Foreperiod Duration Research Articles

Prior time uncertainty reduction of foreperiod duration under two different levels of event uncertainty in schizophrenia.

Schizophrenic and alcoholic Ss judged stimulus durations of .50 and .55 seconds. Stimulus was 1, 3 or 5 dark dots and was preceded by variable foreperiod duration of 1, 3 or 5 seconds. Judgment of stimulus duration was found to be a monotonically increasing function of foreperiod duration. When pitch of sound was correlated with foreperiod duration so that it functioned as prior information, such monotonic function was eliminated for schizophrenics only when the numerosity of dots was constant from trial to trial. The effect of prior information as to foreperiod duration was negligible for both schizophrenics and alcoholics when the numerosity of dots was variable from trial to trial. Uniqueness of schizophrenia was shown to be associated with prior time uncertainty reduction of foreperiod duration in the context of minimal event uncertainty of stimulus.

Reaction Time as a Psychophysical Method in Psychiatric Research*

As shown in Nuechterlein' s systematic and thorough review of the literature, a great deal of research on the use of reaction time (RT) to study attention in schizophrenia has been undertaken. In these studies, the properties or attributes of stimuli (modality, intensity, auditory frequency, and duration) are manipulated not to determine their direct effect on the response, but to infer indirectly differences in attention between patients and normals; e.g., regularity of foreperiod duration in the Shakow paradigm or sequence of sensory modality in the Sutton paradigm. What we propose in this short paper is to turn the paradigm upside down and to discuss the potential fruitfulness of using RT to examine differences between groups in their sensory capacity. In this approach, the attentional variable shifts from the focus of the experiment to the status of one of the major sources of artifact. And, paradoxically, we attempt to show that the RT technique, which is so uniquely suited to the measurement of attentional differences, is also particularly well suited to the reduction of the influence of attention and other similar variables as sources of experimental artifact. Although the advantages of using the RT technique for studying the sensory performance of psychiatric patients are the major topic of this report, it should be noted that many of the proposed advantages may apply equally as well for the use of other response measures in psychiatric research.

The Acquisition of Conditioned Emotional Response as a Function of Intertrial Interval

The effects of intertrial interval (ITI) and foreperiod duration on the acquisition of a conditioned emotional response were investigated using a four-trial conditioning procedure. The optimum ITI was found to be 60 s with a bidirectional gradient for conditioned suppression above and below 60 s. Conditioned supression was found to be directly related to foreperiod duration.

Sequential Effects of Foreperiod Duration as a function of the Frequency of Foreperiod Repetitions

An examination of sequential effects of foreperiod duration in reaction time tasks suggests a description of the subjects' strategy in terms of a tendency to expect foreperiod repetitions. The present experiment examined what factors influence this basic tendency. Two foreperiod distributions differing in the frequency of repetitions (33 and 66%) but with the same frequency of individual foreperiods were used. In both cases faster reaction times coincided with foreperiod repetitions. Important differences appeared nevertheless between the two foreperiod distributions; reaction times for repetitions were faster when repetitions were frequent than when they were not, and repetitions of the same fore-period more than once led to further reaction-time decreases only when foreperiod repetitions were frequent. The tendency to expect repetitions varied from trial to trial in a way which depended on long-term factors such as the frequency with which the expected foreperiod duration coincided with the foreperiod actually presented.

The Foreperiod Effect Revisited

This paper explores four factors which could be important in accounting for the discrepant results which have previously been obtained with respect to the effect of foreperiod duration on reaction time (RT). In some studies a clear effect of foreperiod duration on auditory RT has been found, in contrast to a recent finding that foreperiod duration affected visual RT but not auditory RT. By means of two experiments, the effects of practice, time-on-task, reaction task (a-reaction versus selective reaction) and signal intensity were studied. The latter variable appears to be the principal determinant of the discrepant results in that there is an interaction between signal intensity, foreperiod duration and modality. The results fit the hypothesis that signals beyond a given intensity exert an immediate arousing effect which counteracts the foreperiod effect.

