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Article  |   January 2017
Evolved navigation illusion provides universal human perception measure
Author Affiliations
  • Russell E. Jackson
    Department of Psychology, University of Idaho, Moscow, ID, USA
    rjackson@uidaho.edu
  • Jule Gómez de García
    Liberal Studies Department, California State University San Marcos, San Marcos, CA, USA
    jmgarcia@csusm.edu
Journal of Vision January 2017, Vol.17, 39. doi:10.1167/17.1.39
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      Russell E. Jackson, Jule Gómez de García; Evolved navigation illusion provides universal human perception measure. Journal of Vision 2017;17(1):39. doi: 10.1167/17.1.39.

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Abstract

The ability to replicate an experiment across any scientific discipline rests on the assumption that different experimenters are capable of perceiving the same methods and outcomes. However, the large individual differences in experimenters' visual perception undermine this tenet of the scientific process. Further, common devices for measuring similarity in perceptual capacity do not replicate across human groups. Here, we used evolved navigation theory to predict a universal way to measure human perceptual capacity via a distance illusion. We then compared this descent illusion across groups that we selected specifically for their extreme differences: adults in the United States and a group of indigenous Ixil Maya in Guatemala. The descent illusion was indistinguishable across samples. This illusion is among a growing group of evolved illusions capable of comparing subjective human perception across individuals.

Introduction
The replicable, independent observations required for empirical science are possible only if different scientists are capable of making the same observations (Kuhn, 1970). Distance illusions are among the most common devices for testing perceptual capacity across individuals (Biggs, Stey, Davoli, Lapsley, & Brockmole, 2014; Jackson, 2009; Tinker, 1938). Although illusions depart from reality, the constancy of their experience across individuals reveals the underlying brain mechanisms that humans employ (Chua & Enns, 2005; Eagleman, 2001; Goodale, Milner, Jakobson, & Carey, 1991). From the study of distance illusions, researchers regularly draw conclusions about a singular human nature and consider distance illusions to be broadly constant, universal cognitive mechanisms within our species (Eaglemen, 2001; Henrich, Heine, & Nornzayan, 2010; Wu, Ooi, & He, 2004). 
There is little evidence of universal distance illusions. The majority of perception research has used nonrepresentative samples of participants from Western, educated, industrialized, rich democracies (Henrich et al., 2010). Of the cross-cultural data available, distance illusions either occur at vastly different magnitudes or fail to replicate (Caparos et al., 2012; Henrich et al., 2010; Pollnac, 1977; van der Kamp, Withagen, & de Wit, 2013; Wober, 1970). This failure of cross-cultural replication includes the most well-known illusions tested over the last 110 years (Rivers, 1905). These investigations typically use theories that do not identify species-level evolutionary forces and thus have little predictive power for identifying species-typical behavior (Barkow, Cosmides, & Tooby, 1995). 
In the following study, we tested the predictions of an evolutionary theory across disparate human groups to identify a universal distance illusion. No single study can settle the broader issues of replicability. Here, our goal was to identify the capacity for replicability in a largely unreplicated research area by using an ultimate-level theory. Ultimate-level theories are especially important for generating predictions and specifying phylogenetic, developmental, and environmental contexts for phenomena (Barkow et al., 1995; Marr, 1982; Tinbergen, 1963). Part of the lack of previous replications in this area (see Hutchison & Loomis, 2006; Wagner, 1977) likely stems from mechanistic explanations that do not specify the environments in which phenomena evolved, and thus, they fail to make explicit predictions across the settings of which culture is a part. 
We selected participants who could provide a nearly diametric comparison to the populations tested in the social sciences and in distance perception research in particular. Our participants were Ixil Mayan individuals from the area surrounding Nebaj, El Quiche, Guatemala. Ixiles have experienced little exposure to Western media, have little to no formal education, live in relative poverty, and have a very different experience of the natural world than do members of highly industrialized nations. The likelihood of coincidental replication across cultures, particularly across Ixil and the United States, is exceedingly small—far smaller than the replication likelihood seen in psychology experiments tested within the same culture (Open Science Collaboration, 2015). 
We tested participants for the descent illusion, predicted by evolved navigation theory (Jackson, 2005; Jackson & Cormack, 2007). Evolution researchers propose that selection in the form of navigational mortality resulted in distance overestimation of vertical surfaces, especially from above, where the risk of falling is greatest (Jackson & Cormack, 2007, 2008, 2010). This illusion occurs such that observers overestimate the height of a vertical surface and to a greater extent while standing at its top than bottom. The illusion gives positive values for (eteb)/eb, where et is the observer's estimate of the height of a vertical surface while standing at its top and eb is the same estimate while standing at its bottom. The magnitude of the descent illusion in U.S. samples is roughly 27% (Jackson & Cormack, 2007). Illusion magnitude is as high as 84% when we compare et to the actual distance, making this the largest known real-world distance illusion (for comparison, see Chapanis & Mankin, 1967; Higashiyama & Ueyama, 1988; Howe & Purves, 2005). 
Methods
Procedures followed closely those of previous investigations of the descent illusion (Jackson, 2005; Jackson & Cormack, 2007). Participants estimated the height of a 2.90-m-tall vertical surface while standing at its top and bottom (Figure 1). This surface was a one-story building in Nebaj, El Quiché, Guatemala. Participants gave estimates via distance matching, wherein they directed a research assistant to walk away until the distance between the research assistant and the participant appeared equal to the estimated distance. Participants could use as much time, and make as many adjustments, as they liked. Participants also estimated the length of an equal horizontal distance across rough, sloped ground with the same egocentric distance matching task (see Jackson & Willey, 2013); such a surface poses falling risks and texture differences that have been shown to alter distance estimates (Jackson & Willey, 2011; Wu et al., 2004). After providing distance estimates, participants completed a verbal questionnaire unrelated to the current experiment. 
Figure 1
 
