Many older individuals seeking help from an audiologist have a sloping sensorineural hearing loss. This type of hearing loss will often become apparent to the patient due to decreased speech understanding in noisy environments. The problem of speech understanding, particularly in noise, is twofold. There is the obvious issue of reduced audibility of the signal in the high frequencies, where the listener’s hearing loss is typically most severe, as well as the interfering effects of the competing stimulus. Due to the particularly deleterious effects of background noise for older hearing-impaired (OHI) listeners relative to young normal-hearing (YNH) listeners (Frisina & Frisina, 1997
; Gordon-Salant & Fitzgibbons, 1995
), it is often desirable to improve the signal-to-noise ratio (SNR) for older adults. Hearing aids have been an effective means for improving the audibility of the speech signal but have been less successful at improving the SNR sufficiently. Technologies such as directional microphones and noise-reduction algorithms, designed to improve the acoustical SNR, continue to have promise. Another approach that might also provide benefit, however, is to train the listener to make better use of the existing SNR.
Research in auditory training has a long history, with several key studies conducted in the 1970s and 1980s (Rubinstein & Boothroyd, 1987
; Sweetow & Palmer, 2005
; Walden, Erdman, Montgomery, Schwartz, & Prosek, 1981
; Walden, Prosek, Montgomery, Scherr, & Jones, 1977
). As will be discussed below, results of past studies dealing with both auditory and visual (i.e., lip-reading) training were encouraging (Walden et al., 1977
). However, technical limitations at the time may have restricted their utility. Although some of these early results were promising, showing improved sentence recognition due to auditory or visual consonant training, the rehabilitation programs required a patient to return to the clinic for several hours over an extended time period. Such programs are difficult to justify from a cost-benefit analysis. Patients may not be willing to return numerous times to a clinic for results that are perceived as small for the time expended.
Still, patients may be willing to take part in self-paced training that could be completed at home. The prospects for a home-based training system have given rise to a renewed interest in auditory training, due mainly to the ease with which a training protocol could be administered using personal computers or multi-media players. Even with these advances in available technologies, few objective data exist regarding the benefits of an auditory training program, whether based on consonants, words, or running speech (Sweetow & Palmer, 2005
Walden et al. (1981)
focused on consonant training as a means to improve a listener’s ability to comprehend sentences. Their rationale for consonant training was that improved consonant recognition within a sentence combined with the increased context of meaningful sentences helps to decrease the overall options available from which the listener can choose (Walden et al., 1981
). They trained three groups of adult males on auditory or visual consonant recognition for approximately 7 hr. All of the participants were enrolled in a standard 2-week inpatient group rehabilitation program, with two groups receiving either extra auditory or extra visual consonant recognition training. Although all three groups improved significantly pre- to postrehabilitation, the groups receiving the extra auditory or visual training improved significantly over the control group. When examining the training effect on sentence recognition, they found a moderate correlation between improvements in consonant recognition and improvements in sentence recognition. Others have examined auditory training based on high-context materials, such as sentences or phrases (Blamey & Alcantara, 1994
; Montgomery, Walden, Schwartz, & Prosek, 1984
; Rubinstein & Boothroyd, 1987
). Rubinstein and Boothroyd (1987)
, for example, trained one group of listeners on both consonant recognition and sentence perception, whereas another group of listeners received training only on sentence perception. Although the authors did find a significant but small improvement posttraining in speech-recognition performance (about 5%, averaged across both groups), they did not find any significant difference in performance between the two training paradigms (sentences alone or consonants plus sentences).
In recent years, the Audiology Research Laboratory (ARL) at Indiana University has been investigating various word-based training programs. Variables investigated to date include the number and type of words used during training, the length of the training program, and the number of talkers used for training (Burk & Humes, 2007
; Burk et al., 2006
). Although the overall training time and stimuli have varied across experiments, there have been several consistent outcomes in these studies. First, both YNH and OHI listeners are able to effectively improve their word recognition performance on trained sets of words ranging in size from 75 to 150 items. With approximately 3.5 hr of training, YNH listeners were able to significantly improve their open- and closed-set word recognition in noise (by 52.5% and 16.7%, respectively) for a set of 75 phonetically balanced monosyllabic CVC AB words (Boothroyd, 1995
) presented by 1 female talker. Once listeners were trained on the set of 75 words, their improved performance was maintained when listening to the same words presented by 3 unfamiliar talkers (Burk et al., 2006
). Although large improvements were shown on the trained set of words regardless of the talker, there was much less (although significant) improvement for a novel set of 75 AB words (11.1% and 9.2% for open- and closed-set responses, respectively) and no improvement for running speech. Replicating the measurements with OHI listeners while listening to amplified speech simulating a well-fit hearing aid showed improvements in performance almost identical to that of the YNH listeners. These data point out the ability to improve word recognition in noise for OHI listeners on a limited set of words, yet changes were obviously necessary if any generalization to running speech outside the laboratory was to occur. Based on this first study with AB words, there were several questions needing further investigation: (a) Would a different set of words provide greater generalization to untrained words and/or running speech? (b) would training using several talkers, rather than 1, provide greater generalization to untrained materials? and (c) would increasing the amount of training have an effect on generalization to novel words and sentences?
Several of the above issues were investigated by Burk and Humes (2007)
by examining the benefits of a word-based auditory training protocol based on lexically hard words within a group of YNH listeners. Lexically hard words
were defined, in accordance with the neighborhood activation model (NAM; Luce & Pisoni, 1998
), as words that are relatively rare in frequency of occurrence and have many similar sounding or “neighboring” words. It was conjectured that if listeners could improve their recognition of lexically hard words in noise through training, they might also improve their recognition of untrained lexically easy words. Because everyday communication consists of many “easy” words, overall generalization to both novel “easy” words and running speech might improve. The results were once again similar to those found when examining training improvements with AB words—that is, listeners improved significantly on the trained set of 75 lexically hard words (50.9% and 19.7% for open- and closed-set items, respectively), while improving to a much smaller degree on the untrained lexically easy words (approximately 6%–13%). Increasing the training time from approximately 5 hr to approximately 15 hr and training with multiple talkers (n
= 6) had little effect on the overall improvements in word recognition but did seem to increase the listeners’ abilities to generalize the word-based training to running speech. None of the listeners in the short-term training group improved their hard keyword identification within a novel set of sentences, compared with 50% of those in the long-term training group. Although the same sentences were not repeated at the end of the short-term training, 75% of the listeners improved their hard keyword identification beyond the 95% critical difference when listening to the same sentences presented prior to training. Because the increased training time did seem to affect overall generalization to running speech, the next step was to replicate the long-term training protocol using lexically hard words with OHI listeners. For OHI listeners, it was unknown whether the extended protocol discussed in Burk and Humes (2007)
would provide similar or potentially better results. The following experiment examines the ability of OHI listeners to improve their word recognition in noise for lexically hard words and whether such improvements, if they occur, generalize to novel words and sentences. Of further interest was the effect that training on a new set of words has relative to retention of previously trained materials—that is, does learning a second set of 50–75 words impact the retention of the training benefits for the initial set of 50–75 words?
As will be discussed below, training the OHI listeners on 75 lexically hard words did not generalize to a set of 75 lexically easy words. As a result, the training was extended to include several sessions with lexically easy words. The impact of learning 75 additional lexically easy words on the retention of the initially trained set of 75 (lexically hard) words was investigated. Small decreases in performance for the original set of 75 words were observed following training with the new set of 75 words. Therefore, additional measurements were completed to determine whether this was simply due to forgetting the materials over time or due to some form of interference of the new set of words with those learned originally.