Fig. 2: Four representative behavioral motivations.

A behavioral motivation is described by a pair of variables, namely need threshold (α) and motivation intensity (λ), corresponding to a point in the (α, λ) plane. In a donation game, if both participants choose cooperation (or defection) with probability 0.5, each player’s expected payoff is (b − c)/2. If a player’s need threshold is greater than (b − c)/2, they are referred to as ‘demanding’, whereas they are referred to as ‘undemanding’ if their need threshold is less than (b − c)/2. If a player’s motivation intensity λ has a positive value, this indicates that they are more likely to cooperate if their need is met, which we call ‘philanthropic’ behavioral motivation. If λ is negative, they are more likely to cooperate if their need is not met, which we refer to as ‘aspirational’ behavioral motivation. As such, there are four qualitatively different types of players: undemanding philanthropist, demanding philanthropist, undemanding aspirationalist, and demanding aspirationalist.