http://dx.doi.org/10.1371/journal.pcbi.1002327 (Publisher version)
Friston, K. J., Shiner, T., Fitzgerald, T. H. B., Galea, J. M., Adams, R., Brown, H., et al. (2012). Dopamine, affordance and active inference. PLoS Computational Biology, 8(1): e1002327. doi:10.1371/journal.pcbi.1002327.