Look harder, see less

eye.jpgAccording to a paper in this month’s Nature Neuroscience, sustained attention on an object impairs one’s perception of it.

Psychophysicists Sam Ling and Marisa Carrasco, of New York University, found that although  participants’ sensitivity to the contrast of visual stimuli initially increased when they focused their attention on the stimuli, sustained attention eventually led to impaired sensitivity. This effect  was noticeable after a period of about 16 seconds,  and has not been observed in previous neurophysio- logical and behavioural studies.

Why would this happen? One of the functions of nervous systems is to detect and respond to novel stimuli in the external and internal environment. Focusing on an unchanging stimulus leads to a reduction in the processing of that visual  information to prevent the needless  expenditure of the brain’s computational and metabolic resources. This frees the brain’s capacity for the processing of novel stimuli, making it less likely that something potentially dangerous, such as a predator, will go unnoticed.