Juan Delius

Apomorphine (apo), an unspecific direct dopamine agonist, elicits an intense and lasting pecking bout in pigeons. Apo yielded orderly dose-response functions, and repeated administrations led to sensitization. Strain and individual differences in sensitivity to apo were at least partly due to genetic factors. However, a strong cage-context dependency of the sensitization, which is indicative of conditioning, occurred in both pigeon strains studied. Apo-induced pecking and sensitization also occurred in total darkness. Pigeons could be conditioned to discriminate between an apo state and a non-apo state. A small dose of apo was effective as a conditioned stimulus when paired with a high dose as an unconditioned stimulus. The conditioned response (CR) was strongly specific to the context in which the sensitization to apo took place. The resistance to extinction of the CR could be increased through an oversensitization treatment. The incremental responses arising during the sensitization treatment and the CRs shown afterward by individual pigeons correlated significantly. The sensitization to apo in pigeons is well accounted for by a conditioning schema in which an interoceptive drug state is a conditional conditioned stimulus for the full expression of the incremental response. Variants of the scheme might also account for the sensitization of rodents to psychostimulants. A neural model that embodies the characteristics of the conditioning scheme has been proposed.

U.niversity of Auckland' Until recently it has been doubted whether animals below the pri- mates, and in particularpigeons, are capable of learning to use a ge- neral conoept of identity joddity on perceptual patterns. The present report describes a new experiment, provides additional details concer- ning sorne earlier experiments and revíews two recent studies from other Iaboratorioes, AH the studics employed instrumental díscrimination trai- ning procedures of the "matching-to-sample" or "oddíty-from-sample" type followed by generallzatíon tests using stimuli that were novel to the subjects, The results of aH experíment concord in demostrating that do- mestic pígeons are capable of acquiring the logic "samejdifferent" rela- tion as well as of applying it to novel situations.

This chapter argues that, contrary to widespread opinion, pigeons are capable of forming equivalence classes of visual stimuli. The multiple reinforcement reversal procedure originally introduced by W. Vaughan (1988) and recently developed by M. Jitsumori et al. (2000) might be more advantageous in this respect than the more popular symbolic matching-to-sample procedure advocated by M. Sidman (1992). This may be mainly so because the former method obviates a symmetry stage that is essential to the latter method. Although we show that physical stimulus similarities facilitate the formation of equivalence networks, it has also been demonstrated that functional similarities alone can be sufficient to yield equivalence associations. It is suggested that equivalence formation by reinforcement reversal may be within the capabilities of simple multilayer neural networks and that avians possess nervous systems that are complex enough to incorporate the requisite neuronal circuitry. Thus, th...