Choice reaction times and the theory of intermittency in human performance

One visual signal, drawn from two equi-probable alternatives, was followed at a variable interval by a similar signal, also drawn from two equi-probable alternatives. The relationship between reaction time to the second signal and the interval between signals was studied under the following conditions: (1) Subjects were trained from the beginning to regard the first signal as irrelevant. (2) Subjects were asked to report on the nature of the first signal after they had responded to the second. The interval between signals was one of the five values, 50, 100, 150, 200, 250 millisec. In the regular interval situation the same interval was used over a block of 20 trials. In the random interval situation the values of the interval were randomly arranged, with equal frequency within each block of 20 trials.

The results showed: (1) In the random interval situation there was a definite disturbing effect of the first signal on the reaction time to the second, despite the fact that subjects were trained to disregard the first signal. However, the delays in reaction time were significant only at the shortest interval, 50 millisec. (2) In the regular interval situation this disturbing effect was not evident. (3) The additional requirement of having to report on the nature of the first signal produced no consistent increase in reaction time to the second signal. Some implications of these results for the conception of the human operator as a channel of limited capacity are discussed.     

The refractory period and serial choice-reactions

An experiment is described in which subjects had to make consecutive 2-choice reactions to light and sound stimuli, the interval between signals being fixed for anyone series of presentations. When under these conditions, reaction times to the second signal are compared to those obtained when the first signal is used only as a warning, delays are found for short intervals. These results and the wide individual differences obtained are discussed in relation to theories that have been put forward to account for the delays obtained in serial reaction tasks.     

Parametric coupling and generalized decoupling revealed by concurrent and successive isometric contractions of distal muscles

In two experiments we examined the hypothesis of transient parametric coupling during the specification of peak forces of isometric contractions produced by the left and right hand. In the first experiment participants had to produce bimanual contractions with same and different target forces as rapidly as possible in response to an auditory signal; target forces were cued visually with variable cueing intervals. At short cueing intervals reaction times were longer when different peak forces had to be specified than when same peak forces were cued, and this reaction-time difference declined as the cueing interval was increased. Independent of the cueing interval intermanual correlations of peak forces, rise times, and reaction times were smaller in conditions with different peak forces than in those with same peak forces. In the second experiment imperative signals for left-hand and right-hand contractions were separated in time. Target forces for the first response were cued with variable cueing intervals, while for the second response the cues were presented simultaneously with the second imperative signal. Reaction time of the second response was longer when target forces for the two successive responses were different rather than same, and this reaction-time difference declined when the delay of the second signal was increased as well as when the cueing interval for the first response became longer. These results are consistent with the hypothesis of a transient cross-talk between concurrent processes of peak-force specifications; in addition they indicate generalization of the decoupling required to specify different peak forces concurrently to the specification of temporal response characteristics and to processes of response initiation.     

Perceptual Anticipation and Reaction Time

To determine the effect of perceptual anticipation upon reaction time, two different types of experiment were carried out. In the first a skilled response had occasionally to be altered at a given point after a variable warning period. In the second the subject had to react to two auditory signals separated by a short time interval which was systematically varied, the second signal being expected or unexpected.

It was found that lack of readiness to respond to a signal, as revealed by a lengthened reaction time, may be due either to the subject not having prepared himself, as he was not expecting the signal; or to the subject not being able to prepare himself in time. Preparation for reacting to the second of the two signals, when both are expected and have to be reacted to, never appears to take more than between 0·2 and 0·4 seconds, as judged by reaction time. On the majority of occasions it appears to be complete in 0·2 seconds. These times are shorter than those usually given, because the extra delay due to incorrect anticipation has been excluded. With intervals of 0·1 seconds or less, delay in the second reaction may be due to the mechanical difficulty of responding quickly enough, especially when the two reactions have to be made in opposite directions.

The finding that lack of readiness might be due to the subject not expecting the signal, and the further finding that preparation took longer when a skilled response had to be extended than when it had to be stopped, both suggest that so-called Psychological refractoriness is due to lack of fore period in which to prepare for the response, rather than to a “Psychological refractory phase” comparable to the refractory phase of nerves. If, by dividing his attention, the subject was able to prepare for his next response while making his previous one, so-called Psychological refractoriness could be completely absent.     

Expectancy and intermittency

When a human subject responds to the second of two closely succeeding stimuli, his reaction time to the second stimulus tends to increase sharply as the interstimulus interval decreases. Controversy has centred on the issue of whether this increase is mainly due to the effects of the first stimulus in producing some kind of block in the central analysing systems or whether it is mainly due to the temporal uncertainty of the second signal, as determined by the distribution of interstimulus intervals used.

