Temporal modulation transfer functions based upon modulation thresholds

J Acoust Soc Am. 1979 Nov;66(5):1364-80. doi: 10.1121/1.383531.


The detectability of amplitude modulation in the absence of spectral cues provides a quantitative description of temporal resolution for steady-state signals with relatively small amplitude changes. Modulation thresholds for sinusoidally amplitude-modulated wideband noise were measured as a function of modulation frequency. The resulting "Temporal Modulation Transfer Function" (TMTF) shows a lowpass characteristic for modulation frequencies below about 800 Hz. The lowpass characteristic is extended up to approximately 2 kHz when the increment in average power produced by modulation is eliminated. The important parametric effects are summarized as follows: (1) TMTFs are independent of overall level, except at very low intensities; (2) the time constant indicated by the TMTF decreases as the center frequency of the band-limited, modulated noise is increased; (3) modulation thresholds generally decrease with increasing duration of modulation, particularly at low modulation frequencies; (4) when the carrier is gated for the duration of modulation, the TMTF shows a highpass segment at low modulation frequencies. Although the TMTFs are not directly consistent with the attenuation characteristic of a simple lowpass filter, a model which incorporates such a filter, with a time constant of 2.5 ms, describes the entire TMTF and also describes the modulation functions obtained with square-wave and pulse modulation. The wide bandwidth of initial filtering indicated by the model raises the important question of the role of peripheral filtering in determining the detectability of high-frequency modulation.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acoustic Stimulation*
  • Auditory Threshold*
  • Humans
  • Psychoacoustics