Octave illusion: stimulation frequencies can modulate perception.

The octave illusion (Deutsch, 1974) is a well-known auditory illusion elicited by presenting a dichotic sequence of two tones separated by an octave during which the high and low tones alternate between both ears. This illusion engages an important mechanism of auditory perception, which is pitch perception. Previous studies used central frequencies of the useful musical spectrum to elicit the illusion. However, these studies did not cover part of that spectrum where musical pitch perception decreases (below 200 and above 1600 Hz). The present study aimed to investigate how the relative frequency distribution of percepts changes across a greater proportion of the musical scale to better understand the influence of pitch on illusion perception. Participants were presented with 7 pairs of frequencies from 40-80 Hz to 2000-4000 Hz and had to select a choice (octave, simple, complex) corresponding to their perception. When using pairs of stimuli towards the upper and lower boundaries of the selected range: (1) distributions of percepts significantly differ from the classic 400-800 Hz, (2) the octave percept was reported less frequently, particularly at very low frequencies. Results from this study revealed that the illusion perception differs significantly at the low and high limits of the musical spectrum where reduced accuracy of pitch perception is known to occur. These results support past studies who investigated pitch perception. Furthermore, these results support the model proposed by Deutsch where pitch perception is one of the central frameworks of illusion perception.