The Zwicker tone as a model to investigate auditory processing and tinnitus: a scoping review

The Zwicker tone (ZT) is an auditory illusion experienced by about 50% of the population immediately following a presentation of notched noise (NN). It is a faint, quickly decaying pure tone, the frequency of which falls within the range of the notch. Interestingly, although only half of the general population can perceive ZTs, one study has shown that almost everyone with tinnitus can perceive them. If there is this strong association, the ZT is an easily controllable paradigm that can be employed in the laboratory setting to explore tinnitus related concepts and better interrogate underlying neural mechanisms. This scoping review aimed to catalogue what is currently known about the ZT, and what can be said about its potential relationship with tinnitus. Through a systematic search of the literature, 16 records were identified for inclusion; all reported investigations of ZTs arising after spectrally contrasted in adults who had either normal hearing or tinnitus with/without hearing loss. The proportion of a given sample who were able to hear ZTs varied across studies, from 30 to 100%. The probability of hearing a ZT is modulated by a range of parameters, including: stimulus type (e.g., low-pass versus notched noise), notch centre frequency/width, and stimulus duration. Although these factors modulate the probability of perceiving a ZT, the idea that ZT perception is largely binary is also somewhat supported by individual data. In addition, some variables alter the quality of the percept, e.g., louder stimuli induce a higher pitched ZT. Despite several records drawing comparison between ZT and tinnitus, only one study has thus far investigated ZT in people with tinnitus, albeit finding a highly significant difference in responder rate in tinnitus versus control participants. Several methodological issues potentially affecting responder rate were identified, however, which warrants replication and extension, with careful control. We conclude that (1) Zwicker tone perception relies on a range of factors both stimulus and cognitive related, (2) Further work is required to map the parameters that induce the Zwicker tone and (3) While obvious similarities exist linking tinnitus and Zwicker tones more work is needed to prove the link between the two.