The effect of intensity on relative pitch

In two experiments, we examined the effect of intensity and intensity change on judgements of pitch differences or interval size. In Experiment 1, 39 musically untrained participants rated the size of the interval spanned by two pitches within individual gliding tones. Tones were presented at high intensity, low intensity, looming intensity (up-ramp), and fading intensity (down-ramp) and glided between two pitches spanning either 6 or 7 semitones (a tritone or a perfect fifth interval). The pitch shift occurred in either ascending or descending directions. Experiment 2 repeated the conditions of Experiment 1 but the shifts in pitch and intensity occurred across two discrete tones (i.e., a melodic interval). Results indicated that participants were sensitive to the differences in interval size presented: Ratings were significantly higher when two pitches differed by 7 semitones than when they differed by 6 semitones. However, ratings were also dependent on whether the interval was high or low in intensity, whether it increased or decreased in intensity across the two pitches, and whether the interval was ascending or descending in pitch. Such influences illustrate that the perception of pitch relations does not always adhere to a logarithmic function as implied by their musical labels, but that identical intervals are perceived as substantially different in size depending on other attributes of the sound source.