By substituting for the first stimulus a spontaneous response on the part of the subject and holding the distribution of interstimulus intervals constant, it is shown that the delays in responding to the succeeding signal are eliminated, even at intervals as short as 50 millisec. This is interpreted as evidence in support of the intermittency hypothesis and as a clear indication that the increase in reaction times normally observed is not a result of the distribution of interstimulus intervals.     

Effects of signaling on temporal control of behavior in response‐initiated fixed intervals

Behavior and events distributed in time can serve as markers that signal delays to future events. The majority of timing research has focused on how behavior changes as the time to some event, usually food availability, decreases. The primary objective of the two experiments presented here was to assess how behavior changes as time passes between two time markers when the first time marker was manipulated but the second, food delivery, was held constant. Pigeons were exposed to fixed‐interval, response‐initiated fixed‐interval, and signaled response‐initiated fixed‐interval 15‐ and 30‐s schedules of reinforcement. In Experiment 1, first‐response latencies were systematically shorter in the signaled response‐initiated schedules than response‐initiated schedules, suggesting that the first response was a more effective time marker when it was signaled. In Experiment 2, responding in no‐food (i.e. “peak”) trials indicated that timing accuracy was equivalent in the three schedule types. Compared to fixed interval schedules, timing precision was reduced in the signaled response‐initiated schedules and was lowest in response‐initiated schedules. Results from Experiments 1 and 2 coupled with previous research suggest that the overall “informativeness” of a time marker relative to other events and behaviors in the environment may determine its efficacy.     

Effects of uncertain warning signals on reaction time

Three experiments were conducted in an attempt to assess the effectiveness of a warning signal in reducing reaction time when (1) the signal to respond (danger signal) follows the warning signal with a probability less than 1.0, and (2) the interval between warning and danger signals (W-D interval) is variable. The required response was the depression of a foot pedal, as in automobile braking. It was determined that probabilistic warning information could be effective if observers made use of the W-D interval to prepare to make the response required by the danger signal. It was noted, however, that observers differed considerably in their tendency to do this. A model was proposed for describing different response strategies.     

Effects of stop signal modality, stop signal intensity and tracking method on inhibitory performance as determined by use of the stop signal paradigm

In Experiment 1, the effects of stop signal modality on the speed and efficiency of the inhibition process were examined. Stop signal reaction time (SSRT) and inhibition function slope in an auditory stop signal condition were compared to SSRT and inhibition function slope in a visual stop signal condition. It was found that auditory stop signals compared to visual stop signals enhanced both the speed and efficiency of stopping. The modality effects were attributed to differences in the neurophysiological processes underlying perception. However, Experiment 2 demonstrated that the modality difference was larger for 80 dB(A) auditory stop signals than 60 dB(A) auditory stop signals. This effect was reconciled with the suggestion that loud tones are more capable of eliciting immediate arousing effects on motor processes than weak tones and visual stimuli. The second purpose of the present investigation was to explore the utility (and potential advantages) of an alternative way of setting stop signal delay relative to mean reaction time (MRT). The method that was suggested compensates for inter-individual differences in primary task reaction speed by setting stop signal delays as proportions of the subjects' MRT.     

Evidence of a single-channel decision mechanism limiting performance in a serial reaction task

An experiment is described in which the subject sat facing a display of two neon bulbs. When the left-hand bulb lit he pressed a key under his left hand, and when the right hand bulb lit he pressed a key under his right hand. The left-hand bulb gave brief flashes at random intervals averaging about 4 sec. The right-hand bulb gave a brief flash at regular intervals of about 4 sec.

The experiment repeats (the author believes for the first time) certain essential conditions of Vince's (1948, 1950) experiments and, following detailed scrutiny of every pair of responses, is taken as evidence for the following statements:—

(a) The response to a signal arriving during the reaction time to a former signal will be delayed by an amount approximately equal to the time elapsing between the arrival of the signal and the end of the reaction time to the former signal.

(b) An exception to this may occur when two signals arrive close together. In this case the two signals may be responded to as a single group.

(c) Delays can be occasioned by the monitoring of responses as well as by reactions to signals.

(d) “Grouping” of signal and monitoring may occur when a signal arrives close to the beginning of the movement made in response to a previous signal.

A survey is made of current theories in this field and suggestions given for further research.     

