Modulation of perception by emotion: Altered sensitivity and perceived magnitude of negatively valenced stimuli.

Emotional modulation of visual processing is observed across various domains of perception. We examined whether these modulations affect perceptual sensitivity, the perceived magnitude (biases) of visual stimuli, or both. We asked participants to reproduce the duration (Exp. 1) and size (Exp. 2) of threat-related stimuli (spiders), and those of neutral ones (2D disks and butterflies). Sensitivity was examined by measuring within-subject standard deviations of reproductions for varying magnitudes of the stimuli. Biases were examined by measuring regression to the-mean, a tendency of subjective estimates to gravitate toward the center of the distribution from which stimuli were sampled. Results showed a mild increase in the standard deviations of reproductions of larger magnitudes for negatively valenced stimuli, indicating lower sensitivity. While regression biases were overall observed for these stimuli, biases decreased for the higher levels of intensities, despite their lower sensitivity. Underestimation of above-mean magnitudes was relatively moderated, demonstrating altered relations between the reliability of the sensory input and perceptual biases for these stimuli. Overall, the results suggest that magnitude perception is biased toward the central tendency of the experienced stimuli, even for threatening stimuli; however, biases are milder for the intensified values, presumably to obtain more veridical perception of these stimuli.