The red lines indicate areas where cognitive load is occurring. Your brain traces the shapes on the first row an average of twice as much. Your eye scans the ou

The red lines indicate areas where cognitive load is occurring. Your brain traces the shapes on the first row an average of twice as much. Your eye scans the outside shape and then scans the inner line to determine if there is value in the “hollow” section. Icons without this empty core are processed as definite and only the outer lines are processed. Depending on the outline of the shape, this happens pretty fast. No matter the shape, though, the hollow icons take more time to process. I'd like to see an actual study to back this assertion up. The article makes an off-hand reference to something about how the brain processes the reading of words, but 1) I don't see how that maps to how the brain processes icons and 2) there's no reference cited for that either.