Abstract
Decision bias is traditionally conceptualized as an internal reference against which sensory evidence is compared. Here, we show that individuals are able to strategically shift this internal reference depending on current task demands by changing the rate of sensory evidence accumulation in visual cortex. Participants performed a target detection task during EEG recordings. We experimentally manipulated participants’ decision criterion for reporting target-present using different stimulus-response reward contingencies, inducing liberal and conservative biases in different conditions. Drift diffusion modeling revealed that a strategic liberal bias shift specifically biased sensory evidence accumulation towards target-present choices. In visual cortex, the liberal bias suppressed pre-stimulus 8—12 Hz (alpha) power, which in turn mediated output activity of visual cortex, as expressed in 59—100 Hz (gamma) power. These findings show that observers can intentionally control cortical excitability to strategically bias evidence accumulation towards the decision bound that maximizes reward within a given ecological context.