Heart rate variability during sympatho-excitatory challenges: Comparison between spontaneous and metronomic breathing

Respiration influences heart rate variability, leading to the suggestion that respiration should be controlled to assess autonomic function by using heart rate variability. Clearly, control of respiration is advantageous or even essential in several experimental circumstances. However, control of respiration, by itself, produces a small, but significant, increase in mean heart rate and a decrease in respiratory synchronous variation in heart rate. We tested whether, in some experimental situations, it may be possible to arrive at similar interpretation about autonomic function with and without using control of respiratory rate. heart rate spectral powers from nine subjects were compared between spontaneous and metronomic breathing during two sympatho-excitatory stresses, lower body negative pressure (LBNP) and head up tilt (HUT). The normalized spectral powers in supine and HUT during spontaneous breathing were: 0.43 and 0.75 in very low (VLF) and 0.28 and 0.09 in high frequency (HF) regions. The powers during metronomic breathing were: 0.36 and 0.82 (VLF) and 0.36 and 0.09 (HF). The powers in supine and LBNP during spontaneous breathing were: 0.43 and 0.81 (VLF) and 0.28 and 0.06 (HF). The powers during metronomic breathing were: 0.36 and 0.80 (VLF) and 0.36 and 0.07 (HF). All p values were <0.05. Therefore, changes in heart rate spectral powers during HUT and LBNP were similar during metronomic breathing and spontaneous breathing. These results suggest that in experimental designs such as in our study, using metronomic breathing may not provide any additional insight into autonomic function than that can be obtained during spontaneous breathing.     

Heart Rate Variability During Sympatho-excitatory Challenges: Comparison Between Spontaneous And Metronomic Breathing

Respiration influences heart rate variability, leading to the suggestion that respiration should be controlled to assess autonomic function by using heart rate variability. Clearly, control of respiration is advantageous or even essential in several experimental circumstances. However, control of respiration, by itself, produces a small, but significant, increase in mean heart rate and a decrease in respiratory synchronous variation in heart rate. We tested whether, in some experimental situations, it may be possible to arrive at similar interpretation about autonomic function with and without using control of respiratory rate. Heart rate spectral powers from nine subjects were compared between spontaneous and metronomic breathing during two sympatho-excitatory stresses, lower body negative pressure (LBNP) and head up tilt (HUT). The normalized spectral powers in supine and HUT during spontaneous breathing were: 0.43 and 0.75 in very low (VLF) and 0.28 and 0.09 in high frequency (HF) regions. The powers during metronomic breathing were: 0.36 and 0.82 (VLF) and 0.36 and 0.09 (HF). The powers in supine and LBNP during spontaneous breathing were: 0.43 and 0.81 (VLF) and 0.28 and 0.06 (HF). The powers during metronomic breathing were: 0.36 and 0.80 (VLF) and 0.36 and 0.07 (HF). All p values were <0.05. Therefore, changes in heart rate spectral powers during HUT and LBNP were similar during metronomic breathing and spontaneous breathing. These results suggest that in experimental designs such as in our study, using metronomic breathing may not provide any additional insight into autonomic function than that can be obtained during spontaneous breathing.     

Task difficulty, cardiovascular response, and the magnitude of goal valence

Sixty-four young women expected to perform an easy, moderately difficult, or extremely difficult memory task with the opportunity to earn a small incentive for good performance. Cardiovascular (heart rate, systolic and diastolic blood pressure) and subjective measures were taken immediately prior to task performance. Both systolic blood pressure (SBP) responses and ratings of goal attractiveness were nonmonotonically related to expected task difficulty, with the most pronounced SBP elevations and highest goal attractiveness in the moderately difficult task condition. Product-moment correlations among cardiovascular response measures revealed a strong positive association between systolic and diastolic pressure (but not heart rate) change in the easy condition, positive relationships among all measures in the moderately difficult condition, and no significant correlations in the extremely difficult condition. Subjective measures of arousal were not affected by the task difficulty manipulation. Principal findings are discussed in terms of a theoretical model proposed by Brehm (1979) that states that motivation varies as a nonmonotonic function of the difficulty of goal attainment. Intercorrelations among cardiovascular response variables are considered in terms of their possible indication of the mechanisms underlying blood pressure changes associated with variations in motivation.     

