What Catches Your Eye First (Visual Search)

Some visual features jump out at you instantly, before you've consciously started looking — a red dot among blue ones, a tilted line among upright ones. Vision scientists call this pre-attentive processing: your visual system picks certain features out of a whole scene in parallel, in a fraction of a second, before any deliberate, one-by-one searching begins. The tell is reaction time: a genuinely pre-attentive feature stays roughly as fast to find no matter how big the grid gets. Combine two features so neither alone marks the target, though, and that shortcut disappears — you're back to checking items one by one, and reaction time reads reliably higher than any single feature's. Not every pairing loses the shortcut equally badly, either: some combinations stay closer to single-feature speed than others, though none of them gets it back completely.

Check one feature below to test it on its own, or two at once for a conjunction search. Pick a grid size, press Start, then click the odd one out as fast as you can — every trial gets added to the chart below.

What this teaches: Search a grid for a target defined by one or more features and see how search time changes as the grid grows. It teaches visual search, the difference between pre-attentive (feature) search and conjunction search, and how reaction time reveals the difference.