Gyula Demeter

The ID/ED shift task of the CANTAB battery is thought to be a “clear” set-shifting task
and does not require from the participants to match-to-sample. This subtask is defined as a
test of rule acquisition and reversal. It features: a) visual discrimination and attentional set
formation, b) maintenance, shifting and flexibility of attention. Two dimensions are used in
the test: colour-filled shapes and white lines. Feedback teaches the subject which stimulus is
correct, and after six correct responses, the stimuli and/or rules are changed. These shifts are
initially intra-dimensional (e.g., colour filled shapes remain the only relevant dimension), then
later extra-dimensional (white lines become the only relevant dimension). If at any stage the
subject fails to reach six consecutive correct responses after 50 trails, the test ends. This test
has eighteen outcome measures, assessing errors, and numbers of trials and stages completed
(CANTABeclipse, 2006).
A great advantage of this task compared to the WCST is that it allows the measurement
of response latency. OCD patients performed worst in this task, needed more trails to reach
criterion and more likely failed to complete all phases of the task than control subjects (Veale
et al., 1996; Purcell et al., 1998; Watkins et al., 2005).
One important common result in all this reported shifting tasks is that OCD patients
require more learning trails to reach a specified criterion, which could be interpreted also from
the perspective of impairment at the level of feed-back use. This question needs further
empirical research as the involvement of the orbitofrontal cortex in set shifting. So far we can
say that OCD patients manifest impairments on those shifting task which are considered
sensitive to orbitofrontal deficit.
Set shifting impairment in OCD is a highly debated topic in today’s research literature
and the missing of a straightforward result is probably due to a lot of factors. First, the
different level of sensitivity of the tasks used to measure this ability have to be mentioned,
second the unclear of the psychological functions involved in its realization, third the different
and multiple brain areas involved and fourth the presence of confounding variables such as
the severity of the OCD symptoms, the presence of different comorbid disorders, medication
use and sample matching. An important step in this field will be besides the above mentioned
the specification of the different roles played in the realization of the performance patterns by
these confounding effects.
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