OHP 1: Title Sheet
What I hope to do in this presentation is to give
an overview of the work which Jim Russell and I have been carrying
out over the past couple of years. As I want to go over a reasonable
amount of material in the limited time available, I am afraid
that I will only be able to give a rather superficial coverage
of this work. My hope, however, is that you will come and ask
me more about the talk if you find it interesting and want more
details. A related point is that I am conscious that at a conference
such as this some of the psychological terminology I will use
may be unfamiliar to some of you. Again, in the time available
I won't be able to make things as clear as I perhaps should, but
do come and talk to me later if anything is unclear.
OHP 2: Introduction
Our research investigates the extent to which autism
is associated with what are termed executive deficits. These are
relatively high-level psychological functions which are thought
to be involved in the deliberate and conscious control of behaviour.
Ozonoff et al. define executive control as "...the cognitive
construct used to describe goal-directed future-oriented behaviors
thought to be mediated by the frontal lobes ... including planning,
inhibition of prepotent responses, flexibility, organized search
and working memory".
Executive function is often tested using formal neuropsychological
tasks thought to tap these abilities, such as the 'Wisconsin Card
Sort Test' - a measure of inhibition and flexibility, or the 'Tower
of London' - a test of planning. Many studies have shown that
individuals with autism perform poorly on these tasks; I've only
noted a few key ones here. This has led Ozonoff and others to
ask whether executive problems might explain many of the symptoms
associated with the condition. There are, however, at least two
problems with the proposal that autism is essentially an executive
disorder. Firstly, executive deficits are not specific to autism,
but are seen in some other developmental disorders, and secondly,
the notion of executive control is a nebulous one; we clearly
need to be more specific about which particular control problems
are seen in autism.
To this end we have investigated memory in autism.
One reason for this, which is largely a theoretical one, is that,
as the quote from Ozonoff et al. indicates, working memory may
be required in tests of executive function. The problems seen
in autism on these tasks may therefore be due to working memory
deficits specifically. A second, more empirical, motivation follows
from the fact that executive deficits are also seen in neurological
patients who have suffered damage to the frontal lobes of the
brain. These patients show a particular pattern of memory problems,
and if we can observe the same pattern of deficits in autism then
we will have further evidence that frontal dysfunction may be
important in the disorder.
OHP 3: Working Memory and Executive Deficits
Working memory can be defined as holding information
in mind in order to guide one's behaviour. For example if I am
driving on the continent I need, for the first few minutes or
so at least, to consciously remind myself to drive on the right,
and not on the left as I am used to. This example might also be
seen as an executive task; Pennington writes: "... the extent
to which a task taps prefrontal function is a joint product of
how strong the prepotent response is (driving on the left) and
how difficult it is to maintain the internal representation of
context (the need to drive on the right) in working memory."
Similarly Goldman-Rakic and Diamond would argue for a link between
executive tasks and working memory, and would also claim that
working memory is mediated by the frontal lobes of the brain.
So an executive task may require the inhibition of
an inappropriate response, and working memory. This can be seen
in the Wisconsin Card Sort Test, where the player is required
to sort cards on the basis of one rule, perhaps into piles of
different colours, and then switch to another rule, perhaps sorting
on the basis of shape. When told to switch, the player must hold
the new rule in mind, and inhibit responses consistent with the
previous rule.
The question we were interested to ask then, was
whether the poor performance seen on executive tasks in individuals
with autism might reflect a problem in the working memory component
of these tasks.
OHP 4: Testing Working Memory
We assessed working memory abilities in three groups
of children: children with autism, children with moderate learning
difficulties (MLD), and normally-developing children. In this
study there were 22 children in each group, and children were
matched for verbal mental age (VMA) using the British Picture
Vocabulary Test. The verbal mental ages of the groups ranged from
around 5 to 10 years, with an average of about 7 years.
We gave these children three tasks, all of which
had the same structure, thought to tap working memory. In these
so-called 'dual tasks' children see a series of cards one after
another, and have to work out the solution to a problem shown
on each one while remembering the series of solutions already
obtained. So, in this example, four cards are seen, and at the
end of the trial the child has to respond with the solutions to
each one: response one, response two, response three, response
four. In the first of our tasks children had to count the number
of dots seen on each card, and remember the series of totals.
In the second task children had to identify a dot which differed
from the others seen, and remember the series of spatial positions
in which these dots appeared. And in the third task the children
had to work out a sum on each card, and once again remember the
series of totals.
Performance on these tasks was measured in terms
of the number of cards children could be given and still correctly
remember the series of responses. Though there is not time to
give proper details of our results, they were extremely clear
- the children with autism were unimpaired, and performed as well
as controls on all three tasks. So children with autism do not
appear to have working memory problems, at least not as measured
here. Having shown this we went on to see whether we could find
any other positive evidence of 'frontal' patterns in memory performance.
OHP 5: Frontal Patterns Of Memory
The frontal lobes are thought to be involved in at
least two other aspects of memory in addition to working memory.
One proposal is that they underpin the strategic recall of information.
Incisa Della Rocheta and Milner write: "frontal-lobe lesions
result in deficits where retrieval requires deliberate and strategic
effort". Evidence for this suggestion comes from a number
of studies which have demonstrated impaired free-recall and unimpaired
cued recall in frontal patients - the argument here being that
free-recall requires the subject to generate retrieval strategies
for themselves, while cued recall removes the need to behave strategically.
Frontal patients also fail to show strategic behaviours during
recall, such as clustering and ordering items into categories.
