Respiratory modulation of startle: effects on subjective intensity and psychomotor response times

Respiratory cycle time modulates reflexive startle eye blink responses to
acoustic stimuli. Responsible for this effect seems to be the afferent input
of slow adapting pulmonary stretch receptors. It remains unclear, however,
whether this respiratory modulation of startle (RMS) effect is also reflected
in the modulation of higher cognitive, evaluative processing of the startle
stimulus. Twenty-nine healthy volunteers received 80 acoustic startle stimuli
(100 or 105 dB(A); 50 ms; binaural; instantaneous rise time), which were presented
during peak and ongoing inspiration and expiration, while performing
a paced breathing task at 0.25 Hz. Participants first responded to the startle
probes by `as fast as possible' button pushes and then rated the perceived
intensity of the acoustic stimuli. Psychomotor response time was divided into
pre-motor (from stimulus onset to home button release; represents stimulus
evaluation) and motor response time (from home button release to target button
press). Intensity judgements were higher and evaluative response times
accelerated during on-going expiration. No effect of respiratory cycle phase
was found on eye blink responses and motor response time. We conclude,
therefore, that respiratory cycle phase affects higher cognitive, attentional
processing of acoustic startle stimuli.