Lateralization and sequential relationships in the octave illusion.

Subjects made lateralization judgments concerning sequences of dichotic chords whose components stood in octave relation. In condition 1, each ear received a sequence consisting of 400- and 800-Hz tones in alternation, such that when one ear received the 400-Hz tone, the other ear simultaneously received the 800-Hz tone. Condition 2 was identical to condition 1, except that the alternating tones were at 600 and 1200 Hz instead. In condition 3, dichotic chords at 400 and 800 Hz alternated with dichotic chords at 600 and 1200 Hz. In all conditions, the amplitude relationships between the higher and lower tones were varied, and the percent lateralization to the higher frequency signal was plotted as a function of these amplitude relationships. In all conditions, when the tones at the two ears were equal in amplitude, lateralization tended to be toward the ear receiving the higher frequency signal. Averaged across subjects, this tendency in condition 1 was overcome only when the lower frequency signal was 12 dB higher in amplitude, and, in condition 2, when it was 9 dB higher. However, in condition 3, the tendency was overcome when the lower frequency signal was 3 dB higher in amplitude. The lateralization effect was thus shown to be influenced by the sequential relationships between the frequencies presented to the two ears.