The effect of warning interval on signal detection and event-related slow potentials of the brain

The amplitude of a slow potential wave in the EEG was examined during performance of a signal detection task under several fixed intervals between warning signal and critical signal. It was observed that the probability of detecting the critical signal decreased as the interval increased, and that this effect was due to a change in sensitivity rather than a change in criterion. The time-course of the change in sensitivity was related to that of the slow potential wave, which peaks shortly after the warning signal and then declines over a period of several seconds, and is interpreted as a component of the orienting response. It is suggested that the mechanism whose function is reflected in this wave also accounts for some effects of foreperiod duration and warning signal characteristics in reaction time tasks.

Sequential effects of foreperiod duration and conditional probability of the signal in a choice reaction time task

The aim of the present study was to determine whether the negative relationship usually found between reaction time and foreperiod duration in the variable foreperiod paradigm is entirely due to sequential foreperiod effects. It has been shown that when a particular foreperiod has been preceded by a longer one on the previous trial, reaction time is longer than when the preceding foreperiod was equal or shorter. This may be sufficient to explain the increase in reaction time observed for short foreperiods in variable foreperiod conditions. The present results show that, when sequential effects were controlled by the elimination of all trials where the foreperiod was shorter than the preceding one, the negative slope of the reaction time-foreperiod function diminished but did not disappear. The results suggest an interpretation of the role of conditional probability of stimulus arrival in terms of variation in the tendency to reprepare when the moment initially chosen for preparation appears to fall short of the moment at which the stimulus is actually presented.

High order sequential effects and the negative gradient of the relationship between simple reaction-time and foreperiod duration

In a simple RT task with variable interstimuli intervals (ISI), the negative slope of the RT-ISI duration relationship is generally interpreted as an effect of the increasing conditional probability of the response signal (RS). A previous study using 6 different ISIs has shown that the first order sequential effects (SE) contribute, for a part, to this slope. The aim of the present experiment was to investigate, up to the fifth order, the SEs observed when two different ISIs (1.5 and 3.0 sec) are used. The results show that SEs also intervene in the tendency for the Ss to be preferentially prepared when the RS occurs at the end of the long ISIs. They are discussed according to the hypothesis that the role played by these SEs in the negative slope of the RT-ISI relationship is primarily due to the opportunity given the Ss in such an experiment to make two successive preparations.

The impact of warning signal intensity on reaction time and components of the contingent negative variation

Slow EEG potentials were recorded during performance of a simple reaction task in which warning signal intensity was varied from trial to trial under foreperiod durations of 1, 3 and 8 sec. As shown by speed of reaction, the warning signal had an activating effect which increased with its intensity and decreased with foreperiod duration. This effect was related to the amplitude of a slow potential which appears in the EEG shortly after presentation of the warning signal. This potential is interpreted as a component of the orienting response regulating sensitivity to subsequent stimulation, so that reaction time is affected through change in the effective intensity of the imperative signal.

Free-looking time for randomly generated polygons with experimenter present: effects of content and duration of foreperiod.

Free-looking time for randomly generated 18-sided polygons was measured with E present after Ss had been exposed to 2-, 20-, or 45-sec. foreperiods containing either darkness, homogeneous white light, or similar polygons. Free-looking time increased monotonically as a function of foreperiod duration for all three kinds of foreperiod stimuli. Free-looking time following darkness significantly exceeded that following homogeneous light or polygons. Content and duration of foreperiod did not interact. The results are consistent with a tendency by Ss to imitate foreperiod durations during the free-looking period coupled with a constant increment in free-looking time whenever there is a transition from a dark foreperiod to a lighted free-looking period. The results are not consistent with an effect of perceptual deprivation under the conditions tested.

