GAP DETECTION IN A TONAL SEQUENCE WITH A FREQUENCY CHANGE
This study investigated how the detection of a gap inserted in a sequence of successive tones would be affected by changing frequencies of the tones. In an experiment, a silent gap was inserted either between the 7th and the 8th tones, the 8th and the 9th tones, or the 9th and the 10th tones in a 12-tone sequence. In the sequence, the frequency of the first 8 tones was always 800 Hz, while the frequency of the following 4 tones was manipulated from 800 Hz to 3200 Hz. The results showed that detection performance was severely impaired when the gap coincided with the frequency change between the 8th and the 9th tones. The impairment was more marked for larger frequency changes and for shorter gap durations. Performance was relatively unimpaired when the gap was inserted before or after the frequency change. These results suggest frequency-uncertainty effects on gap detection (Watson, Foyle, & Kidd, 1990) are due to frequency changes in a sequence, rather than frequency uncertainty per se. The results were also discussed in the context of the perceptual organization of auditory events (Nakajima & Sasaki, 1996; Nakajima, Sasaki, Remijn, & Ueda, 2004; Van Noorden, 1975).