The effect of presentation level on memory performance

A loss of speech intelligibility at high presentation levels is called rollover. It is a phenomenon that increases in prevalence as people age. Whether the adverse effect of high presentation levels extends to processes subsequent to speech intelligibility, such as memory, is unknown. The present study examined this question on the basis of the previous finding that older but not younger adults showed memory impairment when acoustically distorted words were presented at 50 dB SL compared with an undistorted baseline presented at 65 dB SPL. One question investigated in the present study was whether a presentation level of 50 dB SL put older listeners at the cusp of rollover and whether this subsequently impaired memory. Moreover, we wanted to know whether and at what level it was possible to induce a similar impairment in younger listeners.

We used a paired-associate memory paradigm in which five word pairs per list were presented at a rate of 4 secs per word pair. After each list, the first word of one of the pairs was presented again and the listener was asked to recall the second word. Over the course of the experiment, all list positions were tested an equal number of times. The word pairs, which were acoustically distorted using a jittering algorithm, were presented at 40 dB SL to all younger and older participants and just below an uncomfortably loud level for younger listeners only. Intelligibility of the distorted words was equated across age groups for each presentation level. The effect of presentation level on memory performance was investigated and compared with data of a previous study that used the same design but presented the distorted and undistorted words at 50 dB SL to both age groups. A total of 58 younger and 24 older adults were tested in two experiments.

The results showed that for older adults, memory performance for distorted words was decreased in all list positions at a presentation level of 50 dB SL compared with 40 dB SL and an undistorted 65 dB SPL baseline. This effect did not occur for younger listeners. However, when younger adults were tested at a very high presentation level, they showed the same memory decrease compared with the baseline as older adults showed for 50 dB SL.

A high presentation level of distorted words can adversely affect memory even after intelligibility is equated for. Moreover, older listeners are affected at lower presentation levels. Hence, the choice of sound level, particularly for older listeners, is important and may affect their level of cognitive performance beyond its effects on intelligibility. Higher presentation levels may not always lead to better performance when the task involves recall of words previously heard.