Motivated but not engaged: The implicit achievement motive requires difficult or unclear task difficulty conditions to exert an impact on effort

Integrating the achievement motive literature and motivational intensity theory, we expected the implicit achievement motive (nAch) to directly determine effort mobilization when task difficulty is unclear. However, nAch should interact with task difficulty in determining effort mobilization when task difficulty is clear. Participants worked on an easy versus difficult memory task (Study 1) or a clear versus unclear arithmetic task (Study 2). We used the Picture-Story-Exercise to assess nAch and pre-ejection period (PEP) to operationalize effort. As predicted, PEP reactivity was strong in the difficult-high-nAch condition and in the unclear-high-nAch condition but low in the other three conditions. Supporting motivational intensity theory, our results showed that nAch requires difficult or unclear task conditions to exert a noticeable impact on effort.     

Fast breathing facilitates reaction time and movement time of a memory-guided force pulse

Slow controlled breathing can be beneficial for performance of continuous and serial motor tasks. However, how controlled breathing influences discrete motor task performance remains unclear. We sought to determine the impact of paced breathing frequency on measures of movement initiation (reaction time: RT), accuracy (absolute endpoint error: AE; constant error: CE), and variability (trial-to-trial variability: V), in a goal-directed discrete motor task. We hypothesized slow breathing would be accompanied by faster RT, reduced AE and CE, and less V compared to faster breathing rates. Participants (N = 47) performed a memory-guided force pulse pinch task targeted at 10% of their maximum voluntary contraction while breathing at metronome-paced slow, normal, and fast frequencies. During each breathing condition, heart rate variability (HRV) as indexed by the standard deviation of ‘NN’ intervals (SDNN) was measured to ensure objective manipulation check of participants breathing at their set pace. Following each breathing condition, participants provided subjective ratings using the Affect Grid and Visual Analog Scales for arousal, hindrance, and dyspnea. Manipulation check results indicated participants correctly breathed at metronome paces, as indexed by increased HRV for slow breathing and decreased HRV for fast breathing. Results indicated that fast breathing reduced reaction time and movement time, and increased ratings of arousal, hindrance, and dyspnea. In contrast, slow breathing increased reaction time, and levels of hindrance and dyspnea were similar to normal breathing. Breathing frequency did not differentially impact accuracy or variability across conditions. Findings provide evidence that breathing frequency affects fundamental movement parameters, potentially mediated by factors other than arousal.     

Task difficulty moderates the revelation effect

Tasks that precede a recognition probe induce a more liberal response criterion than do probes without tasks—the “revelation effect.” For example, participants are more likely to claim that a stimulus is familiar directly after solving an anagram, relative to a condition without an anagram. Revelation effect hypotheses disagree whether hard preceding tasks should produce a larger revelation effect than easy preceding tasks. Although some studies have shown that hard tasks increase the revelation effect as compared to easy tasks, these studies suffered from a confound of task difficulty and task presence. Conversely, other studies have shown that the revelation effect is independent of task difficulty. In the present study, we used new task difficulty manipulations to test whether hard tasks produce larger revelation effects than easy tasks. Participants (N = 464) completed hard or easy preceding tasks, including anagrams (Exps. 1 and 2) and the typing of specific arrow key sequences (Exps. 3–6). With sample sizes typical of revelation effect experiments, the effect sizes of task difficulty on the revelation effect varied considerably across experiments. Despite this variability, a consistent data pattern emerged: Hard tasks produced larger revelation effects than easy tasks. Although the present study falsifies certain revelation effect hypotheses, the general vagueness of revelation effect hypotheses remains.     

The effects of internal versus external information processing on symptom perception in an exercise setting

The purpose of our study was to determine the effects of internal versus external attentional focus on symptom perception and performance in an exercise setting. Fifteen introductory psychology undergraduates ran 1 mile under each of three experimental conditions: "word-cue," in which subjects were required to focus externally by listening for a target word heard repeatedly over headphones; "breathing," in which subjects were directed to attend to their own breathing and heart rate; and a control. Results indicated that participants reported significantly less symptomatology, particularly exercise-relevant symptoms, in the word-cue condition than in the breathing or control conditions. The findings are discussed with reference to previous theory in this area, and methodological differences between this and earlier research are delineated.     

The effects of dual-tasking on arm muscle responses in young and older adults

This study examined whether dual-tasking affects an individual’s ability to generate arm muscle responses following a loss of balance. Nineteen young and 16 older adults recovered their balance in response to a surface translation. This balance task was either completed on its own or while counting backwards by 2’s (easy counting difficulty) or 7’s (hard counting difficulty). With increasing counting difficulty, less attentional resources were assumed to be available for balance recovery. The ability to generate arm muscle responses was quantified through the measurement of electromyographic (EMG) onset latencies and amplitudes from three arm muscles. Results indicated that the attentional requirements of the counting task did not greatly affect EMG onset latencies or amplitudes for both young and older adults. Even when an effect was observed, the magnitude of change was small (e.g., ∼3 ms earlier EMG onset and ∼2.0%MVC smaller EMG amplitude during the dual- compared to the single-task conditions). Thus, the generation of arm muscle responses do not appear to require a significant amount of attentional resources and the decreased ability to cope with cognitive interference with ageing is unlikely to explain why older adults have difficulty in generating arm responses following a loss of balance.     

