Octave illusion elicited by overlapping narrowband noises.

The octave or Deutsch illusion occurs when two tones, separated by about one octave, are presented simultaneously but alternating between ears, such that when the low tone is presented to the left ear the high tone is presented to the right ear and vice versa. Most subjects hear a single tone that alternates both between ears and in pitch; i.e., they hear a low pitched tone in one ear alternating with a high pitched tone in the other ear. The present study examined whether the illusion can be elicited by aperiodic signals consisting of low-frequency band-pass filtered noises with overlapping spectra. The amount of spectral overlap was held constant, but the high- and low-frequency content of the signals was systematically varied. The majority of subjects perceived an auditory illusion in terms of a dominant ear for pitch and lateralization by frequency, as proposed by Deutsch [(1975a) Sci. Am. 233, 92-104]. Furthermore, the salience of the illusion increased as the high frequency of the content in the signal increased. Since no harmonics were present in the stimuli, it is highly unlikely that this illusion is perceived on the basis of binaural diplacusis or harmonic binaural fusion.