Hand Washing Induces a Clean Slate Effect in Moral Judgments: A Pupillometry and Eye-Tracking Study

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.

Physical Cleansing Biases Recognition Performance for (Im)moral Social Issues

“…This valence effect occurred independently of whether cleansing was performed before or after the learning phase, but the effect was absent in the control group that did not cleanse the hands. This result pattern is in line with the findings reported by Kaspar, Krapp et al (2015) who found an effect of hand cleansing on social judgments but no effect on visual information sampling as indicated by eye movement behavior on pictorial social scenes. The results of both studies contradict the notion that the effect of physical purity is temporally limited to the early stage of information sampling and encoding.…”

“…If the assumed effect of cleansing exclusively occurs when cleansing is performed before the learning phase, this will indicate that the effect of physical purity is temporally limited to the early stage of information sampling and encoding. It might be that this is the case with respect to memory performance, which differs remarkably from visual processing investigated by Kaspar, Krapp et al (2015). In contrast, if the effect occurs when hands are cleansed after the learning phase, this will indicate that cleansing has an effect on the retrieval of information from memory.…”

“…However, as recently outlined (cf. Kaspar, Krapp et al, 2015), these seemingly contradicting results might be explained by different attribution processes: harsher moral judgments are expected when cleanliness cognitions restore one's own moral self-image, whereas milder moral judgments are likely to occur when the state of cleanliness is attributed to the judged target.…”

“…Moreover, Kaspar, Krapp et al (2015) recently reported that hand cleansing affected moral judgements about visually depicted social scenes but that it did not show an effect on how their participants had scanned the visual stimuli before stimulus evaluation, as indicated by eye tracking data. The authors concluded that the impact of physical cleansing does not touch early processes of sensory information sampling.…”

“…Kaspar, Krapp, and König (2015) recently hypothesized that effects of physical cleansing (on moral behavior and in terms of clean slate phenomena) reflect a change in the weighting or selection of cognitive information. They concluded:…”