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

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

Emotions' impact on viewing behavior under natural conditions.

Human overt attention under natural conditions is guided by stimulus features as well as by higher cognitive components, such as task and emotional context. In contrast to the considerable progress regarding the former, insight into the interaction of emotions and attention is limited. Here we investigate the influence of the current emotional context on viewing behavior under natural conditions.In two eye-tracking studies participants freely viewed complex scenes embedded in sequences of emotion-laden images. The latter primes constituted specific emotional contexts for neutral target images.Viewing behavior toward target images embedded into sets of primes was affected by the current emotional context, revealing the intensity of the emotional context as a significant moderator. The primes themselves were not scanned in different ways when presented within a block (Study 1), but when presented individually, negative primes were more actively scanned than positive primes (Study 2). These divergent results suggest an interaction between emotional priming and further context factors. Additionally, in most cases primes were scanned more actively than target images. Interestingly, the mere presence of emotion-laden stimuli in a set of images of different categories slowed down viewing activity overall, but the known effect of image category was not affected. Finally, viewing behavior remained largely constant on single images as well as across the targets' post-prime positions (Study 2).We conclude that the emotional context significantly influences the exploration of complex scenes and the emotional context has to be considered in predictions of eye-movement patterns

Sequence of images (example).

<p>One positive or negative IAPS image serving as prime was followed by three neutral target images belonging to the three different image categories (nature, urban, fractal), respectively. The emotional content of primes as well as the order of target images were randomized.</p

Eye movement parameters on neutral targets of three categories in Study 2 and in our previous study [<b>21</b>].

<p>In Study 2, the sequence of target images was intermingled with emotion-laden IAPS images, while in the previous study the targets were presented solely. Note: We only report the results of the first presentation run of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0052737#pone.0052737-Kaspar2" target="_blank">[21]</a>. The experimental setup and the analysis of parameters were identical in both studies.</p

Differences in eye-movement parameters between emotional primes (negative, neutral, and positive) and targets embedded into corresponding emotional contexts.

<p>(A) mean fixation duration, (B) mean saccade length, and (C) mean entropy quantifying the spread of fixation distributions. On the left side of each figure, emotional primes are contrasted. On the right side, nature target images embedded into different emotional contexts are contrasted. Vertical lines on top of bars indicate standard error of the mean.</p

Eye-movement parameters on emotion-laden and neutral images.

<p>Eye-movement parameters on negative and positive IAPS images serving as emotion-laden primes (left side) and parameters on neutral target images (nature, urban, and fractal) depending on target type and emotional context in which target images were embedded (right side). Vertical lines above bars indicate standard error of the mean. Note: The axis of ordinates differs between primes and targets with respect to the scaling. Moreover, the experimental setups of Studies 1 and 2 were identical, and therefore, absolute parameter values are comparable between both studies.</p

Sequence of images within an emotional context condition.

<p>The emotional context was built by positive or negative IAPS images, or by neutral fractal images. Primes were presented in a block intermingled by nature target images, whereby the occurrence of target images was unpredictable.</p

Time dependency of fixation duration and saccade length.

<p>Fixation duration (left side) and mean saccade length (right side) for negative and positive primes as well as for nature target images depending on the emotional context in which they were embedded. Vertical lines on data points indicate standard error of the mean.</p