A major body of Tinbergen's research focused on what he termed the supernormal stimulus. This was the concept that one could build an artificial object which was a stronger stimulus or releaser for an instinct than the object for which the instinct originally evolved. He constructed plaster eggs to see which a bird preferred to sit on, finding that they would select those that were larger, had more defined markings, or more saturated colour—and a dayglo-bright one with black polka dots would be selected over the bird's own pale, dappled eggs.