is reduced when the stimulus (noise) is only experienced in one ear rather than both ears. Even the very first prepulse of a test session induces inhibition, which indicates that conditioning and learning are not necessary for this effect to occur. However, the lack of conditionality has been questioned. However a thousandth prepulse also induces inhibition; the phenomenon is highly robust Response and reaction are affected by interval duration and attention. It is thought that the short intervals used in PPI task do not give enough time for the activation of a volitional response: the reaction to pulses and prepulses separated by short time frames is believed to be involuntary. Prepulses could be attended or ignored, and attention affects the outcome. In one study, normal college students were instructed to attend to one of the kind of prepulses, high- or low-pitched, and ignore the other. Attended prepulse caused significantly greater inhibition at the 120 ms interval compared to the ignored one, and significantly greater facilitation at the 2000 ms interval. This reflects the tendency of subjects to expect to hear a particular frequency of pulsed sound, an effect that is highly pronounced when the prepulse occurs two seconds before the pulse and when there are other pulses being heard which are being consciously "ignored". Increased prepulse duration leads to increase in PPI: the longer the prepulse, the greater the reduction in subsequent startle responses. Steady background noise facilitates the startle response, while pulsed background produces inhibition. History of scientific work Prepulse inhibition was first described in 1862 by Sechenov and was rediscovered at least twice before Howard S. Hoffman discovered it again in 1963. Hoffman was the first to use the term prepulse. He continued his work on startle into the 1980s. His many papers on the reflex and its modification laid the groundwork for the widespread use of prepulse inhibition today in studies of schizophrenia and other disorders. One possible reason it was discovered and rediscovered is that it got confused with Pavlovian conditioning. Another is that it didn't fit nicely into theories of the times. Disruption Disruptions of PPI are studied in humans and many other species. The most studied are deficits of PPI in schizophrenia, although this disease is not the only one to be associated with such deficits. They have been noted in panic disorder (Ludewig, et al., 2005), schizotypal personality disorder, obsessive-compulsive disorder (Swerdlow et