Deficits in Perception
Deficits in perception: Obviously, cognitive psychologists learn a great contract about normal perceptual processes by studying perception in normal participants. Though, we also sometime gain understanding of perception by studying people whose perceptual processes diverge from the norm.
Agnosias and Ataxias
Perceptual deficits deliver an exceptional way to test hypotheses with respect to how the perceptual system works. There are two different visual pathways, one is for identifying objects means “what”, the other for indicative where objects are located in space and how to manipulate them means “where” or “how”. The what or how hypothesis is best sustained by evidence of processing deficits: There are both deficits that impair people’s ability to recognize what they see, and deficits that impair people’s aptitude to reach for what they see means “how”.
Binocular disparity: The closer an object is to you, the larger the disparity between the views of it as sensed in each of your eyes.
Binocular convergence: Because your two eyes are in slightly different places on your head, when you rotate your eyes so that an image falls straight to the central part of your eye, in which you have the maximum visual acuity, each eye must turn inward slightly to register the same image. Whenever we try to see an object which is closer to our eye then our eye must turn inward. Your muscles send messages to your brain concerning the degree to which your eyes are turning inward, and these messages are understood as cues indicating depth.
Difficulties Perceiving the “What”
Consider first of all the “what.” People who undergo from an agnosia have trouble to perceive sensory information Agnosias sometime are affected by damage to the border of the temporal and occipital lobes or restricted oxygen flow to areas of the brain, at times as a result of traumatic brain injury. There are many kinds of agnosias. Not all of them are optical. Normally, people with agnosia have usual sensations of what is in front of them. They can perceive the colors and shapes of objects and persons but they cannot recognize what the objects are they have trouble with the “what” pathway.
Disruption in the temporal region of the cortex can cause simultagnosia. In case of simultagnosia, an individual is un-able to pay attention to more than one object at a time. A person with simultagnosia would not see each of the objects represented in figure shown below. Rather, the person might report seeing the hammer but not the other objects.
Prosopagnosia consequences in a severely impaired ability to recognize human faces. A person with having prosopagnosia might not recognize her or his own face in the mirror.
Difficulties in Knowing the “How”
A diverse kind of perceptual deficit is related with damage to the “how” pathway. This deficit is optic ataxia, which is a damage in the ability to use the visual system to guide movement. People usually with this deficit have trouble reaching for things. All of us have had the experience of coming home at night and trying to find the keyhole in the front door. It’s too dark to see, and we have to grope with our key for the keyhole, often taking quite a while to find it. Someone with optic ataxia has this problem even with a fully lit visual field. The “how” pathway is impaired.
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