The contingent negative variation related to preparatory set in a reaction time situation with variable foreperiod

It is well established that when the foreperiod varies over a short range from trial to trial, simple reaction time decreases as foreperiod duration increases. An experiment was conducted to relate this development of preparatory set to the slow change of cortical potential known as the contingent negative variation (CNV). Ten subjects were presented with an auditory warning signal and a visual reaction signal, with interstimulus intervals of 500, 600, 700, 800 and 900 msec arranged in random order. The hypotheses that reaction time decreases and CNV amplitude increases as monotonic functions of foreperiod duration were upheld. These data combine with those already in the literature to suggest that the form of the CNV reflects the development of preparatory set.

Relation between the time-course of Hoffmann-reflexes and the foreperiod duration in a reaction-time task

The time-course of H-reflexes amplitude was studied in the two soleus muscles during the preparatory period (PP) of a go-no-go choice reaction time (RT) task. A click, as warning signal (WS), started the PP. The subject (s) performed an extension of the left foot when a visual response signal (RS) located on the left occurred. No response was to be performed when a visual signal located on the right occurred with the same probability as the former. Three groups of 5 Ss performed in conditions which differed in the PP duration only. One hundred, 300 and 700 msec durations were used. It was found that the WS triggered an increase of H-reflexes of identical delay (about 100 msec) and amplitude for the two shorter PPs. When the click was presented alone, out of a RT-context, reflexes showed a similar time-course, but with a weaker amplitude. When the PP was of 700 msec duration, the peak of H-reflexes was of lesser amplitude and considerably delayed. Under this condition a decrease of amplitude extended until the RS. No significant difference was observed between the two muscles tested, except that a slight correlation appeared between the RT and amplitude of H-reflexes recorded in the left soleus only. Reaction time was affected by the location of the reflexes-testing during the PP. A facilitatory effect was found when the amplitude of H-reflexes was high, whereas when amplitudes decreased the RTs became longer. The effect of the PP duration upon the time-course of H-reflexes amplitude was interpreted as an arousal effect of the WS for the short PPs, and by the evolution of a preparatory process for the long PP. The bilateral decrease of H-reflexes amplitude during the second part of the PP, the slight correlation between RT and H-reflex amplitude observed unilaterally and the effects of testing H-reflexes upon RT, were discussed with reference to previous experiments showing that a depression of spinal excitability during the PP of a simple RT task intervenes in the muscle involved in the response performance only. Main discrepancies between the two series of results seem to be related to the differences between the two RT situations used.

Sequential Effects Related to Foreperiod Duration in Simple Reaction Time

In a simple reaction-time (RT) experiment with variable interstimulus interval (ISI), where a steep decreasing RT-ISI relationship resulted from the use of a time mark during the ISI course, shortest RTs were found when ISI for 1 trial equalled ISI for the previous trial. RT increased more when the ISI for the previous trial was longer than when it was shorter than ISI for the actual trial.

Stimulus intensity and foreperiod effects in intersensory facilitation.

Intersensory facilitation refers to the more rapid reaction time (RT) to a target in one modality and an accessory stimulus in a different modality compared to a RT to the target alone. Prior studies suggest two processes contribute to the phenomenon, termed the preparatory state and energy integration which refer to the action of accessory stimulation in providing forewarning and intensifying the reaction signal, respectively. Experiment I factorially varied foreperiod duration, light (target) intensity and tone (accessory) intensity in a discriminative RT task. The results were that foreperiod (preparatory state) and intensity (energy integration) effects were additive, implying that they affected separate processing stages. Accessory stimulus intensity affected false alarm rate on catch trials. This suggests that energy integration involves a form of response bias (increased likelihood of responding) and not facilitation (more rapid information processing). Experiment II indicated that comparable energy integration effects obtain with tone as target and light as accessory, as well as vice versa. The findings further indicated that RT to a bisensory pairing is more rapid when attention is directed to the more potent member of the pair.

