Perceptual Restoration of Degraded Speech Is Preserved with Advancing Age

Abstract

Cognitive skills, such as processing speed, memory functioning, and the ability to divide attention, are known to diminish with aging. The present study shows that, despite these changes, older adults can successfully compensate for degradations in speech perception. Critically, the older participants of this study were not pre-selected for high performance on cognitive tasks, but only screened for normal hearing. We measured the compensation for speech degradation using phonemic restoration, where intelligibility of degraded speech is enhanced using top-down repair mechanisms. Linguistic knowledge, Gestalt principles of perception, and expectations based on situational and linguistic context are used to effectively fill in the inaudible masked speech portions. A positive compensation effect was previously observed only with young normal hearing people, but not with older hearing-impaired populations, leaving the question whether the lack of compensation was due to aging or due to age-related hearing problems. Older participants in the present study showed poorer intelligibility of degraded speech than the younger group, as expected from previous reports of aging effects. However, in conditions that induce top-down restoration, a robust compensation was observed. Speech perception by the older group was enhanced, and the enhancement effect was similar to that observed with the younger group. This effect was even stronger with slowed-down speech, which gives more time for cognitive processing. Based on previous research, the likely explanations for these observations are that older adults can overcome age-related cognitive deterioration by relying on linguistic skills and vocabulary that they have accumulated over their lifetime. Alternatively, or simultaneously, they may use different cerebral activation patterns or exert more mental effort. This positive finding on top-down restoration skills by the older individuals suggests that new cognitive training methods can teach older adults to effectively use compensatory mechanisms to cope with the complex listening environments of everyday life.

Effects of age and hearing loss on the intelligibility of interrupted speech

“…A remarkable and numerously replicated finding of mid twentieth-century research was that under some conditions, accurate speech perception is possible even if half of the original speech signal is periodically masked by noise or replaced by silence (Miller and Licklider, 1950;Powers and Speaks, 1973;Huggins, 1975;Powers and Wilcox, 1977;Nelson et al, 2003;Nelson and Jin, 2004;Buss et al, 2009;Jin and Nelson, 2010;Saija et al, 2014). Despite these physical constraints, listeners are able to exploit the inherent perceptual redundancies of naturally produced speech and use the remaining low-level speech cues to obtain high-level linguistic information.…”

Individual differences in top-down restoration of interrupted speech: Links to linguistic and cognitive abilities

“…Some of these manipulations involved interrupting speech stimuli with periodic silent intervals, where the listener had to reconstruct the speech stream from the remaining samples (e.g., Chatterjee et al, 2010), and some others involved filling the silent intervals with loud noise bursts, which induced continuity illusion and phonemic restoration, quantified by an increase in intelligibility of interrupted speech (e.g., Benard and Başkent, 2013). Further, to capture cognitive effects fully, such as potential effects of cognitive slowing down due to aging, slow speech rates were also included (Saija et al, 2013). As a result, a number of settings were used to measure top-down restoration, with two interruption rates (1.25, 2.50 Hz) at two speech rates (slow, normal), presented with or without filler noise, producing eight testing conditions.…”

“…During signal processing, first the speech rate was changed. For slowing down, sentences were lengthened to twice the original duration, preserving the original pitch using PRAAT software (Saija et al, 2013). The normal and slow-rate sentences were interrupted with the two interruption rates, with a duty cycle of 50%, and with 10-ms cosine-ramping on and off transitions.…”

“…For example, restoration seems to be easier with speech segments that are linked by context and linguistic rules (Sivonen et al, 2006;Verschuure and Brocaar, 1983;Wang and Humes, 2010). Linguistic skills, vocabulary, and verbal comprehension were indirectly suggested to be of importance in the perception of interrupted speech (Bashford et al, 1992;Saija et al, 2013). Training improves the intelligibility of interrupted speech, and aging can have an effect on it, both implying an involvement of the cognitive system (Benard and Başkent, 2013;Saija et al, 2013).…”

“…Linguistic skills, vocabulary, and verbal comprehension were indirectly suggested to be of importance in the perception of interrupted speech (Bashford et al, 1992;Saija et al, 2013). Training improves the intelligibility of interrupted speech, and aging can have an effect on it, both implying an involvement of the cognitive system (Benard and Başkent, 2013;Saija et al, 2013). Despite these suggestions, however, to date, no systematic study has been performed to directly and fully establish if and to what degree such association exists between linguistic and cognitive factors and the top-down restoration of interrupted speech.…”