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Running head: BIASES IN THE VISUAL PERCEPTION OF HEADING 1 Biases in the Visual Perception of Heading Master’s Thesis
| Content Provider | Semantic Scholar |
|---|---|
| Copyright Year | 2017 |
| Abstract | Earlier research has shown that heading can be accurately estimated from visual cues. Nevertheless, a multitude of studies has shown that people commit constant errors when estimating heading from visual cues. The exact origin of these biases remains unclear despite many research efforts. The visual stimuli used in past research on heading estimation varied considerably – a factor which might have systematically influenced heading accuracy. Therefore, we examined the possible effect of divergent stimuli characteristics on heading estimation in the current study. Measurements of twenty participants (12 females) with a mean age of 25.80 years (SD = 3.53) were obtained during the study. Participants were shown stimuli depicting horizontal linear motion in the ground plane and were asked to judge the direction of heading as well as to provide vection ratings. Stimuli shown differed in characteristics related to Field of View (FOV), disparity, motion profile, and layout of the scene. A model explaining hypothesized relationships and effect on estimation bias with a partial mediating effect of vection was proposed and estimated via path analysis. Findings indicated that bias away from the fore-aft axis found in this study could not be explained by visual properties alone. FOV, disparity and scene had only in combination with certain stimuli headings a marginal effect on magnitude of bias, but not its direction. Vection had no mediating effect. However, all characteristics had an effect on vection ratings. Visual properties thus marginally affect heading estimation, but exact source(s) of biases remain an objective for future research. BIASES IN THE VISUAL PERCEPTION OF HEADING 3 Biases in the Visual Perception of Heading Heading is defined as the direction of horizontal linear self-motion. Heading estimation is essential to everyday tasks such as locomotion and navigation. The Central Nervous System (CNS) is able to estimate heading from inertial cues, by means of the vestibular system and several other sensory cells distributed throughout the body, but also from visual cues (Howard, 1982). Visually, we estimate heading from optic flow, which was first described by Gibson in 1950 and has since been subject of a large number of studies (see Lappe, Bremmer, & Van Den Berg, 1999, for a review). Optic flow refers to the pattern of motion generated as reflections of objects move across the retina when we move ourselves (Gibson, 1950). As we move on a straight path, this pattern of visual motion radially expands from a singular point along the direction of heading, the Focus of Expansion (FOE). Heading can be estimated by localizing this point. When there is perfectly lateral movement, the direction of heading cannot be derived from the FOE, but can be estimated from direction of vectors represented in the optic flow. Although errors in heading estimation found in research are generally not more than a few degrees (Telford, Howard, & Ohmi, 1995; Warren & Kurtz, 1999; Warren, Morris, & Kalish, 1988), systematic biases are found across studies (Crane, 2012; Cuturi & MacNeilage, 2013; De Winkel, Katliar, & Bülthoff, 2015, 2017). The exact source(s) of these biases remain unclear, but it has been proposed that these biases have a neurophysiological cause: Visual optic flow cues are mainly processed in the dorsal medial superior temporal (MSTd) area of the brain and neural populations in this area show an overrepresentation of lateral preferred directions (Gu, Fetsch, Adeyemo, DeAngelis, & Angelaki, 2010; Saito et al., 1986). It has been shown that such a distribution of preferred directions can lead to a bias away from the fore-aft axis and to a more sensitive discrimination of headings laying near BIASES IN THE VISUAL PERCEPTION OF HEADING 4 straight ahead (Gu et al., 2010). From an evolutionary standpoint, this sensitivity could be functionally relevant because we mostly move forward in our daily environments (Cuturi & MacNeilage, 2013). However, this hypothesis cannot explain all of the biases found across past studies, because the nature of the biases reported in the literature is highly variable. Some studies show biases towards the fore-aft axis, i.e., underestimation, (D’Avossa & Kersten, 1996; De Winkel et al., 2015; Van Den Berg & Brenner, 1994a) while other studies show biases away from the fore-aft axis, i.e., overestimation, (Cuturi & MacNeilage, 2013; Telford & Howard, 1996; Warren, 1976). Therefore, these biases might have extraneous origins. De Winkel and colleagues (2015) suggest that the observed variability could stem from divergent characteristics of the visual stimuli used in different studies. In the following section, we list properties of the visual stimuli used across studies and discuss how these characteristics may affect bias. Field of View A salient difference between studies is the variability in Field of View (FOV). The equipment used in past studies