Low luminance contrast sensitivity: effects of training on psychophysical and optokinetic nystagmus thresholds in man.
We compared psychophysical contrast sensitivity function (psi-CSF) and optokinetic contrast sensitivity function (OKN-CSF) in man, for the combination of three spatial and three temporal frequencies. psi-CSF was defined as the inverse of the contrast threshold, that is the contrast value of a sinusoidal grating for which a subject was able to identify the width of a drifting grating. OKN-CSF was defined as the inverse of the contrast value of the grating which triggered an involuntary optokinetic nystagmus. In highly experienced subjects, OKN-CSF was overall higher than psi-CSF. More precisely, differences between both contrast sensitivity functions occurred mainly in the low spatio-temporal frequency range (below 4 c/deg and 9 Hz). In naive subjects, psi-CSF reached the level of OKN-CSF after two consecutive test sessions. OKN-CSF did not change with training. Similarly, high spatio-temporal frequency psychophysical thresholds did not change with training and, moreover, approximated OKN-CSF thresholds. Low spatio-temporal frequency psychophysical sensitivity was initially lower than corresponding OKN-CSF sensitivity; however, after only two training sessions, the two functions were indistinguishable due to a selective increase in psychophysical low spatio-temporal frequency sensitivity.
Masson
G
G
URA CNRS 1166 Cognition & Mouvement, University Aix Marseille II, France.
Mestre
D R
DR
Blin
O
O
Pailhous
J
J
D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D008297:Male; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology; D011214:Practice, Psychological; D011601:Psychophysics; D012684:Sensory Thresholds / Q000502:physiology*; D013997:Time Factors