Human observers are very good at deciding whether briefly flashed novel images contain an animal and previous work has shown that the underlying visual processing can be performed in under 150 ms. Here we used a masking paradigm to determine how information accumulates over time during such high-level categorisation tasks. As the delay between test image and mask is increased, both behavioural accuracy and differential ERP amplitude rapidly increase to reach asymptotic levels around 40-60 ms. Such results imply that processing at each stage in the visual system is remarkably rapid, with information accumulating almost continuously following the onset of activation.

Efficient processing of our complex visual environment is essential and many daily visual tasks rely on accurate and fast object recognition. It is therefore important to evaluate how object recognition performance evolves during the course of adulthood. Surprisingly, this ability has not yet been investigated in the aged population, although several neuroimaging studies have reported altered activity in high-level visual ventral regions when elderly subjects process natural stimuli. In the present study, color photographs of various objects embedded in contextual scenes were used to assess object categorization performance in 97 participants aged from 20 to 91. Objects were either animals or pieces of furniture, embedded in either congruent or incongruent contexts. In every age group, subjects showed reduced categorization performance, both in terms of accuracy and speed, when objects were seen in incongruent vs. congruent contexts. In subjects over 60 years old, object categorization was greatly slowed down when compared to young and middle-aged subjects. Moreover, subjects over 75 years old evidenced a significant decrease in categorization accuracy when objects were seen in incongruent contexts. This indicates that incongruence of the scene may be particularly disturbing in late adulthood, therefore impairing object recognition. Our results suggest that daily visual processing of complex natural environments may be less efficient with age, which might impact performance in everyday visual tasks.