The Delayed Matching-to-Sample Task - Are Pigeons Too Smart To Remember?

Abstract

The delayed matching-to-sample (DMS) task is a commonly used task to assess memory in animals. The current study assesses the possibility of an alternative method to solve the task, using simple strategies. A new tracking system was implemented, using cameras to track pigeons’ positions to eliminate researcher bias and allow analysis to be performed with relative ease. A first experiment assessed four pigeons on the DMS task, with differential outcomes, as the nature of the difference in reward opportunity associated with the different stimuli was most likely to result in a difference in positioning between the stimuli. The pigeons all demonstrated a significant difference in position between the stimuli. Furthermore, the tracking system worked. A second experiment then assessed the impact of interference on the same pigeons’ positions and found that three of the four pigeons showed a greater difference in position when interference was present. Finally, a third experiment assessed three different pigeons’ positions on a DMS task with common outcomes as eliminating the difference in reward opportunity enabled assessment of the natural differences acquired by pigeons when solving the task. Again, all three pigeons displayed significant differences in the position associated with the two stimuli. We have provided a new method of behavioural tracking that may be used in many animals, such as pigeons and rats, to further explore animal behaviour during a variety of tasks and to assess the effectiveness of these tasks as measures of cognitive processes. The differences in position raise the possibility that animals may adopt simple strategies to bypass memory to solve the DMS task.