Task Difficulty, Heart Rate Reactivity, and Cardiovascular Responses to an Appetitive Reaction Time Task

Cardiovascular responses of 72 young men were assessed during an appetitive reaction time task where winning money incentives was either easy, difficult, or impossible. The impossible condition led to reduced responses (e.g., longer pre-ejection period (PEP) and pulse transit time (PTT) and greater falls in systolic and diastolic pressures) as well as reports of trying less hard than the easy or the difficult condition. Regardless of task difficulty, subjects showing greater heart rate (HR) increases at task onset maintained higher HR levels than low HR reactors throughout the task. Overall, these high HR reactors also showed higher SBP and shorter PEP, PTT and left ventricular ejection time than low HR reactors, although these differences were less pronounced by the end of the task. Based on their responses to various standardized inventories, high and low HR reactors did not differ in behavioral traits such as Type A, suppressed hostility, or active coping as the preferred coping style. However, a subsample of subjects with extreme scores indicating suppressed hostility (N = 12) did show elevated HR and systolic pressure during both relaxation and the appetitive task.     

Task Difficulty, Type A Behavior Pattern, and Cardiovascular Response

Forty-one young male subjects performed either an easy or moderately difficult arithmetic task with the opportunity to earn a monetary incentive if they did well. Cardiovascular (heart rate, systolic and diastolic blood pressure) and subjective responses were assessed immediately prior to and 5 min following task performance. Results indicated greater systolic (SBP) responses during the Pre-task period for subjects expecting to perform the difficult task. Behavior pattern classifications based on the Jenkins Activity Survey revealed Higher Pre-task heart rate (HR) elevations among Type As compared to Bs in the Difficult task condition, and greater Pre-task SBP responses in As compared to Bs irrespective of task difficulty. There also was some evidence of an association between SBP reactivity and scores on the Thurstone Activity scale. Change-scores reflecting SBP and HR reactivity were correlated in the Pre-task period of the Difficult but not the Easy condition. Predictions regarding the impact of motivational arousal upon goal attractiveness were not supported, possibly for methodological reasons.     

On electromyographic (EMG) gradients and movement-related brain activity: significance for motor control, cognitive functions, and certain psychopathologies.

Electromyographic (EMG) voltage that rises continuously during motor performance or mental activity and falls precipitately at the end is known as an EMG gradient. Our review is based on 55 studies of EMG gradients, which were published during the period 1937-1994. The extremely wide diversity of situations yielding EMG gradients suggests the possibility that these gradients may be universal accompaniments of organized goal-directed behavioral sequences, overt and covert. Motor tasks and cognitive tasks (without any requirements for motor output) were found to have this in common: they both produced EMG gradients. EMG gradients were not observed during simple, repetitive exercises. On the efferent side, we propose a dual model for the production of EMG gradients, which is based on empirical findings. This model is discussed in relation to current views on central and peripheral neural control of muscle contractions, and on the electrical properties of extrafusal and intrafusal muscle fibers, with particular reference to surface electromyography. The complex relations between EMG gradient steepness and mental effort seemed well represented by the dual model, which was also useful in the interpretation of certain EMG gradients that were found in patients with anxiety disorders, tension-type headaches, and auditory hallucinations, respectively. On the afferent side, drawing on data from human and animal studies, we consider the evidence for movement-related brain activity generated by proprioceptive input, in relation to different types of feedback to the central nervous system during tasks that produce EMG gradients. On electromyographic (EMG) gradients and movement-related brain activity: significance for motor control, cognitive functions, and certain psychopathologies.     

