Positive Expectation Effects on Early Emotional Processing

Plain-language summary

Insights into the mechanisms of expectation effects in the emotional domain can be invaluable for the development of potential therapeutic interventions for mood disorders. Recent findings demonstrate that positive expectations alone can induce a positivity bias on the behavioral and the neural level (Baker et al.,2022, Mostauli et al., 2025). This is intriguing given that antidepressant treatments, which have high placebo rates are reported to reduce a negativity bias commonly observed in depression. Research on placebo analgesia has shown that both higher-order cognitive expectations and lower-level learning mechanisms, such as conditioning, play a key role in placebo effects. The role of such lower-level processes is particularly underexplored in affective placebo effects. Closing this gap is crucial, as the long-term modulation of the emotional system likely depends on cognitively less demanding, bottom-up processes shaped by learning and conditioning. This is particularly relevant in clinical populations, where cognitive resources may be limited, but there is an abundance of prior experiences (i.e., learning). The present study therefore investigates how treatment expectations influence early psychophysiological processing of emotional stimuli. Beyond behavioral measures, we will directly assess early neural and attentional mechanisms using sensory event-related potentials (ERPs) and reflexive gaze shifts. By combining EEG and eye-tracking, we aim to identify early markers of expectation effects during emotional processing in healthy participants (N=44 plus 15% potential dropout, 50% women), who perform an emotion classification task. Emotional faces will be presented at varied levels of stimulus visibility (alpha transparency), allowing us to model perceptual sensitivity and response bias without inducing ceiling effects. Treatment expectation will be induced by verbal instructions using an established protocol (e.g. Baker et al., 2022, Mostauli et al., 2025). We hypothesize that positive expectations enhance mood and decrease reaction times paralleled by better accuracy. Further, we hypothesize that positive treatment expectation enhances gaze shifts toward the mouth region which is the primary diagnostic feature for happy faces. On the neural level we expect that positive expectations modulate EEG signal patterns associated with early emotional valence processing. Additionally, whole-brain and time-frequency analyses, as well as representational similarity analyses, are planned to further explore into neural expectation effects and potential changes in the hierarchical representation of emotional processing.

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