The effects of task difficulty, background noise and noise reduction on recall

A review of auditory processing and cognitive change during normal ageing, and the implications for setting hearing aids for older adults

Throughout our adult lives there is a decline in peripheral hearing, auditory processing and elements of cognition that support listening ability. Audiometry provides no information about the status of auditory processing and cognition, and older adults often struggle with complex listening situations, such as speech in noise perception, even if their peripheral hearing appears normal. Hearing aids can address some aspects of peripheral hearing impairment and improve signal-to-noise ratios. However, they cannot directly enhance central processes and may introduce distortion to sound that might act to undermine listening ability. This review paper highlights the need to consider the distortion introduced by hearing aids, specifically when considering normally-ageing older adults. We focus on patients with age-related hearing loss because they represent the vast majority of the population attending audiology clinics. We believe that it is important to recognize that the combination of peripheral and central, auditory and cognitive decline make older adults some of the most complex patients seen in audiology services, so they should not be treated as "standard" despite the high prevalence of age-related hearing loss. We argue that a primary concern should be to avoid hearing aid settings that introduce distortion to speech envelope cues, which is not a new concept. The primary cause of distortion is the speed and range of change to hearing aid amplification (i.e., compression). We argue that slow-acting compression should be considered as a default for some users and that other advanced features should be reconsidered as they may also introduce distortion that some users may not be able to tolerate. We discuss how this can be incorporated into a pragmatic approach to hearing aid fitting that does not require increased loading on audiology services.

Time-specific Components of Pupil Responses Reveal Alternations in Effort Allocation Caused by Memory Task Demands During Speech Identification in Noise

Daily communication may be effortful due to poor acoustic quality. In addition, memory demands can induce effort, especially for long or complex sentences. In the current study, we tested the impact of memory task demands and speech-to-noise ratio on the time-specific components of effort allocation during speech identification in noise. Thirty normally hearing adults (15 females, mean age 42.2 years) participated. In an established auditory memory test, listeners had to listen to a list of seven sentences in noise, and repeat the sentence-final word after presentation, and, if instructed, recall the repeated words. We tested the effects of speech-to-noise ratio (SNR; -4 dB, +1 dB) and recall (Recall; Yes, No), on the time-specific components of pupil responses, trial baseline pupil size, and their dynamics (change) along the list. We found three components in the pupil responses (early, middle, and late). While the additional memory task (recall versus no recall) lowered all components' values, SNR (-4 dB versus +1 dB SNR) increased the middle and late component values. Increasing memory demands (Recall) progressively increased trial baseline and steepened decrease of the late component's values. Trial baseline increased most steeply in the condition of +1 dB SNR with recall. The findings suggest that adding a recall to the auditory task alters effort allocation for listening. Listeners are dynamically re-allocating effort from listening to memorizing under changing memory and acoustic demands. The pupil baseline and the time-specific components of pupil responses provide a comprehensive picture of the interplay of SNR and recall on effort.

A decrease in physiological arousal accompanied by stable behavioral performance reflects task habituation

Despite the evidence of a positive relationship between task demands and listening effort, the Framework for Understanding Effortful Listening (FUEL) highlights the important role of arousal on an individual’s choice to engage in challenging listening tasks. Previous studies have interpreted physiological responses in conjunction with behavioral responses as markers of task engagement. The aim of the current study was to investigate the effect of potential changes in physiological arousal, indexed by the pupil baseline, on task engagement over the course of an auditory recall test. Furthermore, the aim was to investigate whether working memory (WM) capacity and the signal-to-noise ratio (SNR) at which the test was conducted had an effect on changes in arousal. Twenty-one adult hearing aid users with mild to moderately severe symmetrical sensorineural hearing loss were included. The pupil baseline was measured during the Sentence-final Word Identification and Recall (SWIR) test, which was administered in a background noise composed of sixteen talkers. The Reading Span (RS) test was used as a measure of WM capacity. The findings showed that the pupil baseline decreased over the course of the SWIR test. However, recall performance remained stable, indicating that the participants maintained the necessary engagement level required to perform the task. These findings were interpreted as a decline in arousal as a result of task habituation. There was no effect of WM capacity or individual SNR level on the change in pupil baseline over time. A significant interaction was found between WM capacity and SNR level on the overall mean pupil baseline. Individuals with higher WM capacity exhibited an overall larger mean pupil baseline at low SNR levels compared to individuals with poorer WM capacity. This may be related to the ability of individuals with higher WM capacity to perform better than individual with poorer WM capacity in challenging listening conditions.

