The Magic Number 4 in Visual Attention

Steven Franconeri
Department of Psychology
University of British Columbia

Performance across several visual tasks, such as memory for spatial 
position, multiple object tracking, or rapid counting (subitizing), 
often seems to suggest that the visual system can localize or track a 
fixed number of objects at once. These fixed capacities, usually of 
about 3 or 4 objects, are often taken as strong constraints on possible 
architectures of visual attention. However, for each of these tasks, 
there is debate over whether capacities are truly fixed. We critically 
examine these limits, and show that manipulations of task difficulty 
can push these limits down to 1 object, or up to 8 objects.  We discuss 
the possible architectural roots of this limit, as well as potentially 
related limits in the binding of object features.