Difference limen for dynamic center‐of‐gravity signals.

Abstract

We hypothesize that central auditory processing of the dynamic center‐of‐gravity (COG) of a pair of tones is similar to that for a single tone that undergoes sinusoidal frequency modulation (FM). The signal COG can be moved dynamically by introducing amplitude modulation to two fixed‐frequency anchor tones separated by one, or more, equivalent rectangular bandwidths (ERB). The phase relationship between the sinusoidal amplitude modulators of the anchor tones is used to control the magnitude of the COG deviation. In this study, the amplitude of the anchor tones and the depth of AM were identical between intervals. The phase relationship of the modulators was manipulated to control the deviation in the COG. To test our hypothesis, we compared FMDLs with COGDLs at three center frequencies and three modulation rates. First, difference limens were measured for the FM signals in partial replication of [Ozimek and Sek (1990)]. Next, COGDLs were measured. Initial attempts to match COG deviation to FM deviation were unsuccessful because the task was too difficult. Consequently, the modulation depth of the COGDL signals was fixed at 0.5, which resulted in replicable performance across subjects. Data for both the FMDL and COGDL task will be discussed. [Work supported by NIH and ASEE.]