Date of Award

December 2014

Degree Type

Thesis

Degree Name

Master of Science

Department

Communication Sciences and Disorders

First Advisor

Sabine Heuer

Committee Members

Wendy Huddleston, Carol Seery

Keywords

Cognitive Flexibility, Eye-Tracking, Functional Communication, Switching Task

Abstract

Introduction: Cognitive flexibility, a domain of the executive functions, has been demonstrated to influence functional communicative ability, specifically the ability to maintain the topic of conversation, take appropriate conversational turns, self monitor, repair communicative breakdowns, and use of alternative communication modalities. The assessment of cognitive flexibility is essential for the clinical evaluation and treatment of individuals with neurological disorders interfering with communication, however, confounds related to language comprehension and expression impact test validity. This is due to the reliance on verbal and physical response requirements, the understanding of complex linguistic instruction, and concomitant cognitive and physical impairments. Therefore, new methods designed to reduce these confounds are needed.

Cognitive flexibility has been validly indexed between mono-and bilingual speakers using nonlinguistic switching tasks. Nonlinguistic switching tasks require participants to match stimuli according to a specific search criterion, such as color or shape. In the non-switch (singe-task) condition, the matching criterion remains the same across all trials and the associated cognitive demand is low. In the switching condition (mixed-task), the matching criterion switches unpredictably between search criterion and the associated cognitive demand is high. The difference in cognitive demand between the non-switch and switch conditions and within the switch condition allows for the calculation of cost, a measure of cognitive flexibility.

The nonlinguistic switching tasks used to examine cognitive flexibility within the mono-and bilingual speakers are promising for use with individuals with language impairments of a neurological origin. However, motoric response requirements possibly invalidate test results due to the presence of concomitant physical impairments. Therefore, the application of eye-tracking methods has excellent potential because eye tracking does not require verbal, written, or gestural responses; or the manipulation of devices, such as a computer mouse or joystick.

Purpose: The purpose of this study was to develop and validate a novel eye-tracking task to assess cognitive flexibility using a switching task paradigm, and to determine the sensitivity to differences in cognitive switching demand between and within the single and mixed-task conditions.

Method: The eye movements of 20 language-normal participants were recorded as they looked at a computer screen and participated in experimental single- and mixed-task conditions. The eye-tracking measures latency of first fixation, first pass gaze duration, and first fixation duration on the target image were computed across all trials. The general switching cost, specific switching cost, and mixing cost, as indicated by response differences between and within the single-and mixed-task and switch conditions were calculated.

Results: The eye-tracking measures latency of first fixation on the target and first pass gaze duration on the target significantly indexed general switching cost and mixing cost, while first fixation duration on the target failed to demonstrate significance.

Pearson Correlation Coefficients were computed between eye-movement measures and test performance on standardized measures of cognitive flexibility including the Comprehensive Trail Making Test (CTMT) and Visual Elevator subtest of the Test of Everyday Attention (TEA). Some significant correlations were observed between the T-scores and raw times scores of the Comprehensive Trail Making Test and latency of first fixation on the target, however, no eye-tracking measures correlated significantly with the Visual Elevator subtest of the Test of Everyday Attention.

Implications: The novel eye-movement method validly indexed switching cost. The eye-tracking indices latency of first fixation and first pass gaze duration provided promising evidence that the eye-tracking task is sensitive to differences in cognitive demand. The nonlinguistic nature, lack of motoric requirements, and inclusion of practice trials render it a promising assessment tool for individuals with aphasia. Continued development of the eye-tracking method using the nonlinguistic switching task is warranted in order to enhance our understanding of the relationship between functional communication and cognitive flexibility and to improve the assessment methods for individuals with neurologic communication deficits.

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