Frontiers in Psychology (May 2015)
Prediction of arguments and adjuncts in aphasia: Effects of event-related and verb-specific knowledge
Abstract
Previous research suggests that on-line access to lexically-stored verb argument structures is relatively preserved in some people with aphasia[9] (PWAs), despite their increased difficulty in producing verbs as compared to nouns[2]. Accessing lexically-stored argument structures facilitates prediction and integration of verbal arguments relative to lexically unspecified adjuncts[1,8,10]. The anticipatory processing of verbal arguments has also been shown to be affected by event-related plausibility constraints, based in world knowledge[4]. While access to world knowledge and argument structure is preserved in many PWAs, how and when these resources interact during verb-argument processing among PWA has not been investigated. The current study examined how argument status and event plausibility affect on-line processing of locative event participants via a modified visual-world task[6]. PWAs (n=9) and age-matched neurotypical adults (ONs, n=16) listened to a partial sentence and were instructed to click on the image that “best finished” the sentence. Stimuli were sentences ending with a locative phrase truncated at the preposition: “The boy is turning twelve, so his friends are bringing/ meeting him excitedly to/at …” The incomplete locative phrase was either an argument or an adjunct (location is an argument of “bring” but an adjunct of “meet”). Accompanying images depicted the agent and theme of the sentence, an unrelated distractor, and a location target, either plausible (a fair) or implausible (a bar). Proportions of gazes to the location target were analyzed in 100ms bins during the 2 seconds following the offset of the pronoun (“him.”) ONs showed clear early (100-200ms, 300-700ms) and late (1100-1800ms, 1900-2000ms) plausibility effects (circled in Fig. 1a), as well as early (200-300ms) and late (1300-1400ms) effects of argument status on target gazes (see arrows, Fig. 1a) and a late interaction effect of argument status and plausibility (1100-1200ms, see asterisk, Fig. 1a). Early effects of plausibility and argument status for ONs were truly anticipatory, appearing while the sentence was still on-going. Plausibility effects on target gaze were more limited in PWA, appearing at two points following pronoun offset (500-600ms and 1000-1100ms, circled in Fig. 1b). Conversely, argument effects were more widespread for PWAs, although they emerged later (700-900ms and 1000-1100ms, see arrows, Fig. 1b). PWAs also showed a much later interaction effect between plausibility and argument status (at 1800ms, see asterisk, Fig. 1b). These results suggest that older adults rely more on event-related plausibility than on argument status during the processing of locative event participants, and that these effects interact late in processing. The effect of argument status is more prevalent but delayed in PWAs compared to ONs, and the interaction of plausibility and argument status is also present but delayed. This pattern is compatible with findings suggesting that PWAs access verbs’ lexical representations during sentence comprehension[9] and that this access may affect linguistic performance[5], but that lexical access is delayed in PWAs when compared to age-matched controls[7,11]. This slowed lexical access can lead to impairments in syntactic comprehension[3]. The current results indicate that similar effects may also be present in verb-argument prediction and the processing of semantic roles.
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