EPS Mid-Career Award 2004: brain mechanisms of attention

There are many varieties of "attention", to some extent separate yet working together to produce coherent perception, thought, and behaviour. Using data from human behaviour, functional neuroimaging, and single-cell recording in the behaving monkey, I consider different levels of attention and their basis in physiological mechanisms of biased competition. Beginning with visual attention, I suggest that processing is competitive in many brain systems that code visual input. Competition is biased towards stimuli that match task requirements and is integrated between systems coding different object properties. The result is flexible, object-based attentional selection. In the second part of the paper, I describe recent experiments on attentional competition within and between sensory modalities. Though competition is often modality specific, more global levels of interference are also easy to demonstrate. In the third part of the paper, I move to frontoparietal cortex and to a pattern of similar brain regions recruited by many different cognitive demands. This multiple-demand (MD) pattern, I suggest, reflects neurons with highly flexible response properties, adapting to represent the information and events of many different tasks. Biased competition in MD regions may play a central role in broad attentional capacity limits and attentional focusing. More generally, I suggest that biased competition is characteristic of many different cognitive domains and brain systems. Coherent "attention" develops as different systems converge to work on related cognitive content.     

The impact of task difficulty expectations on intrinsic motivation

Two studies investigated expectations of task difficulty induced prior to task involvement and their impact upon an individual's subsequent intrinsic interest. Expectations of task difficulty were manipulated through easy/hard instructions by the experimenters. Interest, but not performance, varied as function of expected task difficulty, with “easy” eliciting greater interest than “hard” instructions. The generality of this finding was supported by its demonstration in studies utilizing different experimenters (male, female), subject populations (children, college), and tasks (perceptual-motor, cognitive).     

The functional anatomy of inspection time: a pilot fMRI study

Seven healthy subjects underwent functional magnetic resonance imaging (fMRI) of the brain while performing an inspection time task. Employing a block-type design, the task had three difficulty levels: a control condition, an easy (200 ms stimulus duration), and a more difficult (40 ms) discrimination. Based on group results, there were widespread significant areas of difference in brain activation and deactivation when pairwise comparisons were conducted among the three task conditions. When the difficult condition was compared with the easy condition, there was relative activation in areas of the following brain regions: cingulate gyrus and some frontal and parietal lobe areas. Areas within the following regions showed relative deactivation (greater blood oxygenation level-dependent, BOLD, signal in the easy condition): frontal, temporal, and parietal lobe. There were overlaps between these areas and those found to be active while performing higher cognitive tasks in other functional brain imaging studies. These pilot data encourage future studies of the functional anatomy of inspection time and its relevance to psychometric intelligence.     

Self-control and its influence on global/local processing: An investigation of the role of frontal alpha asymmetry and dispositional approach tendencies

People often inhibit or override their dominant response tendencies in order to complete tasks successfully. Exerting such self-control has been shown to influence attentional breadth differently depending on approach-motivated tendencies, as indexed by individuals’ behavioral activation system (BAS) scores. Approach motivation and attentional breadth have previously been associated with frontal alpha asymmetry (i.e., lateralized cortical activity in the frontal regions) where greater left-frontal activation is associated with greater approach motivation and reduced attentional breadth. The process model of self-control posits that exercising self-control leads to a subsequent increase in approach behavior in high BAS individuals, and this could be due to a shift towards left-hemisphere-frontal processing. This was the first study to examine both frontal asymmetry and attentional breadth before and after exercising self-control in low and high BAS individuals. Greater BAS, and greater difficulty exercising self-control, both positively related to more narrowed attentional breadth after completing the manipulation relative to before, but only after exercising self-control. However, breadth of attention and changes in attentional breadth were unrelated to frontal asymmetry, suggesting that the influence of self-control on individuals’ attentional breadth was not due to changes in frontal activation patterns.     

