The purpose of this pilot study is to understand how memory changes with aging and if failures of working memory during rapid sound processing may account for some of the speech perception difficulties reported by older Veteran listeners especially those with hearing loss. A period of processing interference (and limitation) has been identified during rapid auditory or visual processing, called the attentional blink (AB). Specifically, when subjects are asked to report on two targeted events embedded in a rapid stream of distractor events, the ability to report on the second target is diminished when it occurs at an interval of approximately 200-400ms following the first target, as if the person had blinked. This has been identified as a failure of working memory consolidation and is robust during both visual and auditory processing (Arnell, 2005). Much is known about how auditory AB affects young normal hearing listeners but little is known of its effect on older listeners or listeners with hearing loss. Since cognition and memory failures are common adjuncts of aging, a lengthened period of processing interference is very likely to be present among older listeners. This is important because speech is rapid and older listeners often report difficulty in complex auditory environments. Further, older listeners, who are more likely to have hearing loss, continue to report more problems hearing in noisy environments even with their hearing aids optimally functional. The presence of a prolonged period of processing interference in the auditory system could account for some of these complaints and, if more completely understood, could be remediated. Experiments used in this project are similar to published auditory AB studies (Vachon and Tremblay, 2005). Up to 72 subjects, ages 18-30 and 60-75 years will be invited to participate. Subjects will undergo a complete audiological evaluated done to assign them into one of four groups of 15 subjects each. Groups will be composed of young subjects with normal hearing (YNH), young subjects with no more than moderate hearing impairment (YHI), older subjects with normal hearing (ONH) and older subjects with no more than moderate hearing impairment (OHI). Each subject will be asked to listen to between 18 and 26 non-overlapping tones each 30ms in duration followed by a 60ms silent interval. Specifically, 26 distractor tones (between 452 and 3462 Hz) will be heard. T1 will be a 5000 Hz pure tone and T2 will be a complex tone composed of log-related frequencies (600, 775, 1002, 1295, 1674 Hz). The presentation rate of the tone stream will be 11.1/second (90ms stimulus onset asynchrony). Sequences could contain (in equal probability) a) no target, b) T1 only, c) T2 only or d) both targets. When T1 is presented it will occur as item 7-15, randomly assigned and, on no-T2 trials, is followed by 10 tones. When T2 is presented it could occupy any of eight post-T1 positions (lag 1 to 8) randomly selected or, when absent, is replaced by a distractor tone. At the end of each stream, the subject will be required to make an untimed judgment about whether the stream contained T1 (yes/no) and T2 (yes/no). 550 judgments will be obtained in 2 hours of testing. This project is self-paced. The hypothesized findings are that young listeners with or without hearing impairment will have more difficulty reporting on T2 when it follows T1 by approximately 200-400ms than at any other interval, consistent with a standard auditory AB. However, older listeners without hearing impairment will demonstrate a more prolonged period of interference (>400ms) with slightly poorer performance overall while older listeners with hearing impairment will have an even longer lasting period of processing interference and overall larger deficit (poorer performance) suggesting that increasing age and hearing impairment combine to increase the auditory AB for these participants. These results would provide a much-needed explanation of the ways in which rapid processing (precisely what speech is) is degraded by hearing impairment, aging, and a combination of the two.
Hearing loss is one of the most common health concerns affecting 1 in 3 Americans over 60 years of age rising to 1 in 2 for those over 85 years old. The VA issued nearly 476,000 hearing aids in 2009 at a cost of over $195.5M, reducing the impact that hearing impairment adds to social and emotional isolation. Contributions to hearing abilities provided by cognitive and memory processes are universally recognized as essential to adequate speech communication, but these processes are not well understood. Cognitive limitations in the ability to rapidly process sequential sounds occur with all listeners but may have more impact on older Veterans with and without hearing impairment. This is important since speech is rapid and sequential. If this processing limitation can be characterized more completely, it could eventually guide the development of real- world relevant tests and therapies, thereby extending the benefits of hearing aids for all Veterans.