Observer positions during vertical estimates. Icons indicate the same observer while estimating the vertical surface from above (outline) and below (solid). Dashed lines indicate path of estimate.
Figure 1
 
Observer positions during vertical estimates. Icons indicate the same observer while estimating the vertical surface from above (outline) and below (solid). Dashed lines indicate path of estimate.
Participants consisted of 30 (16 female, 14 male) Ixil Mayan people aged 19 to 66 years living in the vicinity of Nebaj, El Quiché, Guatemala. Nebaj is located in a mountainous area that poses considerable cultural and media isolation. We collected these data in conjunction with an ongoing project documenting the Ixil language (Gómez de García, Axelrod, & García, 2010). All communication with participants took place in Ixil, supplemented by Spanish. Two research assistants conducted all procedures: one who was a native speaker of Ixil and fluent in Spanish and another who was a native Spanish and English speaker. Both research assistants were blind to the true distance, and the research assistant who communicated with participants was blind to the predictions and background of this research. All participants provided informed consent prior to participation. All methods conformed to the World Medical Association Declaration of Helsinki guidelines for the treatment of human participants, and the university institutional review board approved all procedures. 
Results
The average descent illusion magnitude was 27.7% for Ixil participants, which is effectively indistinguishable from the 27.2% illusion experienced by participants in the United States, tsingle sample(29) = 0.103, p = 0.919 (see Figure 2). 
Figure 2
 
Mean descent illusion magnitude ((eteb)/eb) across current Ixil and previous U.S. samples (Jackson & Cormack, 2007). Error bars represent 95% confidence intervals.
Figure 2
 
Mean descent illusion magnitude ((eteb)/eb) across current Ixil and previous U.S. samples (Jackson & Cormack, 2007). Error bars represent 95% confidence intervals.
Ixil participants' average height estimates from the top of the 2.90-m wall were 4.43 ± 0.33 m (95% confidence interval), whereas estimates from the bottom were 3.54 ± 0.27 m (see Figure 3). The average estimate from the top of the vertical surface exceeded the actual distance by 53%. Nearly all observers overestimated more from the top than bottom (28/30, pbinomial.5 = 4.3 × 10−7). Observers' estimates of the horizontal surface were 3.43 ± 0.17 m. 
Figure 3
 
