Saturday, August 24, 2013

I See. Do you?

Describing the Visual System

Simply stated, light waves pass through the cornea, pupil, and iris (Breedlove, Watson, & Rosenzweig, 2010). The iris controls the amount of light coming into the eye and the lens changes shape to focus light on the retina (Sinauer Associates, Inc., producer, 2010). Within the retina, (especially the fovea) visual information processing begins and stimulates neurons in the visual system. Light strikes the retina and activates approximately 100 million rods and 4 million cones, which are the visual receptors, or photoreceptors in the eye, that send information to a million ganglion cells (Breedlove et al., 2010). The ganglion cells transmit information through the optic nerve and to parts of the brain including the thalamus (Breedlove et al. (2010). The thalamus transmits the neural signals to the primary visual cortex (the retinogeniculostriate pathway) which translates the information that allows individuals to make sense of what they see.

Context Affects Visual Perception

Objects are more easily recognized when in a familiar context (Palmer, 1975). For example, a loaf of bread is more readily identifiable than a mailbox when it sits on a kitchen counter. Palmer (1975) described context effects as the "effects of the environment of an object on the perception of that object, independent of the intrinsic properties of the object itself" (p. 519).

According to Breedlove et al. (2010), context affects visual perception by relative means. For example, a color will appear lighter when situated directly next to a darker color, and darker when situated directly next to a lighter color. Breedlove et al. further explained that the process of lateral inhibition enhances the boundary areas because of the visual system's modification of brightness. Similarly, the visual system places significance on movement, so when an object is moving in an individual's visual field, it will take precedence over a stationary object. Movement increases visibility (Breedlove et al., 2010). Watanabe and Shimojo (2001) used ambiguous audiovisual presentations to demonstrate the affects of sound on the visual perception of moving objects. These are examples of how the brain responds to many factors, such as surrounding contexts.

This reminds me of ambiguous figures that people "see" in a variety of ways. There may be little to no context surrounding the figure, so the individual's brain creates what it sees, based on retained experience, beliefs, and expectations. Segall, Campbell, and Herskovits (1966) found that Westerners were far more prone to inaccurately perceive some optical illusions, and attributed this to living in the 'carpentered world' which trains the eye to perceive according to a particular set of visual experiences. These ideas suggest there are many influences that impact how individuals process visual information (Bar, 2004). Additionally, they support the idea that seeing is far more complex than the mechanics of vision, and that believing in a "universality in perception is risky" (Toch & Smith, 1968, p. 1).

Potential Costs and Benefits of Context Affecting Visual Perception

One benefit of context affecting visual perception is that it provides the most salient information to the user which, in turn, provides safety (Bar, 2004; Breedlove et al., 2010). The affects of motion on visual perception provided the ability to remain safe and protected from moving predators as well as supported the ability to hunt, utilizing the movement of an animal to track it. Further, the effects of context allow people to approximate safety and danger, without knowing the exact nature of a situation. For example, seeing steam rising from a pot of hot water provides information without having to involve the sense of touch.

One of the shortcomings of the visual perception system is that we do not see things the way they are, but rather, we see them the way we are, so, in essence, we give up the ability to see accurately to see contextually. This has the potential to cause mistakes, miscalculations, miscommunications, and other inaccuracies. In some ways, humans are constrained by their visual perceptions, lacking the ability to perceive their surroundings without individualized perception. Further, since context relies, at least in part, on experience, the lack of certain experiences may hinder the ability to utilize context to help accurately identify an object or circumstance that may be dangerous.

Bar, M. (2004). Visual objects in context. Nature Reviews Neuroscience, 5(8), 617-629. doi: 10.1038/nrn1476

Breedlove, S. M., Watson, N. V., & Rosenzweig, M. R. (2010). Biological psychology: An introduction to behavioral, cognitive, and clinical neuroscience. (6th ed.) Sunderland, MA: Sinauer Associates, Inc. Publishers.

Palmer, S. E. (1975). The effects of contextual scenes on the identification of objects. Memory & Cognition 3, 519–526.

Segall, M. H., Campbell, D. T., & Herskovits, M. J. (1966). The influence of culture on visual perception. Indianapolis: Bobbs-Merrill.

Sinauer Associates, Inc. (Producer). (2010). Visual pathways in the human brain. [Streaming video]. Retrieved July 6, 2013, from

Toch, H., & Smith, H. C. (1968). Social perception: The development of interpersonal impressions : An enduring problem in psychology. Princeton, N.J.: Van Nostrand.

Watanabe, K., & Shimojo, S. (2001). When Sound Affects Vision: Effects of Auditory Grouping on Visual Motion Perception. Psychological Science, 12(2), 109-116.

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