Sequential effects within a short foreperiod context: evidence for the conditioning account of temporal preparation

Responses to an imperative stimulus (IS) are especially fast when they are preceded by a warning signal (WS). When the interval between WS and IS (the foreperiod, FP) is variable, reaction time (RT) is not only influenced by the current FP but also by the FP of the preceding trial. These sequential effects have recently been proposed to originate from a trace conditioning process, in which the individuals learn the temporal WS-IS relationship in a trial-by-trial manner. Research has shown that trace conditioning is maximal when the temporal interval between the conditioned and unconditioned stimulus is between 0.25 and 0.60 s. Consequently, one would predict that sequential effects occur especially within short FP contexts. However, this prediction is contradicted by Karlin [Karlin, L. (1959). Reaction time as a function of foreperiod duration and variability. Journal of Experimental Psychology, 58, 185-191] who did not observe the typical sequential effects with short FPs. To investigate temporal preparation for short FPs, three experiments were conducted, examining the sequential FP effect comparably for short and long FP-sets (Experiment 1), assessing the influence of catch trials (Experiment 2) and the case of a very dense FP-range (Experiment 3) on sequential FP effects. The results provide strong evidence for sequential effects within a short FP context and thus support the trace conditioning account of temporal preparation.     

Response force is sensitive to the temporal uncertainty of response stimuli

Three experiments examined whether temporal uncertainty about the delivery of a response stimulus affects response force in a simple reaction time (RT) situation. All experiments manipulated the foreperiod; that is, the interval between a warning signal and the response stimulus. In the constant condition, foreperiod length was kept constant over a block of trials but changed from block to block. In the variable condition, foreperiod length varied randomly from trial to trial. A visual warning and response stimulus were used in Experiment 1; response force decreased with foreperiod length in the variable condition, but increased in the constant condition. This result is consistent with the hypothesis that responses are less forceful when the temporal occurrence of the response stimulus is predictable. In a second experiment with an auditory warning signal and a response stimulus, response force was less sensitive to foreperiod manipulations. The third experiment manipulated both the modality and the intensity of the response signal and employed a tactile warning signal. This experiment indicated that neither the modality nor the intensity of the response signal affects the relation between response force and foreperiod length. An extension of Näätänen’s (1971) motor-readiness model accounts for the main results.     

Effects of foreperiod interval upon reaction time, alpha blocking, and heart rate under variable conditions with reduced learning factors

The present experiment was to investigate the effects of foreperiod interval upon reaction time (RT), alpha blocking, and heart rate (HR) under conditions in which learning factors and conditional probability were minimized. Twenty college students were given a series of 44 randomized foreperiod intervals (0–30 sec). The fastest RT was obtained at 0.6 sec foreperiod. Alpha blocking provided the same trend as that of RT, showing that the 0.6 sec foreperiod yielded the largest alpha blocking. Positive correlation was observed between the speed of RT and alpha blocking (r = 0.56, p<0.001). HR curve was different from those of RT and alpha blocking. No significant correlation was obtained between RT and HR. The results were discussed, particularly, in terms of the theory of classical conditioning.     

Dynamic adjustment of temporal preparation: Shifting warning signal modality attenuates the sequential foreperiod effect

We examined sequential effects in the variable foreperiod (FP) paradigm, which refer to the finding that responses to an imperative signal (IS) are fast when a short FP trial is repeated but slow when it is preceded by a long FP trial. The effect has been attributed to a trace-conditioning mechanism in which individuals learn the temporal relationship between a warning signal (WS) and the IS in a trial-by-trial manner. An important assumption is that the WS in a current trial (i.e., trial FP_n) acts as a conditioned stimulus, such that it automatically triggers the conditioned response at the exact critical moment that was imperative in the previous trial (i.e., trial FP_n−1). According to this assumption, a shift from one WS modality in trial FP_n−1 to another modality in trial FP_n is expected to eliminate or at least reduce the sequential FP effect. This prediction was tested in three experiments that included a random variation of WS modality and FP length within blocks of trials. In agreement with the prediction, a shift in WS modality attenuated the asymmetry of the sequential FP effect.     

Lateral stimulus-response compatibility effects in the oculomotor system.

