Research articleVirtual postural threat facilitates the detection of visual stimuli
Introduction
Studies have consistently shown that humans are able to detect emotional or threatening stimuli faster and more efficiently than emotionally-neutral or positive stimuli. For instance, sad or angry faces
are detected faster than neutral or happy faces [1], and images of snakes or spiders can be detected faster than those of flowers or mushrooms [2]. Fear-relevant stimuli have an advantage in capturing attention [3], and the presentation of fearful faces has been shown to facilitate contrast sensitivity [4].
Few studies have examined how the perception of neutral visual stimuli may be influenced when presented in a threatening or arousing situation. When inducing fear in human participants with the threat of electric shock, Lojowska et al. observed an improved perception of coarse, low-spatial frequency features of gratings, at the expense of perception of high-spatial frequency features [5]. Likewise, enhanced arousal states have been shown to increase contrast perception in a reward-driven paradigm [6], and decrease stereo-acuity thresholds as well as visual contrast thresholds during cold-pressor stimulation [7]. However, most prior studies are performed in a safe and constrained lab environment, with participants often seated and their head fastened in a chin rest fixated on a computer screen. In addition, stimuli are often presented primarily in the central line of vision with artificial contrast gratings. Thus, little is known about how arousal or fear might influence visual perception in a less constrained and more natural-appearing visual setting that requires attention to both focal and peripheral cues. One way to investigate detection of briefly presented stimuli in the entire visual field is by measuring the useful field of view (UFOV), defined as the area from which information can be extracted at a brief glance [8]. UFOV relies on visual sensory function, visual processing speed and visual attention [9], and decreases as a function of cognitive load [10,11] and postural demand [12].
For the current study we adapted a UFOV task from Reed-Jones et al. [12], to investigate how a postural threat, induced by standing on a virtual elevated platform, influences sensory perceptions in focal as well as peripheral fields of view. Standing on real or virtual elevated surfaces evokes psychological changes, such as decreased balance confidence and increased state anxiety, and fear, as well as increased physiological changes in arousal and postural control [13,14,15,16]. Evidence of sensory changes while standing under postural threat include increased proprioceptive and vestibular reflex responses, and increased perturbation-evoked cortical responses [17,18,19], however, no studies to date have examined its effect on visual responses during stance.
Prior studies suggest that enhanced levels of arousal can lower visual perception thresholds in humans [6,7], and that threat increases attention in the area of focus as well as the periphery, thus leading to a “perceptual benefit” in the entire visual field [4]. Therefore, our primary hypothesis was that stimulus detection rates would be higher when participants are exposed to high compared to low postural threat. We further hypothesized that detection rates would decrease for targets of higher eccentricities (i.e. farther from the field of focus) [20]. Based on previous work, we expected that exposure to an increased postural threat would correspond to a decrease in self-reported balance confidence, an increase in state anxiety and fear, and an increase in sympathetic activation [13,15,16].
Section snippets
Participants
Ten healthy young adults (6 female, mean age 25.5 ± 3.03 years) volunteered for the study. All participants were right-handed and had normal vision or corrected for it with the use of contact lenses. Individuals who self-reported a history of extreme fear of heights or panic attacks were excluded from the study. Informed consent was obtained prior to participation. All experimental procedures were approved by the behavioural ethics board of UBC, and were conducted in accordance with the
Results
As shown in Fig. 2, participants reported lower balance confidence (Z = -3.493, p < .001, r = .28), and greater state anxiety (Z = -2.25, p = .024, r = .36), and fear (Z= -3.129, p= .002, r= .70), when standing in HIGH compared to LOW conditions. No difference in sense of presence between HIGH and LOW condition was reported (Z= -1.254, p= .21, r= .18). No significant differences were observed for mean EDA levels between the HIGH (M= 13.75, SD= 7.9) and LOW (M= 12.16, SD= 8.01) conditions (Z=
Discussion
The present study examined the effects of a virtual height-induced postural threat on the detection of visual stimuli across a broad horizontal visual field in healthy young adults. Consistent with previous studies [13,14,15,22], participants demonstrated decreases in balance confidence and increases in state anxiety and fear when exposed to the virtual postural threat. Participants reported similar values for sense of presence in LOW and HIGH conditions, with moderate levels of presence on
Conclusion
We observed that human visual detection is facilitated by a virtual postural threat in the wide horizontal field of view. The results of this study expand upon previous observations of threatening or emotional stimuli to neutral stimuli, presented under threatening conditions, to better understand the influence of threat on human visual perception.
Declaration of Competing Interest
The authors report no declarations of interest.
Funding
The project was funded through operating funds from the Natural Sciences and Engineering Research Council of Canada (NSERC) to M. Carpenter. M. Vermehren was supported by the German Academic Exchange Service (DAAD).
CRediT authorship contribution statement
Mareike Vermehren: Methodology, Software, Formal analysis, Investigation, Writing - original draft, Visualization. Mark G. Carpenter: Conceptualization, Writing - review & editing, Supervision.
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