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SUMMARY:Colour vision across the life span: perception and brain imaging -
  Dr. Sophie Wuerger\, University of Liverpool
DTSTART:20091119T130000Z
DTEND:20091119T140000Z
UID:TALK19901@talks.cam.ac.uk
CONTACT:John Mollon
DESCRIPTION:Colour vision starts in the retina where light is absorbed in 
 three different cone classes\, sensitive to long-\, medium-\, and short-wa
 velength light. The cone signals then feed into three different post-recep
 toral channels\, a luminance channel and two chromatic channels. Interesti
 ngly\, these two chromatic channels do not correspond to perceptually sali
 ent colour mechanisms (red\, green\, yellow\, blue) and recent evidence su
 ggests that the two sub-cortical chromatic channels are recombined in visu
 al cortex into orderly hue maps. I will report fMRI studies consistent wit
 h a hue map in V1. \n\nSecondly\, I will report behavioural experiments wi
 th a large sample of adult colour-normal observers of a wide age range sho
 wing that the cortical hue mechanisms are almost invariant with age.  In c
 ontrast\, the sensitivity along the protan\, deutan and tritan line declin
 es with age\; the latter measurements are likely to reflect the sensitivit
 y of more peripheral mechanisms.\n\nOur results suggest that the human vis
 ual system is able to compensate for retinal (peripheral) signal changes b
 y adjusting the relative cone weightings of the hue mechanisms. Such an ad
 aptive weighting is useful to maintain colour constancy throughout the lif
 e span in the presence of known changes in the ocular media (yellowing of 
 the lens) and retinal sensitivity losses. It may also be responsible for t
 he (relatively) small inter-observer variability compared to the large dif
 ferences in the observers’ retinal make-up. The mechanism underlying thi
 s hue compensation is still poorly understood\, but it is likely that it u
 tilises invariant sources in our visual environment. \n\n
LOCATION:Kenneth Craik Room\, Craik-Marshall Building\, Downing Site
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