Time-driven effects on processing grammatical agreement

Abstract

"Agreement" is a grammatical relation between words; e.g., the verbal suffix -s reflects agreement with a singular subject (He run-s). Previous studies with time intervals under 2.5 s between disagreeing words have found a left-lateralized negative brain potential, arguably reflecting detection of the morphosyntactic violation. We tested the neurophysiological effects of number agreement between the first and last word in sentences at temporal distances between 1.75 and 3.25 s. Distances were varied by visually presenting sentences word by word at different rates. For distances under 2.5 s, a left-lateralized negativity was observed. At a 3.25-s interval, an anterior, slightly right-lateralized negativity was found. At an intermediate distance of 2.75 s, the difference between disagreement and agreement at left electrodes correlated with participants' working memory span. Results indicate that different brain processes occur when agreement involves agreement domains approaching and exceeding 3 s than when the agreement dependency involves shorter temporal intervals.

Keywords: ERP; LAN; P600; agreement; grammatical dependency; left anterior negativity; short-term memory; working memory.

Figure 1

Example sentences showing (A) agreement and (B) disagreement between grammatical subject and sentence-final predicate adjective, as well as the time intervals between subject pronoun and predicate adjective resulting from the different rates of word presentation.

Figure 2

ERPs from six channels at the four different rates of word presentation for sentence-final adjectives that agree (black line) or disagree (gray line) with the sentence-initial pronoun as regards number. Between 300 and 450 ms, there was a left-lateralized negativity at fast and midfast rates and a slightly right-skewed anterior negativity at slow rate of word presentation. Disagreement also produced a late posterior positivity at fast and midfast rates (P600). Most closely corresponding 10–20-system channels are: F7, FZ, F8, T5, PZ, and T6.

Figure 3

Topographical distribution of the negativity at the different temporal distances created by the variation in presentation rate, indicated within parentheses. Average ERPs in the LAN time window (300–450 ms) for the subtraction disagreement–agreement are shown.

Figure 4

Correlation between individual working memory span score and average difference between disagreement and agreement ERPs (left negativity, LN) at midslow left channels, 300–450 ms.

Figure 5

Results at midslow word presentation rate for two groups scoring highest and lowest on the working memory span test, respectively, at a left anterior electrode. The negativity at left channels for the high span group in the LAN time window is shown.