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Re: Sensitivity to increments and decrements

Dear Chris,

In examining the detection of increments and decrements in intensity, it is important to distinguish between two different methods that can have very different results: "gated" tones vs. "ongoing" tones. In the gated-tones method used in the Sinnott et al. (1985) paper, a standard 250 ms tone was presented twice per second for three seconds (i.e., six repetitions) and then a comparison tone of the same duration was presented in the same repeating configuration. The question was whether or not the standard and comparison tones had the same intensity. In the gated configuration, the difference in intensity as measured by neural firing rate is probably a pretty good model of the information underlying the decision. For this reason, increments and decrements are expected to have similar detectability, and this is what Sinnott found, at least for humans.

The ongoing-tone paradigm, in which differences between increments and decrements are found more often, involves the presentation of a continuous or long-duration tone into which a change in intensity is introduced. In this stimulus, the decrement is subject to forward masking, whereas the increment is not, and so differences might be expected. In my dissertation (Gallun and Hafter, 2006), I suggested that changes in ongoing tones could be detected by modulation- sensitive mechanisms. In such a mechanism, forward masking would result in reduced modulation depth for decrements, and thus higher thresholds. Such mechanisms would be less able to detect changes in tones gated on and off in the manner used by Sinnott. Consistent with this difference in mechanism is the difference in JNDs for the two methods, with ongoing tones yielding JNDs about half the size of those for gated tones. The duration and number of the changes will also influence the amount of forward masking and thus the difference between increments and decrements. For more details and references, please feel free to contact me off-list.

Frederick "Erick" Gallun
Research Investigator

National Center for Rehabilitative Auditory Research
Portland VA Medical Center
3710 SW US Veterans Hospital Road (NCRAR)
Portland, Oregon 97239

-----Original Message-----
From: AUDITORY - Research in Auditory Perception
[mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Christian Kaernbach
Sent: Saturday, November 10, 2007 2:43 AM
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: Sensitivity to increments and decrements

Dear List,

Is there anything known about the existence of differences in the=20
sensitivity to intensity increments versus to intensity decrements?

Laurent Demany pointed me to a paper by Sinnott et al. (1985) who found=20
no such difference in humans, while they found an advantage for=20
increments in monkeys:
Sinnott, J. M., Petersen M. R., Hopp, S. L. (1985).
Frequency and intensity discrimination in humans and monkeys.
Journal of the Acoustical Society of America, 78, 1977-1985.
Is this finding (as to the symmetry of human increment / decrement=20
sensitivity) unchallenged?

Best regards,

Prof. Dr. Christian Kaernbach
Allgemeine Psychologie
Institut f=FCr Psychologie
Christian-Albrechts-Universit=E4t zu Kiel
Olshausenstr. 62
D-24098 Kiel