The procedure was scripted and standardised and a team of 21 experimenters gathered data from the 228 participants. Participants were always tested individually. Participants were informed that the task would involve watching a clip of basketball players and that they should pay attention to either the white team or the black team and count the number of passes of the ball between the players of the team on which they were to focus, The task given was varied to give two types of task:'easy' (the participant kept a mental note of all the passes their team made), and 'hard' (the participant kept separate mental notes of the number of aerial passes and the number of bounced passes that their team made). The procedure enabled the manipulation of the following variables: The type of video (transparent or opaque), The type of event (Umbrella women or gorilla), The difficulty of the focused task: easy or hard. This gave 16 test conditions in total, and each participant was tested in only one of these conditions after giving their informed consent to take part. After viewing the tape, participants were asked to immediately record the number of passes on paper and were then asked a number of surprise questions: (i) While you were doing the counting, did you notice anything unusual on the video? (ii) Did you notice anything other than the six players? (iii) Did you see a gorilla [women carrying an umbrella] walk across the screen?. If they said 'yes', they were asked to provide details. If they mentioned the unexpected event at any point, the rest of the questions were not asked. The participants were also asked if they has seen anything similar before, if they said 'yes' then their data was not used in the results. At the end of the procedure, the observer participants were fully debriefed, which included a repeat showing of the video if necessary.