Residual attentional capacity amongst young and elderly during dual and triple task walking

Walking is considered an automatic function which demands little attentional resources. Thus a residual attentional capacity is available for a concurrent task (dual task). Minor age-related deficits in postural control may minimize the residual attentional capacity, however this may not be detected by a simple examination of the individuals gait performance. This study investigated the use of challenging dual task combinations to detect age related changes in gait performance. Eleven community-dwelling elderly (mean age 76 years) and 13 young subjects (mean age 26 years) participated in the study. The participants walked along a figure-of-eight track at a self-selected speed. The effect of introducing a concurrent cognitive task and a concurrent functional motor task was evaluated. Stride-to-stride variability was measured by heel contacts and by trunk accelerometry. In response to the cognitive task the elderly increased their temporal stride-to-stride variability by 39% in the walking task and by 57% in the combined motor task. These increases were significantly larger than observed for the young. Equivalent decreases in trunk acceleration autocorrelation coefficients and gait speed were found. A combination of sufficiently challenging motor tasks and concurrent cognitive tasks can reveal signs of limited residual attentional capacity during walking amongst the elderly.     

Relationships between dual-task related changes in stride velocity and stride time variability in healthy older adults

Dual-task related gait changes have been previously reported for healthy older adults, suggesting that gait control requires attention. Compared to balance control, the involvement of attention in the control of the rhythmic stepping mechanism, as reflected by stride time variability, is not well known. In particular, under dual-task, the relative contributions of a second, attention-demanding task and changes in walking speed remain unclear. Thus, the aims of this study were (1) to assess whether walking with a slow-selected speed or walking while performing an attention-demanding task affected stride time variability in a sample of healthy older participants, and (2) to establish whether stride time variability under dual-task conditions is related either to the decrease of walking speed or the simultaneous attention-demanding task, or to both. Forty-five healthy older participants performed four experimental conditions: (1) walking at a normal self-selected speed, (2) walking at a slow self-selected speed, (3) performing a verbal fluency task when sitting on a chair, and (4) performing the verbal fluency task while walking at self-selected walking speed. Gait parameters were recorded across 15 meters, using Physilog. Results showed a significant dual-task related decrease in mean values of stride velocity, as well as a significant increase in mean values and coefficients of variation of stride time. These dual-task related changes in stride time were explained by the simultaneous performance of the verbal fluency task, the decrease of gait speed and the variability between participants. Although a relationship exists between decreased walking speed and increased stride time variability, the dual-task related increase of stride time variability was also significantly associated with the attention-demanding task, suggesting some attentional control for the rhythmic stepping mechanism of walking in healthy older adults.     

Hiding and finding: The relationship between visual concealment and visual search

As an initial step toward developing a theory of visual concealment, we assessed whether people would use factors known to influence visual search difficulty when the degree of concealment of objects among distractors was varied. In Experiment 1, participants arranged search objects (shapes, emotional faces, and graphemes) to create displays in which the targets were in plain sight but were either easy or hard to find. Analyses of easy and hard displays created during Experiment 1 revealed that the participants reliably used factors known to influence search difficulty (e.g., eccentricity, target—distractor similarity, presence/absence of a feature) to vary the difficulty of search across displays. In Experiment 2, a new participant group searched for the targets in the displays created by the participants in Experiment 1. Results indicated that search was more difficult in the hard than in the easy condition. In Experiments 3 and 4, participants used presence versus absence of a feature to vary search difficulty with several novel stimulus sets. Taken together, the results reveal a close link between the factors that govern concealment and the factors known to influence search difficulty, suggesting that a visual search theory can be extended to form the basis of a theory of visual concealment.     

Attentional bias to emotional stimuli is altered during moderate- but not high-intensity exercise

Little is known regarding how attention to emotional stimuli is affected during simultaneously performed exercise. Attentional biases to emotional face stimuli were assessed in 34 college students (17 women) using the dot-probe task during counterbalanced conditions of moderate- (heart rate at 45% peak oxygen consumption) and high-intensity exercise (heart rate at 80% peak oxygen consumption) compared with seated rest. The dot-probe task consisted of 1 emotional face (pleasant or unpleasant) paired with a neutral face for 1,000 ms; 256 trials (128 trials for each valence) were presented during each condition. Each condition lasted approximately 10 min. Participants were instructed to perform each trial of the dot-probe task as quickly and accurately as possible during the exercise and rest conditions. During moderate-intensity exercise, participants exhibited significantly greater attentional bias scores to pleasant compared with unpleasant faces (p < .01), whereas attentional bias scores to emotional faces did not differ at rest or during high-intensity exercise (p > .05). In addition, the attentional bias to unpleasant faces was significantly reduced during moderate-intensity exercise compared with that during rest (p < .05). These results provide behavioral evidence that during exercise at a moderate intensity, there is a shift in attention allocation toward pleasant emotional stimuli and away from unpleasant emotional stimuli. Future work is needed to determine whether acute exercise may be an effective treatment approach to reduce negative bias or enhance positive bias in individuals diagnosed with mood or anxiety disorders, or whether attentional bias during exercise predicts adherence to exercise.     

