Effect of ageing on attended visual stimuli in the presence of cognitive mental load.

Purpose: This study was designed to compare the effects of mental load, caused by concurrent auditory tasks, on attended and non-attended visual stimuli in older and younger adults.

Methods: Participants performed a visual orientation discrimination task involving two spatially separated Gabor patches of 4 cycles/degree and 55% contrast. Participants received either a valid-cue, invalid-cue or a neutral-cue for the patch whose orientation they were required to determine. An auditory n-back task was performed simultaneously to impose mental load. Repeated-measures ANOVA was used for investigation of main effects and interactions of ageing, mental load and attention condition on orientation discrimination.

Results: A total of 27 younger (mean age ± SD, 22.6 ± 1.3 years) and 23 older adults (54.7 ± 4.3 years) participated in the study. There was a significant effect of age (p = 0.01) and mental load (p < 0.001) on the proportion of correct orientation discrimination responses. Attentional condition significantly affected the proportion of correct responses (p = 0.02), but there was no significant interaction between attention, mental load and age group (p = 0.85). There was no overall difference in the proportion of no responses (the proportion of trials in which the participants failed to respond) between the two age groups (p = 0.53) nor on the overall effect of attention on the proportion of no responses (p = 0.25). There was, however, a significant effect of mental load on the proportion of no responses (p = 0.002).

Conclusion: Although mental load reduced performance equally for both age groups and for all attentional conditions, older adults had poorer overall performance. Therefore, a given mental load is more likely to drive older observers to unacceptable levels of task performance.