Multiplexed auditory synchronization: Measuring distraction in listeners with normal hearing and with tinnitus

Abstract

Despite numerous sounds presented to our ears, people typically want to choose to listen to only one. Some unwanted sounds can be distracting and harder to suppress while others are just background noise. Along with environmental sources of sound, individuals with tinnitus have an additional competitor: an unflagging auditory percept with no external generator. For some individuals with tinnitus, this phantom sound impinges on them constantly; for others, the phantom fades harmlessly into the background unless they attend to it. The difference in how these groups experience tinnitus may be related to their abilities to suppress distracting sounds more generally. To test this hypothesis, we developed a novel paradigm for measuring behavioral and neurophysiological measures sensitive to the level of distraction provided by competing sounds. Participants are presented with a target stimulus organized around nested timescales, including temporal fine structure (~500 Hz), envelope (~25-80 Hz), envelope changes (~7 Hz), and embedded context (~0.5 Hz). EEG is recorded to capture synchronization to the features across these timescales as participants make perceptual judgments about the embedded context. These target stimuli are presented alongside two different types of distractors—melodic and noise distractors—which share low-level acoustic features but differ in the amount of distraction they produce. Normal hearing participants are more distracted by the melodic distractors than the noise distractors. While the inclusion of the distractor reduces synchronization across all timescales, only the slowest synchronization to envelope changes, the envelope change following response (ECFR), is sensitive to the level of distraction. The ECFR is reduced when the target is paired with the melodic distractor compared to the noise distractor and is also reduced when participants make errors in perceptual judgment about the target stimulus. Results in participants with tinnitus are in line with results from participants with normal hearing. When behavioral and ECFR results are compared between a group with lower tinnitus burden and a group with greater tinnitus burden, the groups do not differ. Our novel paradigm simultaneously provides information about synchronization to up to 9 different features of auditory stimuli at nested timescales. This paradigm has yielded the ECFR, a newly described synchronization measure that is sensitive to the level of auditory distraction. Such a measure may prove useful in a variety of populations who have difficulty suppressing awareness of unwanted sounds. In participants with tinnitus, this measure was not associated with the level of tinnitus burden, suggesting that suppression of externally presented distractors and internally generated phantom sounds utilize different resources.