Abstract
Ambiguity and its removal are important factors for acoustic environmental analysis in the auditory system. We report on a melody devised to cause acoustic illusion which has not been studied systematically. The stimulus consisted of sustained tones A4 and E5 with the C#5 tone given intermittently. The following three kinds of sensation were possible; 1) repetition of C#5 with the two sustained tones; 2) the melody consisting of repetition of C#5 -A4; 3) the melody consisting of repetition of C#5-E5. To remove the ambiguity, a single voice phrase of repeating C#5-A4 (or E5) four times was given before the ambiguous melody. Many people kept hearing the same phrase at least for a while. This shows the existence of ambiguity and its removal. To quantify and model this phenomenon, the distribution time spent before changing to a different phrase from the given one was measured. We applied a model to the measured transition times. The model assumes that the listener's internal state (corresponding to the three kinds of perception mentioned above) is determined randomly. When a same decision is made a prescribed number of times (threshold), the perception changes to the corresponding state.
