Abstract
Recent history often lingers into our perceptual decisions, leading to systematic biases. These biases, which occur in many visual tasks, may reflect how the brain integrates and segregates events in time. However, what triggers them and when remains unclear. Here we show that history biases depend largely on the expectation of making a perceptual decision and the attentional state it follows. In a behavioural experiment, observers were asked to reproduce the orientation of a sequence of Gabor patches using adjustment responses. On separate blocks, we varied the proportion of trials requiring a response (25%, 50%, or 75% of trials). We found that the proportion of responses affects the type and strength of history biases: in blocks where the response was the most likely case, non-response trials led to repulsive biases —i.e., adjustment errors were shifted away from the orientation shown on the preceding trial. Conversely, the bias was mostly attractive in blocks where responses were less likely. These results suggest that observers use the probability of responses in each block to anticipate the next event, re-engaging attention when a response is expected. To investigate the neural correlates, we then used electroencephalography data (EEG) recorded in a separate experiment. Observers performed a similar orientation reproduction task, with 50% of response and non-response trials randomly intermixed. This revealed typical EEG signatures of attentional and cognitive control processes after trials without a response, whose role in history biases was previously unknown. Overall, our findings suggest that history biases are modulated by internal states, such as expectations and attentional fluctuations, shedding new light on the underlying mechanisms and factors involved.