Eye movement reaction time (RT) was measured in simple and choice RT situations in which monaural tones were presented to the left or right ear. In the choice RT conditions, tones of one frequency signaled a left looking response and tones of another frequency signaled a right looking response. In the simple RT condition, tones were presented in 2 blocks signaling right or left looking responses. RTs were measured by electro-oculogram (EOG), with electrodes placed over the outer canthus of each eye. In the choice RT condition, oculomotor RTs were faster when the tones signaling right or left looking were presented in the ears corresponding to the direction of looking than when they occured in the opposite ear. No such correspondence was present in the simple RT condition. Ss also performed a manual choice RT task. The lateral stimulus- response (S-R) compatibility effects obtained confirmed previous findings and were of the same magnitude as those obtained in the oculomotor response modality. Asymmetry in correlations between oculomotor and manual compatibility effects suggests differential hemispheric mediation.     

The relationship between estimates of foreperiod duration and simple time reaction

The relationship between estimates of foreperiod length and simple reaction time (RT) was examined using constant foreperiods. It was learned that neither the average accuracy nor the variability of the foreperiod estimates necessarily manifested themselves in appropriate simple RT change. Of secondary interest was the discovery that the average accuracy of foreperiod duration estimations differed greatly from that obtained for similar time lengths in a time-estimation task. Finally, an attempt was made to determine whether subjects actually utilized the directional knowledge of results inherent in the imperative stimulus to influence their foreperiod duration judgments. Unfortunately, the evidence obtained did not permit a definite answer regarding this possibility.     

Mental fatigue and temporal preparation in simple reaction-time performance

Performance decrements attributed to mental fatigue have been found to be especially pronounced in tasks that involve the voluntary control of attention. Here we explored whether mental fatigue from prolonged time on task (TOT) also impairs temporal preparation for speeded action in a simple reaction-time task. Temporal preparation is enabled by a warning signal presented before the imperative stimulus and usually results in shorter reaction time (RT). When the delay between warning and imperative stimuli - the foreperiod (FP) - varies between trials, responses are faster with longer FPs. This pattern has been proposed to arise from either voluntary attentional processes (temporal orienting) or automatic trial-to-trial learning (trace conditioning). The former account suggests a selective RT increase on long-FP trials with fatigue; the latter account suggests no such change. Over a work period of 51 min, we found the typical increase in overall RT but no selective RT increase after long FPs. This additivity indicates that TOT-induced mental fatigue generally reduces cognitive efficiency but leaves temporal preparation under time uncertainty unaffected. We consider this result more consistent with the trace-conditioning account of temporal preparation.     

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.     

Effects of Response Probability on Response Force in Simple RT

Response force (RF) was measured in a simple reaction time (RT) experiment varying response uncertainty by cuing the probability of the response on each trial. In all cases, RF decreased as response probability increased. The dependence of RF on response probability was insensitive to foreperiod length and to the use of loud auditory response signals, although the dependence of RT on response probability was sensitive to both of these manipulations. In combination with previous findings, these results provide evidence that RT and RF can be dissociated. We describe an extension of Naatanen's readiness model that can account for the effects of response probability on RF and RT. According to this model, the distance between motor activation and a threshold for action is relatively large when subjects are unprepared, and a large increment is needed to exceed this threshold, resulting in slow but foreceful responses. A possible neurophysiological implementation of this model is suggested.     

The Effect of Motor Preparation on Changes in H Reflex Amplitude During the Response Latency of a Warned Reaction Time Task

Monosynaptic Hoffman reflexes (H reflexes) were recorded from the soleus muscle during the response latency of a warned reaction time (RT) task that required plantarflexion of the foot. The task was done under four conditions of predictability of the response signal (RS), created by the factorial combination of foreperiod duration (1 and 4 s) and variability (fixed and variable). RT varied systematically with RS predictability and was facilitated in conditions that favored prediction of the RS. The response latency was divided into two successive phases by the onset of reflex augmentation: a premotor phase of constant reflex amplitude and a succeeding motor phase marked by progressively increasing reflex amplitude. Reflex augmentation during the motor phase was coupled more closely to the imminent movement than to the preceding signal to respond. The duration of the premotor phase was unaffected by RS predictability, but the duration of the motor phase (like RT) was shorter when the RS was more predictable. The maximum H reflex amplitude reached during the motor phase was greater when the RS was more predictable. The tonic level of H reflex amplitude during the premotor phase was greater in conditions that made prediction of the RS difficult. A second experiment showed that this difference was present throughout the foreperiod.

