Much of the research and discoveries regarding how our brain functions can be attributed to cruel acts of fate- the brain injuries and disorders which damage key areas of the brain. It is through studying how these injuries and disorders affect human behavior, that we gain insight into how different brain structures contribute to human functional capability. The literature of neuropsychology is filled with countless case histories that document how specific brain lesions have affected a particular patient?s abilities.
As early as 1868, the case of Phineas Gage provided us with an example of brain damage and how it can lead to discoveries about brain function. Phineas Gage, a dynamite worker, was involved in an explosion that drove a 1.25 inch-wide iron bar through the front of his head. Gage survived, but his behavior was completely changed. His friends who knew him well said he was another person. Once a calm man, his personality became belligerent. Gage?s injury effected primarily his left frontal lobe. This case gave insight into how frontal lobe lesions can alter personality (Kolb & Whishaw, 1990).
Alexander Luria, the famous Russian neuropsychologist, expanded the use of the case history by studying one individual and his brain injury over 25 years. His book The Man With a Shattered World documents a patient?s
struggle to overcome the cognitive deficits resulting from a bullet wound to the brain during World War II. Dr. Oliver Sacks has popularized the case study as a window into how the brain functions through his many articles and books including The Man Who Mistook His Wife For a Hat, in which he takes us into the strange world of Dr. P who suffered from an unusual syndrome called visual agnosia. Visual agnosia is a syndrome in which an individual is able to see, but is not able to attach meaning to what he sees (Weiten, 1998). Perhaps even more bizarre are recent case histories describing individuals who are able to perceive the world around them without any conscious knowledge of that perception. Studies of disorders such as blindsight, inverse Anton?s Syndrome, prosapagnosia, and blind touch, provide us with an opportunity to understand the complex process of perception.
Blindsight is a pattern of behavior that is displayed by individuals who are blind due to a damaged striate cortex. In cases of blindsight, the patient claims not to see something within their field of view, but shows in their behavior that they are stimulated by this object that they claim not to be seeing (Natsoulas, 1997). Individuals with blindsight, despite their blindness, were able to look towards a stimulus in their field of view, and point to it, but not identify it. In one study, a patient with complete cortical blindness was presented with a large moving striped display. The patient was able to follow this moving stimulus with his eyes, but claimed that he could not see it. Research into cases of blindsight have shown that the striate cortex plays an essential role in the conscious experience of visual perception (Cowey & Stoerig, 1991).
Inverse Anton?s syndrome describes a condition in which patients who are esentially cortically blind, but do have small areas of visual capability in the middle of their visual field, deny the ability to see. This is the opposite of Anton?s syndrome, in which patients who are cortically blind deny their blindness (Hartman et al., 1991).
In a case study of inverse Anton?s syndrome, a 56 year old male was diagnosed with blindness due to bilateral cerebral infarction. The patient stated that he had no visual ability, but he was able to navigate an unfamiliar area without assistance. He attended meetings of the Society for the Blind, but he never applied for services. In a visual examination, he reported that a test stimulus (a cloth) was moving. When asked how he detected the movement, he insisted that he ?felt? it. A test was done in which words were flashed on a screen in front of him. The patient was correct in reading 51% of the words, with 47% of his errors being visual
errors (for example, mistaking the word ?smile? for ?while?). In another test, the patient was able to recognize and describe five displayed facial emotions, as well as identify famous faces. A modified version of the Stroop Task was also conducted on the patient. The Stroop Task is a test in which the names of colors are written in an ink of a different color, and the person must identify the color that the word is written in, ignoring the written word. This is a test that is usually used to identify the individual?s ability to deal with perceptual interference, although it was used on this particular patient in order to see if he could identify colors. In this test, the patient was able to accurately identify 12 of the 20 colors presented despite having no conscious awareness that he was identifying the colors through his visual capability (Hartman et al., 1991).
Recent studies of prosapagnosia, the inability to recognize faces despite apparent recognition of most other stimuli, have provided us with additional insight into perception. It has been found that patients with prosapagnosia report to seeing a face, but are not able to identify the person, even if that person is someone they know. Some prosapagnosic patients have even reported that they are unable to recognize their own face in the mirror. In Pallis? description of a prosapagnosic patient, he states, ?He failed to identify his wife during visiting hours. She was told one day, without his possible knowledge, to walk right past his bed, but he did not show the least sign of recognition? (Farah, 1990, p. 71).
Recent investigations of prosapagnosic patients have shown evidence that a separation exists between consciously identifying a person and unconsciously knowing who that person is. It has been demonstrated that prosapagnosic patients show increased electrodermal activity (EDA) when presented with familiar faces, although they report no conscious recognition of them (Shearer & Mikulka, 1996). In 1984, Bauer conducted a study on a prosapagnosic patient in which he presented him with a series of photographs of familiar faces. While viewing the pictures the patient heard a list of names read aloud, one of which was the name of the person in the photograph, and was told to make a negative response to each name. Bauer used the ?guilty knowledge? (lie detector) test to measure the patient?s EDA while hearing the names. When the patient made a negative response to the correct name, his EDA was significantly higher indicating that on some level below conscious awareness he was able to identify the face (Farah, 1990).
Blind touch is another good example of a disorder that tells us about perception without awareness, although through the tactile sensory system. Paillard and his colleagues did a case study on a patient who displayed a complete anesthesia on the right side of her body from a large lesion of the left hemisphere. She was totally lacking in the perception of pain and temperature and could burn or cut herself without conscious knowledge. Despite this, the patient was able to point with her left hand to places on her right hand where she had been touched, even though she reported that she didn?t feel the touch (Kolb & Whishaw, 1990).
According to John C. Marshall, in healthy individuals our perceptual systems may operate too smoothly and seamlessly for us to fully appreciate the complexity of their structures and function. It is very possible that brain damage, by tragically destroying isolated parts of the brain, will help us better understand how the normal brain functions (Farah, 1990). Opening our eyes and seeing the world is something that we take for granted. These case studies illustrate that perception, and awareness of that perception, may involve several separate and complex processes. There truly is more to perception than meets the eye.
1. Cowey, Alan & Stoerig, Peter. (1991). The neurobiology of blindsight. Trends In Neuroscience, 14 (4), 140-145.
2. Farah, Martha J. (1990). Visual agnosia. Cambridge, MA: The MIT Press.
6. Shearer, Donald & Mikulka, Peter. (1996). Effect of facial familiarity and task requirement on electrodermal activity. The American Journal of Psychology, 109 (1), 131-134.