The Role of Envelope Waveform, Adaptation, and Attacks in Binaural Perception

The human binaural system is capable of using interaural temporal disparities in the fine structure and the envelope of sounds. At high frequencies, the lack of phase-locking to the fine structure restricts the use of interaural timing disparities to envelope cues only. However, it is still unclear which specific envelope waveform features ranging from “classical” onsets (and offsets) to periodic variations such as sinusoidal amplitude modulations play a role as dominant cues. Moreover, a major drawback of these classic features is that a variation of parameters such as overall level, bandwidth, and modulation depth or modulation rate necessarily cause a covariation of “secondary” parameters such as, e.g., attack and decay times, steepness, pause, and hold durations (off-/on-times). Here, psychophysical measurements and auditory model predictions to assess the role of these secondary parameters are presented. Just noticeable differences in the interaural time difference were measured for amplitude-modulated 4-kHz tones with systematic modifications of the envelope. The results indicate that the attack times and the pause times prior to the attack are the most important features. A model including neuronal adaptation prior to the binaural stage is suggested. The model was also tested with the dichotic pip trains from the concurrent study by Siveke et al. presented at this ISH.