Monaural and binaural detection thresholds of amplitude modulation

This study is concerned with the amplitude modulation (AM)
detection thresholds for monaural and binaural listening. In the first
experiment, using a Two-Alternative Forced-Choice (2AFC) method with an adaptive
procedure 2-up 1-down, the monaural and binaural AM detection thresholds were
measured. Sinusoidal carrier at a frequency of 160, 500, 1000 or 4000 Hz was
amplitude-modulated by a single sinusoidal modulator at a frequency of 4, 32, 64
or 128 Hz. Due to a significant intersubject scatter of the results it was
impossible to estimate the difference between the thresholds determined for
monaural and binaural presentation of the stimuli. Therefore, in the next
experiment, psychometric functions for AM detection for both monaural and
binaural listening were determined. This experiment was carried out for
sinusoidal carriers at frequencies of 5000, 2000 and 6000 Hz and for sinusoidal
modulator at frequencies of 4, 64 and 128 Hz. The results of this experiment
showed a statistically significant difference between slopes of the psychometric
function (after the percent of correct responses was converted to the
detectability, d', domain) for monaural and binaural stimuli presentation.
Assuming that the AM threshold coincided with d' = 1 it can be stated that
monaural and binaural AM thresholds are significantly different.