A Glimpse of Memory Through the Eyes: Pupillary Responses Measured During Encoding Reflect the Likelihood of Subsequent Memory Recall in an Auditory Free Recall Test

The aim of the current study was to investigate whether task-evoked pupillary responses measured during encoding, individual working memory capacity and noise reduction in hearing aids were associated with the likelihood of subsequently recalling an item in an auditory free recall test combined with pupillometry. Participants with mild to moderately severe symmetrical sensorineural hearing loss (n = 21) were included. The Sentence-final Word Identification and Recall (SWIR) test was administered in a background noise composed of sixteen talkers with noise reduction in hearing aids activated and deactivated. The task-evoked peak pupil dilation (PPD) was measured. The Reading Span (RS) test was used as a measure of individual working memory capacity. Larger PPD at a single trial level was significantly associated with higher likelihood of subsequently recalling a word, presumably reflecting the intensity of attention devoted during encoding. There was no clear evidence of a significant relationship between working memory capacity and subsequent memory recall, which may be attributed to the SWIR test and RS test being administered in different modalities, as well as differences in task characteristics. Noise reduction did not have a significant effect on subsequent memory recall. This may be due to the background noise not having a detrimental effect on attentional processing at the favorable signal-to-noise ratio levels at which the test was conducted.

The Effects of Task Difficulty Predictability and Noise Reduction on Recall Performance and Pupil Dilation Responses

OBJECTIVES

Communication requires cognitive processes which are not captured by traditional speech understanding tests. Under challenging listening situations, more working memory resources are needed to process speech, leaving fewer resources available for storage. The aim of the current study was to investigate the effect of task difficulty predictability, that is, knowing versus not knowing task difficulty in advance, and the effect of noise reduction on working memory resource allocation to processing and storage of speech heard in background noise. For this purpose, an "offline" behavioral measure, the Sentence-Final Word Identification and Recall (SWIR) test, and an "online" physiological measure, pupillometry, were combined. Moreover, the outcomes of the two measures were compared to investigate whether they reflect the same processes related to resource allocation.

DESIGN

Twenty-four experienced hearing aid users with moderate to moderately severe hearing loss participated in this study. The SWIR test and pupillometry were measured simultaneously with noise reduction in the test hearing aids activated and deactivated in a background noise composed of four-talker babble. The task of the SWIR test is to listen to lists of sentences, repeat the last word immediately after each sentence and recall the repeated words when the list is finished. The sentence baseline dilation, which is defined as the mean pupil dilation before each sentence, and task-evoked peak pupil dilation (PPD) were analyzed over the course of the lists. The task difficulty predictability was manipulated by including lists of three, five, and seven sentences. The test was conducted over two sessions, one during which the participants were informed about list length before each list (predictable task difficulty) and one during which they were not (unpredictable task difficulty).

RESULTS

The sentence baseline dilation was higher when task difficulty was unpredictable compared to predictable, except at the start of the list, where there was no difference. The PPD tended to be higher at the beginning of the list, this pattern being more prominent when task difficulty was unpredictable. Recall performance was better and sentence baseline dilation was higher when noise reduction was on, especially toward the end of longer lists. There was no effect of noise reduction on PPD.

CONCLUSIONS

Task difficulty predictability did not have an effect on resource allocation, since recall performance was similar independently of whether task difficulty was predictable or unpredictable. The higher sentence baseline dilation when task difficulty was unpredictable likely reflected a difference in the recall strategy or higher degree of task engagement/alertness or arousal. Hence, pupillometry captured processes which the SWIR test does not capture. Noise reduction frees up resources to be used for storage of speech, which was reflected in the better recall performance and larger sentence baseline dilation toward the end of the list when noise reduction was on. Thus, both measures captured different temporal aspects of the same processes related to resource allocation with noise reduction on and off.

Cognitive Hearing Science: Three Memory Systems, Two Approaches, and the Ease of Language Understanding Model

Purpose The purpose of this study was to conceptualize the subtle balancing act between language input and prediction (cognitive priming of future input) to achieve understanding of communicated content. When understanding fails, reconstructive postdiction is initiated. Three memory systems play important roles: working memory (WM), episodic long-term memory (ELTM), and semantic long-term memory (SLTM). The axiom of the Ease of Language Understanding (ELU) model is that explicit WM resources are invoked by a mismatch between language input-in the form of rapid automatic multimodal binding of phonology-and multimodal phonological and lexical representations in SLTM. However, if there is a match between rapid automatic multimodal binding of phonology output and SLTM/ELTM representations, language processing continues rapidly and implicitly. Method and Results In our first ELU approach, we focused on experimental manipulations of signal processing in hearing aids and background noise to cause a mismatch with LTM representations; both resulted in increased dependence on WM. Our second-and main approach relevant for this review article-focuses on the relative effects of age-related hearing loss on the three memory systems. According to the ELU, WM is predicted to be frequently occupied with reconstruction of what was actually heard, resulting in a relative disuse of phonological/lexical representations in the ELTM and SLTM systems. The prediction and results do not depend on test modality per se but rather on the particular memory system. This will be further discussed. Conclusions Related to the literature on ELTM decline as precursors of dementia and the fact that the risk for Alzheimer's disease increases substantially over time due to hearing loss, there is a possibility that lowered ELTM due to hearing loss and disuse may be part of the causal chain linking hearing loss and dementia. Future ELU research will focus on this possibility.