Manchester Centre for Audiology and Deafness, University of Manchester, Manchester, United Kingdom.
National Institute for Health Research Nottingham Biomedical Research Centre, Nottingham University Hospital's National Health Service Trust, Nottingham, United Kingdom.
Ear Hear. 2020 Jul/Aug;41(4):907-917. doi: 10.1097/AUD.0000000000000812.
Cognitive load (CL) impairs listeners' ability to comprehend sentences, recognize words, and identify speech sounds. Recent findings suggest that this effect originates in a disruption of low-level perception of acoustic details. Here, we attempted to quantify such a disruption by measuring the effect of CL (a two-back task) on pure-tone audiometry (PTA) thresholds. We also asked whether the effect of CL on PTA was greater in older adults, on account of their reduced ability to divide cognitive resources between simultaneous tasks. To specify the mechanisms and representations underlying the interface between auditory and cognitive processes, we contrasted CL requiring visual encoding with CL requiring auditory encoding. Finally, the link between the cost of performing PTA under CL, working memory, and speech-in-noise (SiN) perception was investigated and compared between younger and older participants.
Younger and older adults (44 in each group) did a PTA test at 0.5, 1, 2, and 4 kHz pure tones under CL and no CL. CL consisted of a visual two-back task running throughout the PTA test. The two-back task involved either visual encoding of the stimuli (meaningless images) or subvocal auditory encoding (a rhyme task on written nonwords). Participants also underwent a battery of SiN tests and a working memory test (letter number sequencing).
Younger adults showed elevated PTA thresholds under CL, but only when CL involved subvocal auditory encoding. CL had no effect when it involved purely visual encoding. In contrast, older adults showed elevated thresholds under both types of CL. When present, the PTA CL cost was broadly comparable in younger and older adults (approximately 2 dB HL). The magnitude of PTA CL cost did not correlate significantly with SiN perception or working memory in either age group. In contrast, PTA alone showed strong links to both SiN and letter number sequencing in older adults.
The results show that CL can exert its effect at the level of hearing sensitivity. However, in younger adults, this effect is only found when CL involves auditory mental representations. When CL involves visual representations, it has virtually no impact on hearing thresholds. In older adults, interference is found in both conditions. The results suggest that hearing progresses from engaging primarily modality-specific cognition in early adulthood to engaging cognition in a more undifferentiated way in older age. Moreover, hearing thresholds measured under CL did not predict SiN perception more accurately than standard PTA thresholds.
认知负荷（CL）会损害听众理解句子、识别单词和识别语音的能力。最近的研究结果表明，这种影响源于对声音细节的低级感知的破坏。在这里，我们试图通过测量 CL（双任务）对纯音听阈（PTA）的影响来量化这种破坏。我们还询问了 CL 是否对老年人的 PTA 影响更大，因为他们在同时进行多项任务时，分配认知资源的能力下降。为了具体说明听觉和认知过程之间接口的机制和表示，我们对比了需要视觉编码的 CL 和需要听觉编码的 CL。最后，研究了在 CL 下执行 PTA 的成本、工作记忆和噪声中的言语感知（SiN）之间的联系，并在年轻和老年参与者之间进行了比较。
44 名年轻成年人和 44 名老年成年人分别在 CL 和无 CL 下进行 0.5、1、2 和 4 kHz 纯音 PTA 测试。CL 由整个 PTA 测试过程中的视觉双任务组成。双任务包括对刺激进行视觉编码（无意义图像）或亚语音听觉编码（书面非词的押韵任务）。参与者还接受了一系列 SiN 测试和工作记忆测试（字母数字排序）。
年轻成年人在 CL 下 PTA 阈值升高，但仅在 CL 涉及亚语音听觉编码时。当 CL 涉及纯粹的视觉编码时，CL 没有影响。相比之下，老年成年人在两种类型的 CL 下都表现出升高的阈值。当存在时，年轻和老年成年人的 PTA CL 成本大致相当（约 2 dB HL）。在两个年龄组中，PTA CL 成本的大小与 SiN 感知或工作记忆均无显著相关性。相比之下，仅 PTA 在老年人中与 SiN 和字母数字排序均有很强的相关性。
结果表明，CL 可以在听力敏感度水平上产生影响。然而，在年轻成年人中，这种影响仅在 CL 涉及听觉心理表示时才发现。当 CL 涉及视觉表示时，它对听力阈值几乎没有影响。在老年成年人中，两种情况下都存在干扰。结果表明，听力从成年早期主要依赖特定于模态的认知发展到老年时更不区分地依赖认知。此外，CL 下测量的听力阈值不能比标准 PTA 阈值更准确地预测 SiN 感知。
