The Effect of Using Unisensory Event Certainty on the Psychological Refractory Period

Abstract

In many situations where a person is required to react to two stimuli that occur in rapid succession there will be a lag in the response time of the second reaction. This lag in response is what is known as a “psychological refractory period” (PRP). The PRP is thought to be a limit of some mechanism in the brain to process successively occurring stimuli occurring between 50 – 250 milliseconds apart. Five different theories attempt to explain the mechanism underlying the PRP. This study tests one of them: the expectancy theory. Expectancy theory states that PRP depends on the subject’s ability to expect the second of the two events. The study included 80 right-handed male college students aged 18 to 27. For the study an apparatus was constructed that contained three lights and two buttons. The center light was a warning light to alert the subject that the other lights were going to light up. The other lights were on the opposite sides of the apparatus, and the two buttons corresponded to these two lights. The subjects were told to keep their fingers on the buttons, and release a button the moment the corresponding light lit up. Releasing the button would turn the light off. A clock was connected to each of the side lights, and would keep track of time only when the light was on. In some cases only one of the side lights would light up, and in others both lights would light up with a 50 millisecond delay for the second light. The 80 subjects were divided into four groups, Group I was told which stimulus would light up first, Group II was told whether one or two of the lights would light up, Group III was told neither, and Group IV was told both pieces of information. The results showed that with exception of Group IV, all groups had a faster reaction time with a single stimulus than with the first stimulus of two. While some subjects had a slower reaction to the first stimulus than the second, the overall group data shows a much slower reaction time to the second stimulus than the first in all groups. Group IV performed the quickest, followed by Group I, Group II, and finally Group III.