Virtual postural threat facilitates the detection of visual stimuli

Highlights

• Investigated the detection of visual targets under a height-induced postural threat

• Participants performed a modified useful field of view task in a virtual environment

• State anxiety and fear increased with high threat; balance confidence decreased

• Detection rates for visual stimuli increased with increased postural threat

• Suggests that detection of visual stimuli is facilitated in threatening environments

Abstract

Prior studies have shown that enhanced levels of arousal can increase specific aspects of visual perception. The current study investigated the effect of a height-induced postural threat on the detection of central and peripheral visual targets. Ten healthy young adults performed a modified useful field of view task in a virtual environment under low and high postural threat. Each individual completed two blocks of standing trials at ground level (low postural threat), and on a virtual platform raised 7 m above the ground (high postural threat). Under high compared to low postural threat, individuals demonstrated decreases in self-reported balance confidence and increases in state anxiety and fear. With increased threat, detection rates for visual stimuli increased, independent of the location of the stimulus in the field of view. These findings suggest that detection of visual stimuli is facilitated in threatening environments, likely driven by a combination of emotion, attention and other higher cognitive influences.

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].