Neural Coincidence Detection Strategies during Perception of Multi-Pitch Musical Tones

Multi-pitch perception is investigated in a listening test using 30 recordings of musical sounds with two tones played simultaneously, except for two gong sounds with inharmonic overtone spectra, judging roughness and separateness as the ability to tell the two tones in each recording apart. Of the sounds, 13 were from a Western guitar playing all 13 intervals in one octave, the other sounds were mainly from non-Western instruments, comparing familiar with unfamiliar instrument sounds for Western listeners. Additionally the sounds were processed in a cochlea model, transferring the mechanical basilar membrane motion into neural spikes followed by post-processing simulating different degrees of coincidence detection. Separateness perception showed a clear distinction between familiar and unfamiliar sounds, while roughness perception did not. By correlating perception with simulation different perception strategies were found. Familiar sounds correlated strongly positively with high degrees of coincidence detection, where only 3–5 periodicities were left, while unfamiliar sounds correlated with low coincidence levels. This corresponds to an attention to pitch and timbre, respectively. Additionally, separateness perception showed an opposite correlation between perception and neural correlates between familiar and unfamiliar sounds. This correlates with the perceptional finding of the distinction between familiar and unfamiliar sounds with separateness.