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Re: By any other name...

Thanks, Dan, Daniel, and Yoshitaka, for your excellent comments. I agree with you,
of course, yet there is still something that bothers me. If it does not really matter
whether a signal is present or absent, why do researchers make the effort to
put a gap in the signal? Why not just mask a continuous signal instead?
If the masker is strong enough, it should not matter. However, the finding of
perceived continuity will seem much LESS SURPRISING when the signal
was actually present than when it was absent. So, the actual introduction of
a signal absence seems like a psychological trick on the part of the investigator.
This does not apply, of course, in cases like the one described by Yoshitaka, where
some percept is synthesized out of nothing, as it were.

On 3/22/07, Bruno Repp <repp@xxxxxxxxxxxxxxxx> wrote:
If objective methods cannot prove the absence of the signal,
then I would argue that the signal is in fact present. Is an
objective proof of signal absence typically presented in studies of
the auditory continuity effect?

I don't think the objective presence or absence is very interesting; there is a range of circumstances in which a more optimally configured detector might be able to detect the absence of a perceptually restored tone (although those circumstances may be surprisingly narrow).

What is more interesting is that even in genuinely undecidable circumstances,
when, as Yokashita puts it, the signal is objectively "either present
or absent",
the perceptual system does not report that ambiguity but instead returns a
confident answer.  Moreover, in the case of continuity, that answer is not the
locally simplest answer (no spectral peaks = no perceived tones), but instead
is the "simplest" answer on a much broader scale (continuous tone more likely
than tone with a gap synchronized with noise burst).

Maybe the objection is that *of course* the perceptual system will do the
reasonable thing of assuming continuity when there is no counter-evidence.
But the computational implementation of a system that can capture and
apply this kind of definition of "reasonableness" is much more complex than
a lay person might expect from the auditory system - and a majore challenge
for those of us interested in modeling perceptual sound analysis.

If objective methods cannot prove the absence of the signal,
then I would argue that the signal is in fact present.

This reminds me of the discussion we had a few years ago about the WW2 aircrews who could conjure up the illusory experience of listening to favorite pieces of music in among the earsplitting drone of the aircraft engines during long missions. Since no objective measure can distinguish the presence or absence of Beethoven's 5th at 20 dB below the air conditioning noise in my office, why am I not perceiving it (or only that one, and not the infinity of other unmeasurably-quiet signals that are also "present")?


Bruno H. Repp
Haskins Laboratories
300 George Street
New Haven, CT 06511-6624
Tel. (203) 865-6163, ext. 236
Fax (203) 865-8963

NOTE: I am at Rutgers University, Newark, two days each week,
usually Wednesday and Friday, and don't read my
Haskins e-mail on those days. To reach me at Rutgers, send
e-mail to <repp@xxxxxxxxxxxxxxxxxxxxxx>.