These results suggest that conditions that favor prediction of the RS enhance motor preparation. Changes in motor preparation (which affect RT) affect the processes underlying reflex augmentation in the motor phase. Enhanced preparation may allow more efficient organization of the descending commands to move, causing higher levels of spinal excitability to be reached in a briefer time. The higher tonic reflex amplitudes in the premotor phase and throughout the preceding foreperiod, in conditions that make prediction of the RS difficult, appear to reflect heightened general arousal.     

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.     

Lengthening fixed preparatory foreperiod durations within a digit magnitude classification task serves mainly to shift distributions of response times upwards

In this study, the effect of lengthening foreperiod duration (i.e. the time between the presentation of a warning signal and a subsequent target stimulus) on choice RTs is examined. The foreperiod durations used were either 2 or 8 s and were fixed within pure blocks of trials. The task was to determine whether a single-digit target stimulus was either smaller or larger than 5 and responses were provided manually. An additive relation between foreperiod duration length and numerical distance from 5 was present in the mean RTs. Subsequent ex-Gaussian analyses of the shapes of the RT distributions indicated that they become shifted upwards as the foreperiod increased with relatively smaller increases in the sizes of their tails. It is argued mainly that the latter finding is incompatible with the strategic time estimation view of the fixed foreperiod duration effect.     

Developmental changes in response preparation to visual stimuli

We examined how preparation to respond changes with age. Subjects from four age groups (5- to 7-, 8- to 11-, 12- to 17-, and 18- to 24-yr.-olds) were given a simple visual RT task with foreperiod duration varied between 300 and 2000 msec. Analysis showed that in addition to the expected effects of age and foreperiod, there were qualitative differences between the performance of adults and children: 5- to 7-yr.-olds reacted quickest after a foreperiod shorter than that required by adults to perform best. Conversely, preadolescents' optimal foreperiod was relatively longer than that of either older or younger subjects. In addition, the youngest subjects showed an inability to maintain preparation as efficiently as older subjects. Implications for the development of response preparation are discussed.     

The effect of motor preparation on changes in h reflex amplitude during the response latency of a warned reaction time task

Monosynaptic Hoffman reflexes (H reflexes) were recorded from the soleus muscle during the response latency of a warned reaction time (RT) task that required plantarflexion of the foot. The task was done under four conditions of predictability of the response signal (RS), created by the factorial combination of foreperiod duration (1 and 4 s) and variability (fixed and variable). RT varied systematically with RS predictability and was facilitated in conditions that favored prediction of the RS. The response latency was divided into two successive phases by the onset of reflex augmentation: a premotor phase of constant reflex amplitude and a succeeding motor phase marked by progressively increasing reflex amplitude. Reflex augmentation during the motor phase was coupled more closely to the imminent movement than to the preceding signal to respond. The duration of the premotor phase was unaffected by RS predictability, but the duration of the motor phase (like RT) was shorter when the RS was more predictable. The maximum H reflex amplitude reached during the motor phase was greater when the RS was more predictable. The tonic level of H reflex amplitude during the premotor phase was greater in conditions that made prediction of the RS difficult. A second experiment showed that this difference was present throughout the foreperiod. These results suggest that conditions that favor prediction of the RS enhance motor preparation. changes in motor preparation (which affect RT) affect the processes underlying reflex amplitudes in the premotor phase and throughout the preceding foreperiod, in conditions that make prediction of the RS difficult, appear to reflect heightened general arousal.     

The Effect of Load Uncertainty on Neuromotor Control in Catching: Gender Differences and Short Foreperiods

Abstract

To reveal how the CNS copes with load uncertainty in catching, electromyography (EMG) was recorded in 15 females and 14 males while catching visually identical balls of known and unknown weights under varied (1–10?s) and constant (1?s) foreperiods (warning time). EMG integrals, which represented total muscle activity, were computed for three time intervals prior to the catch (anticipatory), and one interval after (compensatory). Load uncertainty caused the CNS to utilize an anticipatory strategy in several muscles, primarily during the ball-flight interval, characterized by preparation to catch balls of unknown weight by utilizing an average of 99.7% of the muscle activation used to catch the heaviest ball under the known weight condition. The constant 1?s foreperiod, which permitted precise temporal anticipation of ball release, did not influence the anticipatory strategy adopted by the CNS to cope with load uncertainty. There were no observed differences in the neuromotor control used by men and women to manage load uncertainty in catching, although there was an interesting difference in the way men and women employed the triceps to prepare to catch balls of a known weight.     

