Perception Threshold for Pressure by a Soft Textile Actuator

Electroactive textile (EAT) has the potential to apply pressure stimuli to the skin, e.g. in the form of a squeeze on the arm. To present a perceivable haptic sensation we need to know the perception threshold for such stimuli. We designed a set-up based on motorized ribbons around the arm with five different widths (range 3 - 49 mm) for psychophysical studies. We investigated the perception threshold of force pressure and ribbon reduction in two studies, using two methods (PSI and 1up/3down staircase), comparing sex, the left and right arm, the lower and upper arm, and stimulated surface area with a total of 57 participants. We found that larger stimulation surfaces require less pressure to reach the perception threshold (0.151 N per cm 2 for 3 mm width, 0.00972 N per cm 2 for 49 mm width on the lower arm). This indicates a spatial summation effect for these pressure stimuli. We did not find significant differences in perception threshold for the left and right arm and, the upper and lower arm. Between male and female participants we found significant differences for two conditions (10 mm and 25 mm) in Experiment 1, but we could not reproduce this in Experiment 2.

Understanding the combined effects of sleep deprivation and acute social stress on cognitive performance using a comprehensive approach

Background

Sleep deprivation (SD) and acute social stress are common, often unavoidable, and frequently co-occurring stressors in high-risk professions. Both stressors are known to acutely induce inflammatory responses and an increasing body of literature suggests this may lead to cognitive impairment. This study examined the combined effects of total SD and acute social stress on cognitive performance and took a comprehensive approach to explore their (shared) underlying mechanism leading to cognitive decline.

Method

We recorded cognitive performance on a response inhibition task and a multitask and monitored a range of inflammatory, psychophysiological and self-reported markers in 101 participants, both before and after one night of either sleep (control group: N = 48) or SD (N = 53), and both before and after a social stressor (Trier Social Stress Test).

Results

SD decreased cognitive performance. The social stress test also results in cognitive performance decline in the control group on the response inhibition task, but improved rather than decreased performance of sleep deprived participants on both tasks. The subjective ratings of mental effort also reflect this antagonistic interaction, indicating that the social stressor when sleep-deprived also reduced mental effort. In the inflammatory and physiological measures, this pattern was only reflected by IL-22 in blood. SD reduced blood IL-22 concentrations, and the social stress reduced IL-22 in the control group as well, but not in sleep-deprived participants. There were no interactive effects of SD and social stress on any other inflammatory or psychophysiological measures. The effects of the social stress test on autonomic measures and subjective results suggest that increased arousal may have benefited sleep-deprived participants' cognitive performance.

Discussion

SD generally decreased cognitive performance and increased required mental effort. By contrast, the isolated effects of a social stressor were not generic, showing a positive effect on cognitive performance when sleep deprived. Our study is the first that studied combined effects of sleep deprivation and acute social stress on cognitive performance and inflammatory markers. It provides a comprehensive overview of effects of these stressors on a range of variables. We did not show unequivocal evidence of an underlying physiological mechanism explaining changes in performance due to (the combination of) sleep deprivation and social stress, but consider IL-22 as a possible cytokine involved in this mechanism and certainly worth following up on in future research.

The Effect of Actuation Speed on the Perception Threshold of a Squeezing Soft Actuator

The actuation speed of a pressure stimulus may influence its perception threshold. This is relevant for the design of haptic actuators and haptic interaction. We ran a study using a motorized ribbon to apply pressure stimuli (squeezes) to the arm at three different actuation speeds and used the PSI method to find the perception threshold for 21 participants. We found a significant effect of actuation speed on the perception threshold. Namely, a lower speed seems to increase the thresholds of normal force, pressure and indentation. This could be due to multiple factors like temporal summation, stimulating a larger population of mechanoreceptors for faster stimuli, and different responses of SA and RA receptors to stimuli of varying speeds. Our results show that actuation speed is an important parameter for the design of new haptic actuators and the design of haptic interaction for pressure.

Vibrotactile and Visual Threat Cueing with High G Threat Intercept in Dynamic Flight Simulation

In a TNO and FOI joint study, nine fighter pilots participated in a threat detection and intercept experiment in the Swedish Dynamic Flight Simulator. Visual threat cueing with a simulated Gripen aircraft head-up display (HUD) symbology was compared with combined visual and vibrotactile threat cueing by means of the HUD symbology and a TNO Tactile Torso Display consisting of 60 vibrators in a matrix covering the pilot's torso. Each fighter pilot detected and intercepted 32 threats while pulling G-loads up to +8-9Gz. The high G-loads neither critically affected the tactile vest equipment nor the human sensory system, and visual/tactile cueing generated an overall faster RT to threat pop-ups compared with visual cueing alone. The pilots' highest ratings of the tactile cueing were for capturing attention and indicating initial threat direction at threat pop-up. Thus, tactile threat cueing could enhance visual cueing and threat awareness in fighter aircraft.