Assessing inhibitory control: a revised approach to the stop signal task

The stop signal task (stop task) is designed to assess inhibitory control and is a frequently used research tool in clinical disorders such as ADHD and schizophrenia. Previous methods of setting stop signal delay and of assessing inhibitory control are problematic. The current study reports two modifications that improve the task as a measure of inhibitory control. The first modification was to set stop signal delays proportional to go mean reaction time (go MRT) to better account for inter-subject variability in go MRT. Twenty-eight normal children were tested, and all standard, stop task dependent measures were obtained when delays were set by this method. The second modification was to calculate a novel dependent measure called the area of inhibition (AOI) which provides a more complete measure of inhibitory control than the slope of the relative finishing time z-scores (ZRFT-slope). Implications for the assessment of inhibitory control in clinical populations are discussed.     

Effects of delayed conditioned reinforcement in chain schedules.

The contingency between responding and stimulus change on a chain variable-interval 33-s, variable-interval 33-s, variable-interval 33-s schedule was weakened by interposing 3-s delays between either the first and second or the second and third links. No stimulus change signaled the delay interval and responses could occur during it, so the obtained delays were often shorter than the scheduled delay. When the delay occurred after the initial link, initial-link response rates decreased by an average of 77% with no systematic change in response rates in the second or third links. Response rates in the second link decreased an average of 59% when the delay followed that link, again with little effect on response rates in the first or third links. Because the effect of delaying stimulus change was comparable to the effect of delaying primary reinforcement in a simple variable-interval schedule, and the effect of the unsignaled delay was specific to the link in which the delay occurred, the results provide strong evidence for the concept of conditioned reinforcement.     

The role of the response in psychological refractoriness.

Two experiments on the PRP were performed in which the signal information was kept constant while varying the response information. The first experiment shows that delays are considerably increased by increasing response information. The second experiment re-affirms this result using unidimensional rather than multidimensional signals. The relevance of these results to theories of PRP is discussed.     

Specification of movement amplitudes for the left and right hands: evidence for transient parametric coupling from overlapping-task performance

Bimanual coordination tasks suggest transient cross-talk between concurrent specification processes for movements of the left and right hand that vanishes as the time for specification increases. In 2 experiments with overlapping and successive unimanual tasks, the hypothesis of transient coupling was examined for a psychological-refractory-period paradigm. Time for specification was manipulated by varying the delay between first and second signal (Experiment 1) and by precuing the first response (Experiment 2). Participants performed rapid reversal movements of same or different amplitudes with the left and right hands. With different amplitudes, reaction times (RTs) of the second responses were longer than with same amplitudes at short delays, and this disappeared at longer delays in Experiment 1. In Experiment 2, precuing also reduced the difference between RTs of second responses in same-amplitude and different-amplitude trials. These findings are consistent with the hypothesis of transient coupling during amplitude specification obtained with bimanual tasks.     

Imitative responses and the rate of gain of information

A series of experiments is described on audio-verbal reaction times. In the first experiment the signals were letters or digits recorded on magnetic tape and presented through earphones. In the second experiment the signals were nonsense syllables drawn from vocabularies of different size. The subjects responded by repeating what they heard as soon as it was presented and reaction times were recorded. It is shown that the size of the group from which the signal is drawn has little effect on the reaction time to that signal. A distinction is drawn between situations in which the rate of gain of information may be expected to apply and situations in which it may not apply. It is suggested that many highly practiced skills fall into the latter category.     

Division of attention between simultaneous and successive nonverbal signals varying in discriminability

Impaired performance indexed by accuracy usually accompanies the division of attention between simultaneous difficult signals. Presenting the signals successively reduces the impairment. Presenting easy signals eliminates it. Both variables crucial to these findings, relative time of onset and discriminability, were manipulated in the first experiment using a two-choice recognition paradigm involving bimodal signals. The results showed that, when a difficult signal was followed by two simultaneous easy ones, in a different modality from the first, performance was significantly worse on each than on the same signals presented alone. Simultaneous presentation of all three signals further increased the impairment for the difficult signal, but not for the easy ones. In the second experiment, the discriminability of the following signals was varied. The results showed, that when a difficult signal was followed by either two simultaneous easy signals, in a different modality from the first, or by two difficult ones, performance was significantly worse than on the same difficult signal presented alone. Further, when the preceding difficult signal was auditory, but not when it was visual, performance was better with easy following signals than with difficult ones. It is argued that an adequate account of the results from the two experiments requires the following assumptions concerning the processing of multiple signals: (1) a loss associated both with the acquisition and the storage of information, (2) preferential processing of visual signals over auditory ones. Proposals are made for the incorporation of both assumptions into a single model of divided attention.     