Participants' distance estimates of a vertical surface while standing at its top and bottom. The solid bisecting line indicates the point of equivalency. Each axis indicates true distance (dashed line) and average estimate (x) with 95% confidence intervals (error bars).
Figure 3
 
Participants' distance estimates of a vertical surface while standing at its top and bottom. The solid bisecting line indicates the point of equivalency. Each axis indicates true distance (dashed line) and average estimate (x) with 95% confidence intervals (error bars).
Discussion
The current data feature a rare replication. The likelihood of replicating any distance illusion is probably very low, given the broad lack of similar evidence in this research area. In addition, the average magnitude of such illusions is small, and so regression to the mean alone should have resulted in a smaller illusion than this large-magnitude replication. Further, the replicated value of the descent illusion could have been quite different in many ways: negative across a wide range, near zero, or positive across a wide range of values different from the replication seen here. The expectation for most distance illusions is a failure to replicate and certainly not to replicate so closely and at the large magnitude appearing in these data. Although other accounts of similar illusions might also expect transfer, evolved navigation theory appears uniquely supported by the present results inasmuch as the magnitude of the illusion seems unaffected by evolutionarily inconsequential environmental and cultural variation, consistent with an early evolutionary origin of this bias. 
These data do not suggest that the descent illusion is invariable. Evolved navigation theory identifies that this illusion should vary based on context-specific falling risks and life history variables related to navigation and injury (Jackson, 2009). Such variables are more likely to produce variation within culture than between cultures. As expected, there are individual differences in illusion magnitude within-sample that are evident in previous investigations (Jackson & Cormack, 2007) and these data (see Figure 3). Nearly all participants experience the descent illusion, but the magnitude of the illusion varies across individuals. A direct method for measuring such variability is via test-retest data, which were unavailable for this study. An important aspect of future research is to test repeatedly within and between cultures in order to measure population variability directly. Our current efforts within this area are promising (Jackson & Kizer, 2016). Variability within the population is an important quality that makes these distance illusions especially fit to test individual differences in perception, despite relative invariance between populations (see also Dean, Thomson, Norris, & Durgin, 2016). 
Researchers predicted this illusion from evolved navigation theory, which specifies how natural selection acting on navigational behavior likely shaped cognitive and locomotor mechanisms (Jackson, 2005; Jackson & Cormack, 2007, 2008, 2010). Evolved navigation theory predicted the descent illusion by identifying that humans avoid navigating overestimated distances (Jackson, 2013) and by proposing that distance perception reflects ancestral navigational risks (Jackson & Cormack, 2010; Jackson & Willey, 2011). One such risk identified by this theory is descent, which is reliably riskier than ascent. This is due, in part, to human biometry that places the eyes and hands further from the navigated surface during descent and with less controlled momentum than the tightly guided muscle movements of ascent. Indeed, falling is more likely on descent than ascent (Haslam & Bentley, 1999; Svanstrom, 1974; Tinetti, Speechley, & Ginter, 1988). 
Conclusions
