This is an open request to psychophysicists or neurophysiologists in vision
research. I am baffled by my recent experimental results in human thresholds
during dark adaptation. I used pinpoint red stimuli at 2 arc degrees and large
(2 cm) blue stimuli at 20 arc degrees. Subjects were first dark adapted
for 30 min. I then fixed stimulus intensities to 50% detection (mean of
ascending and descending series). During the next 3 hours, red stimulus
thresholds constantly
and significantly increased, while blue stimulus thresholds remained
absolutely stable. The subjects required increasingly intense red stimuli
to remain at the 50% detection level. Everywhere I have looked in the lit,
cone thresholds asymptote at 20-30 minutes in dark adaptation. Can anybody
explain to me what is the meaning of my results ? has this effect been
reported before ? What is its' physiological basis ?
Claude M.J. Braun, PhD
Professeur Titulaire
Laboratoire de Neurosciences Cognitives
Universite du Quebec a Montreal
CP 8888 Succursale Centre-Ville
Montreal, Quebec, Canada H3C 3P8
telephone: 514-987-4814
fax: 514-987-8952
e-mail: BRAUN.CLAUDE@UQAM.CA
Claude M.J. Braun, PhD
Professeur Titulaire
Laboratoire de Neurosciences Cognitives
Universite du Quebec a Montreal
CP 8888 Succursale Centre-Ville
Montreal, Quebec, Canada H3C 3P8
telephone: 514-987-4814
fax: 514-987-8952
e-mail: BRAUN.CLAUDE@UQAM.CA