Sequential discrimination tasks are widely used in psychophysical 
studies. In a typical such task, a subject is presented with a first
stimulus (f1),and then, after a delay of a few seconds, with a second
stimulus (f2), after which the subject must make a decision based on a
comparison of the two (f2 > f1?). Sequential discrimination thus
requires at least three components: loading working memory with a
particular value (f1), storing that value over a few seconds, and then
computing with the stored value, by comparing the second stimulus (f2)
to the memory of f1. We present a remarkably simple model, consistent
with neurophysiological recordings in prefrontal cortex of monkeys
performing a sequential discrimination task, that is able to carry out
all three components of the task within a single, integrated,