To recognize a transposed melody, two properties can be hypothesized to function as a significant invariant feature: a melodic contour, an up-down movement; and melodic intervals, the distances between consecutive pitches. Both properties are realized by changing the frequency of notes. Frequency changes are coded in two different ways in the early stages of the auditory process: tonotopicity and periodicity. In the first experiment, to investigate how differently transposed melodies are recognized depending on the two types of cue, two stimulus types were used: band noise (BN) providing mainly the tonotopic cue, and rippled noise (RN) providing the periodic cue. The results indicated that the contour invariance could be extracted from both cues. It was also indicated that the interval size information was contaminated in the contour information. A second experiment tested functional differences between the BN and RN stimuli in providing tonal contexts. The results showed that only the RN stimulus produced a “tonality” effect, which was reflected by an acute sense of “equality.” The results verify that the periodic cue provides more accurate information for the melodic interval recognition than the tonotopic cue. The current study reaffirmed that local cues individually affected global features, that is, melodic contour and tonality.
In this study, changes of the absolute threshold of hearing were measured by presenting a previous sound in the contralateral or ipsilateral ear. The sound pressure level (SPL) of a previous sound was 40, 60, or 80 dB to investigate the dependence of the threshold change on the SPL of a previous sound. The previous and test sounds were pure tones at the same frequency of 500 Hz and had a duration of 3 s. The previous sound was presented 0.5 s before presenting the test sound. The threshold changes were obtained by subtracting the threshold with a previous sound from the threshold without a previous sound. As results, the threshold was decreased when the previous sound was presented in the contralateral ear at all previous sound SPLs, and the threshold decrease level became larger significantly as the SPL of the previous sound increased in some experimental subjects. This result shows the threshold decrease phenomenon has a tendency in which the effect is enhanced depending on the previous sound SPL. On the other hand, in the ipsilateral ear, the threshold was increased by presenting the previous sound. And the threshold increase level became smaller significantly as the SPL of the previous sound increased in some subjects.
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