Acoustic Gestalt: On the perceptibility of melodic symmetry

Abstract

The important role of symmetry perception in the visual domain has been well documented in a large number of studies. Less clear, however, is its effect and potential role as a Gestalt grouping principle in the audio domain. We investigated the perceptibility of melodic symmetry using a series of algorithmically generated sonifications. Twenty-eight naïve participants were presented with a series of nine symmetrical sonifications, nine partially symmetrical sonifications (with approximately half of the mirrored elements changed), and nine asymmetrical sonifications. The participants were asked to identify the sonifications as belonging to one of those three categories. The sonifications utilized Karplus-Strong string synthesis and had a duration between 500 and 8,000 ms. The sonifications were presented three times each in order to check for participants’ consistency. Although participants tested far closer to chance level than perfect accuracy, we observed large effect sizes on measures of both accuracy and consistency. We found an effect of the number of tones in a melody on accuracy, with sonifications containing more tones being more difficult to attribute to the correct category. Sonifications with shorter duration and a faster tempo were also found to be more difficult to attribute accurately, indicating some minimum duration of the melody as well as the individual tones constituting the melody. We also found evidence of a significant effect of age on participants’ consistency, with older listeners performing more consistently.