Abstract
Most signals from the auditory world have temporal patterns of amplitude
modulation that either emanate from the signal source or result from
environmental interference (e.g. air turbulence). To investigate
mechanisms associated with the segregation and processing of amplitude-modulated
signals, we trained European starlings (Sturnus vulgaris) to detect
a signal noise band embedded in several flanking noise bands (FBs).
We manipulated the envelope correlation between the signal and FBs,
the onset synchrony between signal and FBs (0 or100 ms), signal duration
(60 or 400 ms) and the spectrum level of the FBs (15 or 50 dB). The
lowest signal-detection thresholds were found when the envelopes
of the FBs were correlated with each other but different from the
signal envelope (the 'co-uncorrelated' condition). Detection thresholds
were on average 7 dB higher when both the signal and the FBs had
correlated envelopes (the 'all correlated' condition). Thresholds
were even higher when the envelopes of all noise bands were independent
(the 'all uncorrelated' condition). The difference in detection thresholds
between the co-uncorrelated and the all correlated conditions is
termed 'comodulation detection difference' (CDD). Differences in
signal duration and masker level had significant effects on detection
threshold, but not on CDD magnitudes; differences in onset synchrony
had no effects. We compare data from starlings with those from previous
psychoacoustic studies of humans, and discuss possible mechanisms
on which these perceptual effects may rely. Our behavioural data
are the reference for a companion study investigating CDD at the
neuronal level of the starling M.A. Bee et al. (2007) Eur. J. Neurosci.,
26, 1979-1994.
Users
Please
log in to take part in the discussion (add own reviews or comments).