Purchase this article with an account.
Adam Reeves, Rebecca Grayhem; Early scotopic dark adaptation; change in gain versus change in noise. Journal of Vision 2007;7(9):794. doi: 10.1167/7.9.794.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Just after turning off a steady adaptation field, the log threshold for cone vision abruptly drops half-way to absolute threshold, before the leisurely process of dark adaptation begins. The abrupt drop is due, we have argued, to the removal of photon-driven (square-root) noise consequent on shuttering the adaptation field (Krauskopf & Reeves, Vision Research 20, 193–196; Reeves, Wu, Schirillo, Vision Research, 38, 2639–2647). We now document that the same half-way drop occurs with rod-mediated vision, over a range of 3 log units of field intensity, using stimulus parameters which isolate rods (a 1.3 deg, 200 ms, 500 or 530 nm test spot, seen at 10 deg eccentricity in Maxwellian view). The comparison between increment thresholds and thresholds obtained just after the field is extinguished extends the range of the well-known Rose- DeVries square-root law from low scotopic levels, where rods do not adapt, to higher levels at which rods do light adapt. That both rod and cone increment thresholds approach or equal Weber's law indicates that in both systems, not only does photon noise from the field drive up threshold (following the Rose-DeVries square-root law), but light adaptatio reduces sensitivity by a further factor, also proportional to the square-root of field intensity.
This PDF is available to Subscribers Only