The Subliminal Threshold Estimation Procedure (STEP): A calibration method tailored for successfully estimating subliminal thresholds

A major challenge in the study of unconscious processing is to effectively suppress the critical stimulus while ensuring it evokes a strong enough signal to be processed unconsciously. A possible way to achieve these goals is by calibrating stimulus strength. While calibrating stimulus strength is common in psychophysics, current calibration methods are not designed to find the maximal intensity in which the stimulus can still be rendered unconscious. Here, we demonstrate how calibration can be utilized to estimate, for each observer, this targeted threshold. We present a novel calibration procedure: the Subliminal Threshold Estimation Procedure (STEP), specifically designed for estimating the individual upper subliminal threshold. Using simulations, we showed that STEP outperforms existing calibration methods, which yielded strikingly low accuracy. We then further validated STEP using three empirical experiments. Together, these results establish STEP as highly beneficial for the study of unconscious processing.