Writing and long-term memory: Evidence for a “translation” hypothesis

Two experiments investigated the effects of writing upon memory. In the first experiment an incidental learning procedure was employed: One group of subjects read words silently and wrote visually presented words, and a second group of subjects listened to auditorily presented words and wrote heard words. Recognition of heard words was substantially enhanced by writing, whereas the effect of writing on memory for read words was less powerful. A second experiment employing an intentional learning procedure replicated these findings and demonstrated the robustness of the beneficial consequences of writing on memory for heard words. These findings are conceptualized within a framework that proposes that translations between specialized processing domains that occur at encoding lead to the formation of distinctive memories and, hence, to better retention.     

The double step analysis of rapid manual aiming movements

The present paper examines the control principles underlying rapid manual tracking responses to horizontal double-step stimuli. The paper reports an experiment concerned with responses made to step-stimuli presented in quick succession. The amplitude of the second-step was varied between the initial step-position and the home-base. Double-step response parameters were analysed as a function of the determinant time interval (D) between the second step and the onset of the initial response. The initial response amplitude was observed to vary as a function of D. Amplitude transition functions were constructed representing the transition of the initial response amplitude between the two step positions; their slopes, furthermore, depended on the amplitude of the second target step. No delays in the initial reaction time with the interstimulus interval were observed. Minor delays to the onset of a corrective response were observed. These delays were in part related to a movement time constraint that is independent of any limitations in central processing capacity. The present findings for the manual control system are compared to double-step tracking analyses of the oculomotor control system.     

Separating the “Sinner” from the “Sin”: Religious Orientation and Prejudiced Behavior Toward Sexual Orientation and Promiscuous Sex

This study extends research on the relationship between religious orientation, sexual prejudice, and antipathy toward value‐violating behaviors. If intrinsic religion leads individuals to “love the sinner but hate the sin,” homosexual sexually promiscuous targets should be treated similarly to heterosexual promiscuous targets. One hundred female introductory psychology students were provided the opportunity to help two students. They had no information about the first student. The second student disclosed through a note that she was gay or said nothing about sexual orientation, and further stated that she was sexually promiscuous or celibate. Participants scoring high in intrinsic religiousness helped the disclosing student less when she revealed she was sexually promiscuous, but did not help a gay discloser less than a straight discloser. High intrinsic scores seemed to be related to antipathy toward the value‐violation, but not toward the gay person as an individual.     

Bisecting RT with lateralized readiness potentials: Precue effects after LRP onset

Recent work has sought to use the time at which the Lateralized Readiness Potential (LRP) first develops (LRP onset) as a temporal landmark to bisect experimental effects on reaction time (RT). Many studies have found experimental effects on the time between the signal and LRP onset, but few have found effects on the time between LRP onset and RT (LRP-RT interval). The primary goal of this study was to produce an effect on the LRP-RT interval. We employed precuing, a manipulation likely to influence motor-programming processes at the end of the RT interval. Subjects performed a 4-alternative choice-RT task in which a signal prompted a button-press with the index or middle finger on the left or right hand. Precues preceded the signals and were either informative, reducing the set of response alternatives from four to two, or uninformative. Besides RT and LRP, we also measured electromyographic (EMG) activity and the P300 ERP component. RT, P300 latency, and the interval between the signal and LRP onset were all shorter with informative than uninformative precues, but the timing of EMG activity relative to RT remained the same. Most importantly, precuing affected the LRP-RT interval. Implications for bisecting RT with LRPs and the identity of processes affected by precuing are discussed.     

Timing multimodal events in pigeons

The peak procedure was used in two experiments to study pigeons' ability to time multimodal events. In the first experiment, birds were trained to time a single event consisting of a 9-s tone or light followed by a 21-s fixed interval associated with a signal of light or tone (signal of the other modality). On occasional empty trials, different lengths of the first signal were followed by a long period of the second signal. Peak response times as a function of the duration of the first signal were linear and had a slope of close to one in all birds. This indicates that the birds were timing only the second signal. In a second experiment, two complex events were used in training. One consisted of a 9-s tone or light followed by a 21-s fixed interval associated with a light or tone. The other consisted of a 21-s tone or light followed by a 9-s fixed interval associated with a light or tone. Different durations of the first signal were again used on empty trials. Peak response times as a function of the duration of the first signal were again linear in all birds. The slope of the function was less than one but greater than zero for 3 birds. This indicates that these birds were partly timing the entire complex event of 30-s duration and partly timing only the second signal of the event. A model is proposed in which the bird takes as a criterion for timing a weighted average of different target criteria. Comparisons with the performance of rats are made.