Speech and Hearing Sciences ETDs

Publication Date



The notion of cerebral dominance has been explored since the time of Broca. Two non-invasive techniques designed to assess hemispheric dominance have subsequently been developed. These two methods are commonly referred to as dichotic listening (simultaneous auditory stimulation) and rapid visual field stimulation (tachistoscopic viewing).

It has been found in dichotic listening studies that when verbal material is presented simultaneously to both ears, the stimuli are correctly identified most often in the right ear. Similar results have been found in tachistoscopic studies, with verbal material eliciting a right visual field advantage. Collectively, these findings have been used to support a left hemispheric dominance for processing verbal material, since the right ear and visual field are strongly connected to the left hemisphere.

It has been argued that the right visual field preference in tachistoscopic presentation may actually be reflecting a strong link between a visual stimulus and its auditory image in the brain. In order to explore this notion further, a tachistoscopic study was designed using subjects who lacked sufficient auditory input with which to develop auditory imagery for visual stimuli.

Twenty deaf and 20 normal hearing subjects were selected. Of these 40 subjects, 20 subjects (10 normal hearing and 10 deaf) were familiar with the manual alphabet. The visual stimuli selected for tachistoscopic presentation were 16 orthographic letters and the corresponding 16 manual alphabet letters. A total of four tasks was presented. All subjects completed one task in which orthographic stimuli were presented and an orthographic symbol was required as a response, and one task in which a manual stimulus was presented and a manual symbol was required as a response. In addition, the 20 subjects familiar with the manual alphabet completed one task requiring orthographic symbol to manual symbol matching and a final task requiring manual symbol to orthographic symbol matching.

The major findings of the present study were as follows:

1. A slight right visual field preference was noted on the average when linguistically meaningful stimuli were presented.

2. An equivocal visual field performance was noted on the average when the stimuli that were presented were assumed to be linguistically non-meaningful.

3. On overall right-left visual field performance, deaf subjects showed a reduced right-left difference when compared to the normal hearing subjects.

In conclusion, it is indicated by the results that although auditory imagery is not essential for the right visual field advantage to be exhibited, the absence of auditory influences may reduce the magnitude of this advantage.

Degree Name

Speech-Language Pathology

Level of Degree


Department Name

Speech and Hearing Sciences

First Committee Member (Chair)

William J. Ryan

Second Committee Member

Robert D. Wertz

Third Committee Member

Richard B. Hood

Fourth Committee Member

David J. Draper



Document Type