Re: Night vision (Student question)
Lots of possibilities -- distribution/density of rods, level of and rate of regeneration of rhodopsin (possibly related to diet -- eat carrots), clarity of any tissue through which light must pass on way to retina. Or, maybe the brother and husband are just better guessers on the SAT. ;-) What most people describe as guessing yields better performance than would be expected by truely random guessing, and this applies to perceptual phenomena too (signal detection theory and all that). - Original Message - From: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Monday, November 06, 2000 6:15 AM Subject: Night vision (Student question) Folks, Are there any explanations for variations in the acuity of night vision from person to person (other than owning night vision goggles)?
Night vision (Student question)
Nancy Melucci asks: > >Are there any explanations for variations in the acuity of night vision? Visual sensitivity under low light conditions depends on several factors, all of which might vary among individuals. Dark adaptation (recovery of sensitivity following exposure to bright light) depends on the speed with which the visual pigment rhodopsin is regenerated in the rods. Rhodopsin is formed from vitamin A (which is why severe deficiencies of vitamin A produce deficits in night vision). I don't know whether individual differences in vitamin A would be manifested as differences in quality of night vision - it generally takes a severe deficit to show up as impaired night vision. Any one know whether there are differences in the speed of the regeneration process? Several other factors might vary enough between individuals to create differences in quality of night vision: Clarity of the cornea (people with cataracts will have worse night vision), the lens, or of the viteous humor will determine how much light actually stimulates the retina. Less light transmitted, less to reach the retina to be detected. The size of the pupil when it is fully dilated might vary - the bigger the opening, the more light the eye can gather. Animals that have excellent night vision (like owls) have large eyes and pupils that are capable of great dilation. As we age, we accumulate pigments in the foveal region of the retina (which also reduce our sensitivity to blue light) and these will filter out light and affect vision under low-light conditions. (This has been suggested as the reason why little old ladies like those blue rinses - to them their hair looks white, without them their hair might have a dingy, yellowed cast.) Two other possibilities that are far more speculative: Are there large enough individual differences in amount of convergence among receptors in the periphery to produce differences in sensitivity? There are some variations in the chemical composition of the photopigments for color vision and these have slightly different sensitivity contours (thus, there are different varieties of red-green anomolous color vision, depending on which variant of the red/green photopigment the person has). I suppose it is possible that there might also be variants in rhodopsin, but I don't know of any research on that. Claudia Stanny Claudia J. Stanny, Ph.D.e-mail: [EMAIL PROTECTED] Department of PsychologyPhone: (850) 474 - 3163 University of West Florida FAX:(850) 857 - 6060 Pensacola, FL 32514 - 5751 Web:http://www.uwf.edu/psych/stanny.html
Re: Night vision (Student question)
What I have read is the opposite - Males appear to have better visual acuity under photopic conditions, while females have lower absolute thresholds under scotopic - and can be seen in childhood. Females also may dark adapt faster. There are other gender differences as well related to acuity. I'm pulling this information from: Coren, Ward, & Enns (1994) Sensation and Perception (4th ed.) At 06:15 AM 11/6/00 -0500, [EMAIL PROTECTED] wrote: Folks, Are there any explanations for variations in the acuity of night vision from person to person (other than owning night vision goggles)? A student asked what the explanation would be, according to her, her brother and husband see better in the dark than she does . I also wonder since this is a subjective and ancedotal account, if night vision has been studied with this in mind (finding out who might have better than average night vision and what neuroanatomical or neurochemical conditions would make this so.) Thanks for any help you can give me. Nancy Melucci Los Angeles Harbor College Deb Dr. Deborah S. Briihl Dept. of Psychology and Counseling Valdosta State University Valdosta, GA 31698 (229) 333-5994 [EMAIL PROTECTED] Well I know these voices must be my soul... Rhyme and Reason - DMB
Re: Night vision (Student question)
