Attending multiple items decreases the selectivity of population responses in human primary visual cortex

Area of Science:

• Cognitive Neuroscience
• Visual Perception
• Neuroimaging

Background:

• Task performance declines with increased numbers of items to attend (set size).
• The neural basis for this set-size effect on cognitive performance remains debated.

Purpose of the Study:

• To investigate the neural mechanisms underlying performance decline with increasing set size.
• To examine how attending to multiple items affects neural representations of visual stimuli.

Main Methods:

• Utilized functional magnetic resonance imaging (fMRI) in human observers.
• Employed a forward encoding model of orientation selectivity.
• Generated population tuning functions for attended stimuli (single vs. dual items).

Main Results:

• Observed clear population tuning functions for attended items, peaking at stimulus orientation.
• Found a set-size-dependent decrease in the precision of orientation-specific population responses.
• Demonstrated that attending to two items reduced the selectivity of population tuning functions for each item.
• Showed that the loss of precision in population tuning predicted behavioral costs.

Conclusions:

• Attending to multiple items degrades the precision of perceptual representations.
• This reduced precision provides a neural explanation for behavioral impairments in tasks with larger set sizes.
• Findings elucidate the neural basis of the set-size effect in visual attention.