Metaphors we listen with: Neural correlates of timbral brightness investigated by pitch-timbre interference and fMRI

Description:

Brightness is among the most studied aspects of music perception, and arguably among the most important timbral cues actively shaped by performers, composers, and audio engineers. Psychoacoustically, sounds described as bright exhibit a high-frequency emphasis in the spectrum and sounds with more high-frequency energy are described as bright. However, relatively little is known about the neural mechanisms that facilitate those metaphorical descriptions. Does timbral brightness involve the contribution of visual processing areas of the brain? Do sounds seem bright because our auditory and visual systems communicate directly, or because they each link to a supramodal area where a higher level, more abstract representation of what brightness entails is coded?

We conducted a study using a pitch-interference task functional magnetic resonance imaging (fMRI). In the scanner, participants decided which of two sounds presented successively was higher in pitch (pitch comparison) or brighter (brightness comparison). Stimuli were synthetic harmonic complexes differing in F0 and spectral centroid (two each). We manipulated congruency of pitch and brightness, yielding a 2x2 factorial design. Interactions between numerical value and brightness level of digits have been shown to modulate activity in the parietal lobe, an area previously implicated in magnitude processing. Implementing an analogous auditory paradigm, this study investigated the neural correlates of timbral brightness. We hypothesized that brighter tones would elicit regions of supramodal representations in the parietal lobe and/or visual areas compared to the non-bright tone.

Scanning took place at CUBIC (Combined Universities Brain Imaging Center), London and the University of Oregon Lewis Center for Neuroimaging in Eugene, OR.

This study provided a clearer understanding of the crossmodal basis for timbral brightness, which could have a number of conceivable applications in composition and performance. Results will help us resolve a question remarked upon since antiquity: why do we conceptualize sounds by way of comparison with the other senses? We will disseminate our findings in a peer-reviewed journal such as Music Perception.