OBJECTIVE: To study the effect of chronologic age on central auditory functions using dichotic speech tests and to study whether and how the age effect in dichotic listening is related to cognitive ability.

DESIGN: Dichotic speech tests and cognitive tests were performed on 30 bilaterally 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 material were digits, low-redundancy sentences and consonant-vowel syllables. The subjects reported stimuli heard in both ears (free report) or in one ear (directed report to left or right ear). The cognitive test battery comprised tests focusing on short-term memory, verbal information-processing speed and phonologic processing.

RESULTS: A decreased overall performance in all dichotic speech tests was observed 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 compared with when focusing on stimuli heard in the right ear, whereas the younger group showed almost equal results for left- and right ear-focusing conditions. An age effect was also seen in reaction times recorded in the cognitive tests and in the scores of the reading span test. These cognitive parameters 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 correlation with cognitive test parameters.

CONCLUSIONS: Effects of chronologic age in dichotic speech tests in the elderly 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 varying degree of correlations between cognitive function and dichotic test parameters. 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.

A cognitive test battery sensitive to processes important for speech understanding was developed and investigated. Test stimuli are presented as text or in an auditory or audiovisual modality. The tests investigate phonologic processing and verbal information processing. Four subject groups, young/elderly with normal-hearing and young/elderly with hearing impairment, each including 12 subjects, participated in the study. The only significant effect in the text modality was an age effect in the speed of performance, seen also in the auditory and audiovisual modalities. In the auditory and audiovisual modalities, the effects of hearing status and modality were seen in accuracy parameters. Interactions between hearing status and modality, both in accuracy and in reaction times, show that hearing-impaired subjects have difficulties without visual cues. Performing the test battery in noise made the tasks more difficult, especially in the auditory modality and for the elderly, affecting both accuracy and speed. Test-retest measurements showed learning effects and a modality-dependent variability. The test battery has proven useful in assessing the relative contribution of different input signals and the effects of age, hearing impairment, and visual contribution on functions important for speech processing.

Cognitive tests of speech understanding were administered (presented as text, or in auditory or audiovisual modality) and perceived effort was rated. This was done in four background conditions: in silence, and in three types of noise (S/N=+10 dB) varying in temporal structure and meaningfulness. Four groups of 12 subjects each (young/elderly with normal hearing and young/elderly with hearing impairment) participated. The presence of noise had a negative effect on accuracy and speed of performance in the speech processing tasks, and resulted in higher scores of perceived effort, even when the stimuli were presented as text. Differences in performance between noise conditions existed. In the subjective scores, the noise with temporal variations, but without meaningful content, was the most disruptive of the three noise conditions. In the objective scores, the hearing-impaired subjects showed poorer results in noise with temporal variations. The elderly subjects were more distracted by noise with temporal variations, and especially by noise with meaningful content. In noise, all subjects, particularly those with impaired hearing, were more dependent upon visual cues than in the quiet condition.

Speech recognition and cognitive functions important for speech understanding were evaluated by objective measures and by scores of perceived effort, with and without hearing aids. The tests were performed in silence, and with background conditions of speech spectrum random noise and ordinary speech. One young and one elderly group of twelve hearing-impaired subjects each participated. Hearing aid use improved speech recognition in silence (7 dB) and in the condition with speech as background (2.5 dB S/N), but did not change the perceived effort scores. In the cognitive tests no hearing aid benefit was seen in objective measures, while there was an effect of hearing aid use in scores of perceived effort, subjects reported less effort. There were no age effects on hearing aid benefit. In conclusion, hearing aid use may result in reduced effort in listening tasks that is not associated with improvement in objective scores. © 2005 British Society of Audiology, International Society of Audiology, and Nordic Audiological Society.