Forward optic flow is prioritised in visual awareness independently of walking direction

Abstract

When two different images are presented separately to each eye, one experiences smooth transitions between them. Previous studies have shown that exposure to signals from other senses can enhance perceptual awareness of stimulation-congruent images. Surprisingly, despite our ability to infer perceptual consequences from bodily movements, evidence that action can have an analogous influence on visual experience is scarce and mainly limited to local (hand) movements. Here, we investigated whether one’s direction of locomotion affects perceptual awareness of optic flow patterns. Participants walked forwards and backwards on a treadmill while viewing highly-realistic visualisations of self-motion in a virtual environment. We hypothesised that visualisations congruent with walking direction would predominate in visual awareness over incongruent ones, and that this effect would increase with the precision of one’s active proprioception. These predictions were not confirmed: optic flow consistent with forward locomotion was prioritised in visual awareness independently of walking direction and proprioceptive abilities. Our results suggest that kinaesthetic-proprioceptive processing plays a limited role in shaping visual experience. This seems at odds with Bayesian accounts of perception but is in-line with Cancellation theories, which imply that crossmodal influences of self-generated signals are suppressed as a redundant source of information about the outside world.

Perceptual Awareness of Optic Flows Paced Optimally and Non-optimally to Walking Speed

“…As expected, optic flow speeds were far higher when matched with the faster ( Me = 1.52, SD = 0.51 m/s) than with the slower walking pace ( Me = 0.97, SD = 0.30 m/s), Z = 5.84, p < .001, r = .87. In general, the results indicated a large overestimation of matched optic flow speeds in relation to actual walking velocities (faster: 0.69 m/s [2.5 km/hr]; slower: 0.42 m/s [1.5 km/hr]), which is in line with previous reports on perceived self-motion speed in VR setups (Banton et al., 2005; Caramenti et al., 2018, 2019; Durgin, Fox, et al., 2005; Motyka et al., 2021; Powell et al., 2011). Even though the magnitude of overestimation differed greatly between participants, the estimates were strongly correlated between walking speed conditions, r s = .82, p < .001.…”

“…The plausibility of such locomotion-driven effects is also supported by evidence of the widespread presence of locomotion-speed-related signals in the early stages of visual processing (for reviews, see Busse, 2018; Chaplin & Margrie, 2020; Parker et al., 2020) and the salient role of the primary visual cortex in integrating motor-based predictions of visual flow with the actual bottom-up signals (Attinger et al., 2017; Leinweber et al., 2017; Saleem et al., 2013). Notably, in contrast to self-motion speed, the direction of one’s locomotion was not found to promote visual awareness of congruent (expanding/contracting) optic flow patterns in previous binocular rivalry studies (Motyka et al., 2021; Paris et al., 2017). Interestingly, similar feature dependence of effects seems to hold for manual movements: whereas null findings were reported in studies manipulating spatial congruence between actions and visual rotation (Dogge et al., 2018; Suzuki et al., 2019; Veto et al., 2018), stimuli whose motion was driven by one’s hand movements—either in directionally congruent (Maruya et al., 2007) or both congruent and incongruent manners (Suzuki et al., 2019)—showed enhanced access to visual awareness as compared with uncoupled (prerecorded) visual changes.…”

“…Similarly, null findings were reported when voluntary facial expressions (frowns and smiles) were used as proprioceptive manipulation and corresponding emotional faces were used as visual stimuli (Korb et al., 2017). Crucially in the context of this paper, two previous studies did not show enhanced visual awareness of optic flow patterns congruent with the direction of one’s locomotion (Motyka et al., 2021; Paris et al., 2017). Nevertheless, action effects were found in two studies comparing conditions in which visual motion was either time coupled to one’s manual actions or uncoupled (i.e., advanced independently of the presence and speed of hand movements).…”

“…At this stage, we employed the relatively liberal inclusion criteria determined in our previous study (cf. Motyka et al., 2021), that is, at least three full perceptual transitions per block, mean duration of exclusive percepts (left/right button presses) greater than 0.33 s, and a proportion of mixed percepts lower than 90%. Eight participants did not meet at least one of these requirements.…”

“…Faster and slower optic flow speeds were predetermined individually in a task in which participants adjusted the perceived optic flow speed to match their walking pace (cf. Motyka et al., 2021). The use of this procedure was motivated by the fact that physically accurate optic flows appear too slow when presented under the conditions of restricted peripheral vision in head-mounted displays (Banton et al., 2005; Caramenti et al., 2018, 2019; Powell et al., 2011).…”