Voluntary Heart Rate Control During Static Muscular Effort

To test the hypothesis that voluntary heart rate (HR) control is possible with simultaneous muscular effort, 8 male subjects were trained in feedback assisted bidirectional HR control, and also practiced hand grip exercises requiring different levels of effort for 3 consecutive daily sessions. In a fourth session subjects were required to increase and decrease HR while simultaneously performing muscle contractions of 0%, 10%, 30% and 50% of maximum voluntary contractions. Substantial and reliable variations in HR were produced by instructions and by muscular effort during the first 3 sessions; and in the fourth session bidirectional HR control continued even with the relatively elevated baselines induced by muscular effort. Concomitant chin EMG levels did not vary with degree of muscular effort nor with instructions to increase or decrease HR, but increased over the course of any type of trial. Discussion suggests the use of artificially elevated baselines as a strategy for studying HR deceleration and concludes that the present study provides strong evidence of subjects' abilities to voluntarily control HR during muscular effort. This conclusion lends support to the notion that biofeedback therapies may be of clinical utility in real life by modulating the eliciting effects of stressors.     

Do segmental reflexes play a role in the distribution of external intercostal EMG activity in the rabbit?

External intercostal muscle is considered as an inspiratory muscle. Its electromyographic (EMG) activity is exquisitely sensitive to proprioceptive afferents and is predominant in zones with the greatest respiratory effect. In the current series of studies, we assessed the contribution of segmental reflexes to this particular distribution of activity in anesthetized rabbits. We first established a parallel between gradients of activity and mechanical advantage. The sensitivity of external intercostal EMG activity to rib displacement was then assessed in the 3rd and 5th interspaces and in the dorsal, middle and ventral muscle bundles of the 3rd interspace. Finally, persistence of the dorso-ventral gradient was tested after a dorsal rhizotomy (interspaces 3-5). There were no differences in the sensitivity to rib motion in the studied positions. After rhizotomy, the dorso-ventral gradient of activity persisted at rest and with inspiratory resistive loading. We, therefore, conclude that the neuromechanical matching of respiratory drive in the external intercostal muscles is not the result of segmental reflexes.     

Cardiac and somatic activation in the continuous perceptual-motor task: the significance of threat and serious-mindedness

The significance of serious-mindedness and task-contingent threat for cardiac and somatic activation were tested in a mixed design. Ten serious-minded and 10 playful state-dominant subjects were recruited from a larger sample to form extreme-groups according to their responses to the Telic Dominance Scale. They all performed a continuous perceptual-motor task with and without threat of aversive electric shock as punishment for inferior performance (counterbalanced). Results supported the following conclusions: serious-mindedness was associated with passive forearm EMG activity, whereas playfulness was related to active forearm EMG activity. Threat of shock interacted with serious-mindedness to cause particularily high HR with threat versus low HR in the no-threat treatment. Error-scores and scores on perceived task difficulty did not explain group differences in physiological activation. The results were discussed in relation to a hypothesis of cardiac-somatic uncoupling during effortful active coping, the pyramidal and extrapyramidal pathways to the skeletal muscles, and to effort expended in the serious-minded and playful motivational states.     

Mood-regulative hedonic incentive interacts with mood and task difficulty to determine effort-related cardiovascular response and facial EMG

Based on the mood–behavior-model [Gendolla, G.H.E., 2000. On the impact of mood on behavior: an integrative theory and a review. Review of General Psychology, 4, 378–408], we investigated the joint effect of mood-regulative hedonic incentive, mood states, and task difficulty on effort-related cardiovascular response. Cardiovascular and facial EMG reactivity of 80 participants were assessed during a baseline period, mood inductions, and an either easy or difficult memory task with either pleasant or unpleasant consequences of success. For unpleasant consequences, we anticipated that mood would interact with task difficulty to determine cardiovascular response: relatively high reactivity under negative-mood/easy and positive-mood/difficult conditions and relatively low reactivity under positive-mood/easy and negative-mood/difficult conditions. In contrast, we expected for pleasant consequences an increase of cardiovascular response in the negative-mood/difficult condition because here mood-regulative incentive justified the high effort required by a difficult task in a negative mood. Results were generally as expected and facial EMG reactivity indicated efficient mood manipulations. In summary, the findings further support the predictions of the mood–behavior-model.     

