Social rewards are often compared in experimental designs with non-social ones: a popular pair is money (non-social) vs. a smile (social). However, we often forget that money and smiles differ on many more dimensions than just sociality. For example, money is tangible, but a smile is not. Can we then draw informative conclusions about the differences in the brain processing of social and non-social rewards? We argue that to do so, we need to use a multidimensional view on rewards.
You can find the original article here (open access).
What are social and non-social rewards?
A reward in psychology is something that we want or desire, something that we like and enjoy getting, and something that we would work towards to get it. Some rewards are obvious, like food: Parents may promise kids they would get a sweet treat for a dessert if they eat their veggies for dinner, or as adults we can decide to treat ourselves to a tasty cake of chocolate once we have finished this report we have to do for the boss. Food is a great reward, because it’s hard-wired to our brain: It’s linked to survival and gives straightforward pleasure. Similarly, our brains are “tuned” to enjoy social rewards, like smiles, appreciative gestures, and encouraging praises.
Imagine that your tough boss gives you feedback on your latest report. Now imagine two scenarios: They use the words “You did a great job!”, or say nothing, but you find a small bonus in your next pay check. If the boss is normally quite stingy with praise, this may be a huge reward for you to hear such words of appreciation. On the other hand, it is also very rewarding to receive more money for your work. Thus, both a praise and money are rewards, but they are very different in many ways.
Rewards in research
It is clear that social and non-social rewards (like smiles and money) are common in our every-day lives and are very important for our psychological functioning. Because of that, reward processing is an important topic in neuropsychology, which tries to explain its mechanisms on neural and behavioural levels (what does the brain do, and what kind of behaviour it entails, respectively). Surprisingly, it is still unclear whether social rewards are somewhat privileged in processing, or are processed similarly to non-social rewards. For example, the social motivation hypothesis of autism claims that the brains of persons with autism are less “tuned” to the social rewards, than non-social rewards, so this line of research often contrasts these kinds of rewards (by showing, for example, smiles and money as rewards in an experiment). On the other hand, some studies suggest that the brain may be bringing all sorts of rewards to some kind of “common currency”, and social and non-social rewards are processed in the same brain areas of what is referred to as the reward network (see Haber & Knutson, 2010).
Altogether, these studies suggest that there are both similarities and differences in neural processing between social and non-social rewards. However, in our paper we argue that research comparing social and non-social rewards often neglects important dimensions that can be entangled with the sociality (social vs. non-social) dimension. To see that, let’s look at the common example of social and non-social rewards in psychology: smiles and money.
Smile vs. money
Comparing brain responses to receiving a smile or money may potentially reveal a difference between social and non-social rewards. However, it can also reveal a difference between intangible and tangible rewards! Consider this: A smile from your boss for a job well done can be very rewarding, but it is not something you can quantify, touch, put in the pocket, and take away with you (in a literal way). However, a bonus in your pay check for the same job is something tangible: you can withdraw this money and touch it, put in the pocket, feel it. A smile and money obviously differ in tangibility: money is tangible and smile is not. Hence, the difference between smile and money is not only their sociality, but also their tangibility.
What is more, there are other dimensions on which smile and money can be differentiated. For example, a smile is primary reward (we are “programmed” to like them), and money is secondary (we only learn in life that this is something rewarding). Also, a smile is immediate and transient (its rewarding value lasts as long as its exposure), whereas money is lasting and distant, at least in an experiment, as it is normally delivered at its end. Hence, the difference between smile and money is not only their sociality, and tangibility, but also primacy, temporal proximity and duration.
Multidimensional view on rewards
We saw that smiles and money differ not only in their sociality (one is social and one non-social), but also in other dimensions (tangibility, primacy, temporal proximity and duration). Importantly, all fo these dimensions have been shown to be processed differently in the brain (see our full article for details)! This multidimensional perspective offers important insight: If we measure how the brain responds to smiles and money in an experiment and find differences, these observed differences cannot be fully ascribed to the social vs. non-social contrast, because they could also stem from differences in tangibility, primacy, proximity, and duration.
Here we looked closely into one comparison of social and non-social rewards: smiles and money. However, such comparisons and similar are very common in psychological research. Thus, we argue that researchers should be carefully considering different dimensions on which rewards could be described before they assign observed experimental contrasts to one of them. In our article, we propose a more comprehensive, multidimensional view on rewards in experimental settings, which allows more informed and better-controlled comparisons of social and non-social rewards. Altogether, these methodological considerations aim to inform and improve future experimental designs in research utilizing rewarding stimuli, especially in the social domain.
Chevallier, C., Kohls, G., Troiani, V., Brodkin, E. S. & Schultz, R. T. The social motivation theory of autism. Trends in Cognitive Sciences 16, 231–238 (2012).
Haber SN, Knutson B. The reward circuit: Linking primate anatomy and human imaging. Neuropsychopharmacology (2010) 35:4–26.