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Re: Sensitivity to increments and decrements

Title: RE: [AUDITORY] Sensitivity to increments and decrements

Dear Christian and List,

Although not directly relevant to your initial question about the symmetry of intensity increment and decrement thresholds in humans, I have some unpublished behavioral data that suggest that the asymmetry in monkeys may be more modest than was suggested by Sinnott and colleagues (1985).

While working with Henry Heffner I tested three monkeys for the detection of increments and decrements in the intensity of a 625-Hz tone (Sinnott et al used 1 kHz tones). Increment thresholds ranged from 1.8 to 2.7 dB (M = 2.2 dB), whereas decrement thresholds ranged from 2.5 to 3.8 dB (M = 3.0 dB). One animal obtained thresholds of 2.7 and 2.6 dB in the two conditions.

Despite the similarity of increment and decrement thresholds in our “normal” monkeys (a 0.8 dB difference on average), some might be interested to note that auditory cortex lesions affected the two tasks differently. First, a monkey with a large bilateral lesion had an increment threshold of 3.5 dB (near normal), and a decrement threshold of 9.5 dB (elevated). Second, a monkey with a unilateral lesion had a decrement threshold of 3.8 dB when the sound was delivered in the free field or to the ipsilesional ear alone, but was unable to detect a decrement of even 16 dB in its contralesional ear.

These findings are consistent both with an earlier observation hidden in a paper by Strominger, Oesterreich & Neff (1980) that found a monkey with a bilateral auditory cortex lesion to have difficulty detecting even a 40 dB intensity decrement, and with Neff's classic "neural model" of auditory discrimination (e.g., Neff WD (1961) Neural mechanisms of auditory discrimination; In, Sensory Communication, W Rosenblith (Ed.), John Wiley & Sons, NY, NY).

Regardless of whether an asymmetry might exist for the detection of intensity increments and decrements in humans or monkeys, I think it’s fair to expect that the processes involved in detecting a barking dog might differ from those involved in detecting a dog that held its tongue (or at least barked more quietly).


P.S. I would expect Erick Gallun to weigh in here soon with insights from some of his human psychophysical data.  

Ian A. Harrington, PhD

Department of Psychology
Augustana College
639 38th St.
Rock Island, IL 61201

email: IanHarrington@xxxxxxxxxxxxx
phone: (309) 794-7243

-----Original Message-----
From: Christian Kaernbach [mailto:auditorymail@xxxxxxxxxxxx]
Sent: Sat 11/10/2007 2:42 AM
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: [AUDITORY] Sensitivity to increments and decrements

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