I previously wrote about this UCLA pilot study here. What follows is the description of this experiment from Ivar Lovaas' recent book (Lovaas, 2002):
A pilot study done at the UCLA (University of California, Los Angeles) Autism Clinic provides a particularly vivid example of apparent sensory deficits in children with autism. In an attempt to ascertain where a nervous system sensory "block" may be located, the chilren's heart rates, galvanic skin response, pupillary dilations and constrictions, and orientation to stimuli were recorded. Clapping one's hands directly behind a child's back and observing a failure to startle is often used as a diagnostic indicator of autism. We failed to observe a response to hand clapping even though the clapping was loud. Subsequently, and without prior warning, we increased the loudness and fired a very loud noise (from a starting pistol) 2 feet behind each child's back. This sound was of sufficient strength to elicit a major startle in attending adults. In contrast, little or no change was detected in any of the children's behaviors, despite the sensitivity of the measurement instruments employed. However, there were major alterations in all recordings when, instead of firing the loud starting pistol, the children heard the slight sound of a candy bar being unwrapped out of sight. It seemed as if the children would attend to their environment if there was a payoff for doing so. In evaluating the outcome of this experiment, it is important to be reminded of the large differences among persons with autism. In regard to the experiment with the starting pistol, a child with a fear of unusual sounds, such as those from vacuum cleaners or ambulance sirens, may well have reacted differently from those children we observed in the study.
Lovaas, O.I . (2002). Teaching Individuals with Developmental Delays: Basic Intervention Techniques. Austin, TX: Pro-Ed.