Lexical processing depends on sublexical processing: Evidence from the visual world paradigm with aphasia
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1
Rice University, Psychology, United States
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2
University of Iowa - Iowa City, Psychology, Communication Sciences and Disorders, Linguistics, United States
Introduction
Previous studies have reported that some patients show strikingly better perception of speech at the lexical than sublexical level (e.g., Miceli, Gainotti, Caltagirone, & Masullo, 1980). This appears to challenge the claim that lexical processing depends on processes like phonological categorization (e.g., McClelland & Elman, 1986). However, early studies did not closely match the difficulty of the sublexical and lexical tasks. When using closely matched tasks using natural speech tokens, we found that no patient was better at lexical than sublexical tasks (Dial & Martin, 2015), suggesting that findings from previous studies reflected task difficulty. However, these tasks had a working memory (WM) component, and measured late, decision-stage (rather than online) processing. The current study sought converging evidence that lexical processing depends on sublexical processing while minimizing WM demands and using eye-tracking in the visual world paradigm as a measure of online speech perception, measured during the perception process (e.g., McMurray, Aslin, Tanenhaus, Spivey & Subik, 2008).
Method
Eight individuals with aphasia completed phoneme (sublexical) and word (lexical) identification tasks using auditorily presented synthetic speech tokens varied on a voice-onset time (VOT) continuum from 0 (voiced, “b”) to 40 (voiceless, “p”) msec. For phoneme identification, participants selected one of four written syllables (ba, pa, sha, la) that matched a spoken syllable. For lexical identification, participants selected one of four pictures that matched a spoken word (e.g., beach, peach, shirt, ladder). Eye movements to potential referents were recorded from the end of the auditory stimulus to item selection.
Results/Conclusions
To examine the final product of categorization, we examined identification data (the ultimate mouse response; see Figure 1A). Data were fit with a four-parameter logistic function, providing the category boundary (the point at which “p” was chosen 50% of the time), slope, and the maximum and minimum asymptotes (reflecting the responses to the endpoint stimuli). Our analysis of the real-time processing (the fixations to each referent) focused on within-category sensitivity to the VOT, accounting for individual differences in the category boundary (e.g., McMurray et al., 2008). We examined the proportion of competitor fixations from 300 to 3000 msec as a function of VOT (Figure 1B).
A high correlation was observed between performance on the phoneme and lexical tasks (Figure 1C/D). This was seen in both the identification data (in the difference between the maximum and minimum asymptotes, the amplitude, see Figure 1A), r (6) = .72, p = .043, and in fixation proportions, r (6) = .67, p = .068. Using Crawford and Howell’s (1998) modified t-test, patients whose amplitude or fixation proportion was significantly different from controls on the phoneme task showed the same pattern on the lexical task. Overall, patients were more likely than controls to choose competitors (smaller amplitude) and to fixate competitors. Critically, no patient was impaired on the phoneme task but within normal range on the lexical task. The current study thus provides converging evidence that with closely matched stimuli and tasks, sublexical and lexical perception are highly related and likely subserved by similar brain mechanisms.
References
Crawford, J. R., & Howell, D. C. (1998). Comparing an individual's test score against norms derived from small samples. The Clinical Neuropsychologist, 12(4), 482-486.
Dial, H. R., & Martin, R. (2015). Evaluating proposed dorsal and ventral route functions in speech perception and phonological short-term memory: Evidence from aphasia. Frontiers in Psychology, Conference Abstract: Academy of Aphasia 53rd Annual Meeting. doi: 10.3389/conf.fpsyg.2015.65.00075
McClelland, J., & Elman, J. (1986). The TRACE model of speech perception. Cognitive Psychology, 18, 1-86.
McMurray, B., Aslin, R., Tanenhaus, M., Spivey, M., & Subik, D. (2008). Gradient sensitivity to within-category variation in words and syllables. Journal of Experimental Psychology: Human Perception and Performance, 34(6), 1609-1631.
Miceli, G., Gainotti, G., Caltagirone, C., & Masullo, C. (1980). Some aspects of phonological impairment in aphasia. Brain and Language, 11, 159-169.
Keywords:
sublexical,
lexical,
visual world paradigm,
eye tracking,
Aphasia
Conference:
54th Annual Academy of Aphasia Meeting, Llandudno, United Kingdom, 16 Oct - 18 Oct, 2016.
Presentation Type:
Poster Sessions
Topic:
Academy of Aphasia
Citation:
Dial
HR,
McMurray
B and
Martin
R
(2016). Lexical processing depends on sublexical processing: Evidence from the visual world paradigm with aphasia.
Front. Psychol.
Conference Abstract:
54th Annual Academy of Aphasia Meeting.
doi: 10.3389/conf.fpsyg.2016.68.00086
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Received:
29 Apr 2016;
Published Online:
15 Aug 2016.
*
Correspondence:
Ms. Heather R Dial, Rice University, Psychology, Houston, Texas, 77005, United States, heather.raye.dial@gmail.com