THE EFFECT OF REPEATED PREPULSE-BLINK REFLEX TRIALS ON BLINK REFLEX MODULATION AT SHORT LEAD INTERVALS

The amplitude of a blink reflex is inhibited if the reflex eliciting s timulus is preceded by a short prestimulus (e.g. < 250 ms). If the pre stimulus duration is longer than 1; s, blink reflex amplitude is facil itated. The present study investigated the effect of repeated presenta tions of prestimulus-blink eliciting stimulus pairings on blink reflex modulation. Subjects in Experiment 1 (N = 59) were presented with a s equence of 12 blocks of 7 trials. Within each block, one trial was a b link stimulus alone, whereas the blink stimulus was preceded by a pres timulus on the other trials. Prestimulus intervals were 30, 60, 120, 2 40, 500 and 2000 ms. Prestimuli were presented continuously throughout the prepulse interval. The amount of reflex magnitude inhibition at t he 60, 120, 240 and 500 ms lead intervals and reflex latency shortenin g at 30 and 60 ms decreased over blocks. The amount of reflex facilita tion at a lead interval of 2000 ms was not reduced. In Experiment 2 (N = 22), two groups of subjects were presented with a sequence of blink stimulus alone presentations and prestimulus-blink stimulus pairings. The prestimulus lasted for 120 ms in one group and for 200 ms in the second. Blink reflex magnitude inhibition declined in both groups over blocks of trials. However, the groups also differed in responding on the blink stimulus alone control trials. Experiment 3 (N = 24) employe d the same design as did Experiment 2. No difference in control respon ding was found. Similar to Experiment 2, blink inhibition decreased ov er repeated trials in both groups. The present results indicate that p repulse inhibition reflects a process which is affected by repeated pr esentation of prestimulus-reflex stimulus pairings. However, the concl usion that the reduction of prestimulus effects reflects habituation s eems to be premature.