Using lexical semantic cues to mitigate interference effects during real-time sentence processing in aphasia

We examined the auditory sentence processing of neurologically unimpaired listeners and individuals with aphasia on canonical sentence structures in real-time using a visual-world eye-tracking paradigm. The canonical sentence constructions contained multiple noun phrases and an unaccusative verb, the latter of which formed a long-distance dependency link between the unaccusative verb and its single argument (which was base generated in the object position and then displaced to the subject position). To explore the likelihood of similarity-based interference during the real time linking of the verb and the sentence's subject noun, we manipulated the animacy feature of the noun phrases (matched or mismatched). The study's objectives were to examine whether (a) reducing the similarity-based interference by mismatching animacy features would modulate the encoding and retrieval dynamics of noun phrases in real-time; and (b) whether individuals with aphasia would demonstrate on time sensitivity to this lexical-semantic cue. Results revealed a significant effect of this manipulation in individuals both with and without aphasia. In other words, the mismatch in the representational features of the noun phrases increased the distinctiveness of the unaccusative verb's subject target at the time of syntactic retrieval (verb offset) for individuals in both groups. Moreover, individuals with aphasia were shown to be sensitive to the lexical-semantic cue, even though they appeared to process it slower than unimpaired listeners. This study extends to the cue-based retrieval model by providing new insight on the real-time mechanisms underpinning sentence comprehension.

The effect of time on lexical and syntactic processing in aphasia

Processing deficits at the lexical level, such as delayed and reduced lexical activation, have been theorized as the source of breakdowns in syntactic operations and thus contribute to sentence comprehension deficits in individuals with aphasia (IWA). In the current study, we investigate the relationship between lexical and syntactic processing in object-relative sentences using eye-tracking while listening in IWA. We explore whether manipulating the time available to process a critical lexical item (the direct-object noun) when it is initially heard in a sentence has an immediate effect on lexical access as well as a downstream effect on syntactic processing. To achieve this aim, we use novel temporal manipulations to provide additional time for lexical processing to occur. In addition to exploring these temporal effects in IWA, we also seek to understand the effect that additional time has on sentence processing in neurotypical age-matched adults (AMC). We predict that the temporal manipulations designed to provide increased processing time for critical lexical items will 1) enhance lexical processing of the target noun, 2) facilitate syntactic integration, and 3) improve sentence comprehension for both IWA and AMC. We demonstrate that strengthening lexical processing via the addition of time can affect lexical processing and facilitate syntactic retrieval of the target noun and lead to enhanced interference resolution in both unimpaired and impaired systems. In aphasia, additional time can mitigate impairments in spreading activation thereby improving lexical access and reducing interference during downstream dependency linking. However, individuals with aphasia may require longer additions of time to fully realize these benefits.

Classifiers in Mandarin Chinese: Behavioral and electrophysiological evidence regarding their representation and processing

In Chinese, when objects are named with their quantity, a numeral classifier must be inserted between the quantifier and the noun to produce a grammatically correct quantifier + classifier + noun phrase. In this study, we adopted the picture-word interference paradigm to examine participants' naming latencies for multiple objects and their electroencephalogram in four conditions by manipulating two factors, i.e. semantic relatedness and classifier congruency. Results show that in noun phrase production, naming latencies are significantly longer in classifier-incongruent and semantically related conditions than in classifier-congruent and semantically unrelated conditions. Also, an N400-like effect was observed and found to be stronger in classifier-incongruent and semantically unrelated conditions. Together, the behavioral data and event-related potential analyses suggest that the use of classifiers as lexico-syntactic features in Mandarin Chinese takes place via a competitive selection process in noun phrase production.

Early effects of neighborhood density and phonotactic probability of spoken words on event-related potentials

All current models of spoken word recognition propose that sound-based representations of spoken words compete with, or inhibit, one another during recognition. In addition, certain models propose that higher probability sublexical units facilitate recognition under certain circumstances. Two experiments were conducted examining ERPs to spoken words and nonwords simultaneously varying in phonotactic probability and neighborhood density. Results showed that the amplitude of the P2 potential was greater for high probability-density words and nonwords, suggesting an early inhibitory effect of neighborhood density. In order to closely examine the role of phonotactic probability, effects of initial phoneme frequency were also examined. The latency of the P2 potential was shorter for words with high initial-consonant probability, suggesting a facilitative effect of phonotactic probability. The current results are consistent with findings from previous studies using reaction time and eye-tracking paradigms and provide new insights into the time-course of lexical and sublexical activation and competition.