Monitoring 16 Television Screens Showing Little Movement

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Abstract
Altogether 65 observers watched 16 or 24 television screens for L hr. The screens showed mainly still scenes from a prison, with occasional movements lasting 2 to 40 see. The observer had to press an alarm whenever he saw a suspicious incident. During the 1 hr there were 12 suspicious incidents and 72 other movements. Reliably more incidents wore missed when they were brief and indistinct, and when they were scattered over 24 screens instead of over only 16 screens. Having to report all movements, and having to answer questions about movements every 30 sec, also reliably increased the number of missed incidents. Having 24 screens to monitor instead of 16, and having to answer questions, reliably increased the time taken to press the alarm. Incidents were spotted more quickly if there had recently been a movement on an adjacent screen. Sitting nearer also reduced the time taken to press the alarm. The results conform to the principles of human performance derived from simpler experiments on visual vigilance and on visual search.