Behavioral Design
In the trust game, the first player is endowed with SGP$ 20 (about US$16), while the second player is endowed with nothing. In the first stage, the first player decides how much to send (S) to an anonymous and randomly matched second player (20 – S). For every dollar the first player sends, the second player receives three times (3S). In the second stage, the second player decides how much (B) out of 3S to second back to the first player. At the end, the first player receives (20 – S + B) being the amount he/she keeps plus the amount the second player sends back while the second player receives three times the amount sent deducting the amount sent back (3S – B). We use the strategic method [24], in which the second player states his/her response to each of 21 possible choices from the first player. Every participant plays both roles of first and second players without any feedback. At the payment stage with real money, we randomly determine the specific role – first or second mover – for each pair of subjects. The amount sent by first player is used as a measure for trust while the average return amount from the second player is a measure for trustworthiness.
As trust is an inherently risky behavior viz., the trustee may not reciprocate with an act of trustworthiness, we aim to test whether OT is specific to trust in the social interactions or alternatively plasma OT indexes risk in general. We therefore include a risk task using portfolio choice design [25]. In this risk task, subjects are endowed with SGD $20, and decide how much to invest on an experimental stock. For the amount invested, there is 50% chance that it will become 2.5 times, and 50% chance that it will become zero. This design enables us to observe different levels of risk aversion for each subject, and allows ascertainment of the specificity of plasma OT levels towards trust without including a confound i.e. a possible connection between OT and risk attitude.