Abstract
Verbs and other temporal expressions allow speakers to specify the location of events in time, as well as to move back and forth in time, shifting in a narrative between past, present and future. The referential flexibility of temporal expressions is well understood in linguistics but its neurocognitive bases remain unknown. We aimed at obtaining a neural signature of shifting times in narrative language. We recorded and analyzed event-related brain potentials (ERPs) and oscillatory responses to the adverb ‘now’ and to the second main verb in Punctual (‘An hour ago the boy stole a candy and now he peeled the fruit’) and Iterative (‘The entire afternoon the boy stole candy and now he peeled the fruit’) contexts. ‘An hour ago’ introduces a time frame that lies entirely in the past, ‘now’ shifts the narrative to the present, and ‘peeled’ shifts it back to the past. These two referential shifts in Punctual contexts are expected to leave very similar traces on neural responses. In contrast, ‘The entire afternoon’ specifies a time frame that may encompass past, present and future, such that both ‘now’ and ‘peeled’ are consistent with it. Here, no time shift is required. We found no difference in ERPs between Punctual and Iterative contexts either at ‘now’ or at the second verb. However, reference shifts modulated oscillatory signals. ‘Now’ and the second verb in Punctual contexts resulted in similar responses: an increase in gamma power with a left-anterior distribution. Gamma bursts were absent in Iterative contexts. We propose that gamma oscillations here reflect the binding of temporal variables to the values allowed by constraints introduced by temporal expressions in discourse.
Highlights
Discourse appears to play a crucial role in determining the time interval to which ‘now’ may refer in each case
There remains a possibility that, during processing, ‘now’ is initially and tentatively given its default indexical meaning, which can be subsequently recomputed should discourse coherence demand it, based on the available anaphoric antecedents. This is precisely the assumption made by the Hybrid Theory presented above, and contrasted with a purely Indexical Theory and a purely Anaphoric Theory of CBP statistics: Punctual vs Iterative
By analyzing oscillatory brain responses at ‘now’ and at the second verb, we found a pattern that closely matches the key predictions of the Hybrid Theory
Summary
“In the end all she can say is: Oh, but won’t all that be too much trouble, now? being weighted with several troublesome meanings; you may take your choice.”. We consider sentences in which the adverb ‘now’ is followed by a past tensed verb, as in ‘ the boy peeled the fruit’ These constructions occur with some frequency in ordinary language, and they are acceptable so long as ‘now’ can refer to a past time frame, which is either specified by a temporal marker in the preceding discourse, or is common knowledge between speaker and hearer. That ‘now’ and the second main verb (e.g., ‘peeled’) leave specific traces on the EEG signal in PC relative to IC That these brain responses are very similar or identical at ‘now’ and at ‘peeled’ in PC, as follows from the notion that the adverb and the subsequent verb trigger identical time shifts with opposite sign: past-to-present at ‘now’, present-to-past at the verb. We discuss what aspects of EEG signals may be affected by mental time shifting in narratives
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