The distinction of competence from performance issues is often problematic in the differential diagnosis of communication deficits in neurologically impaired patients. Motoric and perceptual deficits are frequent confounding factors when traditional linguistic comprehension test items, requiring overt responses (verbal, gestural, or graphic), are administered. A failure to respond, or to respond correctly, on traditional tests of linguistic comprehension does not necessarily indicate a failure to comprehend, especially in patients with severe motoric difficulties. Problems of linguistic competence in many individuals thus may be frequently overestimated by clinicians' judgements.

The development of methodology for assessing linguistic comprehension via eye movement responses has important implications for research and clinical practice. Major advantages of applying this methodology to research and clinical practice are that it:

• offers an alternative, non-linguistic response mode, providing information about intact comprehension ability that is currently unavailable for many severely inexpressive patients;
• allows for stimulus adaptations to control for perceptual, attentional, and oculomotor deficits;
• does not depend upon patients' understanding of instructions prior to the presentation of actual testing stimuli;
• does not interrupt the comprehension process with intervening verbal instructions, prompts for responses, or demands for subjects' conscious planning of responses;
• allows for a continuous record of processing, simultaneous with processing tasks;
• allows for testing of a broad range of sentence types, lengths, and grammatical structures; and
• may yield important information about prognosis for recovery of linguistic skills and about treatment outcomes.

An additional advantage in studying eye movements in this context is that they are often preserved even in cases of severe motoric and cognitive deficits. Hallowell has previously demonstrated the feasibility of assessing auditory and reading comprehension through eye movements.

The primary objective of the current study was to validate an adaptation of a standard test of auditory comprehension for neurologically impaired adults, using eye movement responses. A widely used, standardised test of reading for patients with aphasia, the Revised Token Test (RT.) (McNeil & Presto, 1978, Pro-Ed) was used as the basis for systematic stimulus and subject response mode modifications. This test was selected to allow for maximal clinical and research applicability of experimental findings. Language-normal adults were used as subjects to ensure the validity of subject responses and to allow for assessment of reliability of findings from modified and standard versions of the test.

The RTT stimuli were presented to subjects in each of two conditions. In the standard testing condition, the test was presented according to the published instructions. In the experimental condition, subjects viewed RTT stimuli on a computer monitor, and were not instructed to "look at" anything.

Results support the feasibility of employing eye movements to index subject responses to auditory linguistic stimuli in the modified testing protocol. Implications for further methodological developments, including visual and verbal stimulus design, and analysis procedures, are discussed, as are possible applications of this methodology to other patient populations.

This work is supported by the National Institutes of Health/ National Institute for Deafness and Other Communication Disorders.