Cognitive effects in dichotic speech testing in elderly persons

Objective: To study the effect of chronologic age on central auditory funct ions using dichotic speech tests and to study whether and how the age effec t in dichotic listening is related to cognitive ability. Design: Dichotic speech tests and cognitive tests were performed on 30 bila terally hearing-impaired subjects, with a pure-tone average better than 50 dB HL. They were between 42 and 84 yr of age and were divided into an older and a younger group comprising 15 subjects each. The dichotic test materia l were digits, low-redundancy sentences and consonant-vowel syllables. The subjects reported stimuli heard in both ears (free report) or in one ear (d irected report to left or right ear). The cognitive test battery comprised tests focusing on short-term memory, verbal information-processing speed an d phonologic processing. Results: A decreased overall performance in all dichotic speech tests was o bserved in the older group. In the syllable test the older subjects showed poorer results when focusing on the stimuli heard in the left ear, as compa red with when focusing on stimuli heard in the right ear, whereas the young er group showed almost equal results for left- and right ear-focusing condi tions. An age effect was also seen in reaction times recorded in the cognit ive tests and in the scores of the reading span test. These cognitive param eters correlate with the results of the dichotic test when focusing to the left, but not when focusing to the right in the directed report condition. In the free report condition the overall performance showed a high correlat ion with cognitive test parameters. Conclusions: Effects of chronologic age in dichotic speech tests in the eld erly have been verified. The degree of effect is dependent on test material , way of reporting and focusing condition. The different listening tasks in dichotic tests put different demands on cognitive ability shown by a varyi ng degree of correlations between cognitive function and dichotic test para meters. Also, the results indicate a strong connection between age-related cognitive decline in the elderly and problems to perceive stimuli presented to the left ear.