Representation of serial order in pigeons (Columbia livia)

Abstract

When monkeys learn a list of arbitrary items they acquire a representation of those items in sequence (e.g., A > B > C > D > E) and knowledge of each item’s ordinal position (e.g., A1st, B2nd, C3rd, D4th, and E5th). In contrast, when pigeons learn a list they show no evidence of having formed a representation or of acquiring knowledge of each item’s ordinal position. This difference between monkeys and pigeons is heralded as one of the few examples in the comparative literature of a qualitative difference between species. Across nine experiments we show that pigeons are able to form a representation of list items in sequence and that they acquire knowledge of each item’s ordinal position. Why did our pigeons demonstrate faculties previous studies have suggested are beyond their ability? The answer is simple: Previous studies did not take into account the critical role that contextual variables play in the performance of pigeons on tasks that are used to test their representational abilities. By devising appropriate tests that address the contextual variables, we show that pigeons can indeed acquire a representation of a list of items in sequence, as well as knowledge of each item’s ordinal position. These findings now add to the evidence in support of Macphail’s (1985) Null Hypothesis.