Effect of the subjective intensity of fatigue and interoception on perceptual regulation and performance during sustained physical activity

Background The subjective experience of fatigue impairs an individual’s ability to sustain physical endurance performance. However, precise understanding of the specific role perceived fatigue plays in the central regulation of performance remains unclear. Here, we examined whether the subjective intensity of a perceived state of fatigue, pre-induced through prior upper body activity, differentially impacted performance and altered perceived effort and affect experienced during a sustained, isometric contraction in lower body. We also explored whether (cardiac) interoception predicted the intensity of experienced perceptual and affective responses and moderated the relationships between constructs during physical activity. Methods Using a repeated-measures study design, thirty male participants completed three experimental conditions, with the intensity of a pre-induced state of fatigue manipulated to evoke moderate (MOD), severe (SEV) and minimal (control; CON) intensity of perceptions prior to performance of the sustained contraction. Results Performance of the sustained contraction was significantly impaired under a perceived state of fatigue, with reductions of 10% and 14% observed in the MOD and SEV conditions, respectively. Performance impairment was accompanied by greater perceived effort and more negative affective valence reported during the contraction. However, effects were limited to comparisons to CON, with no difference evident between the two experimental trials (i.e. MOD vs. SEV). Individuals’ awareness of their accuracy in judging resting heartbeats was shown to predict the subjective intensity of fatigue experienced during the endurance task. However, interoception did not moderate the relationships evident between fatigue and both perceived effort and affective valence. Conclusions A perceived state of fatigue limits endurance performance, influencing both how effortful activity is perceived to be and the affective experience of activity. Though awareness of interoceptive representations of bodily states may be important to the subjective experience of fatigue, interoception does not modulate the relationships between perceived fatigue and other perceptual (i.e. effort) and affective constructs.

Virtual Touch: Sensing and Feeling with Ultrasound.

The sense of touch codes the detection and properties of physical objects on the body via mechanoreceptors within the skin. Technological advancements, such as ultrasonic haptic devices, are now able to ‘touch without touching’, claiming this is virtual touch. An initial aim of the study was to investigate subjective intensity and pleasantness ratings of ultrasound stimulation and the influence of top-down factors using the Touch Experience and Attitudes Questionnaire (TEAQ). Self-reported intensity and pleasantness ratings were measured in response to ultrasound stimuli. A second aim was to record from individual low threshold mechanoreceptors using the technique of microneurography in an attempt to determine which mechanoreceptors are activated by ultrasound stimulation of the skin. The major findings here were that microneurography found SAI and SAII units did not respond to ultrasound stimuli; intensity and pleasantness ratings were significantly different between age groups. Ultrasound can produce a variety of sensations with varying intensity and pleasantness ratings. A limitation of the study was the unexpected force difference generated between modulations. These findings have implications for mid-air haptics, somatosensory affective research, and virtual reality. Future research should focus on microneurography investigation of FA fibre responses to ultrasound.

Cross-modal commutativity of magnitude productions of loudness and brightness

In their fundamental paper, Luce, Steingrimsson, and Narens (2010, Psychological Review, 117, 1247-1258) proposed that ratio productions constituting a generalization of cross-modality matching may be represented on a single scale of subjective intensity, if they meet “cross-dimensional commutativity.” The present experiment is the first to test this axiom by making truly cross-modal adjustments of the type: “Make the sound three times as loud as the light appears bright!” Twenty participants repeatedly adjusted the level of a burst of noise to result in the desired sensation ratio (e.g., to be three times as intense) compared to the brightness emanating from a grayscale square, and vice versa. Cross-modal commutativity was tested by comparing a set of successive ×2×3 productions with a set of ×3×2 productions. When this property was individually evaluated for each of 20 participants and for two possible directions, i.e., starting out with a noise burst or a luminous patch, only seven of the 40 tests indicated a statistically significant violation of cross-modal commutativity. Cross-modal monotonicity, i.e. checking whether ×1, ×2, and ×3 adjustments are strictly ordered, was evaluated on the same data set and found to hold. Multiplicativity, by contrast, i.e., comparing the outcome of a ×1×6 adjustment with ×2×3 sequences, irrespective of order, was violated in 17 of 40 tests, or at least once for all but six participants. This suggests that both loudness and brightness sensations may be measured on a common ratio scale of subjective intensity, but cautions against interpreting the numbers involved at face value.