The descent illusion is one among a growing group of illusions that ostensibly arose in response to navigation risks present over human evolutionary history. Other such illusions include the plateau illusion (Jackson & Willey, 2013), environmental vertical illusion (Jackson & Cormack, 2008), and horizontal visual illusions (Jackson & Willey, 2011). These phenomena provide a previously unavailable capacity to measure the extent to which different individuals are capable of making the same observations. This capacity is essential for ensuring similar comparisons across individuals and has particular import across scientists and disciplines. These findings also provide cross-cultural applications in areas such as economics, policy, and education. Further, these data address the interpretation of visual information in applied areas that include medical imaging, drone piloting, and the remote sensing imagery that is common in astronomy, intelligence gathering, and climate science. Understanding these phenomena is essential for understanding the practice of science across multiple investigators and using the products of science and technology. 
Acknowledgments
We thank Sandra Alvarado, Ixil participant members of the Grupo de Mujeres y Hombres por la Paz, María Luz García, Michael Hughes, Domingo Abraham Cedillo, and Minerva Correa for assistance with data gathering and processing. We also thank Sandra Alvarado and Phil Mohan for comments on previous versions of this manuscript as well as Frank Durgin and an anonymous reviewer for their helpful comments. 
Commercial relationships: none. 
Corresponding author: Russell E. Jackson. 
Address: Department of Psychology, University of Idaho, Moscow, ID, USA. 
References
Barkow B. H., Cosmides L.,& Tooby J. (Eds.). (1995). The adapted mind: Evolutionary psychology and the generation of culture. Oxford, UK: Oxford University Press.
Biggs A. T., Stey P. C., Davoli C. C., Lapsley D.,& Brockmole J. R. (2014). Knowing where to draw the line: Perceptual differences between risk-takers and non-risk-takers. PLoS One, 9, 1–7.
Caparos S., Ahmed L., Bremner A. J., de Fockert J. W., Linnell K. J.,& Davidoff J. (2012). Exposure to an urban environment alters the local bias of a remote culture. Cognition, 122, 80–85.
Chapanis A.,& Mankin D. A. (1967). The vertical-horizontal illusion in a visually-rich environment. Perception & Psychophysics, 2, 249–255.
Chua R.,& Enns J. T. (2005). What the hand can't tell the eye: Illusion of space constancy during accurate pointing. Experimental Brain Research, 162, 109–114.
Dean A. M., Oh J., Thomson C., Norris C. J.,& Durgin F. H. (2016). Do individual differences and aging effects in the estimation of geographical slant reflect cognitive or perceptual effects? i-Perception, 7 (4), 1–18.
Eagleman D. M. (2001). Visual illusions and neurobiology. Nature Reviews Neuroscience, 2, 920–926.
Gómez de García J., Axelrod M.,& García M. L. (2010). In Berez A. L. Rosenblum D. & Mulder J. (Eds.), Fieldwork and linguistic analysis in indigenous languages of the Americas (pp. 9–32 ). Honolulu, HI: Language Documentation & Conservation.
Goodale M. A., Milner A. D., Jakobson L. S.,& Carey D. P. (1991). A neurological dissociation between perceiving objects and grasping them. Nature, 349, 154–156.
Haslam R. A.,& Bentley T. A. (1999). Follow-up investigations of slip, trip and fall accidents among postal delivery workers. Safety Science, 32, 33–47.
Henrich J., Heine S. J.,& Nornzayan A. (2010). The weirdest people in the world? Behavioral and Brain Sciences, 33, 61–83.
Higashiyama A.,& Ueyama E. (1988). The perception of vertical and horizontal distances in outdoor settings. Perception & Psychophysics, 44, 151–156.
Howe C. Q.,& Purves D. (2005). The Müller-Lyer illusion explained by the statistics of image-source relationships. Proceedings of the National Academy of Science USA, 51, 1234–1239.
Hutchison J. J.,& Loomis J. M. (2006). Does energy expenditure affect the perception of egocentric distance? A failure to replicate experiment 1 of Proffitt, Stefanucci, Banton, and Epstein (2003). Spanish Journal of Psychology, 9, 332–339.
Jackson R. E. (2005). Falling towards a theory of the vertical-horizontal illusion. Studies in Perception and Action, 8, 241–244.
Jackson R. E. (2009). Individual differences in distance perception. Proceedings of the Royal Society B, 276, 1665–1669.
