Biomedical subjects

H Farahbod

Publications and source records attributed to H Farahbod.

3 recordsLinked to original sources

PubMed1999

Neural bases of an auditory illusion and its elimination in owls.

Humans and owls localize sounds by detecting the arrival time disparity between the ears. Both species determine the interaural time difference by finding the delay necessary to match the leading signal with the lagging one. This method produces ambiguity with periodic signals, because the two signals can be matched by delaying either one or the other. As predicted, owls localized periodic signals in illusory directions, whereas they always perceived the real source when signal bandwidth exceeded a certain value. This bandwidth also enabled higher-order auditory neurons to discriminate between real and illusory sources.

Acoustic Stimulation↗

PubMed1998

How do owls localize interaurally phase-ambiguous signals?

Owls and other animals, including humans, use the difference in arrival time of sounds between the ears to determine the direction of a sound source in the horizontal plane. When an interaural time difference (ITD) is conveyed by a narrowband signal such as a tone, human beings may fail to derive the direction represented by that ITD. This is because they cannot distinguish the true ITD contained in the signal from its phase equivalents that are ITD +/- nT, where T is the period of the stimulus tone and n is an integer. This uncertainty is called phase-ambiguity. All ITD-sensitive neurons in birds and mammals respond to an ITD and its phase equivalents when the ITD is contained in narrowband signals. It is not known, however, if these animals show phase-ambiguity in the localization of narrowband signals. The present work shows that barn owls (Tyto alba) experience phase-ambiguity in the localization of tones delivered by earphones. We used sound-induced head-turning responses to measure the sound-source directions perceived by two owls. In both owls, head-turning angles varied as a sinusoidal function of ITD. One owl always pointed to the direction represented by the smaller of the two ITDs, whereas a second owl always chose the direction represented by the larger ITD (i.e., ITD - T).

Animals↗

PubMed1998

Effects of interaural decorrelation on neural and behavioral detection of spatial cues.

The detection of interaural time differences (ITDs) for sound localization critically depends on the similarity between the left and right ear signals (interaural correlation). We show that, like humans, owls can localize phantom sound sources well until the correlation declines to a very low value, below which their performance rapidly deteriorates. Decreasing interaural correlation also causes the response of the owl's tectal auditory neurons to decline nonlinearly, with a rapid drop followed by a more gradual reduction. A detection-theoretic analysis of the statistical properties of neuronal responses could account for the variance of behavioral responses as interaural correlation is decreased. Finally, cross-correlation analysis suggests that low interaural correlations cause misalignment of cross-correlation peaks across different frequencies, contributing heavily to the nonlinear decline in neural and ultimately behavioral performance.

Animals↗