Re: pitch discrimination

[Athanassios Protopapas <protopap@xxxxxxxxxxx>]

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@ilsp.gr                       GR-151 25  ATHENS, Greece