Event-related Potential Measurements of Long-term Orientation-specific Contrast Adaptation

Abstract

The visual system continuously adjusts how it responds to current stimulus based on the history of the incoming stimuli, a process referred to as visual adaptation. Most of the previous studies focused on short-term adaptation effects ranging from milliseconds to minutes. Recent work has showed behavioral effects of long-term adaptation (hours and days), but their neural mechanisms remain unexplored. We aimed to uncover the neural bases of long-term orientation-specific contrast adaptation in an electroencephalography (EEG) experiment. Subjects were deprived of vertical contrast for 4 hours using altered reality goggles, which filtered out vertical energy from the scene in real-time. Event-related potentials (ERPs) in response to vertical and horizontal gratings were recorded before and after the long-term deprivation. We hypothesized that ERP response to vertical stimulation would increase in strength, and might decrease in latency, after the long-term deprivation. Results were analyzed by computing simple amplitudes of response, by comparing model fits to the ERP time courses, and by using the spatial pattern of ERP responses to classify trials by stimulation type. Early ERP components in response to vertical increased in amplitude and decreased in latency following adaptation, relative to responses to horizontal, but these differences were not significant. However, model fitting and classification results both revealed significantly greater differences in ERP responses between vertical and horizontal stimulation following adaptation. Collectively, these results suggest that long-term adaptation changes the amplitude of response in early visual cortex.