Cameron, J., Banko, K. M., & Pierce, W. E. (2001). Pervasive negative effects of rewards on intrinsic motivation: The myth continues. The Behavior Analyst, 24(1), 1-44.
Mega meta-analysis of 3 previous ones (Cameron & Pierce, 1994; Eisenberger & Cameron, 1996; Deci, Koestner, & Ryan, 1999).
Found “no evidence for detrimental effects of reward on measures of intrinsic motivation” (Cameron et al., 2001, . 21)