Auditory Object Formation Research Articles

Comodulation masking release and auditory grouping

The detectability of a pure-tone signal masked by a band of noise centered on the signal can be improved by the addition of flanking noise bands, provided that the temporal envelopes of the flanking bands are correlated with that of the on-signal band. This phenomenon is referred to as comodulation masking release (CMR). The present study examined CMR in conditions in which some flanking noise bands were comodulated with the on-signal band, but other flanking bands (termed "deviant" bands) were not. Past research has indicated that CMR is often substantially reduced when deviant bands are present at spectral locations close to the signal frequency. An investigation was undertaken to determine whether the disruptive effects of such bands could be reduced by factors related to auditory grouping. The signal frequency was 100 Hz. In one condition, only 20-Hz-wide comodulated bands, centered on 400, 600, 800, 1000, 1200, 1400, and 1600 Hz, were present. The CMR for this condition, referenced to threshold for the on-signal band only, was approximately 15 dB. In a second condition, two deviant bands were added at 900 and 1100 Hz; their presence reduced the CMR to only 3-4 dB. The number of deviant bands was then increased progressively, from two to eight bands. Deviant bands either shared a common envelope (codeviant), or had unique envelopes (multideviant). The number of bands that were comodulated with the on-signal band was held constant at six.(ABSTRACT TRUNCATED AT 250 WORDS)

Onset coding of spatial information in trains of identical transients

In a study of the effects of onsets in lateralizing bursts of noise, Tobias and Schubert [J. Acoust. Soc. Am. 31, 1595–1605 (1959)] demonstrated that, depending on the duration of the ongoing noise burst, it takes anywhere between 4 to 35 times as much onset interaural time disparity to offset ongoing disparities. They, therefore, demonstrated that onsets do not necessarily provide the major cue to auditory localization. In the present study, onset and ongoing information in a lateralization paradigm is set in spatial conflict to determine the amount of onset interaural difference of time (IDT) necessary to offset ongoing IDTs of transient trains of various durations. The major difference between this study and the Tobias and Schubert study was that this study used identical transients [e.g., interclick interval (ICI) = 1.5 to 2 ms corresponding to a 500‐ to 750‐Hz tone] and not noise bursts. Unlike the Tobias and Schubert study, it was found in this study that a single dichotic click could easily lateralize a contralateral transient train of up to 200 clicks; producing the sensation of a tone lateralized to the position of the initial event. Various ICIs and ongoing durations were tested. In such a context, the precedence effect, the Franssen illusion, and the formation of auditory objects will be discussed. [Work supported by NSE and NIH.]

The role of auditory object formation in sentence perception

Previous work has demonstrated that amplitude‐modulated time‐varying sinusoidal (AM‐TVS) replicas of natural sentences were more intelligible than simple time‐varying sinusoidal (TVS) sentences [T. D. Carrell, J. Acoust. Soc. Am. Suppl. 1 84, S158 (1988)]. The goal of the experiments reported here was to determine the cause of this increased intelligibility. One potential explanation was based on the fact that AMTVS sentences were rated more natural (i.e., more humanlike) than TVS sentences. This increased naturalness might have increased the probability that speech‐specific analysis was brought to bear in decoding the incoming message. The second potential explanation was based on the idea that the comodulation of the three component tones of a TVS sentence might cause them to be grouped together as an auditory object for further processing. It has been suggested that “…amplitude modulation helps form auditory objects from complex sound fields” [W. A. Yost and S. Sheft, J. Acoust. Soc. Am. 85, 848–857 (1989)]. Evidence will be presented in favor of the second explanation. Specifically, the increase in intelligibility will be shown to be related to the comodulation of the three component tones and possibly to the mechanism underlying comodulation masking release (CMR). These findings suggest that the comodulation of the three tones comprising a TVS sentence create an auditory object and that auditory object formation is important in fluent speech understanding.