Frequency modulation detection interference produced by asynchronous and nonsimultaneous interferers

The effect of asynchronous and nonsimultaneous interferers on detection of sinusoidal frequency modulation (FM) was compared with the effect of a sync hronous interferer. In a two-interval, two-alternative forced-choice (2I-2A FC) adaptive procedure, listeners had to detect FM with a modulation freque ncy of 15 Hz, imposed on a 1-kHz sinusoidal carrier (the target). The 200-m s target was presented either alone (baseline condition), or with an interf erer whose timing relative to the target was varied. The interferer was a 2 .3-kHz sinusoidal carrier which was also frequency modulated at a rate of 1 5 Hz. Experiment one showed that thresholds for; detection of FM increased significantly, both with a synchronous FM interferer and also with asynchro nous interferers (starting 200 ms before and stopping 200 ins after the tar get). Moreover, "gapped" interferers that were turned off during presentati on of the target (presented for 200 ms before and for 200 ms after the targ et but not simultaneously) produced the same significant increase in thresh olds as an asynchronous interferer that: was not interrupted. In contrast, thresholds were not affected by the presence of a gapped unmodulated sinuso idal interferer. Experiment two showed that increasing the duration of the silent gap (centered on presentation of the target) between FM interferers from 200 to 600 ms did not abolish the interference. Thus nonsimultaneous F M interferers produced frequency modulation detection interference (FMDI) e ven when the silent gap between the interferers and target clearly led to t he interferers and target being perceived as separate auditory objects. A p ossible explanation for the findings is the existence of an asymmetry in pe rception of steady and modulated sounds, as recently proposed by Cusack and Carlyon [Br. J. Audiol. 34.2, 112 (2000)]. Alternative explanations in ter ms of ringing in a hypothetical modulation filter bank and adaptation seem unlikely. (C) 2000 Acoustical Society of America. [S0001-4966(00)03811-X].