Event-Related Synchronization/Desynchronization in Neural Oscillatory Changes Caused by Implicit Biases of Spatial Frequency in Electroencephalography

Spatial frequency may elicit characteristic mental and neural activity in humans, exhibiting a 1/f fluctuation. However, a visual pattern with only spatial frequency information will not necessarily explicitly affect any reaction, but may do so implicitly. We adopted an implicit association test (IAT), which is widely used in the research of implicit biases, to answer that question. At the same time, we attempted to characterize the neural activities associated with implicit spatial frequency biases by using electroencephalography (EEG). We used two types of checkered-pattern stimuli, high and low density, as targets. The high and low densities correspond to high and low spatial frequencies. There were two evaluative categories, with associated nouns and adjectives carrying a range of positive and negative meanings. EEG data were recorded, and the event-related synchronization (ERS) or desynchronization (ERD) for each event was analyzed based on the intertrial variances for the theta (4–7 Hz), alpha (8–13 Hz), low beta (13–20 Hz), high beta (20–30 Hz), and gamma (30–80 Hz) bands for each strong and weak associative strength comparison between targets. The category (e.g., high spatial frequency–positive or low spatial frequency–negative) was then obtained from the reaction times of the IAT for each subject. The ERS characteristics differed between strong and weak associative strengths, measured at the central areas at around 400–500 ms. This difference suggests that spatial frequency characteristics affect neural oscillatory activity associated with implicit biases of spatial frequency.