Linguistic encoding dominance in stuttering: Some evidence for temporal and qualitative hemispheric processing differences

Abstract

The current study measured naming reaction times of a group of stuttering and nonstuttering subjects to unilateral, tachistoscopically presented pictures. Results of an ANOVA with repeated measures design on the reaction time data showed that a significant interaction proved to exist between the group (stuttering vs. nonstutterers) and visual field (left vs. right) variables. Post-hoc tests showed that left visual field inputs generated significantly faster naming reaction times (85 msec) than those associated with right visual field stimulations for the stutterers, but not for the fluent controls. Analysis of the error data showed that a significant interaction existed between the visual field and error type (in-class, out-of-class, and no-response errors) variables for the stutterers, but not for the fluent subjects. Post-hoc analysis of the stutterers data revealed that right visual field inputs produced significantly greater no-response and in-class errors as compared to the left visual field. The reaction time findings were interpreted to suggest that both hemispheres in the stutterers were capable of generating linguistic tags for Gestalt information, with the right hemisphere emerging as the dominant neurostructure for completing the task demands. The error data suggested further that qualitative differences existed between the two hemispheres regarding their ability to label noun images. The quality and number of encoding errors associated with the left hemisphere were significantly greater as compared to the right hemisphere for the stutterers. Theoretical implications for speech fluency are presented in the context of future research considerations.