How to measure subjective experience

A central challenge in the study of conscious perception is determining whether a particular behaviour stems from changes in the subjective experience of the observer or from non-perceptual sources –such as decision biases. The need for a principled method to distinguish between changes in perception from changes in response biases is particularly urgent when we consider that a cornerstone method for studying (un)conscious perception is to contrast trials in which an observer is aware of the stimulus against trials where the observer reports no conscious experience. This thesis addresses this problem across three empirical chapters by introducing a variation of the adjustment method—the controlled reproduction task—which allows participants to recreate their perceptual experiences free of non-perceptual decision bias. Using this approach, I investigate whether experimental manipulations that typically result in decision biases, such as base rate asymmetries, monetary incentives, visual illusions, and attentional cues, also affect subjective experience. The results show that, while base rate expectations and monetary payoffs influence decision-making, they do not affect subjective experience. In contrast, visual illusions and attentional manipulations consistently influence subjective experience. The contamination of non-perceptual decision criterion shifts is a prevalent issue in the study of consciousness, but also more broadly in psychophysics, perceptual decision-making and metacognition. The findings presented in this thesis demonstrate that criterion shifts that may otherwise occur naturally do not necessarily affect sensory experience, highlighting the importance of using explicit benchmarks of subjective experience like the controlled reproduction task.