Abstract
We review evidence for Macphail’s (1982, 1985, 1987) Null Hypothesis, that nonhumans animals do not differ either qualitatively or quantitatively in their cognitive capacities. Our review supports the Null Hypothesis in so much as there are no qualitative differences among nonhuman vertebrate animals, and any observed differences along the qualitative dimension can be attributed to failures to account for contextual variables. We argue species do differ quantitatively, however, and that the main difference in “intelligence” among animals lies in the degree to which one must account for contextual variables.
Highlights
Specialty section: This article was submitted to Comparative Psychology, a section of the journal Frontiers in Psychology
We argue species do differ quantitatively, and that the main difference in “intelligence” among animals lies in the degree to which one must account for contextual variables
In light of the wealth of data that has accumulated since Macphail (1985) published his Null Hypothesis, the aim of this article is to Macphail Revisited see whether it has stood the test of time: are there really no differences, qualitative or quantitative, in the cognitive abilities of vertebrate animals?
Summary
We review the current status of Macphail’s claim that there are no differences, either qualitative or quantitative, in intelligence across nonhuman vertebrate species. Lionello-DeNolf and Urcuioli (2002) trained their animals so that the sample and comparison stimuli could appear in any of a number of positions, effectively training “position” out as a component of the stimulus response topography Despite this training the pigeons still failed to show any evidence for symmetry, a finding that, marginal as the evidence for symmetry is in non-human primates, further seems to distance pigeons from nonhumans in their ability to form symmetrical relations. The performance across the 10 pairs, as well as the presence of a first-item effect and a missing-item effect, supports the view that in the course of learning a serial-order task monkeys form a linear mental representation of the items and use that representation to guide their behavior, for example, during the pairwise test. It would seem that for the pigeons, for whatever reason, displaying all the pairs at once as in a standard pairwise test is a contextual variable that prevents them from displaying their understanding of the organization of the items of a four-item and five-item lists
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