Abstract
Purpose :
Detecting minimum motion displacements (Dmin) and interpreting biological motion cues (biomotion) are relevant to driving safety, particularly at night. We tested the impact of brief luminance changes (much shorter and dimmer than photostress test) on Dmin and biomotion thresholds in older and younger adults. We also simulated the effect of early cataract in a second group of younger adults to evaluate the impact of ocular scatter independent of ageing.
Methods :
Dmin was measured using a two-frame random-dot-kinematogram (RDK), with the minimum motion displacement that enabled correct identification of direction of motion estimated with a 3-1 staircase. Biomotion was measured using a leftwards or rightwards 13-dot point-light-walker, embedded in noise dots. Number of noise dots varied according to a 3-1 staircase to estimate the threshold number of dots that permitted PLW direction identification. Both motion stimuli consisted of white dots (200 cd/m2) on a black background. Thresholds were measured for the motion stimuli in isolation, and in the presence of a brief (16.6ms), 200 cd/m2 luminance flash presented at intervals before or after the motion stimulus (0, 25, 50, 75ms). Exp 1 tested 25 younger (aged 22-35 years) and 23 older (aged 60-80 years) adults. Exp 2 tested 18 younger adults (aged 20-27 years) with and without a Tiffen Black Pro Mist BPM 2 filter to simulate early cataract.
Results :
Exp 1 showed a main effect of age: older adults had elevated thresholds for both motion tasks (p<0.01) relative to younger. With the added flash, the only condition to elevate thresholds was the flash presented immediately preceding the Dmin stimulus in older adults only (mask timing x group interaction, p<0.01). In Exp 2, the cataract lens elevated Dmin thresholds (p<0.01), particularly when the flash preceded the stimulus (lens x mask, p=0.04). Biomotion was not affected by the luminance flash for any condition.
Conclusions :
Older adults had elevated thresholds for both Dmin and biomotion tasks, however only Dmin was impacted by the presence of a brief, luminance flash. Findings suggest that ocular scatter drives this elevation, at least in part, which may impair night driving ability. Given that biomotion thresholds were not affected by the flash in older adults, or by added optical scatter in younger adults, the reduction of biomotion performance with age is likely to be neurally driven.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.