The interaction between self-bias and reward: Evidence for common and distinct processes

The perceptual matching of shapes and labels can be affected by both self- and reward-biases when shapes are linked either to labels referring to particular individuals (you, friend, stranger) or to different reward values (£8, £2, £0). We investigated the relations between these biases by varying the reward value associated with particular shape-label pairs (circle-you, square-friend, triangle-stranger). Self shape-label pairs (circle-you) always received no reward, while friend shape-label pairs (square-friend) received high reward and stranger shape-label pairs low reward (triangle-stranger), or the reverse (friend-low reward; stranger-high reward). Despite receiving no reward, responses to self-related pairs were advantaged relative to those to low-reward stimuli and did not differ from those to high-reward items. There was also an advantage for responses to high-reward friend pairs relative to low-reward stranger stimuli, and for high-reward stranger stimuli compared to low-reward friends. Correlations across individuals were found across trial blocks for both the self-advantage and the high-reward advantage, but the self- and reward-advantages were uncorrelated. This suggests that the self- and reward-advantage effects have different origins. In addition, the magnitude of the self-advantage varied according to the rated personal distance between a participant and a stranger. For individuals manifesting a close personal distance to strangers, the self-advantage was smaller, and sensitivity to reward influenced the difference between the self- and high-reward conditions. For individuals manifesting a large personal distance to strangers, sensitivity to reward did not affect self-matching. We suggest that self-advantages on perceptual matching arise independent of reward for individuals with a large personal distance to strangers. On the other hand, in individuals with a weak self-bias, high reward and the self modulate a common subjective value system.