Re: pitch discrimination (Athanassios Protopapas )

Subject: Re: pitch discrimination
From:    Athanassios Protopapas  <protopap(at)PANTEION.GR>
Date:    Sun, 6 Jun 1999 15:08:12 +0300

I would certainly not doubt the number of subjects or the thresholds reported by Dr. Watson. My question pertains to the kinds of differences in stimuli, procedure, or threshold estimation that could have led to this difference: They have found that 90% of their subjects can tell 1000 from 1010 Hz and virtually all discriminate 1000 from 1030 Hz. Our subject pool, in which poor readers were purposefully overrepresented, included a sizeable proportion of people (maybe around 20%) who had trouble telling 1000 from 1050 Hz in the particular setting we used. I am not including people who did not establish stable thresholds; presumably the fact that a threshold was obtained far from the procedure floor (500 Hz) can be interpreted to mean that the subject at least understood the task. Performance at this same/different task was highly correlated with performance at the up/down task, which was what the original posting to the list\ referred to. Note that only half of our subjects (52) received the latter task because it was not included in our initial study (which was reported at the ASA meeting in 1997), so the correlation of .78 is only calculated on 52 points. However, one point I wanted to make was that even the subjects with thresholds on the order of hundreds of Hz for the up/down task could perform the task to some extent, ie understood what the "up/down" meant (possibly with the exception of a couple of very poor readers) since they reached stable thresholds in the adaptive procedure far from the procedure floor. My other point with respect to the original question was that poor performance on this task seems to reflect poor frequency representation and not inability to deal with the "up/down" labels (hence the strong correlation). Back to the topic of frequency discrimination. The correlation of performance on the same/different task with a long ISI between the two tones to be compared with performance on the same/different task with 0 ISI between the two tones was only .57 (and the former correlates significantly with (non)word reading and word memory whereas the latter does not). This is why I used the term "frequency representation" instead of frequency discrimination above. It seems that at the level of detecting a frequency transition (is this the same as "frequency discrimination"?) one finds better and more uniform performance than in tasks where a frequency must be retained over a silent interval to be compared from memory. I wish I was better versed in the psychoacoustics literature to understand this a bit more. Still, I am intrigued by the apparently selective correlations between high-level cognitive tasks and relatively simple psychoacoustic tasks. I am well aware of the studies mentioned by Dr Watson on correlations of the same sort. Indeed, I recall being surprised that they did not make a big deal out of the fact that frequency discrimination was significantly correlated to reading tasks (albeit not as much as in our study)---but they had a "temporal processing" theory to test and it is understandable that they placed all emphasis on the temporal tasks of their psychoacoustic battery. Still, theirs and other findings indicate that there are important issues in need of further research regarding psychoacoustics and language (oral and written). The procedural differences that have led to the observed differences in frequency discrimination performance I mentioned above may be a good starting point and I would appreciate the input of Dr Watson or others knowledgeable in the area regarding possible sources of the discrepancy. Thanassi Protopapas -- Athanassios Protopapas, PhD Department of Educational Technology Phone: +30 1 680 0959 Institute for Language and Speech Processing Fax: +30 1 685 4270 Epidavrou & Artemidos 6, Marousi e-mail: protopap(at) GR-151 25 ATHENS, Greece

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