An Empirical Explanation: An Explanation of Perceived Pitch Based on the Statistical Structure of Natural Tonal Sounds
Similar to vision, auditory percepts are likely to reflect aspects of successful behaviour. The predominant pitch heard in response to a stimulus comprising of harmonically-related tones could presumably accord with the probable sources of sound stimuli in the environment through experience with trial and error behavior.
Just as stimuli in vision conflate the physical factors that give rise to a retinal image, sound stimuli at the ear conflate their generative sources (Figure 1) and are not perceived in terms of their corresponding physical properties. Hence we face a similar scenario in audition, where successful behaviour is achievable despite neither perceiving nor having access to the physical world. To address this problem we have explored the relationship between the periodicity of sound stimuli and the sensation this iteration gives rise to, which is called pitch. The conceptual framework for this exploration is generally the same as vision, asking whether the phenomenology of perception can be explained by the empirical provenance of the relevant stimuli.
When a sound stimulus comprising of harmonically-related tones is presented, the predominant pitch heard corresponds to the fundamental frequency even when there is no energy at that frequency (review the Demonstration). This effect, however, does not apply to all such sound stimuli.
The fundamental frequency is generally not perceived when it is less than ~70 Hz (observation known as the ‘pitch-shift of the residue’) and when it is not harmonically related to the rest of the harmonic series of the stimulus (‘spectral dominance’). Finally, studies have found that the salience of the predominant pitch is greatest for fundamental frequencies between ~200 Hz to 500 Hz. Although several explanations have been offered, these aspects of pitch perception remain difficult to rationalize within a single framework.
If, like in vision, what we hear is shaped by trial and error behavior throughout evolution and individual lifetime, pitch percepts could presumably accord with the probable sources of stimuli in the environment. To test this idea, we created a number of artificial sound stimuli and assessed their probabilistic relationship with speech sound periodicities. There are few periodic sounds in nature, of which speech could presumably constitute a dominant source of periodic sounds in the human auditory environment.
In support of our hypothesis, the frequencies of occurrence of speech sound periodicities predicted the aforementioned pitch phenomena, suggesting that audition could have a similar basis as vision.
As a follow-up to these findings, ongoing work in the lab examines other pitch and loudness phenomena. The observations discussed here were based on complex stimuli (i.e. stimuli made up of more than one tone). Studies using pure (sine) tones have also reported other puzzling observations. Perceived pitch perception has been shown to vary with sound intensity, and pitch perception of pure tones does not correspond with tone frequency.
Schwartz D, Purves D (2004) Pitch is determined by naturally occurring periodic sounds. Hearing Research 194: 31-46.