Visual control of an action discrimination in pigeons

Abstract

Recognizing and categorizing behavior is essential for all animals. The visual and cognitive mechanisms underlying such action discriminations are not well understood, especially in nonhuman animals. To identify the visual bases of action discriminations, four pigeons were tested in a go/no-go procedure to examine the contribution of different visual features in a discrimination of walking and running actions by different digital animal models. Two different tests with point-light displays derived from studies of human biological motion failed to support transfer of the learned action discrimination from fully figured models. Tests with silhouettes, contours, and the selective deletion or occlusion of different parts of the models indicated that information about the global motions of the entire model was critical to the discrimination. This outcome, along with earlier results, suggests that the pigeons’ discrimination of these locomotive actions involved a generalized categorization of the sequence of configural poses. Because the motor systems for locomotion and flying in pigeons share little in common with quadruped motions, the pigeons’ discrimination of these behaviors creates problems for motor theories of action recognition based on mirror neurons or related notions of embodied cognition. It suggests instead that more general motion and shape mechanisms are sufficient for making such discriminations, at least in birds.

Keywords: action recognition; biological motion; global perception; occlusion; pigeon.

Figure 1

Example of one of the eight animal models used in these experiments to exemplify the actions of walking and running. It is shown as rendered from a low, close, side perspective. Superimposed on the displays are the different motion paths of five body parts (nose, neck junction, tail junction, fore right foot, and rear right foot). These paths were not present in the stimuli tested with the pigeons.

Figure 2

Mean normalized peck rates for the four pigeons in Experiment 1 tested with different types of PLDs. Error bars indicate the standard error of each condition.

Figure 3

Mean normalized peck rates for the four pigeons in Experiment 2 tested with different contour displays. Error bars indicate the standard error of each condition.

Figure 4

Mean normalized peck rates for the three pigeons in Experiment 2 tested with different silhouette displays. Error bars indicate the standard error of each condition.

Figure 5

Mean normalized peck rates for the three pigeons in Experiment 3 tested in different types of occlusion conditions. Error bars indicate the standard error of each condition.

Figure 6

Mean normalized peck rates for the three pigeons in Experiment 3 tested in different types of featured deletion conditions. Performance with various portions of the stimulus deleted. Error bars indicate the standard error of each condition.