Prior knowledge yields more precise perception of vocal elements in MIDI-converted music

Seth MetcalfeJoseph Allen Harris^*

• Bradley University, Peoria, United States

Perceptual illusions in which gaps in sensory evidence are filled in using prior knowledge are a useful avenue in understanding the constructive nature of our experience. The MIDI vocals illusion, wherein listeners perceive the presence of vocal elements in a digitally-converted audio format with none present, presents a novel opportunity to characterize the role of prior experience in auditory perceptual filling-in. In two experiments, participants reported the occurrence and duration of either imprecise or precise vocal elements in MIDI-converted audio. To isolate the effect of prior exposure on the emergence of the illusion in each experiment, participants first listened to twelve MIDI-converted excerpts from a subset of six songs, with half originally containing vocal elements, and the other half containing only instrumental tracks. Of those six songs, three were designated as "learned" and were presented in their original format during a subsequent learning block, with the remaining three only presented in their MIDI format. This block sequence was repeated three times. An imprecise perceptual illusion emerged regardless of prior exposure to original excerpts, and distinguished between excerpts originally containing vocals and those containing only instrumental elements. A more precise illusory percept (words) emerged only for those MIDI stimuli corresponding to original excerpts presented during the learning blocks. These findings represent the first investigation of the MIDI vocals illusion, and they point to distinct roles of bottom-up sensory features and top-down expectations based on experience in the perceptual filling-in of auditory information.