Recognition of sequential harmonic and inharmonic sound sequences investigated by behavioral and electrophysiological studies

Consonance rating when listening to the two consecutive or simultaneously presented sounds is associated with the ratio of their fundamental frequencies. The simpler ratio is perceived as more consonant. In this thesis, two melodies that consist of the same 10 tones were generated. Melodies had the same contour but differed with the order of tones so formed different harmonic relations between consecutive tones. Non musician participants were asked to choose which melody (harmonic or inharmonic tone sequences) was more consonant and the rating for each melody was not significantly different than each other. However, it was easier for them to notice the same amount of frequency change that occurs in one note of the harmonic sound sequence. Results suggest that better performance of the recognition task for harmonic sequence is related to better encoding and building a higher level expectation due to harmonic relations of sounds. An EEG experiment was conducted to test memory load hypothesis. The sustained anterior negativity (SAN) and power of alpha/beta oscillations were compared as a measure of working memory load. Amplitude of SAN did not reveal a difference in working memory load. However, beta and low gamma power was lower for harmonic sequences in the frontal cortex at the end of the stimulus presentation which suggests a more stable memory trace for harmonic sequences. Nonmatch stimulus elicited a P3b signal with higher amplitude for harmonic condition. This result suggests that a higher level expectation occurs for harmonic condition as all the other parameters that affect P3 signal were well controlled in the experiment.