the ageing cerebellum and RT variability

Michael Hogan Michael.Hogan at UCG.IE
Thu Feb 5 11:56:26 EST 1998



TO ALL THE MEMBERS OF THE LIST I HAVE A COUPLE OF IDEAS AND 
QUESTIONS
 I would  like to ask you if you have come across any recent 
neuroscience accounts of individual differences in speed of 
processing and the impact of aging on these neurological subtrates and
processing speed?  I have read demyelination accounts, but are there
others? 

 I have noted a series of findings which are suggestive. Firstly,
Jensen (1990) has noted that intra-individual variability and mean
speed in RT tasks  load highly on a common factor, but add independent
varaince to estimates of intelligence.  He suggests that
intra-individual variability and not speed is the most basic factor in
information processing efficiency, but that speed and variability both
need to be included in any information processing account of
intelligence.  Extending this arguement to aging intelligence theory,
it seems important to model the independent variance explained in
measures of Gf explained by both speed and intra-individual
variability.  This has not yet been attemped as far as I know.

In a hierarchical ordering of information processing variables, would
you (like Jensen) place intraindividual variability before average
speed of processing in RT tasks?  What might expain increased
intra-individual variability (inhibition, interference, ...or in
neurological terms as Jensen suggests decreased Myelination)? 
 Why has it (intra-ind var in RT) not been modeled adequately by
Salthouse (for example) who seems to have spent the past 15 years
studying the predictive nature of speed of processing for declines
observed in intelligence?  How in your view could sensory
(Lindenberger and Baltes, 1997 finding of predictive nature of sensory
ability using SEM, explaining variance in speed)  ability be placed
before intra-individual variability of RT as a predictor of declines
in Gf?  Does a common cause hypotheses offer a full explanation or is
a more modular theory required?.  How do you explain within a common
cause hypotheses the link between sensory-motor skill as measured by
postural control in samples aged 10 to 20 (Kohen-Raz, 1988), where no
common cause decline should be expected? Even if this relationship
between sensory and sensory-motor skills is seen to accelerate (i.e a
quadratic relationship) with age how can is a common cause hypothesis
specific enough to explain these findings? I hope you can help me
answer some of these questions which are core to my thesis.  All the
best, Michael Hogan UCG, Ireland.

  I am a Phd psychology student and am interested in modeling the role
of the cerebellum into an information processing theory of cognitive
resources.  I am not a neurologist and thus my concepts of cerebellar
control are based on behavioural measures of postural control, visual
tracking etc.  I am interested in asking you a number of questions
regarding the cerebellum: 1) Have you come across any evidence that
the cerebellum is involved in the timing (akin to the Irvy and Keele
concept of cerebellar timing) of information processing components
(e.g., using the RT paradigm).  I am particularly interested to find
out if the cerebellum may be involved in RT variability. The main
reason for this is that RT mean and variability are central predictors
of cognitive performance. 2) What is your knowledge of the impact of
aging (over age 60) on the cytoarchitecture and functions of the
cerebellum.  I know from a behavioural perspective that functions
associated with the cerebellum decline with age, but physiologically,
I am not in any way expert.

I look forward to hearing from you.  All the best.  
Michael Hogan, Ireland.




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