The Perception of Visual UncertaintyRepresentation by Non-Experts

We tested how non-experts judge point probability for seven different visual representations of uncertainty, using a case from an unfamiliar domain. Participants (n = 140) rated the probability that the boundary between two earth layers passed through a given point, for seven different visualizations of the positional uncertainty of the boundary. For all types of visualizations, most observers appear to construct an internal model of the uncertainty distribution that closely resembles a normal distribution. However, the visual form of the uncertainty range (i.e., the visualization type) affects this internal model and the internal model relates to participants' numeracy. We conclude that perceived certainty is affected by its visual representation. In a follow-up experiment we found no indications that the absence (or presence) of a prominent center line in the visualization affects the internal model. We discuss if and how our results inform which visual representation is most suitable for representing uncertainty and make suggestions for future work.

Perceiving blocks of emotional pictures and sounds: effects on physiological variables

Most studies on physiological effects of emotion-inducing images and sounds examine stimulus locked variables reflecting a state of at most a few seconds. We here aimed to induce longer lasting emotional states using blocks of repetitive visual, auditory, and bimodal stimuli corresponding to specific valence and arousal levels. The duration of these blocks enabled us to reliably measure heart rate variability as a possible indicator of arousal. In addition, heart rate and skin conductance were determined without taking stimulus timing into account. Heart rate was higher for pleasant and low arousal stimuli compared to unpleasant and high arousal stimuli. Heart rate variability and skin conductance increased with arousal. Effects of valence and arousal on cardiovascular measures habituated or remained the same over 2-min intervals whereas the arousal effect on skin conductance increased. We did not find any effect of stimulus modality. Our results indicate that blocks of images and sounds of specific valence and arousal levels consistently influence different physiological parameters. These parameters need not be stimulus locked. We found no evidence for differences in emotion induction between visual and auditory stimuli, nor did we find bimodal stimuli to be more potent than unimodal stimuli. The latter could be (partly) due to the fact that our bimodal stimuli were not optimally congruent.

Vestibulo-tactile interactions regarding motion perception and eye movements in yaw

This paper shows that tactile stimulation can override vestibular information regarding spinning sensations and eye movements. However, we conclude that the current data do not support the hypothesis that tactile stimulation controls eye movements directly. To this end, twenty-four subjects were passively disoriented by an abrupt stop after an increase in yaw velocity, about an Earth vertical axis, up to 120°/s. Immediately thereafter, they had to actively maintain a stationary position despite a disturbance signal. Subjects wore a tactile display vest with 48 miniature vibrators, applied in different combinations with visual and vestibular stimuli. Their performance was quantified by RMS body velocity during self-control. Fast eye movement phases were analyzed by counting samples exceeding a velocity limit, slow phases by a novel method applying a first order model. Without tactile and visual information, subjects returned to a previous level of angular motion. Tactile stimulation decreased RMS self velocity considerably, though less than vision. No differences were observed between conditions in which the vest was active during the recovery phase only or during the disorienting phase as well. All effects of tactile stimulation found on the eye movement parameters could be explained by the vestibular stimulus.

Vestibulo-tactile interactions regarding motion perception and eye movements in yaw

This paper shows that tactile stimulation can override vestibular information regarding spinning sensations and eye movements. However, we conclude that the current data do not support the hypothesis that tactile stimulation controls eye movements directly. To this end, twenty-four subjects were passively disoriented by an abrupt stop after an increase in yaw velocity, about an Earth vertical axis, up to 120 degrees /s. Immediately thereafter, they had to actively maintain a stationary position despite a disturbance signal. Subjects wore a tactile display vest with 48 miniature vibrators, applied in different combinations with visual and vestibular stimuli. Their performance was quantified by RMS body velocity during self-control. Fast eye movement phases were analyzed by counting samples exceeding a velocity limit, slow phases by a novel method applying a first order model. Without tactile and visual information, subjects returned to a previous level of angular motion. Tactile stimulation decreased RMS self velocity considerably, though less than vision. No differences were observed between conditions in which the vest was active during the recovery phase only or during the disorienting phase as well. All effects of tactile stimulation found on the eye movement parameters could be explained by the vestibular stimulus.