I'm curious about the equation you mentioned. Has it actually been proven that motivation is directly proportional to expectancy and value but inversely proportional to time and impulsiveness? I mean in humans rather than in ideal utility maximisers (although I don't think ideal utility maximisers are known for their impulsiveness so I'm not even sure if it applies to them).

I didn't even know it was possible to rigorously measure motivation and impulsiveness.