Deficits in Perception PDF

D EFIC IT S IN PER C EPT IO N BY: ISMAEL M. MACAPUDI JR., R PM, CHR A, CSS AGNO SIAS AND ATAXIAS Remember that there are two distinct visual pathways, one for identifying objects (“what”), the other for pinpointing where objects are located in space and how to manipulate them (“where” or “how”)....

D EFIC IT S IN PER C EPT IO N BY: ISMAEL M. MACAPUDI JR., R PM, CHR A, CSS AGNO SIAS AND ATAXIAS Remember that there are two distinct visual pathways, one for identifying objects (“what”), the other for pinpointing where objects are located in space and how to manipulate them (“where” or “how”). The what/how hypothesis is best supported 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 ability to reach for what they see. Difficulties Perceiving the “What” People who suffer from an agnosia have trouble to perceive sensory information (Moscovitch, Winocur, & Behrmann, 1997). Often are caused by damage to the border of the temporal and occipital lobes or restricted oxygen flow to areas of the brain, sometimes as a result of traumatic brain injury (Zoltan, 1996). Generally, people with agnosia have normal sensations of what is in front of them. They can perceive the colors and shapes of objects and persons but they can not recognize what the objects are—they have trouble with the “what” pathway. Disturbance in the temporal region of the cortex can lead to simultagnosia. In simultagnosia, an individual is unable to pay attention to more than one object at a time. Prosopagnosia results in a severely impaired ability to recognize human faces. A person with prosopagnosia might not recognize her or his own face in the mirror. DIFFICULTIES IN KNOWING THE “HOW” Optic ataxia, which is an impairment in the ability to use the visual system to guide movement (Himmelbach & Karnath, 2005). People with this deficit have trouble reaching for things. Ataxia results from a processing failure in the posterior parietal cortex, where sensorimotor information is processed. ANO MALIES IN CO LO R PER CEPTIO N Color perception deficits are much more common in men than in women, and they are genetically linked. However, they can also result from lesions to the ventromedial occipital and temporal lobes. There are several kinds of color deficiency, which are sometimes referred to as kinds of “color blindness.” Least common is rod monochromacy, also called achromacy in which people with this condition have no color vision at all. They see only shades of gray, as a function of their vision through the rods of the eye. In dichromacy, only two of the mechanisms for color perception work, and one is malfunctioning. The result of this malfunction is one of three types of color blindness (color-perception deficits). The most common is red-green color blindness.  The extreme form of red-green color blindness is called protanopia. The other types of color blindness are: Deuteranopia (trouble seeing greens), and tritanopia (blues and greens can be confused, but yellows also can seem to disappear or to appear as light shades of reds).