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Re: Sensitivity to increments and decrements
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.
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?
Prof. Dr. Christian Kaernbach
Institut für Psychologie
Christian-Albrechts-Universität zu Kiel