Predictability effect reflects different contributions from each hemisphere: data from left and right hemisphere damage patients
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1
Institute of Neuroscience, National Yang-Ming University, Taiwan
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2
Department of Rehabilitation, Taipei Tzu Chi General Hospital, Taiwan
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3
School of Medicine, Tzu Chi University, Taiwan
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4
Neurological Institute, Taipei Veterans General Hospital, Taiwan
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5
Department of Neurology, National Yang-Ming University School of Medicine, Taiwan
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6
Institute of Linguistics, Academia Sinica, Taiwan
Introduction
Previous studies have suggested that the two hemispheres make qualitatively different contributions to lexical-semantic processing and language comprehension. Left hemisphere (LH) is biased toward top-down predictive process and thus acts quickly to predict or select a particular word sense for sentence comprehension. On the other hand, right hemisphere (RH) is biased toward to bottom-up integrative process and tends to holds a wide variety of information active for rapid recovery in which the interpretation selected by LH is incorrect. This study aimed to examine above hypothesis by examining effects of contextual predictability (cloze probability of the final word embedded in the sentence) on two event-related potentials (ERPs) components, N400 and frontal positivity, in patients with left hemisphere damage (LHD), right hemisphere damage (RHD) and a group of neurologically-intact age-matched controls. It was hypothesized that N400 primarily reflects the processing benefits in integrating a word into the context (Kutas & Hillyard, 1984) while the frontal positivity may involve in inhibiting or revising a strong prediction when an unexpected item is encountered (DeLong, Quante, & Kutas, 2014; Wlotko & Federmeier, 2007).
Method & results
This study manipulated the predictability (high versus low cloze probability) of the final word in the sentences participants were asked to read a set of sentences for comprehension. Patients were assessed with the Chinese Concise Aphasia Test (CCAT) for their reading comprehension ability. Control group (n =7) revealed a significant predictability effect on N400 and frontal positivity. RHD patients (n = 9), showing almost perfect scores on CCAT, revealed delayed predictability effect on N400, but no effect on frontal positivity. LHD patients revealed large variation on reading comprehension and were thus subdivided into high-ability and low-ability groups based on their CCAT scores. High ability LHD patients (n = 6), having similar comprehension scores with the controls, exhibited a reduced predictability effect on N400 and frontal positivity within a more restricted time window. Low ability LHD patients (n = 8) with poor reading comprehension ability exhibited a much prolonged and reduced predictability effect on N400 in frontal sites and no effect on frontal positivity.
Discussion
Although control, LHD and RHD groups showed comparable reading comprehension ability in behavioral measure, their ERPs data showed different pattern of predictability effect on N400 and frontal positivity. In particular, the double dissociation between RHD and LHD supports different natures of LH and RH in sentence comprehension. To be more specific, RHD, rely on LH, mainly utilizes the predictive process and thus display robust predictability effect on N400. The null effect on frontal positivity also support that the role of RH in revising initial interpretation for incorrect prediction. On the other hand, patients with LH damage resulted in a much reduced predictability effect on N400. However, the intact RH function in LHD allow them to hold unexpected but plausible meanings for revising, although the effect on frontal positivity was much smaller than that in control group.
Acknowledgements
This study was funded by the National Science Council (MOST-101-2628-H-001-006-MY3) and Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation (TCRD-TPE-100-41).
References
DeLong, K. A., Quante, L., & Kutas, M. (2014). Predictability, plausibility, and two late ERP positivities during written sentence comprehension. Neuropsychologia, 61, 150-162.
Kutas, M., & Hillyard, S. A. (1984). Brain potentials during reading reflect word expectancy and semantic association. Nature, 307, 161-163.
Wlotko, E. W., & Federmeier, K. D. (2007). Finding the right word: Hemispheric asymmetries in the use of sentence context information. Neuropsychologia, 45(13), 3001-3014.
Keywords:
ERPs,
Aphasia,
RHD,
reading comprehension,
N400
Conference:
54th Annual Academy of Aphasia Meeting, Llandudno, United Kingdom, 16 Oct - 18 Oct, 2016.
Presentation Type:
Poster Sessions
Topic:
Academy of Aphasia
Citation:
Chang
C,
Chou
C,
Wu
H,
Fuh
J and
Lee
C
(2016). Predictability effect reflects different contributions from each hemisphere: data from left and right hemisphere damage patients.
Front. Psychol.
Conference Abstract:
54th Annual Academy of Aphasia Meeting.
doi: 10.3389/conf.fpsyg.2016.68.00102
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Received:
30 Apr 2016;
Published Online:
15 Aug 2016.
*
Correspondence:
Prof. Chia-Ying Lee, Institute of Neuroscience, National Yang-Ming University, Taipei, Taiwan, chiaying@gate.sinica.edu.tw