Effects of left and right hemisphere damage on sensitivity to global context during lexical ambiguity resolution

Abstract

Background: A great deal of research suggests that both the left hemisphere (LH) and right hemisphere (RH) contribute to the resolution of lexically ambiguous words. If this is indeed the case, then patients with left (LHD) or right hemisphere brain damage (RHD) should exhibit deficits in ambiguity resolution. Although several studies have explored this issue, there is still little consensus regarding the exact nature of the patients' deficits. Moreover, the focus of most studies has been on ambiguity resolution in short, single-sentence contexts, so less is known about the impact of LH and RH damage on ambiguity resolution in larger contexts.

Aims: The goal of the present study was to investigate sensitivity to a global (i.e., two-sentence) context during lexical ambiguity resolution in LHD and RHD patients relative to a group of control participants with no neurological impairment. Control participants were expected to activate only contextually appropriate meanings. In contrast, LHD patients were expected to have difficulty activating ambiguous word meanings or selecting contextually appropriate meanings. RHD patients were expected to have difficulty using context or suppressing contextually inappropriate meanings.

Methods & Procedures: Three groups of participants took part in this study: 10 LHD patients with nonfluent aphasia, 8 RHD patients, and 9 age-matched control participants. A cross-modal sentence priming task was employed where participants first listened to a biased two-sentence passage ending in an ambiguous word. After each passage a visual target word, related to either the first or second meaning of the ambiguous word, was presented for lexical decision. Reaction time data were analysed using a repeated-measures ANOVA. Priming effects were tested by way of planned comparisons.

Outcomes & Results: The performance of both patient groups differed markedly from that of the control group, who only showed priming for contextually appropriate meanings. The LHD patients did not exhibit any significant priming of ambiguous word meanings, whereas the RHD patients only showed priming for the most frequent or dominant meaning of ambiguous words (e.g., the “animal” meaning as opposed to the “emblem” meaning of seal) regardless of context.

Conclusions: Both LH and RH damage can disrupt the process of ambiguity resolution in a global context. Specifically, LH damage is argued to impair the degree of activation of ambiguous word meanings or the time course of meaning activation, while RH damage seems to impair the use of context, leading to frequency-based meaning activation.

Keywords:

• Aphasia
• Language comprehension
• Lexical ambiguity resolution
• Right hemisphere damage
• Semantic priming

Acknowledgments

This research was supported by a Doctoral Research Award from the Canadian Institutes of Health Research to C. M. Grindrod and by a grant from the Canadian Institutes of Health Research to S. R. Baum. We would like to thank Pablo Ruiz and Lisa Trayhern for their assistance in collecting the patient data, Wendi Aasland for recording the stimuli, and Anne Grindrod for her assistance in collecting data for the norming studies. We are also indebted to the patients for their participation and to the speech-language pathologists at the local hospitals and rehabilitation centres for their efforts in recruiting participants.