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Measures of auditory processing in aphasia: Behavioural and electrophysiological analysis

Background: Lesions resulting in aphasia frequently involve areas associated with auditory processing. Investigations using psychoacoustics and/or electrophysiology to examine the auditory processing abilities of aphasic as well as non-brain-damaged individuals have revealed the influence of several variables on findings, including age, type of stimuli, task difficulty/instructions, response modality, and lesion site/size. It is unclear whether both methods of testing are examining similar components of auditory processing and furthermore, if the variables identified as affecting findings for the two testing methodologies influence results in a similar manner. An electrophysiological approach to auditory processing may assist in the objective evaluation of patients who have difficulty consistently providing accurate responses. Aims: The purpose of this investigation was to explore behavioural and electrophysiological CAP abilities of several aphasic individuals using a set of divided attention tasks and to investigate whether electrophysiological results were congruent with those obtained from behavioural testing. Methods and Procedures: Participants were two females and five males, age range 33-73, all suffering left cerebrovascular accidents, resulting in aphasia. Experimental testing included: speech-language evaluation via administration of the Western Aphasia Battery and the Token Test ; hearing evaluation using routine pure-tone audiometry, speech audiometry, and middle ear measurements; behavioural central auditory processing assessment using Pitch Pattern Sequence and Dichotic Digits ; and electrophysiology testing, consisting of evaluation of late auditory evoked potentials (N100, P200, P300) with and without distraction using an oddball paradigm. Outcomes and Results: Results are presented individually for each patient. Overall, patients showed unique results relative to ear advantage pattern and congruence between electrophysiological and behavioural testing. One patient showed inconclusive findings due to a hearing loss; one patient showed no clear ear advantage pattern on either behavioural or electrophysiological testing; one patient showed no ear advantage on dichotic testing but showed a clear pattern on electrophysiology; and one patient showed incongruence in ear advantage pattern between electrophysiological and behavioural testing. Three patients showed congruent ear advantage patterns across both behavioural and electrophysiological testing; however, one showed a right ear advantage and two showed a left ear advantage. Conclusions: Based on these findings, it is evident that the direct and/or statistical relationship between behavioural CAP and electrophysiological findings requires more in-depth exploration. The testing of additional patients is imperative prior to making decisions regarding the utility and value of such a statistical approach. Thus, the use of these and other CAP measures bears additional investigation as clinical and experimental tools in evaluating auditory processing capabilities of the aphasic patient.