Nancy Melucci wrote: > Are there any explanations for variations in the acuity of night > vision from > person to person (other than owning night vision goggles)? See: http://web.utk.edu/~wverplan/biblio10.html for the full article, by William S. Verplanck from University of Tennessee, Knoxville. * "Night Blindness and Nyctalopia. "Some persons report consistent difficulties in seeing at night, even when they are fully dark-adapted. They cannot detect objects readily visible to others and show both confusion and slow recovery after brief exposure to relatively bright light sources. Maneuvering in dimly illuminated spaces and driving or flying at night present serious problems to these individuals. The presence of such a history, whether the disturbance in sight is of recent appearance or long-standing, is usually taken as prima facie evidence of night blindness. "However, a sharp distinction must be made between night blindness as indicated by such reported difficulties and nyctalopia, or true night blindness, which may be diagnosed only on the basis of an accurate measurement of retinal sensitivity. Many, if not most, of those individuals who report difficulty in seeing at night prove to be psychoneurotic. Many who have unusually insensitive retinas, on the other hand, do not report special difficulties in seeing at night, either because they assume that others have the same difficulties, or because they fail to note them in out well-illuminated urban culture, which offers few situations in which intact rod function is required. To establish the presence of nyctalopia, it is essential to use an instrument of established validity for the measurement of retinal sensitivity. "Incidence of Nyctalopia.--No definitive data on the occurrence of nyctalopia in the population are available, since measurements have never been made on a representative sample of the population. From the studies which have been made of selected groups (e.g. school children, service men), it is known that the normal population will include a small percentage of persons of low visual sensitivity whose performance will be as poor as or poorer than that of many individuals whose nyctalopia is associated with disease or degenerative processes. About 2 per cent of the Navy men were disqualified for night duties as "night blind" on this basis. Those so disqualified seldom if ever showed symptoms other than a relatively high absolute terminal threshold, and their reduced sensitivity must be taken as the consequence of the normal variability in the density in the retinal rods and the efficiency of the process whereby rhodopsin, the visual purple, is regenerated. "The incidence of nyctalopia as part of a distinct clinical pattern is not well understood. It has been observed frequently in several diseases, and may appear in certain unusual conditions such as: "(1) Idiopathic Nyctalopia.--Idiopathic nyctalopia is an hereditary absence of rod function, which has been traced through several generations of certain families. Although typically it appears alone, it may be associated with color blindness and myopia. There is no effective treatment. "(2) Oguchi's Disease.--This rare hereditary syndrome, first reported in Japan and later observed in Europe, has its primary symptom nyctalopia with marked contraction of the visual field under low levels of illumination. Ophthalmoscopic examination shows a remarkably gray appearance of this fundus which disappears with dark-adaptation. Day vision is not affected. No treatment as proved of value. "(3) Retinitis Pigmentosa.--Nyctalopia is the first and invariable symptom of retinitis pigmentosa. In the early stages of the disease, dark adaptation takes place, but at a retarded rate. As the disease advances, rod function is progressively lost, and the absolute terminal threshold is elevated. Diagnosis of retinitis pigmentosa is based upon ophthalmoscopic examination. "(4) Glaucoma.--Early impairment and progressive loss of rod sensitivity is observed in glaucoma. "(5) Retinitis Punctata Albescens.--The earliest symptom of this disease is the complete absence of rod function. Often nyctalopia is the only symptom associated with the altered state of the retina. "(6) Other syndromes of the Visual System.--Nyctalopia has been observed as one symptom of each of the following pathologic conditions: myopia, disseminated chorioretinitis, pregnancy, nicotine poisoning, the Lawrence-Moon-Biedl syndrome, gyrate atrophy of the choroid and retina, choroideremia and atrophy of the optic nerve. Nyctalopia may be simulated by opacities of the ocular media. "(7) Overexposure to Sunlight.--Mild transient nyctalopia may appear in persons who have been overexposed to bright sunlight for several days. It will disappear within a few days if the persons will protect their eyes from the sun wither by remaining indoors or by the use of dark sun glasses. "(8) Avitaminotic Nyctalopia.--Epidemics of night blindness hav
Night vision (Student question)
Folks, Are there any explanations for variations in the acuity of night vision from person to person (other than owning night vision goggles)? A student asked what the explanation would be, according to her, her brother and husband see better in the dark than she does . I also wonder since this is a subjective and ancedotal account, if night vision has been studied with this in mind (finding out who might have better than average night vision and what neuroanatomical or neurochemical conditions would make this so.) Thanks for any help you can give me. Nancy Melucci Los Angeles Harbor College