Authors:

CARLYON, R.P., MICHEYL, C., DEEKS, J.M. & Moore, B.C.J.

Reference:

Year of publication:

2004

CBU number:

5986

Abstract:

Auditory processing of frequency modulation (FM) was explored. In experiment 1, detection of a -radians modulator phase shift deteriorated as modulation rate increased from 2.5 to 20 Hz, for 1- and 6- kHz carriers. In Experiment 2, listeners discriminated between two 1-kHz carriers, where, mid-way through, the 10-Hz frequency modulator had either a phase shift or increased in depth by D% for half a modulator period. Discrimination was poorer for D=4% than for smaller or larger increases. These results are consistent with instantaneous frequency being smoothed by a time window with a total duration of about 110 ms. In experiment 3, the central 200-ms of a 1-s. 1-kHz carrier modulated at 5 Hz was replaced by noise, or by a faster FM applied to a more intense 1-kHz carrier. Listeners heard the 5-Hz FM continue at the same depth throughout the stimulus. Experiments 4 and 5 showed that, after an FM tone had been interrupted by a 200-ms noise, listeners were insensitive to the phase at which the FM resumed. We argue that the auditory system explicitly encodes the presence, and possibly the rate and depth, of FM in a way that does not preserve information on FM phase.