Geometric rule learning by pigeons

Abstract

In a series of four experiments using an open field search task, pigeons were trained to find a goal located at the midpoint of the hypothetical line connecting two discrete landmarks positioned in a linear array. Pigeons searched in substrate for an initially visible but eventually invisible goal location containing food reward. In Experiment 1, the apparatus was devoid of orienting cues. After reaching performance criteria in training, critical food-absent test trials were conducted by manipulating the distance between the landmarks (interlandmark distance) to determine the nature of encoded spatial information. Search error and location on novel interlandmark distances suggested pigeons learned a relative geometric relationship between the landmarks as opposed to absolute distance and direction. In Experiment 2, orienting cues were introduced and pigeons were again trained to performance criteria. After reaching performance criteria, pigeons were again tested in the absence of food with novel interlandmark distances. In contrast to Experiment 1, results from Experiment 2 suggested pigeons learned absolute distance from the landmarks. In Experiment 3, pigeons continued to search along the hypothetical line connecting the landmark with rotations of the landmark array in both the presence and absence of an orienting cue indicating learning of relative direction from the landmarks and further evidence for the learning of a geometric relationship between the landmarks. Experiment 4 tested pigeons with each landmark from the array individually in both the presence and absence of the orienting cue and revealed that pigeons used the orienting cue and both landmarks for accurate goal localization. Overall, results implicate a stable frame of reference as critical to spatial coding strategies and suggest pigeons are capable of coding location based on both absolute and relative distance and direction. Findings also suggest pigeons are capable of coding location in a manner consistent with that proposed by the multiple-bearings hypothesis (Kamil & Cheng, 2001) and provide evidence for greater flexibility in pigeons’ navigation and orientation strategies than revealed by previous research.