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Kind characterizes Mary's understanding of color sensation as what it's like knowledge, a sub-category of knowledge-that. She states that while Mary does learn something upon seeing the red tomato for the first time and gains knowledge-how; David Lewis claims Mary is now able to recognize, remember and imagine seeing the color red.
The external body is perceived as the cause of the sensation of color. We say, "The body is red." In reality, though, color exists only in the retina of the eye. It is separate from the external object. Color is a mere sensation in the sense organ. The external object is perceived by the intellect's understanding as being the cause of sensations.
An unusual side effect of digoxin is a disturbance of color vision (mostly yellow and green) called xanthopsia. Vincent van Gogh's "Yellow Period" may have somehow been influenced by concurrent digitalis therapy. Other oculotoxic effects of digoxin include generalized blurry vision, as well as seeing a "halo" around each point of light.
Xanthopsia is a color vision deficiency in which there is a dominantly yellow bias in vision due to a yellowing of the optical media of the eye. The most common causes are digoxin's inhibitory action on the sodium pump, and the development of cataracts which can cause a yellow filtering effect.
There are many diseases known to cause ocular or visual changes. Diabetes , for example, is the leading cause of new cases of blindness in those aged 20–74, with ocular manifestations such as diabetic retinopathy and macular edema affecting up to 80% of those who have had the disease for 15 years or more.
Color vision is categorized foremost according to the dimensionality of the color gamut, which is defined by the number of primaries required to represent the color vision. This is generally equal to the number of photopsins expressed: a correlation that holds for vertebrates but not invertebrates .
The main symptom is loss of vision, with colors appearing subtly washed out in the affected eye. A pale disc is characteristic of long-standing optic neuropathy. In many cases, only one eye is affected and a person may not be aware of the loss of color vision until the examiner asks them to cover the healthy eye.
A fully adequate solution to the problem will have the following features. [citation needed] It will: Recognise that Hume believed the problem to be a genuine counter-example; Recognise that Hume included the example for a purpose; Provide an explanation that harmonizes well with other features of Hume's epistemology.