Cardiovascular Responses to Threat: Effects of the Difficulty and Availability of a Cognitive Avoidant Task

Measures of heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) were taken during an interval immediately preceding a period in which male subjects were to perform an easy or difficult memory task to avoid a noxious noise, or simply wait to receive the noise. As predicted, anticipatory elevations in SBP and HR were relatively higher in the difficult avoidance condition than in the easy and impossible avoidance conditions. In contrast, anticipatory DBP change-scores decreased linearly from easy to difficult to impossible avoidance conditions. Results are discussed in terms of a recent motivational theory suggesting that energy mobilization in the face of threat should be a function of what can, will, and must be done to cope.     

What does distractibility in ADHD reveal about mechanisms for top-down attentional control?

In this study, we attempted to clarify whether distractibility in ADHD might arise from increased sensory-driven interference or from inefficient top-down control. We employed an attentional filtering paradigm in which discrimination difficulty and distractor salience (amount of image “graying”) were parametrically manipulated. Increased discrimination difficulty should add to the load of top-down processes, whereas increased distractor salience should produce stronger sensory interference. We found an unexpected interaction of discrimination difficulty and distractor salience. For difficult discriminations, ADHD children filtered distractors as efficiently as healthy children and adults; as expected, all three groups were slower to respond with high vs. low salience distractors. In contrast, for easy discriminations, robust between-group differences emerged: ADHD children were much slower and made more errors than either healthy children or adults. For easy discriminations, healthy children and adults filtered out high salience distractors as easily as low salience distractors, but ADHD children were slower to respond on trials with low salience distractors than they did on trials with high salience distractors. These initial results from a small sample of ADHD children have implications for models of attentional control, and ways in which it can malfunction. The fact that ADHD children exhibited efficient attentional filtering when task demands were high, but showed deficient and atypical distractor filtering under low task demands suggests that attention deficits in ADHD may stem from a failure to efficiently engage top-down control rather than an inability to implement filtering in sensory processing regions.     

Behavioural,affective, and physiological effects of negative and positive emotional exaggeration

Emotion regulation is essential for the production of socially appropriate affect and successful interpersonal functioning. The relative inability to modulate affect, known as "emotional dysregulation", is associated with many common mood disorders (such as major depressive disorder or bipolar spectrum disorders). Thus, understanding the physiological processes underlying emotional regulation is extremely important. This experiment was designed to explore the affective, behavioural, and physiological responses associated with a rarely studied emotion regulation technique--exaggeration. A total of 52 undergraduate participants watched a 2 minute video designed to elicit either feelings of amusement (positive affect) or disgust (negative affect). Physiological recordings--including skin conductance, interbeat interval (IBI), high frequency (HF) power spectrum of heart rate variability (HRV), and sympathovagal balance (LF/HF)--were recorded for the 2 minutes prior to, during, and after mood induction. As expected, persons asked to exaggerate their responses were rated as behaviourally showing increased arousal relative to individuals in the natural-watch condition. With regard to IBI, those in the exaggerate condition experienced significantly greater IBI reductions (increased heart rate) during reactivity and IBI increases during recovery relative to those in the natural-watch condition (who showed the opposite pattern of response). Moreover, persons in the exaggerate condition evidenced increased sympathovagal balance in response to the emotional videos relative to those in the natural-watch condition. Results generally support and extend previous research findings designed to assess the impact of response-focused affect modulation strategies. Suggestions for future research are presented.     

Specific internal and external attentional focus instructions have differential effects on rowing performance

Directing an individual to focus their attention on internal or external cues can influence performance of skill-based and endurance sports. The present study examined the effects of switching attention across different types of internal and external attentional foci in a rowing task. Novice rowers (19 male, 47 female) focussed attention on one of four different internal cues (or one of four different external cues) at discrete time points while completing a row on an ergometer. Overall, a focus on internal cues resulted in longer distance, higher power output, and higher heart rate than a focus on external cues. However, for the internal condition a focus on arm and leg muscles was associated with higher performance than a focus on breathing. For the external condition, a focus on exerting force on the handle produced higher performance than a focus on the movements of the handle or seat or on the sounds of the ergometer. Global instructions to focus internally or externally influenced performance, but the specific effects within these broad categories were also variable. The advice given to athletes and recreational exercises should consider both the broad attentional focus direction and the specific cues of the task to which attention is directed.