Vision Questions
Larry Daily asks: >1. Do blind people "see" anything? My thought was that someone blind from >birth would have no visual experience at all, or they wouldn't be able to >report it, not having the experience of "normal" vision to compare to. On >the other hand, someone blinded as a result of disease or injury after >growing up sighted - what do they experience? Is it a uniform black (or gray >or some other color) field? Is it like having your eyes closed in a dark >room? > I don't know what the subjective experience would be like. I think perhaps you might be thinking of the phenomenon of blind sight, which occurs sometimes in individuals who lose vision as a result of a brain injury. These individuals have no conscious experience of sight but will duck to avoid getting hit by an object tossed at them and can respond at above-chance levels about whether a light was turned on in their right vs. left visual field when they are told to guess. My understanding of this is that the eyes are functional and sub-cortical visual areas mediate these responses. >2. Are there folks who are color-blind as a result of having no cones at >all? This seems unlikely to me (isn't the fovea all cones?), but I wasn't >sure. Oliver Sacks wrote a book about this unusual condition (The Island of the Color Blind). In addition to being unable to see color, these individuals have extremely poor visual acuity (as you would expect for some one with no foveal vision). They also have great difficulty functioning under ambient light that is stronger than twilight because the rods are bleached under high illumination conditions. > >3. What would cause poor depth perception? Is there a particular brain >region or visual pathway that, if damaged, results in the inability to >perceive depth? Some depth perception is mediated by monocular cues. Other aspects of depth perception are mediated by binocular cells (cells in visual cortex that receive input from both eyes). These are the cells that are stimulated by the Magic Eye posters (remember those?). Animals who are deprived of binocular vision no longer have effective use of these binocular cells (they eventually come to be devoted to one eye or the other during a period of plasticity). (Barlow did some of this work. Sorry, I don't have the reference handy.) This can also happen with a person with uncorrected strabismus. They can still resolve monocular depth cues, but are not as accurate as individuals with an intact binocular cell organization. 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: Vision Questions
Going for 2 and 3 >2. Are there folks who are color-blind as a result of having no cones at >all? This seems unlikely to me (isn't the fovea all cones?), but I wasn't >sure. Color blindness (no color vision at all) can results from either missing all cones or missing 2 of the 3 types. If an individual is missing all cones, it does lead to visual problems other than color blindness - they tend to have problems with bright light (since rods work better in dim light). Complete color blindness can also occur with damage to V4 in the brain. >3. What would cause poor depth perception? Is there a particular brain >region or visual pathway that, if damaged, results in the inability to >perceive depth? Poor depth perception - such as problems with binocular disparity? Ah, that I know (through experience!). The visual system needs appropriate environmental stimuli as it is developing, otherwise, no binocular disparity. If someone has a lazy eye or one eye is a lot stronger than other, this may only partially develop or not develop at all! An individual with one eye would not have binocular disparity. However, you learn monocular cues that can be used for depth perception. >Thanks in advance, >Larry > > >Larry Z. Daily >Assistant Professor of Psychology >Department of Psychology >White Hall, Room 213 >Shepherd College >Shepherdstown, West Virginia 25443 > >phone: (304) 876-5297 >email: [EMAIL PROTECTED] >WWW: http://webpages.shepherd.edu/LDAILY/index.html Deb Dr. Deborah S. Briihl Dept. of Psychology and Counseling Valdosta State University Valdosta, GA 31698 (229) 333-5994 [EMAIL PROTECTED] http://chiron.valdosta.edu/dbriihl/ Well I know these voices must be my soul... Rhyme and Reason - DMB
Vision Questions
