Visual discomfort for flickering sinusoids is not predicted by the spatio-temporal contrast sensitivity function

Visual discomfort, the unpleasant, aversive experience associated with some visual stimuli, is most pronounced for flickering and spatially repetitive stimuli. It has been proposed that the degree of visual discomfort for such stimuli can be predicted by the contrast sensitivity function, peaking at midrange spatial and temporal frequencies. We evaluated the spatio-temporal tuning of visual discomfort for flickering, sinusoidal stimuli. Discomfort increased with spatial frequency for static and slowly flickering stimuli, but decreased with spatial frequency for stimuli flickering at 16 Hz. Discomfort increased with temporal frequency for spatially uniform stimuli, and for all spatial frequencies. Flickering stimuli were more uncomfortable than static stimuli of any spatial frequency. Spatially uniform stimuli flickering at 16 Hz, the highest frequency tested, were rated as the most uncomfortable. These results deviate from the contrast sensitivity function, which predicts that discomfort should be highest for static stimuli, with bandpass spatial frequency tuning. This discrepancy indicates that threshold-level visual sensitivity is not a good predictor of visual discomfort for high contrast stimuli. Our results are however consistent with efficient coding models, which predict higher levels of excitation for high spatial and temporal frequencies when stimuli are presented at a high contrast. They are also consistent with physiological measures of cortical responses to high contrast stimuli.