Abstract
Previous research has demonstrated that manipulating vision can influence balance (Edwards, 1946). Here, we assess the influence of manipulating balance on size perception. In Experiment 1, participants visually matched the widths of beams when balanced and unbalanced by standing on a balance board. When unbalanced, participants estimated the widths to be thinner than when balanced. Experiments 2-5 tested possible mechanisms of this effect. In Experiment 2, participants did not estimate the width of the beam differently when viewing the board for a limited amount of time, suggesting that the effect when unbalanced was probably not due to reduced attention to the beam. Experiment 3 tested another hypothesis: that imbalance increases arousal, which affects perception. Participants' arousal level was increased by jogging in place. They estimated the board as thinner when they jogged as compared to when they were balanced. However, when participants were jogging or unbalanced they may have experienced greater movement in the visual scene. In Experiment 4, we raised participants' level of arousal without having them move, by asking them to count backward by 7s. When participants counted backward, they estimated the width of the beam as thinner than when not counting. In all conditions that produced an effect (unbalanced, jogging, counting by 7s), participants were aroused, but also performed two tasks simultaneously. In the final experiment, participants viewed arousing pictures before estimating widths. In this case, arousal was increased, but a dual-task paradigm was not employed. Again, participants estimated the width of the beams as smaller after viewing arousing images. Overall, the observed effects on size perception seem to be due to higher levels of arousal that may be experienced when unbalanced.