[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: The Auditory Continuity Illusion/Temporal Induction
Dear Al,
I agree completely, Klingons and all.
Dick
--------------------------------------------
Richard M. Warren
University of Wisconsin-Milwaukee
Department of Psychology
PO Box 413
Milwaukee, WI 53201-0413
Phone: (414) 229-5328
Fax: (414) 229-5219
Email: rmwarren@xxxxxxx
On Dec 9, 2005, at 11:12 PM, Al Bregman wrote:
Dear Dick,
Your reply to Fatima is much appreciated. The question of "where" a
process takes place in the brain is very complex. The auditory signal
starts at the object that makes the sound. So a Gibsonian might say
that
the external object participates in the process. Then the sensory
system
registers the sound. If the stimulus features that you described as
being
needed for induction to occur have to be registered by the peripheral
auditory system, then at least to that extent, the latter system is
also
involved. Then information is circulated to a number of brain areas.
It
is likely that without the participation of any of these sites, no
induction would be carried out.
A central question remains: Is there an area of the CNS that is
involved
in auditory induction but not in any other auditory process? That is
what
is required before you could argue that this specific area is the
module
that takes care of auditory induction. Using this strict criterion,
we may
not have enough scientific information to say where *any* auditory
phenomenon is carried out, never mind auditory induction. One might
think
that we can obtain this information from studies involving
brain-imaging .
However, the process of subtraction of a control condition from an
experimental condition in such studies may give misleading answers.
Let me illustrate this point with a fanciful analogy. Suppose some
Klingon
scientists are interested in exactly where an analysis of variance
(ANOVA)
is carried out in a human-built computer (Klingons have enormous
computers
that compute different functions in different places.) They don't know
exactly how a human-built computer works, but they do know how to
measure
things. In particular, they are able to measure the activity level of
every part of the computer as it carries out a number of statistical
processes. By the clever use of the subtraction technique, they find
that
a certain area of the computer's memory (region A) is more active
during an
ANOVA than is any other part of the computer. [Let me reveal that what
they
have discovered is the high level program that specifies the ANOVA
computation; it is, however, written using other high-order processes,
such
as "sum of squares", as primitives (these primitives being calculated
by
helper programs located elsewhere in the computer).]
Our Klingon scientists conclude that the ANOVA is carried out in this
region A. Are they right? Well, yes and no. The process is indeed
coordinated there, but is actually carried out all over the computer.
There are helper programs, such as sum of squares, that are located in
other memory regions. There are also the pieces of hardware for
shifting
numbers from one location to another, testing the equality of two
numbers,
adding, multiplying, inputting and outputting numbers, busses for
connecting these pieces of hardware, etc., which are located all over
the
computer. So it is more correct to say that a large part of the
computer
calculates the ANOVA, not just region A.
It seems to me that this is a direct analogy to the use of the
subtraction
method in fMRI studies. Even assuming that its human practitioners
are as
clever as the Klingon scientists in choosing all the necessary control
conditions, the subtraction method leads them to say that the process
is
*carried out* in the region that shines forth after all subtractions.
The
method effectively discards the contributions of the rest of the brain
to
the process. Studies involving ablation or brain damage have the same
problem. Finding out that the destruction of a particular region
destroys
a certain capacity without affecting any others (a rare finding) still
does
not tell us that the capacity is largely located in that region, only
that
the region is essential for the process.
The conclusion is that imaging and destruction studies cannot in
themselves
tell us where a process is taking place in the brain. Since those are
the
two most powerful techniques that we now have available, this
conclusion is
discouraging. What can we do about it? Well, we can be aware that the
brain is an organ whose parts are highly interactive. Maybe it is not
particularly productive to ask "where" a process is going on. A better
question might be "how". How can processes distributed all over the
brain
collaborate in carrying out a process such as auditory induction.
Best holiday wishes to all,
Al
----------------------------------------------------
Albert S. Bregman,
Emeritus Professor
Psychology Dept., McGill University
1205 Docteur Penfield Avenue
Montreal, Quebec
Canada H3A 1B1
Voice & Fax: +1 (514) 484-2592
----------------------------------------------------