Hello all, My intro students were playing "stump the instructor" yesterday and came up with a number of questions that I had no ready answers for. Can anyone help? 1. Do blind people "see" anything? My thought was that someone blind from birth would have no visual experience at all, or they wouldn't be able to report it, not having the experience of "normal" vision to compare to. On the other hand, someone blinded as a result of disease or injury after growing up sighted - what do they experience? Is it a uniform black (or gray or some other color) field? Is it like having your eyes closed in a dark room? 2. Are there folks who are color-blind as a result of having no cones at all? This seems unlikely to me (isn't the fovea all cones?), but I wasn't sure. 3. What would cause poor depth perception? Is there a particular brain region or visual pathway that, if damaged, results in the inability to perceive depth? Thanks in advance, Larry Larry Z. Daily Assistant Professor of Psychology Department of Psychology White Hall, Room 213 Shepherd College Shepherdstown, West Virginia 25443 phone: (304) 876-5297 email: [EMAIL PROTECTED] WWW: http://webpages.shepherd.edu/LDAILY/index.html
Re: Vision questions
At 6:38 AM -0500 7/23/00, [EMAIL PROTECTED] wrote: >Listpersons, > >Hoping to get some clarification for a student with questions on vision: > >Vitamin A is good for the visual system, right? Does anyone know how this >works? What about all the parental jabbering about not sitting too close to >the TV, or watching TV or reading in low levels of light? Is there any truth >to the threat about "ruining your eyes" in these ways? > >Thanks for your patience and help. > >Nancy Melucci >Huntington Beach, CA Francis Young from Washington State University conducted an extensive research program in the 60's, involving correlational studies, naturalistic experiments, and lab experiments on induced myopia. This is probably some of the work that Stephen is referring to. He argued (as I recall) that large amounts of close work, e.g. reading, caused a "spasm of accommodation" in the muscles controlling the lens. If this spasm continued long enough, the eyeball elongated to compensate. I haven't heard much about this topic lately, so I don't know if his ideas are still supported. Doug Wallen Psychology Department Email: [EMAIL PROTECTED] 23 Armstrong Hall Phone: (507) 389-5818 Minnesota State University, Mankato Fax: (507) 389-5831 Mankato, MN 56001
Re: Vision questions
On Sun, 23 Jul 2000 [EMAIL PROTECTED] wrote: > Listpersons, > > Hoping to get some clarification for a student with questions on vision: > > Vitamin A is good for the visual system, right? Does anyone know how this > works? Right. The photopigment in the rods, rhodopsin, consists of retinal bound to opsin. Retinal is synthesized from vitamin A. When the retinal absorbs a photon of light, it changes its conformation, and initiates a process that leads to electrical activity in the receptor, and ultimately to vision. No vitamin A, no retinal, no vision. What about all the parental jabbering about not sitting too close to > the TV, or watching TV or reading in low levels of light? Is there any truth > to the threat about "ruining your eyes" in these ways? > Not as far as I know. "Eyestrain" is a myth. There was a recent report that children who sleep with a nightlight are more likely to be myopic (near-sighted), with the suggestion that this was causal, but the finding doesn't seem to have held up. But there is better evidence (including experimental animal work) that reading may cause eyeball elongation, and therefore myopia. There's a nice correlation between IQ and myopia, supporting the idea of the bookwormish, high-IQ nerd with glasses. That, at least, doesn't seem to be a myth. I never wore glasses, myself, for most of my life. Draw your own conclusion. Writing from home, from memory, with no references handy to append. Just believe. -Stephen Stephen Black, Ph.D. tel: (819) 822-9600 ext 2470 Department of Psychology fax: (819) 822-9661 Bishop's Universitye-mail: [EMAIL PROTECTED] Lennoxville, QC J1M 1Z7 Canada Department web page at http://www.ubishops.ca/ccc/div/soc/psy Check out TIPS listserv for teachers of psychology at: http://www.frostburg.edu/dept/psyc/southerly/tips/
Vision questions
Listpersons, Hoping to get some clarification for a student with questions on vision: Vitamin A is good for the visual system, right? Does anyone know how this works? What about all the parental jabbering about not sitting too close to the TV, or watching TV or reading in low levels of light? Is there any truth to the threat about "ruining your eyes" in these ways? Thanks for your patience and help. Nancy Melucci Huntington Beach, CA
