Blindsight Research Paper Example | Topics and Well Written Essays - 1750 words

Blindsight - Research Paper Example The result is that there is a reduction in the visual sensitivity that responds to luminance contrast; the case being more severe in case of high spatial and low temporal frequencies (Barbur, Harlow, & Weiskrantz, 1994). It is also a phenomenon that this sensitivity is not totally finished off in case of low spatial and high temporal frequencies and this is the reason that several reports have been made of residual visual capacities; in this is included detecting and discriminating any stimuli that may be present within the field defect. Such is what happens in forced-choice tests (Cowey, 2010). The phenomenon of blindsight does not just state that it is normal vision but in the absence of awareness. Besides the loss of primary visual cortex, there is another issue that has to be considered. Retrograde degeneration of relay neurons within the subsequent areas of the lateral geniculate nucleus and concomitant transneuronal degeneration of as much as 90% of the retinal ganglion cells ( especially the P? ganglion cells) (Cowey, Stoerig, & Perry, 1989) is responsible for the extremely low contrast sensitivity for low temporal and high spatial frequencies, with subsequent damages to the capacity of discriminating form, reduced motion, and wavelength (Cowey, 2010) – these skills are usually dependent upon the parvocellular system (Schiller, Logothetis, & Charles, 1990). Literature Review The problem of blindsight in human beings has a certain exceptional property. This property states that there is a possibility of detecting and discriminating a stimulus even without there being any subjective awareness. That means, a person suffering from blindsight does still have certain visual abilities, and two of these capacities include detection and discrimination of movement (Weiskrantz, 1986). The patients suffering from blindsight are actually blind to conscious visual perception but they do have the ability of performing visual manual reaching works, which means tha t they can respond to visual information although they do not have any visual perception (Sanders, et al., 1974). According to certain studies cortically blind patients have the ability of discriminating the direction of motion of single spots (King, et al., 1996) and bars (Azzopardi & Cowey, 2001); they are better able to discriminate the faster moving things and this suggests that their sensitivity to high temporal frequencies is increased (Barbur, Harlow, & Weiskrantz, 1994). The cases of blindsight that have already been published had been caused due to lesions in the visual cortex. These patients still adhere to their feature of functional vision, for instance the ability to detect movement, to point correctly at light flashes in the absence of conscious visual perception, and to be able to guess if there is a stimulus in the visual blind field. The cortically blind patients do not hold the ability of discriminating the direction of the stimuli movement that does not change its location globally, for example, gratings and random dot kinematograms that depict transformation, comparative movement, and motion in depth (Azzopardi & Cowey, 2001). There is still a possibility of there being a difference in the direction discrimination and random kinematograms, gratings and so on, due to the fact that such stimuli concern themselves with various motion-processing methods that are reliable in relation to the variations that might be present between them regarding their local and global features. When this argument is considered it will be possible for there to be discrimination of direction in the cortically blind visual field on the grounds of a method which directly perceives movement information of the stimulus.