Recent experiments with rats suggest that they show episodic-like or what-where-when memory for a preferred food found on a radial maze. Although memory for when a salient event occurred suggests that rats can mentally travel in time to a moment in the past, an alternative possibility is that they remember how long ago the food was found. Three groups of rats were tested for memory of previously encountered food. The different groups could use only the cues of when, how long ago, or when + how long ago. Only the cue of how long ago food was encountered was used successfully. These results suggest that episodic-like memory in rats is qualitatively different from human episodic memory.
In 4 experiments, the authors asked whether pigeons (Columba livia) would show metamemory by choosing to study a sample stimulus before taking a memory test. In Experiments 1a-1c, pigeons chose between cues that led either to exposure to a sample stimulus or directly to the comparison test stimuli without seeing the sample in a delayed matching-to-sample task. The same choice was used in Experiment 2 to see whether pigeons would take a reminder when memory of the sample was weak. In Experiments 3 and 4, pigeons' responses led to either a choice between red and green side keys with a sample present to guide the choice or a choice with no sample present. The findings of all of these experiments suggest the absence of metamemory in pigeons.
Working spatial memory in dogs (Canis familiaris) was tested in Experiments 1 and 2 on an 8-arm radial maze. When dogs chose freely among all 8 arms containing food in Experiment 1, they learned to enter all 8 arms with progressively fewer arm visits over trials. In Experiment 2, 2 groups of dogs were forced to visit 4 randomly chosen arms on the maze and then tested for memory of these arm visits using a win-shift rule for 1 group and a win-stay rule for the other group. Dogs performed better with the win-shift rule than with the win-stay rule. In Experiment 3, reference memory was investigated by using a 4-arm maze on which 0, 1, 3, and 6 pieces of food were consistently placed on different arms. Dogs learned to visit the arms with the larger amounts before the arms with the smaller amounts. Dogs' memory capacity in these studies was found to be surprisingly low.
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