Submission 437
Perceptual (Un)Certainty Needs to Be Predictable to Be Measured in the EEG
SymposiumTalk-02
Presented by: Shalila Freitag
Visual stimuli without one clear interpretation of highest likelihood (e.g., certain illusions) induce perceptual uncertainty. In a series of studies, we found EEG correlates of this perceptual uncertainty with smaller ERP (Event Related Potential) amplitudes with ambiguous/low-visibility stimuli (perceptual uncertainty) compared to disambiguated/high-visibility stimulus variants (perceptual certainty) (Cohen’s d = 0.6-1.2). The underlying experimental paradigm showed only one stimulus variant (e.g., disambiguated or ambiguous) per condition creating high predictability of successive stimuli. Preliminary results from a pilot study with random presentation of both ambiguous and disambiguated stimulus variants indicated absence of this ERP Uncertainty Effect. The aim of the present study was to confirm this finding and to find the necessary number of repetitions to maximize the ERP Uncertainty Effect.
In an EEG study, we presented Necker lattices (ambiguous/disambiguated) or smiley faces (low/high visibility of emotional expression) in predictably ordered blocks of 12, 48 (Necker and smileys) and 120 (Necker) repetitions. We also showed ambiguous and disambiguated variants of the Necker lattice in random order for 120 stimulus repetitions. The ERP Uncertainty Effect was absent when stimuli were presented randomly. When the order was predictable, the ERP Uncertainty Effect was present for all block lengths tested in both Necker and smiley conditions. Further analysis revealed the effect to reach its maximum after 6 to 10 stimulus repetitions (8.4 to 14 seconds). Our results confirm the importance of predictability to measure perceptual certainty via EEG and give further insights into the timescale of the underlying processes.