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Poster D30, Thursday, November 9, 6:15 – 7:30 pm, Harborview and Loch Raven Ballrooms

Semantic Comprehension Errors in Pure Word Deafness

L. Robert Slevc1, Ryan A. Simmons2, Randi C. Martin3;1University of Maryland, 2Duke University, 3Rice University

Individuals with acquired pure word deafness (PWD) show selective deficits in speech perception despite preserved hearing, preserved abilities in other aspects of language (semantic knowledge, reading, and production), and often preserved perception of non-speech auditory stimuli (environmental sounds and music). PWD typically results from bilateral temporal damage and is often assumed to reflect underlying deficits in rapid temporal processing that disproportionately impact speech perception (e.g., Poeppel, 2001). However speech perception deficits in some cases of PWD, especially cases resulting from unilateral left-hemisphere damage, do not always appear to reflect a deficit in rapid temporal processing (e.g., Slevc et al., 2011), and these cases can show a counterintuitive tendency to make semantically related errors in speech comprehension (e.g., Metz-Lutz & Dahl, 1984). Speech comprehension deficits in individuals with PWD who show semantically related comprehension errors (e.g., repeating "salt" as "pepper") seem unlikely to simply reflect auditory processing deficits. However, there has not yet been a careful investigation of semantic comprehension errors in a PWD patient. Here, we present one such investigation of patient NL, who shows dramatically impaired performance on standardized tasks of speech perception but performs largely within the normal range on non-speech auditory perception, written comprehension, and speech production (Slevc et al., 2011). To determine whether NL makes semantic comprehension errors (e.g., repeating "diamond" as "ring") more often than would be expected by chance, we administered two word repetition tasks and used Latent Semantic Analysis (LSA; Landauer & Dumais, 1997) to quantify the semantic similarity between the target (to-be-repeated) words and the words NL actually said. We then compared the semantic distances for NL’s repetitions to chance estimates of semantic overlap calculated via Monte Carlo simulations. NL’s productions were much more closely related to target words (mean LSA distance = 0.252; 95% CI: 0.173, 0.331) than were chance estimates (mean LSA distance = 0.078; 95% CI: 0.076, 0.079), showing that he does indeed often make semantic comprehension errors despite impaired perception of speech. We also investigated whether NL’s impaired speech perception would be influenced by semantic variables. In both a repetition task and an auditory lexical decision task, NL was more accurate on high compared to low imageability words (e.g., "building" vs. "thing") – a semantic property – but his accuracy was unrelated to the lexical property of word frequency. NL’s perception also was impacted by semantic priming: his repetitions were more closely related to the target words (higher LSA values) after hearing related compared to unrelated words in an auditory semantic priming task. Because NL’s speech perception deficit is accompanied by semantic comprehension errors and is influenced by semantic factors, his deficit seems unlikely to result from perceptual problems alone. Instead, NL’s speech processing might reflect rapid decay of phonological representations, leading to relatively greater influence of weakly-activated semantic representations (cf. some accounts of deep dysphasia; Martin & Saffran, 1992). Alternatively, his speech processing might reflect an overreliance on relatively coarse right hemispheric semantic representations (cf. the right-hemisphere reading account of deep dyslexia; Coltheart, 2000).

Topic Area: Language Disorders

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