I think it’s actually the fact that ‘roles‘ have generally been established once a couple has been together for a while, and when the couple is together in this case they are in execute-the-plan mode.
When it’s just one half of the couple, theres a realization that they have to fill both roles. The mental scavenging required to prioritize/sequence/execute a blend of familiar and unfamiliar actions is going to perturb brain activity.
It is actually other way round. I was more often without other person, so the only me situation was easier to execute and "plan". Other person presence inference sometimes requires more thinking or complications due to acting unpredictably.
Other person makes it easier in a sense that there are two hands and you can split kids. So you don't change diapers while watching other kid. But in terms of how usual situation is, how much cooperation and negotiation it requires, it requires more.
Exactly. When we're used to alternate parenting and work, and rarely do "co-parenting" simultaneously, it can happen that both us assume the other is currently watching after the child, when neither is :-\
We see this in situations involving co-workers and neighbors, friends and even strangers. There's the point-source stimulus and its first order effects we react to but it's mediated by the reactions we observe from those around us participating in the same experience resulting in second-order (and more) effects.
Isn't this effectively the psychology of crowds writ small?
When it’s just one half of the couple, theres a realization that they have to fill both roles. The mental scavenging required to prioritize/sequence/execute a blend of familiar and unfamiliar actions is going to perturb brain activity.