The effect of pitch variation on neural responses in scale illusion

Scale illusion is a perceptual phenomenon in which listeners hear a melody that differs from the actual auditory input. In this illusion, eight descending pure tones descending (starting at 513 Hz) are presented to the right ear, are presented to the right ear, while eight ascending tones (starting at 253 Hz) are simultaneously presented to the left ear. As a manipulation, the 2nd, 4th, 6th, and 8th tones are switched between ears. Listeners often perceive a coherent melodic sequence alternating between ears, forming the illusion. The study investigates how pitch variation —specifically between C major and C minor scales—affects brain activity during the perception of scale illusion. Behavioral experiments were conducted to classify participants into illusion and non-illusion perceivers, and electroencephalography (EEG) was used to assess corresponding brain activity. Results from the behavioral task showed significantly higher accuracy for the C minor scale compared to the C major scale (p = 0.0084). EEG analysis revealed a significant difference in average amplitude at the fifth tone only among non-illusion perceivers (p = 0.028). These findings suggest that the variation in pitch structure between major and minor scales modulates the perception of auditory illusions and the associated neural processing.