COGNITIVE MODELLING (This diagram that appeared in Cognitive
Systems 1 sums up my work in this area)
Reviewing in the 1970s experimental literature on the right-sided
speech
advantage (widely known as, "the right-ear advantage =
REA") I formulated two broad generalisations that seemed
well supported to me:
---(i) dichotic (different stimuli to the two ears at the same
time) lateral differences arise at an early stage of speech
processing, and
---(ii) ear differences are much easier to show with dichotic
than monaural (one stimulus to one ear) presentation of the
speech.
I believe both facts can be explained with minimal
assumptions about underlying neural function, as follows.
(a)
When
listening to a syllable a
"limited capacity channel" in our perceptual system
assigns each distinct part of the incoming acoustic waveform to a
particular phonetic category (e.g. /b/, /d/, /g/, /a/ etc).
(b)
The
internal trace of one of the dichotic stimuli
must wait in temporary (“buffer”) storage while the
other is being assigned its constituent phonemes.
(c)
The
information in this buffer is rapidly
lost, which is what causes better performance on report of the
first stimulus processed.
(d) Following passage through the “phonetic
categorisation” gate, traces are held in a much more durable
form and do not decay at a comparable rate when meeting any
further gates. (This might be because the assigned phonetic
category is part of the listener’s internal
“schemata”.)
I hold that this model disposes of any
necessity for the idea
of "functional decussation" originally used
to
explain the experimental findings on auditory lateral advantage. That
idea is unnecessarily committal on the
underlying neurophysiology (see my manuscript abstracted in Social
and Behavioral Sciences Documents 17, 43-44) though this
does
not, of course, mean that it will not turn out one day to be true
after all. For
a bibliography of over 200 titles in
journals relevant to the model see Cortex 25.