Hand washing induces a clean slate effect in moral judgments: a pupillometry and eye-tracking study.

Kai Kaspar,Vanessa Krapp,Peter König

doi:10.1038/srep10471

Abstract

Physical cleansing is commonly understood to protect us against physical contamination. However, recent studies showed additional effects on moral judgments. Under the heading of the “Macbeth effect” direct links between bodily cleansing and one’s own moral purity have been demonstrated. Here we investigate (1) how moral judgments develop over time and how they are altered by hand washing, (2) whether changes in moral judgments can be explained by altered information sampling from the environment, and (3) whether hand washing affects emotional arousal. Using a pre-post control group design, we found that morality ratings of morally good and bad scenes acquired more extreme values in the control group over time, an effect that was fully counteracted by intermediate hand washing. This result supports the notion of a clean slate effect by hand washing. Thereby, eye-tracking data did not uncover differences in eye movement behavior that may explain differences in moral judgments. Thus, the clean slate effect is not due to altered information sampling from the environment. Finally, compared to the control group, pupil diameter decreased after hand washing, thus demonstrating a direct physiological effect. The results shed light on the physiological mechanisms behind this type of embodiment phenomenon.

Highlights

Physical cleansing is commonly understood to protect us against physical contamination
Hand washing did not undo an unethical deed that participants had previously committed[1], did not change previous decisions[14], and did not substitute a failure experience by success[16], but it changed the weighting of unethical deeds, reduced the need to devaluate non-chosen options, and increased one’s optimism to be more successful in the future, respectively
The present study addresses the three questions described above: (1) we used a pre-post control group design to investigate whether hand washing would cushion increasing stereotyping in moral judgments, as suggested by Smith et al.[22]

Summary

A Pupillometry and Eye-Tracking Study

Physical cleansing is commonly understood to protect us against physical contamination. Hand washing did not undo an unethical deed that participants had previously committed[1], did not change previous decisions[14], and did not substitute a failure experience by success[16], but it changed the weighting of unethical deeds, reduced the need to devaluate non-chosen options, and increased one’s optimism to be more successful in the future, respectively In each of these cases, we can assume that the effect was based on a selective sampling of information. According to the notion of a clean slate effect, washing should reset one’s cognitive state to a more neutral one[17] and, increase peoples’ openness for each individual scene so that they are more motivated to visually explore it before making a moral judgment. If the clean slate effect of hand washing affects physiological arousal, pupil diameter should decrease after hand washing (Hypothesis 3, Physiological Effects)

Methods

Results

Discussion