In a now-classic study by Simons and Chabris (1999), study participants watched two teams pass a basketball among teammates. One team was wearing white shirts, and the other was wearing black shirts. Participants were told to count how many times the team wearing the white shirts passed the basketball, thereby directing their attention to the white shirts and causing them to ignore the black shirts. Interestingly, more than half of the study participants failed to notice when a man wearing a black gorilla suit walked right past the two teams. This phenomenon is known as: