Right Hemisphere Contributions to Lexical Access: Evidence from Word Priming in Unilateral Neglect

Abstract

Right hemisphere damage sometimes spares lexical retrieval yet impairs semantic integration. We tested 24 patients with right hemisphere lesions using a masked word priming paradigm to dissociate form-based from meaning-based processing. Priming effects were attenuated for target words, suggesting right hemisphere participation in semantic binding operations.

Introduction

The lateralization of language function has been traditionally attributed to left hemisphere dominance, particularly for phonological and syntactic processing. However, evidence from neurological patients and functional imaging studies increasingly implicates the right hemisphere in semantic and pragmatic aspects of language understanding. This distributed view suggests that the two hemispheres contribute complementary strengths to language comprehension: the left hemisphere specializes in form-based operations, while the right hemisphere integrates meaning across broader conceptual contexts.

The nature of right hemisphere language contribution remains disputed. One hypothesis posits that the right hemisphere processes semantically distant or unexpected meanings, whereas another suggests a more global role in maintaining coherent semantic context. The present study employs masked word priming—a technique sensitive to automatic, pre-conscious aspects of meaning activation—to characterize the functional profile of right hemisphere lexical processing in patients with unilateral right hemisphere lesions.

Method

Participants

Twenty-four patients with chronic right hemisphere stroke (16 male, 8 female; mean age = 54.7 years) recruited from a regional stroke rehabilitation center and 20 age-matched healthy control participants completed the study. Patients had no history of prior neurological disorder and were at least six months post-stroke to minimize spontaneous recovery. Lesion extent was confirmed via CT or MRI scans.

Procedure

Participants performed a lexical decision task with masked prime–target presentation. Each trial consisted of a 40 ms prime word, a 20 ms mask, and a 500 ms target word, to which participants responded "word" or "nonword" via button press. Half of target words were preceded by semantically related primes (e.g., "DOCTOR–NURSE"), unrelated primes, or identity primes. Nonword targets were always preceded by unrelated primes. One hundred and sixty trials (80 word targets, 80 nonword targets) were administered in a single session with self-paced breaks.

Prior to the masked priming task, participants rated the semantic relatedness of 30 prime–target pairs on a 7-point scale to establish subjective distance. Reaction times and accuracy were recorded for all responses. Following the experimental session, participants completed a post-experimental questionnaire in which they reported awareness of prime words.

Results

Data from two patients with severe neglect affecting the right visual field were excluded, leaving 22 patients in the final analysis. Reaction times were submitted to a 2 (group: patients, controls) × 3 (prime type: semantic, unrelated, identity) ANOVA. A significant interaction emerged, F(2, 80) = 4.21, p < .02. Control participants showed robust semantic priming (unrelated mean = 598 ms, semantic mean = 545 ms; difference = 53 ms), whereas patients showed attenuated priming (unrelated mean = 634 ms, semantic mean = 612 ms; difference = 22 ms), t(21) = 2.13, p < .05.

Identity priming was comparable between groups (control mean difference = 89 ms; patient mean difference = 71 ms; t(40) = 1.47, p = .15), indicating preserved form-based priming in the patient group. Accuracy was high and similar across groups (controls = 94%, patients = 91%). No patient reported conscious awareness of prime words in the post-experimental questionnaire.

Discussion

The preserved identity priming in patients with right hemisphere damage, combined with attenuated semantic priming, suggests a dissociation between form-based and meaning-based lexical activation. This pattern implicates the right hemisphere in automatic semantic integration, consistent with distributed models of language organization. The reduction in semantic priming effect size—though statistically significant—is modest, raising the possibility that left hemisphere mechanisms can partially compensate for right hemisphere damage in semantic priming contexts.

These findings contribute to an emerging picture of right hemisphere language function as integral to semantic coherence and integration, rather than to basic lexical access. Future studies incorporating neuroimaging of the lesioned right hemisphere and event-related potentials may illuminate the time course of hemispheric cooperation in language processing. Clinical implications for language rehabilitation following right hemisphere stroke warrant investigation.

References

Beeman, M., & Chiarello, C. (Eds.). (1998). Right hemisphere language comprehension: Perspectives from cognitive neuroscience. Lawrence Erlbaum Associates.
Joanette, Y., Goulet, P., & Hannequin, D. (1990). Right hemisphere and verbal communication. Springer-Verlag.
Katz, R. B. (1986). Phonologic deficiencies in children with reading disability: Evidence and implications. Annals of Dyslexia, 36, 90–101.
Neely, J. H. (1991). Semantic priming effects in visual word recognition: A selective review of current findings and theories. In D. Besner & G. W. Humphreys (Eds.), Basic processes in reading (pp. 264–336). Lawrence Erlbaum Associates.
Posner, M. I., & Snyder, C. R. R. (1975). Attention and cognitive control. In R. L. Solso (Ed.), Information processing and cognition: The Loyola Symposium (pp. 55–85). Lawrence Erlbaum Associates.
Sergent, J. (1991). Judgments of facial similarity: A window to perception of identity after brain damage? Neuropsychologia, 29(8), 815–829.
Wapner, W., Hamby, S., & Gardner, H. (1981). The role of the right hemisphere in apprehending complex linguistic materials. Brain and Language, 14(1), 15–33.