The relation between physical stimulus properties and the effect of foreperiod duration on reaction time.

Seven subjects were used in an experiment on the relation between signal modality and the effect of foreperiod duration (EP) on RT. With visual signals the usually reported systematic increase of RT as a function of FP duration (1, 5 and 15 s) was confirmed; with auditory signals no difference was found between FP's of 1 and 5 s while the effect at 15 s was equivalent to that found at 5 s with the visual signal. The results suggest that besides factors such as time uncertainty the FP effect is also largely dependent on the arousing quality of the signal.

Time uncertainty and occurence uncertainty of the stimulus in a simple reaction time task

Relatively little attention has been paid to the effect of the so-called ‘catch trials’ on the level of performance in reaction-time experiments. The first investigator to approach systematically this important problem, which is significant also outside the sphere of reaction-time studies, was Gordon (1967), who demonstrated that reaction speed in a simple reaction-time task is an accelerating function of stimulus probability, i.e., the probability of delivery of the stimulus at a trial. The present study aims at clarifying the same problem using a somewhat different experimental setting. Instead of only one foreperiod duration as used by Gordon, four different foreperiods were employed. Also measurements under stimulus-certainty conditions were introduced for purposes of comparison. In addition, the frequency of trials was equalized between experimental conditions involving differing stimulus probabilities, instead of Gordon's equalization of the response rate. Eight subjects participated in 12 experimental sessions. The results suggested a linear relationship between the stimulus probability and the reaction time. Finally, the concept of occurence uncertainty of the stimulus, designating the subject's uncertainty as to whether the stimulus would be presented at a trial, was compared with Klemmer's time uncertainty as a determinant of the simple reaction time, and three factors were proposed to explain the slowing down of reactions as occurence uncertainty increases.

Foreperiod duration and the timecourse of preparation

There is a clear conflict in the literature between studies which report a reduction and those which report a delay of reaction time to a signal (S 2), which is just preceded by a non-informative signal (S 1). The hypothesis is tested that these diverging results are due to the size of the foreperiod (FP) between a warning signal (W) and S 1. In the first experiment S 1 and S 2 were both visual, while S 1 was auditory and S 2 was visual in the second experiment. With two visual signals a delay was found at FP of 1 sec and a reduction at FP of 5 sec, provided that the interval between S 1 and S 2 (ISI) exceeded 150 msec. Insertion of S 1 just before arrival of S 2 virtually eliminates the traditional foreperiod effect. The latter result was also obtained in the second experiment. When S 1 is auditory, the reduction of RT at FP of 5 sec is found at much shorter FPs, and no delay at FP of 1 sec is observed. The results are explained most readily by a preparation theory, which assumes that the speed of preparatory adjustment is variable.

ON EXPECTANCY AND AVERAGE REACTION TIME

The notion of expectancy has often been used in explanations of the relationship between foreperiod variability and simple reaction time. Two interpretations of the notion are distinguished: one is that expectancy or expectancy level is a moment in time, and the other is that expectancy is a regular function of time. The latter interpretation is adopted and it is shown that if expectancy is defined as the conditional probability of signal occurrence, then average reaction time would be linearly related to mean foreperiod duration. It is argued that this result can serve as a basis for unifying apparently diverse explanations of the reaction time—foreperiod relationship. Experimental data are presented which are consistent with the view of expectancy proposed in this paper.

Central refractoriness in simple reaction time: The deferred processing model

The well-known single channel conception of the human operator gives rise very naturally to the deferred processing model for simple reaction time. The predictions of the model principally concern how features of the simple reaction time distribution depend on the foreperiod duration. When developed quantitatively and compared with published data, the predictions seem to be fairly seriously wrong.

INFERRED COMPONENTS OF REACTION TIMES AS FUNCTIONS OF FOREPERIOD DURATION.

INFERRED COMPONENTS OF REACTION TIMES AS FUNCTIONS OF FOREPERIOD DURATION.