Jackson R. E. (2013). Preference for the nearer of otherwise equivalent navigational goals quantifies behavioral motivation and natural selection. PLoS One, 8, 1–4.
Jackson R. E.,& Cormack L. K. (2007). Evolved navigation theory and the descent illusion. Perception & Psychophysics, 69, 353–362.
Jackson R. E.,& Cormack L. K. (2008). Evolved navigation theory and the environmental vertical illusion. Evolution & Human Behavior, 29, 299–304.
Jackson R. E.,& Cormack L. K. (2010). Reducing the presence of navigation risk eliminates strong environmental illusions. Journal of Vision, 10 (5): 9, 1–8, doi:10.1167/10.5.9. [PubMed] [Article]
Jackson R. E.,& Kizer J. E. (2016). Cross-cultural replication of evolved navigation theory predictions. Manuscript in preparation.
Jackson R. E.,& Willey C. R. (2011). Evolved navigation theory and horizontal visual illusions. Cognition, 119, 288–294.
Jackson R. E.,& Willey C. R. (2013). Evolved navigation theory and the plateau illusion. Cognition, 128, 119–126.
Kuhn T. S. (1970). The structure of scientific revolutions (2nd ed.). Chicago: University of Chicago Press.
Marr E. (1982). Vision: A computational investigation into the human representation and processing of visual information. San Francisco: Henry Holt & Company.
Open Science Collaboration. (2015). Estimating the reproducibility of psychological science. Science, 349, aac4716.
Pollnac R. B. (1977). Illusion susceptibility and adaptation to the marine environment: Is the carpentered world hypothesis seaworthy? Journal of Cross-Cultural Psychology, 8, 425–434.
Rivers W. H. (1905). Observations on the senses of the Todas. British Journal of Psychology, 1, 321–396.
Svanstrom L. (1974). Falls on stairs: An epidemiological accident study. Scandinavian Journal of Social Medicine, 2, 113–120.
Tinbergen N. (1963). On aims and methods of ethology. Zeitschrift für Tierpsychologie, 20, 410–433.
Tinetti M. E., Speechley M.,& Ginter S. F. (1988). Risk factors for falls among elderly persons living in the community. New England Journal of Medicine, 319, 1701–1707.
Tinker M. A. (1938). Susceptibility to optical illusions: Specific or general? Journal of Experimental Psychology, 22, 593–598.
van der Kamp J., Withagen R.,& de Wit M. M. (2013). Cultural and learning differences in the Judd illusion. Attention, Perception, & Psychophysics, 75, 1027–1038.
Wagner D. A. (1977). Ontogeny of the Ponzo illusion: Effects of age, schooling and environment on memory. International Journal of Psychology, 12, 161–176.
Wober M. (1970). Confrontation of the H-V illusion and a test of 3-dimensional pictorial perception in Nigeria. Perceptual & Motor Skills, 31, 105–106.
Wu B., Ooi T. L.,& He Z. J. (2004). Perceiving distance accurately by a directional process of integrating ground information. Nature, 428, 73–77.
Figure 1
 
Observer positions during vertical estimates. Icons indicate the same observer while estimating the vertical surface from above (outline) and below (solid). Dashed lines indicate path of estimate.
Figure 1
 
Observer positions during vertical estimates. Icons indicate the same observer while estimating the vertical surface from above (outline) and below (solid). Dashed lines indicate path of estimate.
Figure 2
 
Mean descent illusion magnitude ((eteb)/eb) across current Ixil and previous U.S. samples (Jackson & Cormack, 2007). Error bars represent 95% confidence intervals.
Figure 2
 
Mean descent illusion magnitude ((eteb)/eb) across current Ixil and previous U.S. samples (Jackson & Cormack, 2007). Error bars represent 95% confidence intervals.
Figure 3
 
Participants' distance estimates of a vertical surface while standing at its top and bottom. The solid bisecting line indicates the point of equivalency. Each axis indicates true distance (dashed line) and average estimate (x) with 95% confidence intervals (error bars).
Figure 3
 
Participants' distance estimates of a vertical surface while standing at its top and bottom. The solid bisecting line indicates the point of equivalency. Each axis indicates true distance (dashed line) and average estimate (x) with 95% confidence intervals (error bars).
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