Interestingly, there is reasonable evidence of similar
problems in autism. Boucher and Warrington and Tager-Flusberg
have shown impaired free-recall and unimpaired cued recall in
autism, and some of the work of Hermelin and O'Connor indicates
a failure to utilize semantic information to aid recall. Minshew
and her colleagues have carried out studies using the California
Verbal Learning Test, and argue that the pattern of deficits seen
on this task implies a failure to apply organizational strategies
in recall in autism.
The third suggestion for the role of the frontal
lobes in memory, put forward primarily by Schacter, is that they
are involved in the encoding of spatio-temporal contextual information.
Evidence for this proposal comes from the problems shown by frontal
patients on tasks which require memory for this type of contextual
information, such as re-ordering a sequence of events, making
judgements about the relative recency of events, and making 'source
memory' discriminations. I will give more details about these
tasks in a moment.
So, there is already some evidence of a "frontal"
pattern of memory performance in autism, as shown by deficits
in strategic recall, though we found no evidence of working memory
problems. The question which we asked next was whether we could
find problems in the third domain memory for 'spatio-temporal
context'.
OHP 6: Testing 'Frontal' Memory
These experiments again assessed children with autism, children with MLD and normally developing children. There were 22 children in each group, and individuals were again matched for verbal mental age. The mental ages ranged from around 5 to 9 years, with a mean of around 7 years in each case.
We presented the three tasks thought to tap spatio-temporal memory which I mentioned briefly on the previous overhead. The first of these was a test of the ability to re-order a series of items in their correct temporal sequence. Children were simply shown twelve picture cards, one at a time. Four cards were of different shapes, four of different colours, and four showed pictures of various toys. These three different categories were blocked, so that all four shapes for example were always presented together, but the order of items within a category was randomised. Following a 15 minute delay the children were shown the cards again, and were asked to order the categories into the sequence in which they had been presented, and then to order the four individual cards within each category. We found that the children with autism were no worse than controls in ordering the three categories correctly, or, as the graph shows, in sorting the four items within each set into the order in which they were presented. Note - the graph shows the kendall's T value for ordering of the four cards in each category set
.
The second task assessed children's ability to determine
which of two cards had been seen more recently. In each trial,
twelve picture cards were shown, one at a time. Four cards were
presented in one spatial location, the next four in another spatial
context, and the final four in a third position. Then children
were then shown two of the cards that had been previously presented,
and were asked to decide which they had seen more recently. In
half the trials the two test items were drawn from within the
same spatial context, but in the other cases the two test items
were drawn from adjacent contexts. In the later case the child
could potentially use contextual information to aid the recency
judgement. Eight trials of each kind were presented, and as the
graph shows, the children with autism did not differ from the
controls in their performance on either type of judgement.
OHP 7: Testing 'Frontal' Memory Cont. - Source
Memory
The third test of memory for spatio-temporal context
assessed source memory. Johnson et al. provide a definition of
this term: "a variety of characteristics that, collectively,
specify the conditions under which a memory is acquired (e.g.,
the spatial, temporal, and social context of the event; the media
and modalities through which it was perceived)". In developmental
psychology source memory has typically been assessed by asking
children to remember which person carried out certain acts, or
to decide whether they themselves performed a particular act,
or observed someone else doing it.
We assessed source memory by engaging the children
in a game in which they took turns with the experimenter to place
picture cards onto a central picture board. As well as laying
cards for themselves, the children also placed cards on behalf
of a doll partner. The experimenter similarly played cards from
two sources, for themselves and for their own doll partner. Twenty
four cards were played in total, six from each player or source,
with each player taking their turn to play a card in order. After
all the cards had been laid we asked the children to try to distribute
them back to their original player - in other words could children
remember which source each card had come from?
The graph shows the average number of cards, out
of 24, which children were able to return correctly. Analysis
of these data showed the children with autism were impaired on
this measure, and on a number of other measures which we took
from the task. This suggests that children with autism do have
problems with source memory discriminations, at least as measured
here, in contrast to their unimpaired performance on the previous
two tasks.
OHP 8: Conclusions
This table provides a summary of our results. In contrast to the predictions described initially, we found that children with autism were not impaired on our tests of working memory. They were similarly unimpaired on two tests of memory for spatio-temporal information - carrying out temporal re-ordering, and making relative recency judgements. However they were clearly impaired on our test of source memory.
What do these findings indicate? Firstly, they suggest
that executive problems seen in autism cannot be explained solely
in terms of the working memory demands of executive tasks. In
other words, children with autism's difficulties on tasks like
the Wisconsin Card Sort Test would seem to be due to more 'traditional'
executive deficits, such as planning, monitoring and inhibiting
action.
Secondly, the absence of clear deficits in spatio-temporal
memory and in working memory suggests that the memory problems
seen in autism do not mirror those observed in frontal patients.
However, as I have already mentioned, there is evidence for some
'frontal' memory problems in autism, namely in strategic recall
of information. What we might be seeing in autism therefore is
a problem which is in fact more executive than frontal. Rather
than observing a deficit on all tasks which frontal patients find
difficult, we see impairment when strategic memory is required
- indeed Schacter would argue that memory for spatio-temporal
information is automatic and not strategic. To the extent that
strategic recall might require deliberate planning, monitoring
and perhaps, inhibition of the most obvious method of recall,
it is potentially executive.
Having said this, how does a problem with source memory fit with this proposal? Well, though Schacter would argue that source memory is an automatic process, others would claim that it does in fact require a strategic approach. In particular it seems that monitoring of action plays an important part in source judgements. Work by Bentall has shown that schizophrenic patients who suffer from hallucinations, thought to be indicative of a problem of monitoring, perform poorly on certain source memory discriminations.
In sum then, our results are inconclusive, and the
suggestions I have made are consequently tentative. I think however
that we would want to argue that our work counts against global
'frontal' problems in autism, and points instead to more narrowly
defined deficits, which may well be executive in nature.