Motivation biases behavior but not perception.

Why do people differ in their perceptual judgment despite observing the same situation? According to "motivated perception", a person's motivation can alter how the brain interprets incoming sensory information. Yet, empirical support remains mixed, often due to methodological confounds. Here, we systematically tested whether motivation alters perception or whether it instead biases behavior. Across four experiments, we assessed the quality and quantity of motivation (self-concordance, value) and two key dimensions of perception: bias and sensitivity. Moreover, we tested two potentially mediating mechanisms (gaze position, spatial attention) as well as an implicit perceptual measure. Using smooth pursuit eye movements as an implicit measure of motion perception, we show that motivation biases responses without altering perception (Experiment 2, n = 20). Changes in perceptual sensitivity (Experiment 1, n = 60) and perceptual bias (Experiments 3-4, n = 16 and 24) only arise when participants can freely select their gaze position in response to uncertain or ambiguous visual displays. Our findings therefore challenge the notion of "motivated perception". Instead, they suggest that motivation shapes how we look and respond - but not how we perceive.