title: Acoustic cues underlying auditory distance in barn owls.
abstract: CONCLUSIONS
  We conclude that: (1) among several cues examined, the monaural cue of direct-to-reverberant (D/R) ratio in the ipsilateral ear provides the most information about sound-source distance; (2) interaural level difference (ILD) provides less information about sound-source distance; and (3) a comprehensive theory of three-dimensional auditory localization must incorporate the fact that all of the major acoustic cues change with distance.
  
  
  OBJECTIVE
  Neural mechanisms underlying auditory localization of distance are poorly understood. The present study was an initial step toward filling this gap in knowledge.
  
  
  METHODS
  The binaural room impulse responses of adult barn owls were measured. The sound source was placed at various distances (up to 80 cm) and azimuths (0-90 degrees) relative to the owl's head, with the elevation kept at 0 degrees .
  
  
  RESULTS
  We determined the value of each cue for a 3-10 kHz band, and found that: (1) D/R ratio of signal amplitudes provided the most information about sound-source distance; (2) the ipsilateral D/R ratio represented distance more clearly than the contralateral or binaural-average D/R ratios; (3) ILD of direct signals increased with decreasing distance under certain conditions; (3) interaural time difference (ITD) of direct signals increased with decreasing distance at 90 degrees azimuth; and (4) the spectral patterns of ILD and the monaural direct signals changed with distance in complex ways.
authors: Department of Neuroscience, University of Connecticut Health Center, Farmington, CT, USA. KIM@neuron.uchc.edu
authors: Duck O
authors: DO
authors: Kim
authors: Andrew
authors: A
authors: Moiseff
authors: J Bradley
authors: JB
authors: Turner
authors: Justin
authors: J
authors: Gull
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000162:Acoustics / Q000295:instrumentation; D000222:Adaptation, Physiological / Q000502:physiology*; D000818:Animals; D003463:Cues; D006309:Hearing / Q000502:physiology*; D013017:Sound Localization / Q000502:physiology*; D020305:Strigiformes / Q000502:physiology*