Our brain accomplishes the remarkable feat of processing a continuous stream of incoming sensory information at an astonishing speed. This is possible through simultaneous bottom-up processing of the incoming stimuli and top-down processing of prior knowledge (Kinchla & Wolfe, 1979). Categorization facilitates recognition and also anticipation of the incoming stimuli (also known as predictive coding, e.g., Rao & Ballard, 1999). Therefore, the presentation of written words facilitates the auditory perception of distorted pronunciation (Sohoglu, Peelle, Carlyon, & Davis, 2012). The skill to correctly categorize depends on relevant experience and memory that has been built over time. Perception thus involves a balance between the sensory stimuli and the stored representations in memory. If a category or a mental image is inaccurately matched with the incoming stimuli, biased perception emerges (see examples later). Bias in perception occurs mostly unconsciously and perhaps incessantly—after all, stimuli are unlikely to form a perfect match with stored memory.