A comparison of protocols for passive and discriminative avoidance learning tasks in the domestic chick

A one-trial learning task, where chicks learn that a bead of a particular shape and/or colour has a bitter taste (because it has been coated in 100% methyl anthranilate, MeA) and subsequently avoids it on test, has been widely used by research groups across the world. However, there are some differences in the results reported by different research laboratories. One important difference is found when chicks are trained with a diluted bitter taste on the bead (10 or 20% MeA); memory is not consolidated and fades, lasting for different times. At Monash and La Trobe Universities, memory lasts for 30 min but at the Open University (OU), memory lasts for 4–6 h before fading. Differences in protocol that may explain this apparent discrepancy are whether the chicks have seen the bead before (novelty) and whether the colour or the shape of the bead is an important feature. In this review, we discuss these and other factors that may contribute to the differences in the characteristics of memory processing at Monash and at the OU, such as chick strain, hatchery or laboratory incubated chicks, age at training. It is clear that there is a difference between passive avoidance and discriminative avoidance protocols and this may explain the differences in duration of the memory with weakly reinforced learning. Is the OU task a more salient experience because of the novelty of the bead and therefore a ‘stronger’ learning experience? The different protocols may allow different questions to be addressed.