Binaural perception of amplitude and frequency modulated signals

The investigations focused on the binaural perception of
amplitude modulated (AM) and frequency modulated (FM) signals. They are
comprised of two experiments. In the first experiment binaurally perceived
(matched) modulation depth for AM signals was determined under diotic conditions
(i.e. for the same values of modulation depth coefficient, m, presented to the
left (ml) and right (mr) ears) and under dichotic conditions (i.e. for different
values of these coefficients ml[ampersand]ne;mr). The measurements were made for the
interaural differences in modulation depth coefficient [ampersand]Delta;m, changing from 0
to 100% and a few selected modulating frequencies (4, 64 and 128 Hz) and carrier
frequencies (250 and 1000 Hz). In the second experiment binaurally perceived
(matched) frequency deviation of FM signals was determined under diotic
conditions (i.e. for the same values of frequency deviation, [ampersand]Delta;f, presented
to the left ([ampersand]Delta;f_l) and right ([ampersand]Delta;fr) ear ([ampersand]Delta;fl =[ampersand]Delta;fr) and
under dichotic conditions (i.e. for different values of this deviation
([ampersand]Delta;fl[ampersand]ne;[ampersand]Delta;fr)). The measurements were made for the interaural
differences of frequency deviation changing from 0 to 20 Hz; a few selected
modulating frequencies (32, 64 and 128 Hz) and carrier frequencies (500 and 1000
Hz). It was found in Experiment I that for small interaural differences in
modulation depth, [ampersand]Delta;m, the binaurally perceived modulation depth, m, is
equal to the arithmetic mean of the depths presented to the left and right ears,
whereas for large values of [ampersand]Delta;m, the value of m is smaller than the mean.
The results of Experiment II revealed that the binaurally perceived frequency
deviation is a linear function of interaural differences of this deviation and
is equal to the arithmetic mean of deviations presented to the left and right
ears.