Difficulty and Instrumentality of Imminent Behavior as Determinants of Cardiovascular Response and Self-Reported Energy

College-aged male subjects were presented with an easy or moderately difficult memorization task and were told that they could earn either a very low or a very high chance of obtaining a modest prize if they did well. Cardiovascular (heart rate, systolic blood pressure, diastolic blood pressure) and subjective measures were taken during an interval immediately preceding the task performance period. Results indicated greater systolic blood pressure and self-perceived energy in the moderately difficult condition than in the easy condition only when the probability of attaining the prize (if subjects did well) was high. When the probability of goal attainment (given success) was low, systolic responses and self-reported energy levels were minimal in both task conditions. Predictions regarding the impact of energy levels upon goal attractiveness ratings were not supported, possibly for methodological reasons.     

Recall, Recognition, and Rate: Memory and the Heart

Heart rate (HR) changes during recall and recognition tasks were related to memory load and performance. Current hypotheses imply that heart rate acceleration may indicate the processing of stored information, and, thus relate to task performance. Twenty volunteers performed a recognition task with memory set size varying between five and ten items. The task was divided into input, retain, and test periods. Eight volunteers performed a recall task which was identical except for the form of the memory test. Consistent HR changes showed a deceleration prior to each task period which was followed by acceleration. HR was not influenced by memory load, but did show a small but consistent relationship to performance. In both recall and recognition experiments relatively greater acceleration in the retain period was associated with more accurate memory performance. Similar but less clear effects occurred during information input. In this period degree of deceleration also appeared related to recognition performance. Results were related to previous concepts of HR and attention rather than processes specific to memory.     

Incentive moderates the impact of implicit anger vs. sadness cues on effort-related cardiac response

This experiment investigated the combined effect of implicit affect and monetary success incentive on effort-related cardiac response in a 2 (Affect Prime: anger vs. sadness)×2 (Incentive: low vs. high) between-person design. Sixty-two participants were exposed to affect primes during an objectively difficult short-term memory task. As predicted, by our theorizing about affect primes' systematic impact on subjectively experienced task demand and corresponding effort mobilization, sadness primes led to a weak cardiac pre-ejection period (PEP) response when incentive was low (disengagement), but to a very strong PEP response when incentive was high (high effort). PEP responses were moderate in the anger-prime conditions (low effort). HR responses largely corresponded to those of PEP. The results demonstrate for the first time that high incentive can compensate the effort mobilization deficit of individuals who process sadness primes during a difficult task.     

Physiological response to a minimal social encounter: Effects of gender, ethnicity, and social context

This study examined physiological response to an encounter with and touch by an unfamiliar person. Fifty-five African American (23 male, 30 female) and 51 European American (23 male, 28 female) undergraduates participated. A Black or White interactor entered the room, introduced himself or herself, checked equipment for 30 s, and then took a pulse for 30 s. Entry of the interactor resulted in increased corrugator and zygomaticus facial muscle activity (EMG), increased skin conductance (SC), and heart rate (HR) acceleration. Corrugator EMG was greater among Black subjects; White subjects responded with more zygomatic EMG and SC and greater HR acceleration. Women showed a more positive facial expression than did men. Being touched reduced EMG and HR but resulted in increased SC. White and Black males showed more HR acceleration when encountering a Black male interactor.     

Evidence for effects of task difficulty but not learning on neurophysiological variables associated with effort

Learning to master a task is expected to be accompanied by a decrease in effort during task execution. We examine the possibility to monitor learning using physiological measures that have been reported to reflect effort or workload. Thirty-five participants performed different difficulty levels of the n-back task while a range of physiological and performance measurements were recorded. In order to dissociate non-specific time-related effects from effects of learning, we used the easiest level as a baseline condition. This condition is expected to only reflect non-specific effects of time. Performance and subjective measures confirmed more learning for the difficult level than for the easy level. The difficulty levels affected physiological variables in the way as expected, therewith showing their sensitivity. However, while most of the physiological variables were also affected by time, time-related effects were generally the same for the easy and the difficult level. Thus, in a well-controlled experiment that enabled the dissociation of general time effects from learning we did not find physiological variables to indicate decreasing effort associated with learning. Theoretical and practical implications are discussed.     

