(Image credit: Shuttersto
Cuttlefish can pass the “marshmallow test” — the famous psychological test of self-control.
In this case, the cephalopods were willing to forgo meals when they knew that waiting meant they would be rewarded with more delicious treats, according to a new study. That makes them the first known invertebrates to show the ability to exert self-control.
The common cuttlefish (Sepia officinalis) — relatives of squids and octopuses — are sneaky hunters and impressive camouflagers, with the ability to quickly disappear into any environment. They are also scarily smart; studies previously showed that they have a good memory, can learn the value of different types of prey and can use past experience to help them predict where to find food.
But prior to this study, it w
Self-control is thought to be the cornerstone of intelligence, as it is an important prerequisite for complex decision-making and planning for the future,” said lead author Alex Schnell, a research associate in the Department of Psychology at the University of Cambridge. Not all animals share this trait, and it was previously thought that the ones that do, such as great apes, corvids and parrots, have long and social lives.
To see if a cephalopod should join the ranks, Schnell and her team adapted the famous “marshmallow test” so that it appealed to cuttlefish. In the 1960s, Walter Mischel led an experiment at Stanford University to test how much self-control children have when presented with a preferred treat such as a marshmallow (or other treats such as cookies and pretzels) and two options: either eat the one marshmallow now or wait for 15 to 20 minutes and get rewarded with two marshmallows.
In the current study, Schnell’s team swapped out marshmallows for seafood munchies, after figuring out what six individual 9-month-old (not yet fully adult) cuttlefish preferred to eat. It turned out, all of them preferred live grass shrimp the most, followed by king prawn, with the Asian shore crab coming in last of the three.
They then set up a two-chamber apparatus with transparent sliding drawers. Behind one drawer, they placed a preferred meal (such as live grass shrimp) and behind the other, they placed a less preferred meal (such as Asian shore crab). The doors had symbols on them that indicated whether it would open with a delay (a triangle) or open immediately (a circle), which the cuttlefish learned to recognize.
The drawer with the less preferred meal always opened to the cuttlefish immediately, but the other drawer opened after a delay. In the control condition, the door with the preferred snack didn’t open at all (a square). When the cuttlefish approached one chamber, the researchers immediately removed the snack in the other.