An electrophysiological study on the interaction between emotional content and spatial frequency of visual stimuli

Previous studies suggest that the magnocellular pathway, a visual processing system that rapidly provides low spatial frequency information to fast-responding structures such as the amygdala, is more involved in the processing of emotional facial expressions than the parvocellular pathway (which conveys all spatial frequencies). The present experiment explored the spatio-temporal characteristics of the spatial frequency modulation of affect-related neural processing, as well as its generalizability to non-facial stimuli. To that aim, the event-related potentials (ERPs) elicited by low-pass filtered (i.e., high spatial frequencies are eliminated) and intact non-facial emotional images were recorded from 31 participants using a 60-electrode array. The earliest significant effect of spatial frequency was observed at 135 ms from stimulus onset: N135 component of the ERPs. In line with previous studies, the origin of N135 was localized at secondary visual areas for low-pass filtered stimuli and at primary areas for intact stimuli. Importantly, this component showed an interaction between spatial frequency and emotional content: within low-pass filtered pictures, negative stimuli elicited the highest N135 amplitudes. By contrast, within intact stimuli, neutral pictures were those eliciting the highest amplitudes. These results suggest that high spatial frequencies are not essential for the initial affect-related processing of visual stimuli, which would mainly rely on low spatial frequency visual information. According to present data, high spatial frequencies would come into play later on.