The face of effort: Frowning muscle activity reflects effort during a physical task

It is a common observation that exertion of effort is associated with a specific facial expression. However, this facial expression has never been quantified during physical tasks and its relationship with effort is unknown. The aims of the present study were to measure frowning muscle activity during a physical task with electromyography (EMG) and to investigate the relationship between facial EMG and effort. Effort was experimentally manipulated by increasing task difficulty and inducing muscle weakness. Twenty men performed leg extensions with four relative workloads. The fatigue group (n = 10) repeated the leg extensions after fatiguing eccentric exercise, and the control group repeated just the leg extensions. Facial EMG amplitude, ratings of perceived effort (RPE), and leg EMG amplitude increased significantly with increasing task difficulty and with muscle fatigue. Facial EMG, RPE, and leg EMG all correlated significantly. The results suggest that frowning muscle activity reflects effort during physical tasks.     

Amplitude and bilateral coherency of facial and jaw-elevator EMG activity as an index of effort during a two-choice serial reaction task

In earlier studies, positive but inconsistent relationships have been reported between mental effort and electro-myogram (EMG) amplitude in task-irrelevant limb muscles. In this study, we explored whether facial EMG activity would provide more consistent results. Tonic EMG activity of six different facial and jaw-elevator muscles was bilaterally recorded during a two-choice serial reaction task with paced presentation of auditory or visual signals. In Experiment 1, task load (signal presentation rate) was kept constant for 20 min at the level of the subject's maximal capacity. In Experiment 2, task load was increased in a stepwise fashion over six successive 2-min periods from sub- to supramaximal capacity levels. EMG amplitude and coherency between momentary bilateral amplitude fluctuations were measured. In Experiment 1, EMG amplitude of frontalis, corrugator supercilii, and orbicularis oris inferior showed a strong gradual increase throughout the task period, whereas task performance remained fairly stable. Orbicularis oculi, zygomaticus major, and temporalis EMG showed a much smaller increase or no increase. In Experiment 2, the first three muscles showed a fairly consistent increase in EMG amplitude with increasing task load. Orbicularis oculi and zygomaticus major were not active until task load became supramaximal. Effects of stimulus modality or laterality were not found in any experiment. These results are consistent with the notion that EMG amplitude of frontalis, corrugator, and orbicularis oris provides a sensitive index of the degree of exerted mental effort.     

AN EVALUATION OF FOREARM BLOOD FLOW AS A PSYCHOPHYSIOLOGICAL MEASURE

The usefulness of forearm blood flow (FBF) as a psychophysiological measure was investigated by comparing changes occurring during mental tasks in cardiovascular, sudomotor, and electromyographic measures. The measures were divided into those clearly physiologically independent and those physiologically related. ANOVA results showed that FBF, heart rate (HR), and skin conductance fluctuations (SCF) were equally reactive, and correlational analysis suggested that a close relationship existed between FBF, HR, and SCF, although correlations fell to near zero levels when intra-individual correlations were calculated with between task variance extracted. For some experimental purposes HR response may be considered equivalent to FBF response. The relationship between EMG and FBF was more variable, and tends not to support the idea that FBF is an indirect measure of muscle activity. The reliability of FBF in normal subjects at rest was poor, although it improved when measured during a simple task, and is probably stable enough for most experimental purposes.     

Phasic T-Wave Amplitude and Heart Rate Changes as Indices of Mental Effort and Task Incentive

The sensitivities of T-wave amplitude (TWA) and heart rate (HR) to manipulations of the mental effort (ME) and incentive associated with performance of the backward digit span task were investigated. The experimental task was so chosen because it could be administered without requiring subjects to speak during its performance, thus minimizing the intrusion of respiratory and motor artifacts. The ME required during task performance was manipulated by varying the number of digits presented, creating Hard and Easy trials. The incentive for subjects to perform well was varied by the threat of the delivery of a noxious noise stimulus, which was ostensibly contingent upon adequate performance on some (Test) but not other (Practice) trials. TWA attenuation and HR acceleration were greater on the Hard as compared to the Easy Trials, and on the Test as compared to the Practice trials. No interactions between the ME and Incentive factors emerged for either cardiac variable. These results suggest that the effort and the incentive of subjects during mental work may be indexed reliably by phasic changes in TWA and HR. The conjoint use of these two cardiac measures may also elucidate the involvement of the two autonomic branches during task performance.     

