Temporal modulation transfer functions for AM and FM stimuli in cat auditory cortex. Effects of carrier type, modulating waveform and intensity

Hear Res. 1994 Apr;74(1-2):51-66. doi: 10.1016/0378-5955(94)90175-9.


For 167 single units, recorded from primary auditory cortex in 28 cats, we show that tuning to the modulation frequency (MF) of amplitude-modulated (AM) sound is strongly dependent on carrier type. In general AM noise-bursts and click-trains produce good tuning to MFs with repetition rates around 8-10 Hz. Amplitude- or frequency-modulation of tone-carriers resulted largely in low-pass temporal modulation transfer functions (tMTFs) with a best modulation frequency (BMF) around 4 Hz. Individual BMFs for noise carriers ranged from 3-26 Hz, whereas for tone carriers they were mostly below 6 Hz and rarely above 10 Hz. The sharpness of tuning for broad-band stimuli decreased with increasing duty-cycle of the modulation; it was most pronounced for clicks, next best for exponential sine-AM and broadest for sinusoidal AM. In contrast the reverse was found for tone carriers; the better modulation following was found for sinusoidal modulation and was most likely entirely due to a stronger onset response. Decreasing the modulation depth below 100% showed an increasing influence of onset transients and periodic rebounds, however, the average tMTFs for depths between 50-100% are similar. The optimal intensity level for noise carriers was usually higher than for tone carriers. Overall the modulation-sensitivity of cortical neurons regardless of carrier type and modulating waveform was in the range of modulation frequencies found in music, speech and other complex sounds.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acoustic Stimulation
  • Acoustics
  • Animals
  • Auditory Cortex / physiology*
  • Cats
  • Electrophysiology
  • Evoked Potentials, Auditory / physiology