varied between head-mounted displays (Hummel, Cuturi, MacNeilage, & Flanagin, 2016), projection screens (De Winkel et al., 2015; Gu, DeAngelis, & Angelaki, 2007), LCD screens (Crane, 2014; Cuturi & MacNeilage, 2013) and plain monitors (D'Avossa & Kersten, 1996; Warren & Kurtz, 1999), varying in resolution and display size. Due to these differences, the Field of View also ranged from 40° by 32° (Warren & Kurtz, 1999) up to 160° by 100° (Johnston, White & Cumming, 1973), horizontal by vertical respectively, with most current studies employing a FOV of around 100° by 80° (Butler, Campos, & Bülthoff, 2014; Crane, 2014; Cuturi & MacNeilage, 2013). The FOV may affect bias in heading estimation indirectly by means of the FOE: When the FOV is large enough, the FOE is visible. However, when the FOE is outside the FOV, heading cannot be estimated by locating the FOE. In this case the CNS can still estimate heading by BIASES IN THE VISUAL PERCEPTION OF HEADING 5 triangulation of vectors based on reference points in the optic flow (Koenderink & Van Doorn, 1987), but it has been shown that heading estimates tend to become less precise (Crowell & Banks, 1993; Gu et al.,2007; MacNeilage, Banks, Berger, & Bülthoff, 2010). For studies with smaller FOV, this means that physically, the range of FOEs lying within the bound of the FOV will become smaller, thus leading to more triangulation errors and to biased perceptions. Very small FOVs have already been shown to affect accuracy and to bias heading judgements towards the fore-aft axis (Li, Peli, & Warren, 2002; Warren & Kurtz, 1999). Consequently, it appears that FOV could affect bias in heading estimates by forcing the CNS to apply different estimation strategies, although the effect of FOV on nature of the bias has not yet been systematically studied. Binocular Disparity A second difference between studies is the availability of (binocular) disparity cues when displaying optic flow stimuli. Some studies presented stimuli without disparity either monocular (Banks, Ehrlich, Backus, & Crowell, 1996; Crowell & Banks, 1993) or binocular with the same image for both eyes (De Winkel, Weesie, Groen, & Werkhoven, 2010; Johnston et al.,1973). While other studies presented stimuli with disparity cues, using active stereo glasses (De Winkel et al., 2015; Fetsch, Turner, DeAngelis, & Angelaki, 2009) or anaglyph glasses (Crane, 2012; Butler, Smith, Campos, & Bülthoff, 2010). The availability of disparity cues in optic flow stimuli generates more information for the observer, especially in terms of depth order. The depth order gives information about the relative distance of objects in the environment and can be used to distinguish between self-motion and eye movement or random movements in the optic flow. The distinction between eye or random movement and self-motion can then improve localisation of the FOE and can thus be used to improve heading. In fact, it has been shown that stereoscopic depth cues can improve accuracy of heading estimation in noisy environments (Grigo & Lappe, 1998; Van Den Berg & Brenner, BIASES IN THE VISUAL PERCEPTION OF HEADING 6 1994b). Interestingly, most studies reporting overestimation of heading used stereoscopic stimuli (Crane, 2012; Cuturi & MacNeilage, 2013; Telford & Howard, 1996) whereas studies without disparity primarily report underestimation (Johnston et al., 1973; Li et al., 2002; Warren & Kurtz, 1999). However, the availability of stereoscopic depth cues is not a perfect predictor for the direction of the bias (De Winkel et al., 2015; Warren, 1976), and its precise effect on bias in heading estimation still needs to be assessed experimentally. Visual Scene Various visual scenes have been used throughout studies, differing in content and layout. Most studies used a variation of random dot clouds or star fields as visual stimuli (Butler et al., 2010; Crane, 2012; Warren & Kurtz, 1999), but differed considerably in the specific objects that these clouds consisted of, using either Gaussian blobs (Butler et al., 2010), frontoparallel triangles (Crane, 2012; Cuturi & MacNeilage, 2013; Gu et al., 2010), circles (De Winkel, Grácio, Groen, & Werkhoven, 2010), round particles (De Winkel et al., 2015, 2017), or single pixels (Warren & Kurtz, 1999). Likewise, some studies included a ground plane (Royden, Banks, & Crowell, 1992; Warren & Kurtz, 1999; De Winkel et al., 2015, 2017) while others did not (Crane, 2012; Cuturi & MacNeilage, 2013; Gu et al., 2007). Early research has shown that basic optic flow patterns are sufficient for perceiving heading (Warren & Hannon, 1988) and that heading judgements are largely independent of 3D-layout and density of dots (Warren et al., 1988). However, similar to the presence or absence of binocular disparity cues, the presence or absence of a ground plane affects the type and amount of information from which the observer can judge heading. Specifically, Koenderink and Van Doorn (1987) point out that reference points in the visual scene support distance judgement o |
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| Alternate Webpage(s) | https://essay.utwente.nl/73700/1/Kurtz_MA_BMS.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