Parental Hypertension and Cardiovascular Response to Cognitive and Isometric Challenge

The purposes of this investigation were to contrast the cardiovascular responses of sons of hypertensive and normotensive parents to tasks involving cognitive and isometric challenge, and lo examine the relationship of individual differences in heart rate (HR) reactivity to baseline blood pressure (BP) measurements. Thirty-six male, undergraduate volunteers (18 with and 18 without a parental history of hypertension) were scheduled for two, 1-hr experimental sessions (Days I and II). On Day 1, HR and BP measurements were obtained while subjects performed each of three laboratory tasks: a difficult test in concept formation, serial subtraction, and a sustained handgrip at 30% of maximum voluntary contraction. Each task lasted 3 min and was preceded by a 3-min baseline interval. On Day II, subjects were instructed to relax quietly while baseline measures of HR and BP were recorded. Relative to sons of normotensive parents, offspring of hypertensives exhibited higher mean Systolic BPs during all task periods; no corresponding group differences were observed on either Day I or Day II baseline recordings. Unlike SBP, Diastolic BP measurements did not vary reliably by parental hypertensive/normotensive status. Although the mean HRs of sons of hypertensives were significantly higher than in offspring of normotensives, these differences obtained uniformly across both the baseline and task intervals. Among subjects identified as High HR reactors during the two cognitive tasks, sons of hypertensive parents exhibited Day II baseline SBPs about 9 mmHg higher than did subjects without a parental history of hypertension. Among subjects identified as Low HR reactors, baseline SBPs did not differ reliably between sons of hypertensive and normotensive parents.     

Is cognitive conflict really effortful? Conflict priming and shielding effects on cardiac response

Two experiments with N = 221 university students investigated the impact of primed cognitive conflict on effort assessed as cardiac response in tasks that were not conflict-related themselves. Manifest cognitive conflict in cognitive control tasks is confounded with objective response difficulty (e.g., in incongruent Stroop task trials). This makes conclusions about the effortfulness of cognitive conflict itself difficult. We bypassed this problem by administrating pictures of congruent versus incongruent Stroop task stimuli as conflict primes. As predicted, primed cognitive conflict increased cardiac pre-ejection period (PEP) responses in an easy attention task in Experiment 1. Accordingly, cognitive conflict itself is indeed effortful. This effect was replicated in an easy short-term memory task in Experiment 2. Moreover, as further predicted, the primed cognitive conflict effect on PEP reactivity disappeared when participants could personally choose task characteristics. This latter effect corresponds to other recent evidence showing that personal action choice shields against incidental affective influences on action execution and especially on effort-related cardiovascular response.     

The joint effect of mood, task valence, and task difficulty on effort-related cardiovascular response and facial EMG

This study investigated whether a pleasant task with high potential for mood regulation could eliminate the motivational deficit of people facing a difficult task in a negative mood. Cardiovascular and facial EMG reactivity of 88 University students were measured during habituation, mood inductions, and an either pleasant or unpleasant scenario completion task that was either easy or difficult. In the unpleasant condition cardiovascular reactivity was modest, particularly in the negative-mood/difficult condition. But when the task was pleasant, cardiovascular reactivity in the negative-mood/difficult condition was stronger than in all other conditions, reflecting the elimination of the motivational deficit. Moreover, facial EMG reactivity indicated efficient mood manipulations. In summary, the findings are interpreted as further support for the mood-behavior-model [Gendolla, G.H.E., 2000. On the impact of mood on behavior: an integrative theory and a review. Rev. Gen. Psychol. 4, 378–408].