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Patrick Knopka

Determining and Testing Blindsight
Blindsight is a condition in which patients with brain damage subconsciously feel that they see sightings that aren’t actually visible to the human eye in the present life (Weiskrantz,1996). Blindsight can arise due to lesions in the primary visual cortex (Weiskrantz,1996). Blindsight has also been termed a phenomenon in which there is a discrete visual discrimination in the lack of recognized consciousness (Weiskrantz,1996). According to Alan Cowey, 2010, “some patients can discriminate unseen visual stimuli within a field defect caused by damage to the primary visual cortex.” This implies that some people are “blind to” certain colors and wavelengths that should be visible to the human eye(Weiskrantz,1996). Because brain functioning plays a huge role in perceiving visual information, damage to the brain can result in serious visual limitations such as the phenomenon termed “Blindsight” (Weiskrantz,1996).

Blindsight can be assessed in two general series of testing. The first approach, as stated by Weiskrantz, 1996, is to “measure the influence of a stimulus in the blind hemifield on actually seen stimuli presented to the intact hemifield.” In other words, this approach tests the effects of how stimulated the intact hemifield becomes during the presence of a stimuli as opposed to the effect of how stimulated the blind hemifield becomes during the presence of a stimuli. Most likely, a patient who has blindsight symptoms will not physically see the entire stimuli in the blind hemifield as well as they might in the intact hemifield (Weiskrantz,1996). In fact, a patient may even only see part of the stimuli in the blind hemifield (Weiskrantz,1996). Due to this limitation, a person may try to mentally picture what they “should” be seeing in order to train their primary visual cortex to visually see it (Weiskrantz,1996). In this case, a person is perceptually deceiving themselves. In order to measure blindsight with this approach, the use of reaction time is often taken into consideration (Weiskrantz,1996).

The second approach to measure blindsight is to incorporate the use of reflex measures (Weiskrantz,1996). This approach measures the effects of color and movement in the blind field (Weiskrantz,1996). In particular, Weiskrantz, 1996, states that this approach measures “electrical skin conductance responses [that] have been reported to occur as a result of ‘unseen’ light stimuli presented to the blind field.” Visual sensitivity to light and color is extremely important in measuring blindsight with this approach (Weiskrantz,1996). Blindsight subjects often report an “awareness” that a stimuli is present or moving in front of them, but often cannot distinguish the entirety of that stimuli (Weiskrantz,1996). Imagine being aware that something is in front of you, but you cannot determine exactly what it is in its entirety. That can be a fairly alarming situation for a person. When measuring blindsight, it is important to recognize if any brain activity is associated with visual awareness (Weiskrantz,1996). Not all patients who experience damage to the primary visual cortex report signs of blindsight (Weiskrantz,1996). In fact, only a minority of these patients report signs of blindsight (Weiskrantz,1996). The specific detection of when and how blindsight occurs is not yet apparent (Weiskrantz,1996). However, there are some factors that seem to have an influence in the incidence of blindsight. One of the factors is the age at which brain damage occurred (Weiskrantz,1996). Another factor is the location of the brain damage and its extent within the brain cortex (Weiskrantz,1996). Brain damage is very unique and uniform to each patient; two patients cannot have the same brain injury and expect to have the same limitations as a result (Weiskrantz,1996). Therefore, it is difficult to determine the cause and origin of the phenomenon termed blindsight.

The primary visual cortex is the central station for visualizing input presented through the retina of the human eye (Cowey, 2010). When the primary visual cortex is damaged following a traumatic injury or possible stroke, the patient often may only see part of the input that is presented through the retina (Cowey, 2010). In other words, part of the visual stimuli may seem like it is missing, even though it is truly there. This type of “blindness” has been deemed as “clinical blindness” (Cowey, 2010). Because brain injuries are so unique to the individual person, some scientists have performed studies on monkeys to try to distinguish the exact cause of blindsight. While monkeys are very similar to human beings, there is one major factor that affects these studies- monkeys cannot talk to human beings (Cowey, 2010). When human beings are tested for blindsight, they are asked questions about what they can and cannot see; Monkeys are unable to respond to such questions (Cowey, 2010). Therefore, there is a lack of accuracy in determining the cause of blindsight with the use of monkeys (Cowey, 2010). In order to compensate for this lack of communication, monkeys were rewarded by choosing between two visual stimuli to determine blindsight (Cowey, 2010). Cowey and Stoerig, 2010, referred to this method as “forced-choice guessing.” By using this method, Cowey and Stoerig, 2010, were able to measure the monkeys’ visual stimuli. Their visual stimuli was similar to that of humans in that part of the visual stimuli seemed to be invisible or not there (Cowey, 2010). As a result of such observations, Cowey and Stoerig noted that both humans and monkeys accurately displayed signs of “blindsight.”

Ultimately, it is fairly difficult to test blindsight among a range of human beings and monkeys. Blindsight generally becomes apparent after an injury to the brain (Weiskrantz, 1996). Since the brain is one of the most complex organs in the body, it is difficult to pin point exactly what causes blindsight (Weiskrantz, 1996). Even though two patients may appear to the have a similar brain injury, the effects of the brain injury could be completely different (Weiskrantz, 1996). In other words, since the human brain is unique to the individual person, each patient will most likely have different limitations after the brain injury due to their brain’s uniform structure. Many factors come into play when dealing with brain injuries such as where the lesion occurred, at what age it occurred, how deep the lesion is, how many brain synapses were affected, etc. (Weiskrantz, 1996). Therefore, the specific detection of when and how blindsight occurs is very difficult to measure and continues to be a source of research in the scientific field.

References Antti, R. (2010). Consciousness The Science of Subjectivity. New York: Psychology Press.Cowey, A. (2010). Visual system: how does blindsight arise?. Current Biology, 20(17), R702-R704. Weiskrantz, L. (1996). Blindsight revisited. Current opinion in neurobiology, 6(2), 215-220.

Pknopka (talk) 12:17, 8 November 2013 (UTC)