Perceptual set describes a tendency to perceive some sensory stimuli and to ignore others. This perceptual bias or predisposition is essential to the concept of active perception and involves perceptual concepts such as selection, interpretation, and inference regarding sensory stimuli. Many factors contribute to our perceptual set including our culture, motivations, schemas, attitudes, previous experiences, emotions, and expectations. These factors influence the top-down processing of our perceptual set that influences what we notice and infer about things and what we ignore.
For example, in a classic study do groups of people were either shown a series of numbers or of letters. After this the participants were shown a visually ambiguous image that could be interpreted as either the number 13 or the letter B. The participants who viewed the letters previously were more likely to see the letter B while the participants who viewed the numbers were more likely to say the image was the number 13. Emotions influence our perceptual set in that people who are in an angry mood are more likely to perceive anger and hostility in others and ignore non-hostile behaviors.