empirical research show that specific practices (such as yoga, mindfulness, tai chi, meditation, daoshi and other mind-body disciplines) can modify human perceptual modality. specifically, these practices enable perception skills to switch from the external (exteroceptive field) towards a higher ability to focus on internal signals (proprioception). also, when asked to provide verticality judgments, highly self-transcendent yoga practitioners were significantly less influenced by a misleading visual context. increasing self-transcendence may enable yoga practitioners to optimize verticality judgment tasks by relying more on internal (vestibular and proprioceptive) signals coming from their own body, rather than on exteroceptive, visual cues. past actions and events that transpire right before an encounter or any form of stimulation have a strong degree of influence on how sensory stimuli are processed and perceived. on a basic level, the information our senses receive is often ambiguous and incomplete. however, they are grouped together in order for us to be able to understand the physical world around us. but it is these various forms of stimulation, combined with our previous knowledge and experience that allows us to create our overall perception. for example, when engaging in conversation, we attempt to understand their message and words by not only paying attention to what we hear through our ears but also from the previous shapes we have seen our mouths make. another example would be if we had a similar topic come up in another conversation, we would use our previous knowledge to guess the direction the conversation is headed in. effect of motivation and expectation a perceptual set (also called perceptual expectancy or simply set) is a predisposition to perceive things in a certain way. it is an example of how perception can be shaped by "top-down" processes such as drives and expectations. perceptual sets occur in all the different senses. they can be long term, such as a special sensitivity to hearing one's own name in a crowded room, or short-term, as in the ease with which hungry people notice the smell of food. a simple demonstration of the effect involved very brief presentations of non-words such as "sael". subjects who were told to expect words about animals read it as "seal", but others who were expecting boat-related words read it as "sail". sets can be created by motivation and so can result in people interpreting ambiguous figures so that they see what they want to see. for instance, how someone perceives what unfolds during a sports game can be biased if they strongly support one of the teams. in one experiment, students were allocated to pleasant or unpleasant tasks by a computer. they were told that either a number or a letter would flash on the screen to say whether they were going to taste an orange juice drink or an unpleasant-tasting health drink. in fact, an ambiguous figure was flashed on screen, which could either be read as the letter b or the number 13. when the letters were associated with the pleasant task, subjects were more likely to perceive a letter b, and when letters were associated with the unpleasant task they tended to perceive a number 13. perceptual set has been demonstrated in many social contexts. when someone has a reputation for being funny, an audience is more likely to find them amusing. individual's perceptual sets reflect their own personality traits. for example, people with an aggressive personality are quicker to correctly identify aggressive words or situations. one classic psychological experiment showed slower reaction times and less accurate answers when a deck of playing cards reversed the color of the suit symbol for some cards (e.g. red spades and black hearts). philosopher andy clark explains that perception, although it occurs quickly, is not simply a bottom-up process (where minute details are put together to form larger wholes). instead, our brains use what he calls predictive coding. it starts with very broad constraints and expectations for the state of the world, and as expectations are met, it makes more detailed predictions (errors lead to new predictions, or learning processes). clark says this research has various implications; not only can there be no completely "unbiased, unfiltered" perception, but this means that there is a great deal of feedback between perception and expectation (perceptual experiences often shape our beliefs, but those perceptions were based on existing beliefs). indeed, predictive coding provides an account where this type of feedback assists in stabilizing our inference-making process about the physical world, such as with perceptual constancy examples. embodied cognition challenges the idea of perception as internal representations resulting from a passive reception of (incomplete) sensory inputs coming from the outside world. according to o'regan (1992), the major issue with this perspective is that it leaves the subjective character of perception unexplained. thus, perception is understood as an active process conducted by perceiving and engaged agents (perceivers). furthermore, perception is influenced by agents' motives and expectations, their bodily states, and the interaction between the agent's body and the environment around it.