Abstract
Abstract: :
Purpose: Transient adaptation (TA) refers to losses in the eye's sensitivity during the initial second or two following an abrupt increase or decrease in adapting field (AF) luminance, where loss is defined as the factor by which threshold is elevated shortly after the transition to the new light level compared with the eventual steady–state threshold at the new AF level. The objective of this study was to compare TA in young (25–45 yrs) and elderly (60–80 yrs) subjects (Ss). Earlier studies of TA used primarily younger subjects. Only Blackwell reported that TA was independent of age, a finding that seems at odds with older subjects' complaints about sudden changes in light level (e.g. headlights). Methods: All Ss were initially adapted for 10 minutes to a 12º diameter, uniform, white AF of 1 c/m² and having a superimposed small, central fixation light. Subsequently, AF luminance was increased (or decreased) during each 10 sec trial by 1.0 log unit for 1 second duration. Transient and steady state thresholds were measured using a 2–alternative, spatial forced choice procedure. A small, brief test flash (TF) appeared either above or below the central fixation light on each trial. Transient thresholds were measured at each of several tau values (20, 50, 100, 200, 300, 500 and 700 msec), where tau refers to the time between the onset of change in the AF level and the onset of the brief TF. Steady–state thresholds were measured for AF levels of 10 (increment case) and 0.1 (decrement case) c/m². Results: (a) For brief values of tau, the magnitude of visibility loss was similar for 1 log unit AF increment and decrement, and for both young and elderly Ss. (b) As tau increased from 20 to 700 msec, threshold (visibility loss) decreased and approached the appropriate steady–state level for both young and elderly Ss. (c) However, whereas young Ss were almost completely recovered from the initial visibility loss by the time tau = 300 msec, elderly Ss continued to evidence significant visibility loss for tau values as long as 700 msec. Conclusions: Results "a" and "b" are consistent with earlier research. Result "c", while not consistent with Blackwell's report, is consistent with elderly Ss' complaints about visibility loss during suddent changes in light level.
Keywords: aging: visual performance • aging • temporal vision