Japanese scientists taught monkeys to coordinate their movements with each other
(Image generated by AI)
Japanese researchers taught macaques to move a vertical rod from side to side along a track to see if the animals would coordinate with a mate or with a video.
Macaques that watched each other while they moved the rods coordinated better than those who watched the same actions of the monkey on video.
And the video where the rod moved by itself produced the least effect. This indicates the social nature of motor coordination.
Musicians, dancers and athletes often have to coordinate and synchronize their movements with the movements of another.
Also, in ordinary life, we often repeat the pose of the interlocutor, start walking with someone in step, or even blink to the beat.
This synchronization of movements is also called motor involvement, and it may contribute to social bonding.
In people with autism spectrum disorders, this involvement is often disrupted.
Great apes like chimpanzees and bonobos also coordinate their movements with relatives.
This has also been observed in Japanese macaques.
Saeka Tomatsu and Masaki Isoda, researchers at the SOKENDAI Higher University for Advanced Studies, tested how social this copycat behavior is.
Since macaques can synchronize their movements not only with each other, but also with moving objects, the authors decided to compare how motor involvement works in both cases.
And to find out, they taught 3 Japanese macaques (Macaca fuscata) - N, G and M - to grab a vertical rod with their right hand and move it from side to side in a straight path 25 centimeters long.
There were LEDs at the ends of the track: as soon as the monkey moved the rod to one end, the LED on the other would light up.
For every few moves, the monkeys were given a piece of food as a reward.
The movement of the rod in one direction had to take at least 400 milliseconds - if the monkey pulled it faster, it was not encouraged.
Then the monkeys were planted in pairs in front of each other: each had its own rod.
They started moving it after the start signal and stopped after the stop signal.
If a monkey moved the rod too fast or looked around, its LEDs would turn off, signaling that there would be no reward.
The second monkey could continue to move the stick.
The researchers then calculated the phase difference between the positions of each rod at each point in time.
They found that the phase difference was consistent and roughly constant across all tests for each particular pair.
They calculated the direction and length of the average resulting vector: the direction showed the phase difference itself, and the length showed how constant this difference was (the longer, the more constant).
At the same time, the direction and length of the average resulting vector differed between pairs of monkeys.
Thus, the direction was -0.38 radians for the M-N pair; -0.12 radians for the G-N pair and -2.01 radians for the G-M pair.
That is, the monkeys coordinated their movements with each other - and each pair did it differently.
The researchers then placed a screen between the monkeys that could turn opaque.
Now, in some trials, the animals could not see each other.
When this happened, the phase difference was no longer stable: that is, motor involvement did not occur.
The authors noticed that when the animals saw each other, they moved the rod faster.
(Saeka Tomatsu, Masaki Isoda; PNAS, 2023 https://bit.ly/3N5JGMV)
Scientists also calculated how long the macaques watched each other.
It turned out that in tests where they paid less attention to each other, the phase difference was not so stable.
The social rank of the monkeys also influenced the interaction. N had the highest rank and M had the lowest.
In some tests, the screen became opaque for only one monkey, while the second continued to see the partner.
The constancy of the phase difference was maintained only when N (the highest-ranking macaque) observed M or G, but not vice versa.
Perhaps more dominant individuals are more likely to coordinate their movements with others.
Thus, motor involvement in macaques works better with real-time social interactions - when they look at each other.
- Proceedings of the National Academy of Sciences: https://www.pnas.org/doi/10.1073/pnas.2301614120#fig01
- EurekaAlert: https://www.eurekalert.org/news-releases/990916
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