The contributions of audibility and cognitive factors to the benefit provided by amplified speech to older adults

In this review of recent studies from our laboratory at Indiana University, it is argued that audibility is the primary contributor to the speech-understanding difficulties of older adults in unaided listening, but that other factors, especially cognitive factors, emerge when the role of audibility has been minimized. The advantages and disadvantages of three basic approaches used in our laboratory to minimize the role of audibility are examined. The first of these made use of clinical fits of personal amplification devices, but generally failed to make the aided speech stimuli sufficiently audible for the listeners. As a result, hearing loss remained the predominant predictor of performance. The second approach made use of raised and spectrally shaped stimuli with identical shaping applied for all listeners. The third approach used spectrally shaped speech that ensured audibility (at least 10 dB sensation level) of the stimuli up to at least 4000 Hz for each individual listener. With few exceptions, the importance of cognitive factors was revealed once the speech stimuli were made sufficiently audible.