Post by Anastasia Sares
What's the science?
Some time ago, just before the turn of the new millennium, scientists discovered that when one monkey watched another monkey performing an action, like reaching for an object, neurons fired in the brain as if it was performing the action itself. These neurons, often called ‘mirror neurons,’ are the subject of much debate, with some researchers claiming that they underlie things as complex as human empathy, while others remain more skeptical.
In general, humans are great imitators. It takes little effort for us to repeat someone else’s actions, and much more effort to withhold that response (as any child who has played “Simon Says” will tell you). However, we also seem to be very good at performing separate, complementary actions while working towards a goal. Think of lumberjacks sawing a tree trunk, or musicians performing a duet. What supports these uniquely human activities is what Sacheli and colleagues call a “Dyadic Motor Plan,” and this week in Cerebral Cortex, they aimed to find the brain regions involved. The study was performed at the University of Milano-Bicocca, Milan, Italy, in collaboration with the IRCCS Istituto Ortopedico Galeazzi, Milan, Italy.
How did they do it?
Participants completed a music-like task with interactive and non-interactive conditions. With a “partner” (seen via video displayed on a monitor) they took turns performing one of two actions to a wooden cube (either touching the top with the index finger or pinching the sides of the cube). Each action was paired with a musical tone (G or C). The participant always saw the partner’s action and heard the resulting musical note before performing their own action. Each sequence was four actions long — #1 partner, #2 participant, #3 partner, and #4 participant. A small colored square indicating how the participant should respond during each trial was presented at the end of action #1 (after the participant had seen their partner’s first action). In the non-interactive condition, the square’s color indicated a previously-learned sequence of notes that the participant should perform, regardless of what their partner did. In the interactive condition, the color indicated a previously-learned melody that they were expected to continue along with their video partner, cooperating to produce all the necessary notes. In addition to manipulating interactivity, the authors had participants perform some trials in which their action (tap or pinch) matched their partner’s previous action and some in which the actions did not match. Humans can experience visual interference when they see a partner perform an action different than the one they are about to perform. In other words, it takes more effort to process and execute a non-matching action. The interactive task condition was built so that the partner’s actions could be predicted and were part of a shared goal (i.e., playing a melody together), which should lead to a “dyadic motor plan,” and reduce visual interference.
What did they find?
The authors measured response times as well as brain activity. In the non-interactive condition, the reaction times were longer for non-matching actions: evidence of visual interference. In the interactive condition, however, there was no difference in reaction time between matching and non-matching actions. The authors also found a region of the frontal lobe (the premotor cortex) where the pattern of brain activity differed between conditions. This region was selectively active during the interactive condition regardless of whether the participant’s actions matched their partners, indicating that no differences in brain activity reflected simple imitation of a partner’s action. However, there was an interaction between condition (interactive versus non-interactive) and time during the four-part sequence; the region exhibited greater activity during action #1 versus later in the sequence, before the colored square had been presented. Because the colored square in the interactive condition indicated which goal (melody) participants were working towards with their partner, this brain activity likely reflects the participants' attempt to predict the partner’s next action and musical note.
The authors interpreted this to mean that when we do something together with a partner, our brain tries to predict our partner's contribution to the shared goal to see whether it meets expectations. They also emphasized that this region of the brain is situated in the frontoparietal network, which is involved with predictions like anticipating a partner’s goals.
What's the impact?
This research shows that pursuing common goals with another member of our species has an impact on how our brains process and react to visual information. Mimicking another’s actions may be helpful in some cases, but the reflex to imitate takes a back seat when we have more information and a better sense of context.
Sacheli et al. How Task Interactivity Shapes Action Observation. Cerebral Cortex (2019). Access the original scientific publication here.