No evidence for a role of startle in the startreac effect or for an effect of attention on blink facilitation at very short lead intervals

Presentation of an accessory intense acoustic stimulus coinciding with the onset of the visual imperative stimulus (IS) in a forewarned simple RT task facilitates RTrelative to IS alone trials (StartReac effect) and elicits blinks larger than those seen on control trials. In Experiment 1, 95 or 105 dBA noise bursts of 0 or 30 ms rise time were presented during half the 5 s ISs in a simpleRTtask at lead intervals of 0, 50 and 150 ms and during intertrial intervals. RT was facilitated in the presence of an accessory acoustic stimulus and the extent of RT facilitation decreasedwith increasing lead interval. Blinks were larger at the 0 ms lead interval than at longer lead intervals or during intertrial intervals. However, blink startle magnitude or blink facilitation were not related to RT or RT facilitation suggesting that, contrary to previous suggestions, startle does not mediate the Start- Reac effect. Experiment 2 varied the reporting and response requirements to the IS to assess whether attention to the IS or motor preparation affected blink facilitation at 0 ms. Blinks were elicited 0 or 150 ms after IS onset. RT was shortest in the presence of an accessory acoustic stimulus at 0 ms and slower if presentation of the IS required additional report. Neither motor preparation nor the additional attention requirement to the IS affected the extent of blink facilitation at 0 ms. Thus, blink facilitation at 0 ms seems to reflect on the summation of sub-reflex threshold excitation by the IS and super-reflex threshold excitation by the reflex eliciting stimulus in the motor pathway