  We propose a primitive called PJOIN, for "predictive join," which combines
and extends the operations JOIN and LINK, which Valiant proposed as the basis
of a computational theory of cortex. We show that PJOIN can be implemented in
Valiant's model. We also show that, using PJOIN, certain reasonably complex
learning and pattern matching tasks can be performed, in a way that involves
phenomena which have been observed in cognition and the brain, namely
memory-based prediction and downward traffic in the cortical hierarchy.
