Four Vs. Five

"Your brain finds it easy to size up four objects but not five -- here's why"

Now scientists have discovered why: the human brain uses one mechanism to assess four or fewer items and a different one for when there are five or more. The findings, obtained by recording the neuron activity of 17 human participants, settle a long-standing debate on how the brain estimates how many objects a person sees. The results were published in Nature Human Behaviour on 2 October.