Finger Pairings in Two-Choice Reaction Time Taskscolon: Does the Between-Hands Advantage Reflect Response Preparation?

Two fractionated RT experiments tested whether the response-preparation or response-implementation hypothesis better accounts for the observation that two-choice reaction time (RT) usually takes longer when the responses are performed by the fingers of the same hand (within-hand repertoire) than by the fingers of the two hands (between-hands repertoire). In Experiment I (n equals 8), the effect of repertoire on the premotor time and the motor time were studied. RT was divided into the two periods with respect to the onset of change in electromyographic (EMG) activity of the flexor digitorum profundus. Type of repertoire affected both time periods. In Experiment 2 (n = 16), the effects of repertoire and foreperiod duration on the premotor and motor times of the flexor digitorum profundus and flexor digitorum sublimis were studied. The results of Experiment I were confirmed, and the effects of repertoire and foreperiod duration were found to be additive on premotor time but interactive on motor time. These findings led to rejection of the response-preparation hypothesis and instead supported the view that the central command for the flexion of the right middle finger differs according to the type of repertoire. The command appears to specify a lower rate of recruitment of the prime movers in the within-hand repertoire than in the between-hands repertoire. The execution of the central commands may depend on the state of excitability of the spinal neurons. Analysis of the EMG signals revealed that speed of contraction of the prime movers depends on repertoire when the foreperiod is long but not when it is short. The additivity of the effects of repertoire and of foreperiod duration on premotor time support the view that regardless of the state of preparation of the subject the pattern of EMG activity required for flexion of the right middle finger in each repertoire is specified during the premotor time.     

Effects of variations in force and stimulus uncertainty on fractionated reaction time.

Previous research has shown that reaction time (RT) and premotor time varied as a function of force even in simple-RT paradigm. The present purpose was to examine whether stimulus uncertainty induced by catch trials would cause programming delay until after the signal to respond. Subjects were required to react and produce a designated peak force as soon as possible after a visual stimulus, with and without catch trials. Five different levels of force were 10, 30, 50, 70, and 90% of the maximum grip strength of subjects. Analysis showed that simple RT and premotor time changed as a function of force, regardless of whether catch trials were removed. These findings suggest that stimulus uncertainty is not a necessary condition for programming delay.     

Prediction outcome and choice reaction time: Inhibition versus facilitation effects

In two-choice RT tasks Ss verbally predicted all stimulus presentations, two-thirds of the presentations, or none of the presentations. Effects of stimulus probability were similar for each type of prediction trial: Correct Prediction Outcome (PO), Incorrect PO, and No-Prediction (NP). When comparisons between Prediction and NP trials were between Ss, reactions on NP trials were significantly faster than reactions POs, but were not slower than reactions to Correct POs. However, when Prediction and NP trials occurred within Ss, reactions on NP trials were not faster than reactions to Incorrect POs, but were significantly slower than reactions to Correct POs. Speculations about Ss' implicit stimulus predictions are offered to interpret differential implications of inhibition and facilitation.     

Reweighting sequential effects across different distributions of foreperiods: segregating elementary contributions to nonspecific preparation

In the study of nonspecific preparation, the response time (RT) to an imperative stimulus is analyzed as a function of the foreperiod (FP), the interval between a warning stimulus and the imperative stimulus. When FP is varied within blocks of trials, a downward sloping FP-RT function is usually observed. The slope of this function depends on the distribution of FPs (the more negative the skewness, the steeper the slope) and on intertrial sequences of FP (the longer the FP on the preceding trial, the steeper the slope). Because these determinants are confounded, we examined whether FP-RT functions, observed under three different FP distributions (i.e., uniform, exponential, and peaked) can be predicted, one from the other, by reweighting sequential effects. It turned out that reweighting explained very little variance of the difference between the FP-RT functions, suggesting a dominant role of temporal orienting strategies.