Temporal integration of monaural and dichotic frequency modulation

Frequency modulation (FM) detection at low modulation frequencies is commonly used as an index of temporal fine structure processing to demonstrate age- and hearing-related deficits in auditory perception. In the present study, the rate of improvement with increasing signal duration was used to explore the mechanisms that underlie FM detection. Monaural FM detection has been shown to improve with increased signal duration, yet it is unclear if improvement is related to carrier fine structure or modulation cycles. Improvement in dichotic FM detection with duration may be consistent with monaural FM or dominated by onset cues like other tasks with similar stimulus characteristics relying on interaural timing differences. Experiment I showed that both monaural and dichotic FM thresholds improve with duration independent of the phase of the modulator. Experiment II showed that monaural FM detection is dependent on the number of modulation cycles and not carrier duration. Experiment III showed that, unlike monaural, dichotic FM detection relies on the signal onset. These results further our understanding of the mechanisms of FM detection, and indicate potential future applications of FM detection in the clinic.