Mitchell S. Sommers

One goal of the present study was to establish whether providing younger and older adults with visual speech information (both seeing and hearing a talker compared with listening alone) would reduce listening effort for understanding speech in noise. In addition, we used an individual differences approach to assess whether changes in listening effort were related to changes in visual enhancement—the improvement in speech understanding in going from an auditory-only (A-only) to an auditory-visual condition (AV) condition. To compare word recognition in A-only and AV modalities, younger and older adults identified words in both A-only and AV conditions in the presence of six-talker babble. Listening effort was assessed using a modified version of a serial recall task. Participants heard (A-only) or saw and heard (AV) a talker producing individual words without background noise. List presentation was stopped randomly and participants were then asked to repeat the last three words that were presented. Listening effort was assessed using recall performance in the two- and three-back positions. Younger, but not older, adults exhibited reduced listening effort as indexed by greater recall in the two- and three-back positions for the AV compared with the A-only presentations. For younger, but not older adults, changes in performance from the A-only to the AV condition were moderately correlated with visual enhancement. Results are discussed within a limited-resource model of both A-only and AV speech perception.

It is evident that America, as well as the rest of the world, is getting older. Age-related hearing loss is currently the third most prevalent chronic disability faced by older adults and is consistently ranked as one of the top five factors affecting overall quality of life for persons over 65. What is perhaps less well known is that hearing loss in the slightly younger cohort, made up of people between the ages of 46 and 64, is, in absolute numbers, even more prevalent than for older adults. For example, estimates from the National Health Interview Survey suggest more baby boomers are suffering from moderate and severe hearing loss (10 million) than there are Americans with hearing impairments above the age of 65 (9 million).

The authors conducted 3 experiments that examined the effects of age and dementia of the Alzheimer's type (DAT) on phonological false memories. In addition, the study was designed to investigate the role of inhibitory control in mediating phonological false memories. In Experiment 1, both young-old and old-old participants exhibited increased susceptibility to false remembering, compared with young adults. In Experiment 2, auditory Stroop interference was used as an index of inhibitory abilities and was found to account for a significant percentage of the variance in false recollection. Experiment 3 provided converging evidence for the importance of inhibitory control in phonological false memories by demonstrating that DAT patients are more susceptible to false recall and recognition than healthy older adults. The results are discussed within the inhibitory deficit framework of cognitive aging.

Age differences in perceptual specificity for implicit auditory priming were examined in 3 experiments. All 3 experiments began with a study phase during which participants rated words based on perceptual (shallow encoding) or semantic (deep encoding) attributes. After the study phase, participants were asked to identify filtered versions of repeated and new words (implicit test) and then to make old/new recognition judgments (explicit test). In contrast to earlier findings (D. L. Schacter, B. Church, & D. M. Osowiecki, 1994), older and younger adults were equally sensitive to study-to-test changes in speaking rate (Experiment 1), fundamental frequency (Experiment 2), and voice (Experiment 3). Explicit memory, in contrast, was significantly poorer for older adults but was minimally affected by changes in surface features. Findings from the study are discussed with respect to their implications for establishing the mechanisms mediating perceptual specificity and for their importance in understanding age-related changes in implicit memory.

Two experiments were conducted to examine the importance of inhibitory abilities and semantic context to spoken word recognition in older and young adults. In Experiment 1, identification scores were obtained in 3 contexts: single words, low-predictability sentences, and high-predictability sentences. Additionally, identification performance was examined as a function of neighborhood density (number of items phonetically similar to a target word). Older adults had greater difficulty than young adults recognizing words with many neighbors (hard words). However, older adults also exhibited greater benefits as a result of adding contextual information. Individual differences in inhibitory abilities contributed significantly to recognition performance for lexically hard words but not for lexically easy words. The roles of inhibitory abilities and linguistic knowledge in explaining age-related impairments in spoken word recognition are discussed.

Four experiments were conducted to examine the effects of dementia of the Alzheimer's type (DAT) on talker normalization and lexical discrimination. Talker normalization has been proposed as the principal mechanism underlying listeners' ability to maintain perceptual constancy for speech signals. Lexical discrimination refers to the ability to distinguish individual words from phonetically similar items stored in the mental lexicon. Healthy older adults served as controls. Comparisons of controls and very mildly impaired patients with DAT revealed no significant change in either lexical discrimination or talker normalization. In contrast, individuals with more advanced DAT (mildly demented) exhibited significant declines in both abilities. The results are discussed with respect to the possible roles of general slowing and inhibitory declines as factors affecting speech perception in DAT.

Three experiments were conducted to investigate the effects of variations in talker characteristics, speaking rate, and overall amplitude on perceptual identification in normal-hearing young (NHY), normal-hearing elderly (NHE), and hearing-impaired elderly (HIE) listeners. The three dimensions were selected because variations in voice characteristics and speaking rate affect features of speech signals that are important for word recognition while overall amplitude changes do not alter stimulus parameters that have direct effects on phonetic identification. Thus, the studies were designed to examine how variations in both phonetically relevant and irrelevant stimulus dimensions affect speech processing in a number of different populations. Age differences, as indicated by greater effects of variability for the NHE compared with the NHY listeners, were observed for mixed-talker and mixed-amplitude word lists. Effects of age-related hearing impairment, as indicated by reduced scores for the HIE compared with the NHE group, were observed for variations in speaking rate and talker characteristics. Considered together, the findings suggest that age-related changes in perceptual normalization and selective attention may contribute to the reduced speech understanding that is often reported for older adults.

Three experiments were conducted within the framework of the Neighborhood Activation Model of spoken-word recognition to study how the structural organization of the mental lexicon may contribute to age-related declines in spoken-language processing. Experiment 1 showed that the number and frequency of words that are phonetically similar to a target word had differential effects on perceptual identification in older and younger adults, with older adults being particularly disadvantaged in identifying hard words (words phonetically similar to many other high-frequency words). Experiment 2 showed that age-related deficits in the ability to identify hard words remained under conditions in which performance for a set of easy words (items phonetically similar to relatively few other low-frequency words) was the same for older and younger adults. In Experiment 3, reducing the resources available for identification by changing from single to multiple talkers reduced word recognition more among older than younger adults. Diminished cognitive resources, impaired inhibitory control, and increased general slowing are discussed as explanations for the results.