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Impaired speech perception leads to poor semantic access: ERP evidence from individuals with pathologically or artificially impaired speech perception.

James L. Keidel1, Emma Pilkington2, Louise Evans2, Vincent Deluca2 and Holly Robson2*
  • 1 University of Sussex, School of Psychology, United Kingdom
  • 2 University of Reading, Psychology and Clinical Language Sciences, United Kingdom

Introduction: Recent studies have identified correlations between the comprehension impairment and acoustic-phonological processing in chronic Wernicke’s-type aphasia (WA) (Robson, Grube et al., 2013). This relationship is logical, corresponds to the traditional model of WA (Eggert, 1977; Luria, 1976) and the lesion profile which shows high overlap in the auditory ventral stream (Ogar, Baldo et al., 2011). However, these associations have only been demonstrated with off-line neuropsychological assessments such as spoken word-picture matching and non-word discrimination. The neural dynamics of these offline tasks do not completely overlap; for example, comprehension tasks activate the ventral language network (Giraud, Kell et al., 2004), while discrimination tasks recruit resources from dorsal stream components (Burton, LoCasto et al., 2005). As such, previously identified associations may be mediated by a third factor, such as lesion volume, and the impact of acoustic-phonological processing impairments on comprehension may be more modest. To establish a direct impact of impaired speech perception on comprehension, evidence must be found during online tasks where neural dynamics are configured for comprehension. Methods: Eight individuals with chronic WA and 10 age-matched control participants were recruited. Continuous EEG over 64 electrodes was recorded during a word-picture verification task. Participants were required to confirm or reject whether a spoken word matched a picture. The following conditions were presented: WA: congruent [Cong-cl e.g. bottle-bottle]; incongruent-phonologically far [Phon-f e.g. cap-map]; incongruent-phonologically near [Phon-n-cl e.g. rake-lake]; incongruent-semantically far [Sem-f e.g. tea-water]; incongruent-semantically near [Sem-n-cl e.g. van-lorry]. Control: Three conditions overlapped with the WA group: [Cong-cl]; [Phon-n-cl] and [Sem-n-cl]. In addition, controls were presented with three degraded speech conditions using Saberi speech (Saberi & Perrott, 1999): Congruent degraded speech [Cong-deg]; incongruent-phonologically near degraded [Phon-n-deg]; incongruent-semantically near degraded [Sem-n-deg]. Following ERP pre-processing, amplitude was averaged over the N400 time window (300-500ms: an index of semantic processing) and the phonological mismatch negativity (PMN) window (160-300ms: an index of phonological-lexical processing) over central-parietal and frontal electrodes, respectively. The impact of speech perception impairment and distracter type were investigated in a series of ANOVAs. Results: Incongruency effects were found in both groups for the semantic and phonological incongruent conditions. Individuals with WA displayed significantly smaller N400 responses than control participants over overlapping incongruent conditions (Phon-n-cl; Sem-n-cl: F(1,16)=11.0, p=0.004), Figure 1. This N400 amplitude reduction was replicated in the control group by artificially degrading speech perception (Phon-n-deg & Sem-n-deg. < Phon-n-cl & Sem-n-c: F(1,9)=21.3, p=0.001), Figure 1. Individuals with WA showed significantly reduced N400 responses to near than far distracters in the phonological condition only (Phon-n-cl < Phon-f; Sem-n-cl = Sem-f: F(1,7)=6.0, p=0.044). No significant group differences were found in PMN amplitude, however, a significant relationship was found between PMN responses and phonological discrimination (ρ=-0.87, p=0.003) and language comprehension tasks (ρ=-0.81, p=0.015) in the WA group. Discussion: This study found direct evidence for a reduction in semantic access/retrieval following impaired speech perception during online auditory comprehension. Consistent with previous research, accuracy on offline assessments of language comprehension correlated with early phonological responses but not later semantic activity.

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Acknowledgements

This research was funded by a University of Reading Undergraduate Research Opportunity Placement

References

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Eggert, G. H. (1977). Wernicke's Works on Aphasia: A Sourcebook and Review. The Hague: Mouton Publishers.
Giraud, A., Kell, C., Thierfelder, C., Sterzer, P., Russ, M., Preibisch, C., & Kleinschmidt, A. (2004). Contributions of sensory input, auditory search and verbal comprehension to cortical activity during speech processing. Cerebral Cortex, 14(3), 247-255.
Luria, A. R. (1976). Disturbances of Understanding of Verbal Communication in Patients with Sensory Aphasia. The Hague: Mouton & Co. B. V.
Ogar, J. M., Baldo, J. V., Wilson, S. M., Brambati, S. M., Miller, B. L., Dronkers, N. F., & Gorno-Tempini, M. L. (2011). Semantic dementia and persisting Wernicke’s aphasia: Linguistic and anatomical profiles. Brain and Language, 117(1), 28-33.
Robson, H., Grube, M., Lambon Ralph, M. A., Griffiths, T. D., & Sage, K. (2013). Fundamental deficits of auditory perception in Wernicke's aphasia. Cortex, 49(7), 1808-1822.
Saberi, K., & Perrott, D. R. (1999). Cognitive restoration of reversed speech. Nature, 398(6730), 760-760.

Keywords: N440, Phonological mismatch negativity, Wernicke’s aphasia, Auditory comprehension, Speech Perception, speech perception in noise

Conference: 54th Annual Academy of Aphasia Meeting, Llandudno, United Kingdom, 16 Oct - 18 Oct, 2016.

Presentation Type: Poster Sessions

Topic: Academy of Aphasia

Citation: Keidel JL, Pilkington E, Evans L, Deluca V and Robson H (2016). Impaired speech perception leads to poor semantic access: ERP evidence from individuals with pathologically or artificially impaired speech perception.. Front. Psychol. Conference Abstract: 54th Annual Academy of Aphasia Meeting. doi: 10.3389/conf.fpsyg.2016.68.00066

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Received: 27 Apr 2016; Published Online: 15 Aug 2016.

* Correspondence: Dr. Holly Robson, University of Reading, Psychology and Clinical Language Sciences, Reading, United Kingdom, h.v.robson@reading.ac.uk