Relationship between Memory Load and Listening Demands in Age-Related Hearing Impairment

Abstract

Age-related hearing loss has been associated with increased recruitment of frontal brain areas during speech perception to compensate for the decline in auditory input. This additional recruitment may bind resources otherwise needed for understanding speech. However, it is unknown how increased demands on listening interact with increasing cognitive demands when processing speech in age-related hearing loss. The current study used a full-sentence working memory task manipulating demands on working memory and listening and studied untreated mild to moderate hard of hearing (n = 20) and normal-hearing age-matched participants (n = 19) with functional MRI. On the behavioral level, we found a significant interaction of memory load and listening condition; this was, however, similar for both groups. Under low, but not high memory load, listening condition significantly influenced task performance. Similarly, under easy but not difficult listening conditions, memory load had a significant effect on task performance. On the neural level, as measured by the BOLD response, we found increased responses under high compared to low memory load conditions in the left supramarginal gyrus, left middle frontal gyrus, and left supplementary motor cortex regardless of hearing ability. Furthermore, we found increased responses in the bilateral superior temporal gyri under easy compared to difficult listening conditions. We found no group differences nor interactions of group with memory load or listening condition. This suggests that memory load and listening condition interacted on a behavioral level, however, only the increased memory load was reflected in increased BOLD responses in frontal and parietal brain regions. Hence, when evaluating listening abilities in elderly participants, memory load should be considered as it might interfere with the assessed performance. We could not find any further evidence that BOLD responses for the different memory and listening conditions are affected by mild to moderate age-related hearing loss.

Figure 1

Pure tone audiometry for hard of hearing (red) and normal-hearing (blue) participants. Thin colored lines represent mean over both ears of a participant, and thick colored lines represent the group mean. The black line indicates 30 dB threshold for hearing impairment.

Figure 2

Verbal working memory task. In each trial, two consecutive sentences separated by the presentation of a fixation cross were presented. Beforehand, it was indicated whether participants were supposed to perform task 1, which corresponds to (a) the low memory load condition (i.e., indicate whether a specific word occurred in the last sentence), or task 2, which corresponds to (b) the high memory load condition (i.e., indicate whether the noun/verb was the same in both sentences). Both memory load conditions were presented either at the 80% speech reception threshold (difficult listening condition) or at the 80% threshold +5 dB (easy listening condition).

Figure 3

The interaction effect of listening and memory load conditions in (a) hard of hearing and (b) normal-hearing participants. Error bars denote standard error of the mean.

Figure 4

Difficulty ratings of the task conditions. Participants rated each task condition on a scale from 1-4 with 4 being the most difficult. Error bars depict the standard deviation from the mean.

Figure 5

Main effect of the memory load condition. Peak activation sites include the left supramarginal gyrus, the left middle frontal gyrus, and the left supplementary motor cortex (increased BOLD activity under high compared to low memory load, red) as well as left and right lingual gyri and left and right middle occipital gyri (increased BOLD activity under low compared to high memory load, blue). (a) Left hemisphere view, (b) right hemisphere view, (c) top view (left hemisphere on the left side), and (d) bottom view (left hemisphere on the right side) (p < 0.05, FWE corrected on the cluster level). List of peaks can be found in Table 3.

Figure 6

Neural response as measured by the BOLD response for the main effect of the listening condition. Peak activation sites include the left and right superior temporal gyri under easy compared to difficult listening conditions (blue). There are no significant peaks when comparing difficult to easy listening conditions. (a) Left hemisphere view and (b) right hemisphere view (p < 0.05, FWE corrected on the cluster level). List of peaks can be found in Table 3.