In this experiment we systematically vary the characteristics of the social environment and show that, depending on prenatal sex hormone priming, testosterone administration in women moderates the effect of the social environment on trust. We use the economic trust game and compare one-shot games modelling trust problems in relations between strangers with repeated games modelling trust problems in ongoing relations between partners. The trust game not only models important features of social and economic interactions, manipulating features of the game also allows to systematically vary the relative demands on cognitive empathy.
Our experiment was a double-blind, placebo-controlled study, employing a between subjects design with a total of 82 young, healthy female subjects (mean age (± s.d.) 22.4 ± 2.2 yr). All subjects provided written informed consent to the protocol of the study that was approved by the medical ethics committee of the University Medical Centre Utrecht. The protocol followed established procedures for experiments on testosterone effects and trust games. Testosterone and placebo were administered sublingually. Since the parameters (quantity and time course) for inducing neurophysiological effects after a sublingual testosterone administration are known in women but not in men, we exclusively recruited women. Subjects received a single dose of testosterone or placebo four hours before performing the main game tasks. Administration followed the established Tuiten method. Drug samples consisted of 0.5 mg of testosterone, 5 mg of cyclodextrin (carrier), 5 mg of ethanol, and 5 mL of water. Testosterone was omitted from the placebo samples.
Since effects of testosterone administration on cognitive empathy seem to depend on priming through prenatal testosterone, we included effects of 2D:4D ratio in the analyses. 2D:4D ratio has been established as an individual marker for differences in prenatal testosterone-to-estradiol ratio. 2D:4D ratio was measured from a scan of the right hand of the subjects, a valid method to measure finger lengths.
Each subject played six one-shot trust games with six different partners and a repeated game of six rounds with one and the same partner. Subjects were informed about behaviour of their partner after each game in both series of games. Half of the subjects started with the one-shot games, the other half with the repeated game. Each subject played in the same role throughout all games. As a result, we had twelve observations per subject, six in the one-shot games and six in the repeated game, with a total of 480 observations from 40 investors and 492 observations from 41 trustees.
