Abstract
Visual event-related potentials (ERPs) to objects tend to increase in latency with age. It is unclear how optical and neural factors contribute to this delay, and to the considerable amount of within-age group variability (Rousselet et al., Frontiers in Psychology 2010, 1:19). For instance, age-related slow-down of visual processing might be due to senile miosis - a decrease in pupil size with age that reduces retinal illuminance. To tease apart the contribution of senile miosis and luminance to age-related changes in visual ERPs, we recorded EEG from 55 participants, aged 18-79, in two sessions each. Images of faces and phase scrambled noise textures were presented in 9 blocks of 150 trials each. We used neutral density filters that reduced the original screen luminance in block 1 (60.8cd/m2) by half in each subsequent block, to arrive at 0.59 cd/m2 in block 8. Block 9 was a repeat of block 1. We analysed the time course of face-texture contrasts in every subject using bootstrap statistics. Linear regression on the preliminary data from 26 subjects (10 young: 18-25 years-old, 8 middle-age: 32-59 and 8 older: 60-79) showed a significant age-related delay in ERP integration time at all luminance levels (average slope = 1 ms / year). However, none of these delays remained significant after accounting for pupil size. To investigate if there is a causal relationship between pupil size and processing speed across age groups, we are undertaking two more studies: one study using 1 to 6 mm pinholes to directly manipulate pupil size in young subjects, another study using simultaneous EEG and ERG (electro-retinogram) recordings that will allow us to disentangle cortical and retinal contributions to age-related ERP delays.
Meeting abstract presented at VSS 2012