• Startle;
  • Eyeblink;
  • Prepulse;
  • PPI;
  • Stimulus intensity;
  • Signal-to-noise ratio


Prepulse inhibition (PPI) of the human acoustic startle response is reduced in the presence of background noise of a sufficient intensity, possibly due to a reduction in signal-to-noise ratio (prepulse intensity relative to background noise). We examined this hypothesis by varying prepulse intensity and background noise intensity in order to hold three different signal-to-noise ratios constant (5, 15, and 25 dB(A) above background noise intensity). The results showed that signal-to-noise ratio proved to be a more important factor than absolute stimulus intensity in determining the degree of PPI of startle eyeblink response magnitude. Therefore, the effectiveness of a prepulse is determined by prepulse salience, not intensity, and this effectiveness is equivalent across a range of physical intensities.