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Increment versus decrement detection

Dear colleagues:

I recently conducted some experiments in which participants had to detect a single changed tone in an isochronous melody consisting of 12 successive complex tones (piano tones) of different pitch but equal loudness. The change to be detected was either in intensity or in duration, and it was either an increment or a decrement. These were four separate tasks, not intermixed. The melody containing the change was immediately preceded by the same melody not containing any change. I would be grateful for comments or references that would help me understand the following trends in my data:

(1) Decrements are harder to detect than increments. Is this well known from previous psychoacoustic research? What is the reason?

(2) The pattern of variation in detection scores (hits and false alarms) across the 12 tones in the melody, which reflects influences of pitch contour and other factors, is uncorrelated between increment and decrement detection. It seems like these two tasks have little in common. Why?

(3) In increment detection, both hits and false alarms tend to increase across the 12 tones in a melody, but decrement detection shows the opposite trend. It is as if tones were expected to become softer as the melody progresses. Why?

Many thanks in advance for any helpful replies!


Bruno H. Repp
Haskins Laboratories 300 George Street
New Haven, CT 06511-6624
Tel. (203) 865-6163, ext. 236
Fax (203) 865-8963