On the “time image” in lateralization

Abstract

Lateralization of low‐frequency waveforms is based on interaural time delays and intensity differences. To a large extent, time and intensity are tradable, i.e., a shift of a lateralized image due to a variation of time delay can be neutralized by an appropriate variation of intensity, and vice versa (“time‐intensity trading”). Several experimental results have been reported which are difficult to reconcile with complete trading [e.g., Whitworth and Jeffress, J. Acoust. Soc. Am. 33, 925–929 (1961)]. This had led to the notion of a “time image” and a (separate) “intensity image.” The latter obeys time‐intensity trading, whereas the first does not. As both images appear together in a lateralization experiment with conventional stimuli, it is difficult to separate them introspectively. This has caused many controversies in the literature. Here, we report the existence of at least one class of stimuli that evoke the time image only, and that are insensitive to intensity differences. These signals essentially are dichotically presented white noise, with a conventional (frequency‐independent) interaural time delay τ and, in addition, an interaural 2π phase shift in one (or more) small frequency band(s) below 1500 Hz. Such signals evoke dichotic pitch images with a position that only depends on τ. Results will be reported and discussed in the context of current theories on binaural interaction.