Abstract:

Selective attention modulates multiple stages of visual processing, and nearly all the attentional modulations are affected by normal aging. Studies about the influence of aging on early stages of attentional processing can greatly help to understand the mechanism of cognitive aging. However, the related studies are insufficient and sometimes exhibit inconsistent results. Till now, there is still lack of reviews focusing the aging mechanism of early visual attention from the perspective of time course.
This paper systematically reviews the ERP (event-related potential) studies investigating the aging effect on both pre-stimulus anticipatory attention and sensory stages of attentional processing (less than 200ms post-stimulus). Current evidence shows that: (1) early attentional effects reflected by many ERP components (e.g., ADAN and EDAN reflecting anticipatory attention, N1 reflecting early spatial attention, SP and SN reflecting early feature attention) are delayed in older adults compared to young adults; (2) the amplitudes of early attentional effects showed diverse age-related patterns in different ERP components : while some components (e.g., ADAN, EDAN, and P1 reflecting early spatial attention) appear to be resistant to aging, some other components (e.g., alpha power lateralization reflecting anticipatory attention, N1 reflecting early spatial attention, and SN reflecting early feature attention) seem to be influenced easily by aging, albeit some inconsistent results (e.g., the age-related spatial attention effect on N1 amplitudes is found to be enhanced, preserved, or declined in different studies); (3) while target facilitation reflected by some ERP components (e.g., SP reflecting early feature attention, P1 and N1 reflecting early object attention) is retained in healthy older adults, there is an age-related decline in distractor suppression.
Regarding to the diverse and inconsistent findings about how normal aging affects early attentional effects in ERP amplitudes, there might be multiple reasons. On one hand, it might be due to different task demands and/or different attentional processes (distractor suppression vs. target facilitation) engaged in different studies: (1) different task demands will confuse the observation of, even exert distinct influences on different stages of early attention in healthy older adults; (2) target facilitation and distractor suppression might be two distinguished age-related attentional processes, with distractor suppression more sensitive to normal aging. On the other hand, it might be ascribable to some confounding factors, such as signal-to-noise ratio and individual differences of the elderly across studies: (1) the low signal-to-noise ratio in s aging-related ERP studies might lead to unstable and unconvincing results; (2) the range of age and cognitive function of the elderly samples are different across studies, which might also leads to inconsistent results. Future research should control the confounding factors to obtain stable and comparable results, such as ensuring sufficient trials and/or matching the task demands between the elderly and young. To further understand the aging mechanism, future research can also manipulate these factors to explore their specific effects on early stages of attention, such as providing a neutral condition to separate target facilitation and distractor suppression processes.

Key words: early stages of visual attention, normal aging, anticipatory attention, ERP