Complex broadband sounds are decomposed by the auditory filters into a series of relatively narrowband signals, each of which can be considered as a slowly varying envelope (E) superimposed on a more rapid temporal fine structure (TFS). Both E and TFS information are represented in the timing of neural discharges, although TFS information as defined here depends on phase locking to individual cycles of the stimulus waveform. This paper reviews the role played by TFS in masking, pitch perception, and speech perception and concludes that cues derived from TFS play an important role for all three. TFS may be especially important for the ability to “listen in the dips” of fluctuating background sounds when detecting nonspeech and speech signals. Evidence is reviewed suggesting that cochlear hearing loss reduces the ability to use TFS cues. The perceptual consequences of this, and reasons why it may happen, are discussed.

A sequence of sounds may be heard as coming from a single source (called fusion or coherence) or from two or more sources (called fission or stream segregation). Each perceived source is called a ‘stream’. When the differences between successive sounds are very large, fission nearly always occurs, whereas when the differences are very small, fusion nearly always occurs. When the differences are intermediate in size, the percept often ‘flips’ between one stream and multiple streams, a property called ‘bistability’. The flips do not generally occur regularly in time. The tendency to hear two streams builds up over time, but can be partially or completely reset by a sudden change in the properties of the sequence or by switches in attention. Stream formation depends partly on the extent to which successive sounds excite different ‘channels’ in the peripheral auditory system. However, other factors can play a strong role; multiple streams may be heard when successive sounds are presented to the same ear and have essentially identical excitation patterns in the cochlea. Differences between successive sounds in temporal envelope, fundamental frequency, phase spectrum and lateralization can all induce a percept of multiple streams. Regularities in the temporal pattern of elements within a stream can help in stabilizing that stream.

This special issue presents research concerning multistable perception in different sensory modalities. Multistability occurs when a single physical stimulus produces alternations between different subjective percepts. Multistability was first described for vision, where it occurs, for example, when different stimuli are presented to the two eyes or for certain ambiguous figures. It has since been described for other sensory modalities, including audition, touch and olfaction. The key features of multistability are: (i) stimuli have more than one plausible perceptual organization; (ii) these organizations are not compatible with each other. We argue here that most if not all cases of multistability are based on competition in selecting and binding stimulus information. Binding refers to the process whereby the different attributes of objects in the environment, as represented in the sensory array, are bound together within our perceptual systems, to provide a coherent interpretation of the world around us. We argue that multistability can be used as a method for studying binding processes within and across sensory modalities. We emphasize this theme while presenting an outline of the papers in this issue. We end with some thoughts about open directions and avenues for further research.

A survey of data on the perception of binaurally presented sounds indicates that loudness summation across ears is less than perfect; a diotic sound is less than twice as loud as the same sound presented monaurally. The loudness model proposed by Moore et al. [J. Audio Eng. Soc. 45, 224–240 (1997)] determines the loudness of binaural stimuli by a simple summation of loudness across ears. It is described here how the model can be modified so as to give more accurate predictions of the loudness of binaurally presented sounds, including cases where the sounds at the two ears differ in level, frequency or both. The modification is based on the idea that there are inhibitory interactions between the internal representations of the signals at the two ears, such that a signal at the left ear inhibits (reduces) the loudness evoked by a signal at the right ear, and vice versa. The inhibition is assumed to spread across frequency channels. The modified model gives reasonably accurate predictions of a variety of data on the loudness of binaural stimuli, including data obtained using loudness scaling and loudness matching procedures.

Objectives: The aims were as follows: (1) to explore patterns of uncomfortable loudness levels (ULLs) across frequency and their associated factors for patients with tinnitus and hyperacusis, and (2) to re-evaluate the criteria for diagnosing hyperacusis based on ULLs and scores for the Hyperacusis Questionnaire (HQ). Design: This was a retrospective cross-sectional study. Study sample: 573 consecutive patients for whom ULLs had been measured were included. Results: A good correspondence between the diagnosis of hyperacusis based on the across-frequency average ULL for the ear with the lowest ULLs (ULLmin) and hyperacusis handicap based on HQ scores was obtained with cut-off values of ULLmin ≤77 dB HL and HQ score ≥ 22. A regression model showed significant relationships between ULLmin and the score on the HQ and age. The mean HQ score for patients with a large interaural asymmetry in ULLs was significantly higher than for the remainder. Hyperacusis handicap was associated with strong across-frequency variations in ULLs. Conclusions: Appropriate cut-off values for diagnosing hyperacusis are ULLmin ≤77 dB HL and HQ score ≥22. Large interaural asymmetry and large across-frequency variations in ULLs are associated with higher HQ scores.