While we would all like to believe that our pets greet us at the end of the day because they remember us as their best and most beloved friends, the truth is actually far different from that. A new study led by researchers at the Centre for Cultural Evolution in Stockholm Sweden looked at short term memory in 25 different species of animals from dolphins to bumble bees and the results did not support the belief that our dogs, cats and other pets remember who we are.
The team, team led by Johan Lind, an animal ethologist, found that the average short-term memory span was about 27 seconds. Dogs, the animal in the study most often kept as pets, forget an event within two minutes. Chimpanzees were able to retain information for about 20 seconds, but the average rat had a longer memory retention time than their chimp friends. The memory spans of three other primates-baboons, pig-tailed macaques, and squirrel monkeys-exceeded only bees, which were the only studied subjects that were not primates or birds.
The study's lead researcher, Lind, expressed surprise at the poor performance of the chimpanzees, especially since they are our closest living relative on the evolutionary ladder. The study results suggest that human capacity for memory evolved after we branched from the most recent shared ancestor with chimps, over six million years ago.
The results of this study were published in the journal Behavioural Processes and were drawn from data compiled from over a hundred studies of captive animals. The memory of the different animals was tested using a method of testing the recall of recent random events known as the delayed matching-to-sample (or DMTS) method.
In this test, an animal is typically shown a visual stimulus such as a red circle. The red circle disappears, then, after a delay, it's shown again with another sample stimulus-a blue square, say. The animal, usually with the incentive of a food reward, has to select the original sample it saw.
When a similar test is given to humans, it is easily passed. Studies have shown that people can reliably recall the right symbol after 48 hours or more.
"The data tell us that animals have no long-term memory of arbitrary events," Lind said. Based on the new study, "we think humans' ability to remember arbitrary events is unique."
In humans this ability is called episodic memory. In animals it is different. Rather than remembering specific episodes, animals have "associative memory." Lind offers the example of the cat who fears the carrier because it signals a trip to the vet. The study authors proposed that animals might have specialized memory systems hardwired to remember certain "biologically relevant information" (such as where to find food or how to react to potential danger.)
Researchers added that the DTMS results may be skewed in favor of animals that are more accustomed to the lab environment, which could explain why the rats did better than the chimpanzees. Scientists see the two kinds of memory as an important distinction when trying to understand what mental skills we share with other animals and what's unique about the human mind.
Despite the findings, most pet owners would agree that what kind of memory their dog or cat possesses is not really important as long as the tails wag at the end of a long day.