> On Tue, 15 Oct 2002, Beth Benoit wrote: > > > TIPSters, > > One of my Intro students asked if a person who is color blind > > has a better perception of movement - particularly peripheral > > movement. Since the rods take over for missing cones, and a > > person who is color blind has fewer or no cones, could there > > be a difference? > > > > Here are her words: > > > > "My husband who is color blind and doesn't really have good > > vision <snip>
I'm trying to decide in answering this whether Beth's student or Beth (or both) are using the term "color blind" in its non-technical or technically-correct sense. If the former, they may have in mind not true blindness but color deficiency (dichromaticity), probably of the red-green variety, which is the most common. But Beth's reference to "having no cones" suggests that she may be truly referring to complete color blindness ( monochromaticity or achromatopsia), which is rare. My guess is that Beth's student used the term non-technically to describe her husband's dichromaticity, and Beth, being a techie, took this to mean achromatopsia. If the problem is dichromaticity, I doubt there's an increase in rods. I believe that current theory is that in one of the two forms of red-green colour deficiency (deuteranopia), the cones of what should be the medium wavelength catching receptors are filled with the same photopigment as the long-wavelength receptors. In the other form (protanopia) the reverse happens. So I'd think that there wouldn't be a change in either the number of rods or cones. (OK, I just checked. Kandel (Principles, 4th ed) says "...suggests that, rather than having lost large numbers of L or M cones, the dichromat possesses the normal number but all are L or M". And "suggests" means he's not really sure himself.) As for true color-blindness (achromatopsia), it could be true that the loss of cones is compensated for by an increase in rods. But my best guess here is that it isn't: the number of rods is normal, but there's an absence of cones. Kandel doesn't mention achromatopsia at all. Stephen _____________________________________________________________ Stephen L. Black, Ph.D. tel: (819) 822-9600 ext 2470 Department of Psychology fax: (819) 822-9661 Bishop's University e-mail: [EMAIL PROTECTED] Lennoxville, QC J1M 1Z7 Canada Dept web page at http://www.ubishops.ca/ccc/div/soc/psy TIPS discussion list for psychology teachers at http://www.frostburg.edu/dept/psyc/southerly/tips _________________________________________________________ --- You are currently subscribed to tips as: [EMAIL PROTECTED] To unsubscribe send a blank email to [EMAIL PROTECTED]
