Reviewer #2 (Public Review):
This is a behavioural study (healthy participants) looking at how people trade-off a brief phasic pain stimulus with a monetary reward. People make pairwise choices between a painful electrical stimulus and an amount of money, with different groups receiving offers from different ranges (0-5$; 0-10$) and distributions (skew or not). This allows the authors to estimate indifference points.
There were several findings:
i) a curvilinear intensity x value function, regardless of context.<br />
ii) a context effect: people require more money to accept pain if the range of offers is higher<br />
iii) decisions slowed when accepting pain, especially for high pain<br />
iv) higher trait harm avoidance was associated with high pain avoidance in the task<br />
v) with a skewed (exponential) distribution of trials, subjects end up accepting less pain, but tend to accept higher offers when made.
Some comments on each finding:
i) interpreting the shape (linear, non-linear) of the value function is always a bit tricky - it reminds me of the old data on the power law for stimulus response functions. But especially the issue here is that ratings or %tolerance is bounded, but intensity isn't, so inherently one is likely to get a non-linear function when doing any mapping onto a bounded scale. Of course this isn't really the main point of the study, but is worth noting
ii) the context effects are interesting. Similar effects were shown by Vlaev for the context effect of range. The effect of exponential distribution I think is consistent with Chater's model of relative value effects.
iii) Slower decisions with more pain are interesting. Fields's motivation-decision model deals with inhibiting pain when accepting 'greater' rewards, and shows slower innate pain responses (e.g. tail-flick). Did the authors gather intensity ratings? The lack of a choice difficulty effect is also interesting - is a drift diffusion model applicable (I don't think they placed time-pressure on the response)?
iv) The harm-avoidance finding is not that surprising. How did the authors correct for multiple comparisons across the 5 principal components?
v) for the greater profitability index - is this confounded by the fact that these subjects overall received less pain. This would an issue, for instance, if there was a cumulative effect of overall pain ('I can only take so many pains in one experiment')?
So overall, the study supports and adds to previous findings of a context-dependency deriving from the distribution of rewards, which is a deviation from conventional rational choice theory. It's a nice experiment, appropriately powered and carefully executed, and develops the ideas behind the behavioural economics of pain.