Combination rules for inhibitory stimuli

The effects of multiphasic prepulses on automatic and attention-modulated prepulse inhibition

Prepulse inhibition (PPI) is widely viewed as an operational measure of sensorimotor gating. Previous research has shown that sensorimotor gating can occur automatically and also can be influenced by selective attention. The present research investigated the relationship of the transient detection response (TDR) with automatic and attention-modulated PPI using a novel "multiphasic" prepulse stimulus. Experiment 1 compared discrete versus multiphasic prepulse types in a no-task PPI protocol to validate multiphasic prepulses as effective elicitors of automatic sensorimotor gating. Results revealed that the two prepulse types elicited equivalent levels of PPI. Experiment 2 compared the effectiveness of continuous monophasic versus continuous multiphasic prepulses within a task-based PPI protocol using a lead interval of 120 ms. Results revealed a significant attention effect for monophasic prepulses only. However, robust PPI was produced by the multiphasic prepulses independent of attention as well as over time. These results suggest that multiple influences on PPI can be assessed concurrently depending on prepulse parameters designed to activate the TDR when used in a PPI protocol capable of assessing the effects of selective attention on prepulse processing [corrected]

Further Evidence for the Independent Reflex-Eliciting and Reflex-Inhibiting Effects of a Startle-Blink Eliciting Stimulus

A small change in the environment (a prepulse) that just precedes a startle-eliciting stimulus can reduce the size of the elicited reflex, but a prepulse does not appear to diminish the ability of the startle-eliciting stimulus to depress a startle response elicited a little later. The reflex-eliciting and reflex-modifying effects of startle stimuli seem to be independent. However, most support for this observation rests on a failure to reject the null hypothesis, and relatively little of this research has employed the acoustic startle blink in human beings. The purpose of the present study was to provide additional evidence on this issue. Participants (n = 20) encountered trials in which a prepulse (p) and two 103 dB(A) blink-eliciting noise bursts (S1 and S2) were given in succession. The prepulse (a synchronous word and tone) occurred 150 ms prior to S1. The prepulse inhibited the startle blink to S1, and S1 depressed the blink elicited 1.5 s later by S2. However, regardless of whether p inhibited the blink to S1, S1 maintained the same capacity to depress the blink to S2. In contrast, a softer S1 (88 dB(A); S1attenuated), which produced a blink nearly matching the size of the prepulse-inhibited blink, did not significantly depress the response to S2. Participants also judged the loudness of S1 and S2. The prepulse reduced the perceived intensity of S1, but much less so than caused by reducing the actual intensity of S1, and proportionally much less so than the prepulse reduced the blink to S1. These results provide further evidence for independent reflex-eliciting and reflex-modifying effects of a startle-eliciting stimulus and argue against the notion that prepulses strongly reduce the general sensory impact of the startle stimulus.

Two stimuli are better than one: combination rules for prepulse inhibition revisited

Stimuli that precede elicitation of the startle reflex can inhibit that reflex. J. R. Ison, M. Zuckerman, and J. M. Russo (1975), measuring the startle reflex in the rat, showed that the effect of combining two inhibiting stimuli was greater than that of either alone. They also demonstrated that this combination effect could be described by using the rule for adding the probability of independent events, expressing the effect of each prestimulus as the proportion of the response inhibited by that stimulus. The purpose of this research was to extend those findings using the startle blink in humans. In two experiments, participants encountered trials in which two stimuli (p1 and p2) were given in succession, ending with a blink-eliciting noise (S). In Experiment 1 (N=18) p1 was a synchronous tone and a word (appearing on a computer screen), and p2 was a blink-eliciting noise identical to S. In Experiment 2 (N=30), p1 was a soft tone and p2 was a word. For both experiments, two stimuli were more inhibiting than one, and the effect of combining p1 and p2 was accurately described by the Ison et al. combination rule.

Inhibition of the cutaneous eyeblink reflex by unilateral and bilateral acoustic input: the persistence of contralateral antagonism in auditory processing

The eyeblink reflex elicited by a cutaneous stimulus is inhibited by weak auditory stimuli that are heard just before the blink. It has been shown that monaural prestimuli produce more reflex depression than binaural prestimuli do, suggesting that reflex modification is sensitive to the outcome of antagonistic connections between contralateral auditory inputs. We examined the time course of this antagonism by giving unilateral versus bilateral pairs of noise pips 100 msec before the reflex eyeblink, with the noise pips separated by 0, 1, 4, or 8 msec. Unilateral stimuli were more effective in every condition, but their advantage diminished with increased delay between the two components. The extended bilateral and unilateral trends of increasing reflex depression with increased delay meet at about 15 msec; if this extrapolation is valid, 15 msec represents the upper limit on this system's retention of the location of a brief noise impulse. The rate of convergence of the two temporal functions reflects the decay of the antagonistic effect of one noise on its contralateral counterpart.

Is adjunctive behavior a third class of behavior?

Research during the past 20 years has revealed that intermittent food presentation to a variety of organisms results in an inordinately excessive consumption of water as well as other behaviors including attack, pica, escape, and alcohol consumption. Such behavior has not been thought to be either respondent or operant behavior, but instead has been regarded as a new behavioral category termed "adjunctive behavior." This paper reexamines the rejection of adjunctive behavior as either operant or respondent behavior and concludes that the rejection was premature. This paper also reexamines the argument that there is a unique class of adjunctive behavior and concludes that there is not. It is recommended that given the growing difficulties in maintaining an operant-respondent dichotomy, rather than admitting adjunctive behavior into either of these categories, research efforts should de-emphasize preconceived and outdated notions about categories of behavior and how such behaviors should behave and instead focus on mapping functional relationships between behavior and various procedures for presenting non-contingent stimuli.