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Re: Sensitivity to increments and decrements

Hi Christian,

Chait et al. recently found an asymmetry in reaction times and brain responses for transitions between increases and decreases in interaural correlation (a rough binaural analogue of monaural intensity change).

Such asymmetry is to be expected if the internal representations of the states to be discriminated have different variability. If the internal representation of A is more variable than that of B, an A-->B fluctation is more likely to occur by chance than a B-->A fluctuation, leading to a higher probability of false positive. If the decision mechanism adapts its criteria to equalize false positive rates in both directions, a larger step will be required for detection in one direction than the other. You also expect the same asymmetry if the stimulus states (rather than their representation) differ in variability.

For intensity, you might expect an asymmetry if intensity were coded, say, by the spike rate of a Poisson process. Spike count variance is proportional to spike count mean, leading to the prediction that an increment is easier to detect than a decrement. Is that the case?


Chait, M., Poeppel, D., de Cheveigné, A. and Simon, J. Z. (2007). "Processing asymmetry of transitions between order and disorder in human auditory cortex." J. Neurosci. 27: 5207-5214.

Dear List,

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

Laurent Demany pointed me to a paper by Sinnott et al. (1985) who found no such difference in humans, while they found an advantage for 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 sensitivity) unchallenged?

Best regards,

Prof. Dr. Christian Kaernbach
Allgemeine Psychologie
Institut für Psychologie
Christian-Albrechts-Universität zu Kiel
Olshausenstr. 62
D-24098 Kiel