Cephalopods pass cognitive tests designed for children, confirming they can wait for the best food
The Marshmallow Test , or Stanford Marshmallow Experiment, is the test used to test the intelligence of cuttlefish. In the test (usually used to study the development of cognition in humans) a child is placed in a room with a marshmallow. He is told that if he manages not to eat it for 15 minutes, he will get a second marshmallow and then he can eat both. This ability to delay gratification demonstrates cognitive skills such as planning for the future and was originally conducted to understand at what age a human is intelligent enough to delay gratification if it means a better outcome later.
Being so simple, it can be adapted to animals. Of course, you can’t tell an animal that it will get a better reward if it waits, but you can train it to understand that better food is on the way if it doesn’t eat what’s in front of it right away. Some primates are able to delay gratification, even dogs, albeit inconsistently. Corvids, of course, also brilliantly passed the marshmallow test.
In 2020 it was the turn of cephalopods to undergo the test, which over time are proving to be much more intelligent than previously thought. Scientists have shown that common cuttlefish ( Sepia officinalis ) can refrain from having a meal in the morning, once they learn that dinner will be based on something much more welcome: shrimp.
However, as the team of researchers led by behavioral ecologist Alexandra Schnell of the University of Cambridge pointed out, it was difficult in this case to establish whether this change in behavior was also governed by a capacity for self -control . They then designed another test, on six common cuttlefish. The cuttlefish were placed in a special tank with two closed chambers, equipped with transparent doors that allowed the animals to see inside. There were snacks in the rooms: in one there was an unwelcome piece of raw shrimp, and in the other a much more tempting live shrimp.
There were also symbols on the doors that the cuttlefish had been trained to recognize. A circle meant that the door would open right away. A triangle meant that the door would open after 10 to 130 seconds. A square, used only in the control condition, meant that the door would remain closed indefinitely.
During the test session, the raw shrimp was placed behind the open door, while the live shrimp was only accessible after a certain amount of time. If the cuttlefish tried to go through the door to prey on the crayfish ahead of time, the prey was immediately removed.
The researchers found that all the cuttlefish in the test condition opted to wait for their favorite food (live shrimp). “The cuttlefish in the present study were all able to wait for the best reward and tolerated delays of up to 50 to 130 seconds, which is comparable to what we see in large-brained vertebrates like chimpanzees, crows and parrots,” Schnell said.
All things come to those who wait, cuttlefish know it
The other part of the experiment was to test the learning ability of the six cuttlefish. They were shown two different visual cues, a gray square and a white one.
When they approached one of them, the other was removed from the tank; if they made the “correct” choice, they would be rewarded with a snack. Once the cuttlefish learned to associate one square with a reward, the researchers switched clues, so that the other square became the clue that they would soon be rewarded. Interestingly, the cuttlefish that learned to adapt more quickly to this change were also those able to wait longer for the reward.
It seems that cuttlefish are able to exercise self-control, but it is not clear why. Researchers think this ability to delay gratification may instead have something to do with how cuttlefish get their food. “Cuttlefish spend most of their time camouflaged, sitting and waiting , with alternating short periods of foraging,” Schnell said. “When they’re camouflaged, they’re exposed to all the predators in the ocean that want to eat them. We hypothesized that delayed gratification may have evolved as a by-product of this situation, so that cuttlefish may optimize foraging by waiting to choose better quality food.”
It is a fascinating example of how very different lifestyles in very different species can lead to similar behaviors and cognition.
Future research should try to determine whether cuttlefish are actually able to plan for the future. According to the researchers, their ability to learn and adapt may have evolved to give cuttlefish an edge in the marine world they inhabit.
- Cuttlefish exert self-control in a delay of gratification task. (royalsocietypublishing.org)