Hearing Impairment Affects Older People's Ability to Drive in the Presence of Distracters

Louise Hickson, PhD; Joanne Wood, PhD; Alex Chaparro, PhD; Philippe Lacherez, PhD; Ralph Marszalek, BPsychSci(Hons)

Disclosures

J Am Geriatr Soc. 2010;58(6):1097–1103 

In This Article

Results

Hearing assessment results are summarized in Table 1. The mean better-ear pure-tone average was 27.0 ± 14.5 dB HL (range 2.5–82.5). Based on the better-ear pure-tone average, 45% of participants had some degree of hearing impairment, although fewer than 5% had severe or greater loss. Other features of the participants' hearing was that 78% were bilaterally symmetrical, that is, had the same hearing classification in both ears. For all but one of the remaining participants, there was a difference of only one classification level between ears (e.g., normal in one ear and mild in the other). One participant had normal hearing in one ear and a severe hearing impairment in the other. The correlation between PTAvge in both ears was significant (r (105)=0.9, P<.001). Of the 48 people with better-ear hearing impairment, 46 had a sensorineural hearing impairment, and two had a mixed hearing impairment. Greater hearing impairment was associated with older age (r (105)=0.6, P<.001), poorer speech perception scores in quiet (r (105)=−0.5, P<.001) and in noise (e.g., at 0 db SNR, r (105)=−0.6, P<.001), and more self-reported hearing problems on the HHIE (r (104)=0.7, P<.001). These findings of predominantly mild to moderate bilateral sensorineural hearing impairment in 45% of the sample are typical of this population.[23,25]

To determine which of the hearing function measures best related to driving performance, bivariate correlations among the various measures of hearing function (hearing categories, speech perception in quiet and noise, HHIE scores) and the overall driving Z score were examined. No individual hearing measure significantly predicted overall driving performance after controlling for age, although as can be seen in Table 2, the objective measures of hearing (pure-tone testing and speech perception testing) overall showed stronger correlations with driving performance than self-reported hearing difficulties. The best predictor of overall driving performance was degree of hearing impairment in the better ear. On the basis of this, participants were then split into two groups based on this variable (normal or mild hearing impairment, with better ear pure-tone average ≤40 dB in one group, and moderate to severe impairment, with average >40 dB in the other) so that it was possible to examine interactions between this variable and the repeated-measures variable of distraction. This better-ear 40-dB cutoff between groups is appropriate because the more severe functional effects of hearing impairment are generally considered to occur beyond this level.[26]

A 2 × 3 mixed ANOVA with the factors of hearing (normal to mild impairment vs moderate to severe impairment) and distraction (none, visual, or auditory) on the overall driving Z scores revealed a main effect of distraction (F(2,208)=15.9, P<.001). Overall performance was better under the no-distracter condition than under either of the two distracter conditions; the visual and auditory distracter conditions did not differ significantly.

There was also a significant interaction between the level of hearing impairment and distraction (F(2,208)=5, P=.01). As can be seen in Figure 1, in both hearing impairment groups, the auditory and visual distracters resulted in poorer performance than the no-distracter condition, but the two distracter conditions did not differ significantly from one another. The differences between the no-distracter conditions and each of the two distracter conditions, was much larger in those with poorer hearing function, suggesting that those with hearing impairment are compromised to a far greater extent when required to undertake a secondary task while driving.

Figure 1.

Mean performance Z score for the driving task in each condition as a function of hearing status. Error bars are ± 1 standard error.

A 2 × 3 mixed ANOVA with the factors of hearing (normal to mild impairment or moderate to severe impairment) and distraction (none, visual, or auditory) on the individual driving measures revealed a significant main effect of distracter condition on two of the measures: overall time to complete the course (F(2,208)=4.4, P=.01) and number of signs recognized (F(2,208)=30.1, P<.001). The effect of distracter condition was not significant for any of the other driving measures, including cone gap perception and hazards hit.

In terms of time to complete the course, participants took longer to complete the course under the visual distracter condition than under the no-distracter or the auditory distracter conditions. The auditory and no-distracter conditions did not differ in terms of time to complete the course. In terms of signs read (Figure 2), participants correctly perceived a greater number of road signs under the no-distracter condition, less under the visual condition, and least overall under the auditory condition. All pairwise differences of this main effect were significant. There was also a significant interaction between hearing function and distraction in terms of the effect on sign recognition (F(2,208)=4, P=.02). In both groups, after controlling for age, the auditory and visual distracters resulted in poorer performance than the no-distracter condition, but the two distracter conditions did not differ significantly, although there was a marginally significant difference between the auditory and visual distracter conditions in the hearing-impaired group (P=.08).

Figure 2.

Mean number of road signs correctly recognized under each condition as a function of hearing status. Error bars are ± 1 standard error.

To establish whether performance on the distracter tasks might have partly influenced the above results, the proportions of distracter sums missed and of those answered incorrectly were further analyzed. A 2 × 2 mixed ANOVA with the factors of hearing (normal to mild impairment or moderate to severe) and distraction (visual or auditory) on each of these measures revealed no significant main effects of hearing function or distraction and no significant interaction between the factors, indicating that the modality of distracter presentation (auditory or visual) did not affect engagement with the task. Overall, participants answered 67% of all sums correctly.

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