properties of the MEG response index specific lexical processes and demonstrate that masked priming can be effectively combined with MEG to investigate the nature of lexical processing.

Evidence for Early Morphological Decomposition: Combining Masked Priming with Magnetoencephalography

“…In line with previous experiments that combined MEG with masked priming (Monahan et al, 2008), no consistent pattern of peaks was observed across all participants in later time-windows beyond the component peaking at about 220 msec. We nevertheless investigated whether the prime–target relationship had any effects on possible M350 latencies, as could be hypothesized on the basis of earlier MEG studies, albeit without masked priming (e.g., Pylkkänen, Llinas, & Murphy, 2006; Pylkkänen & Marantz, 2003).…”

“…The magnetic field contour of the peak (Figure 3) resembled a typical M170 contour elicited by written words (see, e.g., Harris, Pylkkänen, McElree, & Frisson, 2008; Fiorentino & Poeppel, 2007; Stockall, Stringfellow, & Marantz, 2004; Pylkkänen & Marantz, 2003), that is, an outgoing magnetic field in the left posterior sensors and an incoming field in the right posterior sensors. This peak, as predicted, was exceptionally similar in timing, distribution, and magnetic field contour to that reported in Monahan et al (2008). Ten channels with the strongest magnetic field were selected separately for each participant from only the source (outgoing magnetic field) of this component in the left hemisphere for quantitative analyses, given that the sink (ingoing magnetic field) was not clearly visible across participants due to limitations of the sensor configuration as well as subjects’ head position in the scanner.…”

“…On the basis of Monahan et al's (2008) results, we predicted that the latency of the left hemisphere component peaking roughly 220 msec post-onset of the target would show priming effects when the prime–target relationship is semantically transparent as well as when it is opaque but not when the prime and the target are only orthographically related. For the peak latencies (see Table 3), a repeated measures ANOVA (Condition × Relatedness; with Greenhouse–Geisser correction) showed a significant main effect of Relatedness ( F (1, 15) = 11.8, p = .004) and an interaction between Relatedness and Condition ( F (2, 30) = 4.78, p = .016), demonstrating that the priming effects differed across conditions.…”

“…The peaks in the MEG signal are likely to reflect less overlapping neural generators than those in the EEG, and the within-subjects nature of MEG can also be assumed to improve the sensitivity of observing small latency differences between conditions, as opposed to EEG, where grand averages are often employed. A recent study (Monahan, Fiorentino, & Poeppel, 2008) showed that masked priming and MEG can be effectively combined. They did not manipulate morphological structure but used identical words (VIDEO–video) as primes and targets.…”

A habituation account of change detection in same/different judgments

“…A relative increase for same trials would suggest that repetitions produce potentiation, whereas a decrease would support the habituation account. A number of MEG studies have shown that habituation occurs in the time window of 100-350 ms after onset, with nonlexical and lexical habituation effects appearing in the early versus late parts of this window, respectively (see Monahan, Fiorentino, & Poeppel, 2008, for a review). Although these studies evidenced neural habituation with word stimuli, their focus was mainly on repetition priming effects instead of on determining mechanisms of change detection.…”