Event Abstract

Left middle temporal gyrus lesion predicts impairment of phonotactic processing

  • 1 Georgetown University Medical Center, United States
  • 2 MedStar National Rehabilitation Hospital, United States
  • 3 NIH/NIDCD, Brain Imaging and Modeling Section, United States

Introduction Sublexical phonotactic knowledge is important for speech perception (Vitevitch & Luce, 1998, 1999; Vitevitch, Luce, Pisoni, & Auer, 1999). It has recently been suggested that phonotactic regularities are extracted from lexical forms and thus brain areas associated with lexical processing may be involved in phonotactic processing (Gow Jr & Nied, 2014; Obrig, Mentzel, & Rossi, 2016). Although great progress has been made in understanding the brain basis of speech perception, few studies have specifically examined the brain basis of phonotactic knowledge. Consequentially, the neural substrates of phonotactic processing remain unclear. To address this gap, the current study applied support-vector-regression lesion-symptom mapping (SVR-LSM) to the study of behavioral impairments following left hemisphere stroke. Decreased sensitivity to the phonotactic regularity of speech was found to associate with lesions of the left anterior temporal lobe, including left anterior middle temporal gyrus (MTG), a region previously implicated in lexical processing. Methods Participants included 41 left-hemisphere stroke survivors aged 38 to 77 years (M = 58.74, SD = 12.57), and 33 age-matched healthy participants aged 26 to 80 years (M = 59.20, SD = 9.53). All participants were native speakers of English. Patients included in the study had left-hemisphere ischemic or hemorrhagic stroke at least 6 months prior to the study. Participants completed a computerized lexical decision task in which they listened to a series of words/non-words and decided whether each was a real word. Stimuli included 30 six-phoneme words/nonwords. The nonwords were selected from a corpus developed by DeWitt (2012) and were either phonotactically regular or irregular. Participants’ response times (RTs) and accuracies were collected. After excluding outliers (3.6% of data), inverse Gaussian transformation was used to normalize RTs. Linear mixed effects models were used to analyze the data. Model fitting was performed in a backward-stepwise iterative fashion, followed by forward fitting of maximal random effects structure. Final model included fixed effects of backward digit span (to account for executive and working memory deficits), group and phonotactic condition. For SVR_LSM, for each patient, the slope of the regression line for the responses to the two phonotactic regularity conditions of non-words were calculated using a mixed effects model. To control for participants’ backward digit spans, a linear regression was performed between participants’ previously calculated slopes of the regression lines and their backward digit spans. The residuals of the regression model were used as the dependent variable in the SVR_LSM. Results and Discussion RT analysis revealed a significant interaction of group and phonotactic regularity [t = 2.19, p = 0.02]. Compared to controls, stroke survivors were less sensitive to phonotactic regularity. Lesion-symptom mapping found a causal relationship between the integrity of left anterior MTG (as well as temporal pole) and sensitivity to the phonotactic regularity of speech tokens (see Figure 1). Results are consistent with a model of phonotactic knowledge wherein phonotactic sensitivity derives from the processing of lexical forms in left temporal cortex.

Figure 1


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Keywords: phonotactics, Sublexical processing, Left-hemisphere stroke, lesion-symptom mapping, Middle temporal gyrus

Conference: Academy of Aphasia 55th Annual Meeting , Baltimore, United States, 5 Nov - 7 Nov, 2017.

Presentation Type: poster presentation

Topic: General Submission

Citation: Ghaleh M, Lacey EH, DeWitt I and Turkeltaub PE (2019). Left middle temporal gyrus lesion predicts impairment of phonotactic processing. Conference Abstract: Academy of Aphasia 55th Annual Meeting . doi: 10.3389/conf.fnhum.2017.223.00005

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Received: 01 May 2017; Published Online: 25 Jan 2019.

* Correspondence: Dr. Maryam Ghaleh, Georgetown University Medical Center, Washington, DC, United States, mg1477@georgetown.edu