FAA Office of Aerospace Medicine
Civil Aerospace Medical Institute

Report No: DOT/FAA/AM-67/10

Title and Subtitle: Interaural intensity difference limen.

Report Date: May 1967

Authors: Rowland RC, Tobias JV.

Abstract: The ability to judge the direction (the azimuth) of a sound source and to discriminate it from others is often essential to flyers. A major factor in the judgment process is the interaural intensity difference that the pilot can perceive. Three kinds of intensity-difference thresholds were compared for the purpose of determining interaural-binaural and interaural-monaural relations.

Five subjects were tested at 250, 2000, and 6000 Hz, using a variation of the Bekesy technique. Responses to 27 interaural intensity combinations were measured at each frequency. Monaural and binaural conditions were included. Each of 24 of the combinations was measured under 0 and 180 degrees interaural phase conditions, and all were measured at 50, 35, and 20 dB HL (ISO).

Results indicate that interaural-difference thresholds decrease as a function of level, as might be predicted. These thresholds vary as a function of the frequency and apparent azimuth of the fused tone, but are relatively insensitive to variations in interaural phase. Interaural intensity-difference thresholds differ significantly from both monaural and binaural difference thresholds.
Key Words: hearing, thresholds (physiology), psychoacoustics, auditory perception, intensity, auditory signals.

No. of Pages: 12