Serial Dependence in Perceptual Decisions Is Reflected in Activity Patterns in Primary Visual Cortex

Sensory signals are highly structured in both space and time. These regularities allow expectations about future stimulation to be formed, thereby facilitating decisions about upcoming visual features and objects. One such regularity is that the world is generally stable over short time scales. This feature of the world is exploited by the brain, leading to a bias in perception called serial dependence: previously seen stimuli bias the perception of subsequent stimuli, making them appear more similar to previous input than they really are. What are the neural processes that may underlie this bias in perceptual choice? Does serial dependence arise only in higher-level areas involved in perceptual decision-making, or does such a bias occur at the earliest levels of sensory processing? In this study, human subjects made decisions about the orientation of grating stimuli presented in the left or right visual field while activity patterns in their visual cortex were recorded using fMRI. In line with previous behavioral reports, reported orientation on the current trial was consistently biased toward the previously reported orientation. We found that the orientation signal in V1 was similarly biased toward the orientation presented on the previous trial. Both the perceptual decision and neural effects were spatially specific, such that the perceptual decision and neural representations on the current trial were only influenced by previous stimuli at the same location. These results suggest that biases in perceptual decisions induced by previous stimuli may result from neural biases in sensory cortex induced by recent perceptual history.