Effect of the subjective intensity of fatigue and interoceptive awareness on perceptual regulation and performance during sustained physical activity

Background: The subjective experience of fatigue impairs an individual’s ability to sustain physical endurance performance. However, precise understanding of exactly how the perception of fatigue limits performance remains unclear. Methods: Here, we examined whether subjective intensity of perceived fatigue, pre-induced through prior upper body activity, differentially impacted performance and altered perceptual (effort) and affective responses during a sustained, isometric contraction in lower body. We also explored whether (cardiac) interoceptive awareness moderated the relationship between the perception of fatigue and effort. Using a repeated-measures study design, thirty male participants completed three experimental conditions, with the intensity of the pre-induced state of fatigue manipulated to evoke severe (SEV), moderate (MOD) and minimal (control; CON) perceptions prior to the performance of a sustained, sub-maximal contraction in the dominant knee extensors. Results: Participants’ capacity to sustain the isometric contraction was significantly impaired (vs. CON, MOD: -9.5 ± 19.1%, p=0.007; SEV: -13.7 ± 17.2%, p<0.001), with perception of effort higher (SEV, MOD vs. CON: b=-0.90, p<0.001), when perceptions of fatigue were elevated. However, the effect on performance (SEV vs. MOD: -2.5 ± 19.9%, p=0.455) and effort perception (SEV vs. MOD: b=-0.06, p=0.612) was not dependent upon the manipulated intensity of the pre-induced state of fatigue. Perceived fatigue was shown to predict the perception of effort during the endurance task. However, disassociation of perceptual constructs was evidenced with perceived effort, but not fatigue, associated with endurance time (CON: r=-0.57, p=0.004; MOD: r=-0.69, p<0.001; SEV: r=-0.59, p=0.003). Interoceptive awareness was shown to attenuate the relationship between perceived fatigue and effort, but only when fatigue was elevated within the experimental manipulations (b=-4.45, p=0.005). Conclusions: Perception of fatigue indirectly limits endurance performance by exerting influence over sensory processes making a physical task appear more effortful. Moreover, this effect is influenced by individual awareness of interoceptive representations of bodily states.

Dark, loud, and compact sounds induce frisson

Frisson is characterised by tingling and tickling sensations with positive or negative feelings. However, it is still unknown what factors affect the intensity of frisson. We conducted experiments on the stimulus characteristics and individual’s mood states and personality traits. Participants filled out self-reported questionnaires, including the Profile of Mood States, Beck Depression Inventory, and Big Five Inventory. They continuously indicated the subjective intensity of frisson throughout a 17-min experiment while listening to binaural brushing and tapping sounds through headphones. In the interviews after the experiments, participants reported that tingling and tickling sensations mainly originated on their ears, neck, shoulders, and back. Cross-correlation results showed that the intensity of frisson was closely linked to the acoustic features of auditory stimuli, including their amplitude, spectral centroid, and spectral bandwidth. This suggests that proximal sounds with dark and compact timbre trigger frisson. The peak of correlation between frisson and the acoustic feature was observed 2 s after the acoustic feature changed, suggesting that bottom-up auditory inputs modulate skin-related modalities. We also found that participants with anxiety were sensitive to frisson. Our results provide important clues to understanding the mechanisms of auditory–somatosensory interactions.

Expressive Suppression of Negative and Positive Emotions in Russia and Azerbaijan

Expressive suppression may have negative consequences when used as an emotional regulation strategy. However, the extent of these consequences is very different in strongly individualist and collectivist cultures, as studies comparing the USA and China have revealed. The aim of the present study was to investigate the effects of expressive suppression in Russia and Azerbaijan where the levels of individualism/ collectivism are comparable and moderate. The subjects (N = 111, mean age 20 years, females, 59 Russians and 52 Azerbaijani) were induced with emotional states (joy, neutral, sadness) using validated video clips and were randomly assigned to the normal viewing or the expressive suppression condition, replicating the classical experiment of J. Gross. We found that suppression of joy: 1) did not affect the subjective intensity of joy in both groups, but was associated with increase of background negative emotions in Russians; 2) was associated with reduced activity of cheek muscles in both groups and with increased activity of forehead muscles in Russians; 3) did not have any significant effects on sympathetic nervous system activity. The suppression of sadness: 1) did not affect the subjective intensity of sadness in both groups, but was associated with increased in background positive emotions in Russians; 2) was associated with reduced activity of forehead muscles in Russians, but not in Azerbaijani; 3) did not have any significant effects on sympathetic nervous system activity. The findings suggest that, unlike the USA, in Russia and Azerbaijan expressive suppression is a typical emotional regulation strategy, which explains the absence of sympathetic activation.