373
Conditioned Blocking: Schizophrenia
Figure 1. Schematic drawing of the task situation for measuring conditioned blocking: a “house” is divided into
two rooms, each with walls that the mouse-cursor (upper-left) cannot cross. Three colour cue panels appear (upper
middle) and the subject searches for a safe-spot (e.g. lower arrow). The subject is awarded +15 points (upper
right) on reaching this goal. Delays are awarded minus points (upper left). The upper arrow (right) indicates an
alternate mirror-image starting point for one of the two conditioning tasks.
Task procedure
Testing started between 9:00 and 11:00 a.m. with 1 day between the first (A) and the
second sessions (B). A was the subject’s own IeamingcontroJ session and B was the blocking
test session. Subjects were instructed to bring the mouse-like cursor to one of two possible
“safe spots", demonstrated during joystick calibration. The safe-spot would shimmer yellow
and +15 points were awarded (inter-trial interval, 2 s). The mouse might start in either
room and the goal was always in the other room.
At the start of each trial one of two sets of colour panels lit up for 1 s. These sets were
cues as to which of the two safe-spots was the goal on a particular trial. In A (phase 1)
there was a set of three colours throughout training. Subjects were warned to attend to
these. If they did not reach the goal within 8 s they got 5 minus points for each additional
second. When subjects had reached the learning criterion (88% in eight trials without minus
points), they proceeded to 21 test trials when the first and third colours were presented
alone for response (alternately first-third and third-first from each colour set). The main
measure was the latency to find the goal after the colour originally presented on the right
minus that on the left. Data for the first test trial were discarded due to the inevitable
surprise of seeing only one colour cue.
Session B, presented 48 ħ later, started with one of two pairs of colours. After achieving
a 50% criterion over eight trials (B phase 1) a third colour was added until the full learning
criterion had been reached (B phase 2). CB would be expected in the response latency to
the third (added) colour when presented alone in the test phase with respect to the first
colour (alone), seen from the start of the session. The start positions to the same colour set