Super-size me: self biases increase to larger stimuli

Prior work has shown that simple perceptual match responses to pairings of shapes and labels are more efficient if the pairing is associated with the participant (e.g., circle-you) than if it is associated with another familiar person (e.g., square-friend). There is a similar advantage for matching associations with high-value rewards (circle-£9) versus low-value rewards (square-£1) (Sui, He, & Humphreys Journal of Experimental Psychology: Human Perception and Performance, 38, 1105-1117, 2012). Here we evaluated the relations between the self- and reward-bias effects by introducing occasional trials in which the size of a shape was varied unexpectedly (large or small vs. a standard medium). Participants favored stimuli that were larger than the standard when stimuli were associated with the self, and this enhancement of self bias was predicted by the degree of self bias that participants showed to standard (medium) sized stimuli. Although we observed a correlation between the magnitudes of the self and reward biases over participants, reward-bias effects were not increased to large stimuli. The data suggest both overlapping and independent components of the self and reward biases, and that self biases are uniquely enhanced when stimuli increase in size, consistent with previously reported motivational biases favoring large stimuli.