Russell E. Jackson

Evolved navigation theory and the descent illusion.

Researchers often assume that height perception results from all of the same mechanisms as does other distance perception (Avraamides, Loomis, Klatzky, & Golledge, 2004; Foley, Ribeiro-Filho, & Da Silva, 2004; Wu, Ooi, & He, 2004). Evolved navigation theory (ENT) proposes that natural selection has differentiated some psychological processes, including height perception, in response to the navigational outcome of falling. We tested predictions from three theories in two experiments. Only ENT predicted greater height perceived from the top than from the bottom of a vertical surface (because descent results in falls more often than does ascent). Participants across experiments perceived an average of 32% greater vertical distance when viewing from the top than when viewing from the bottom. We discuss selected implications and suggest ENT for uniting isolated findings, including the vertical-horizontal illusion.

Animacy, perceptual load, and inattentional blindness

Inattentional blindness is the failure to notice unexpected objects in a visual scene while engaging in an attention-demanding task. We examined the effects of animacy and perceptual load on inattentional blindness. Participants searched for a category exemplar under low or high perceptual load. On the last trial, the participants were exposed to an unexpected object that was either animate or inanimate. Unexpected objects were detected more frequently when they were animate rather than inanimate, and more frequently with low than with high perceptual loads. We also measured working memory capacity and found that it predicted the detection of unexpected objects, but only with high perceptual loads. The results are consistent with the animate-monitoring hypothesis, which suggests that animate objects capture attention because of the importance of the detection of animate objects in ancestral hunter–gatherer environments.

Individual differences in distance perception

Distance perception is among the most pervasive mental phenomena and the oldest research topics in behavioural science. However, we do not understand well the most pervasive finding of distance perception research, that of large individual differences. There are large individual differences in acrophobia (fear of heights), which we commonly assume consists of an abnormal fear of stimuli perceived normally. Evolved navigation theory (ENT) instead suggests that acrophobia consists of a more normal fear of stimuli perceived abnormally. ENT suggests that distance perception individual differences produce major components of acrophobia. Acrophobia tested over a broad range in the present study predicted large individual differences in distance estimation of surfaces that could produce falls. This fear of heights correlated positively with distance estimates of a vertical surface—even among non-acrophobic individuals at no risk of falling and without knowledge of being tested for acrophobia. Acrophobia score predicted magnitude of the descent illusion, which is thought to reflect the risk of falling. These data hold important implications in environmental navigation, clinical aetiology and the evolution of visual systems.

Reducing the presence of navigation risk eliminates strong environmental illusions

Many researchers have assumed that navigational costs, as opposed to the visual stimuli per se, produce several large-magnitude distance illusions-in spite of the absence of experimental data. We used virtual reality to remove the presence of realistic falling costs, while leaving the visual information otherwise intact. This resulted in removal of the distance illusions proposed to have evolved in response to falling costs. These data hold important implications in vision research and ecological psychology, as well as in applied settings such as aviation.

Evolutionary Relevance Facilitates Visual Information Processing

Visual search of the environment is a fundamental human behavior that perceptual load affects powerfully. Previously investigated means for overcoming the inhibitions of high perceptual load, however, generalize poorly to real-world human behavior. We hypothesized that humans would process evolutionarily relevant stimuli more efficiently than evolutionarily novel stimuli, and evolutionary relevance would mitigate the repercussions of high perceptual load during visual search. Animacy is a significant component to evolutionary relevance of visual stimuli because perceiving animate entities is time-sensitive in ways that pose significant evolutionary consequences. Participants completing a visual search task located evolutionarily relevant and animate objects fastest and with the least impact of high perceptual load. Evolutionarily novel and inanimate objects were located slowest and with the highest impact of perceptual load. Evolutionary relevance may importantly affect everyday visual information processing.

Evolved Navigation Theory and Horizontal Visual Illusions.

Environmental perception is prerequisite to most vertebrate behavior and its modern investigation initiated the founding of experimental psychology. Navigation costs may affect environmental perception, such as overestimating distances while encumbered (Solomon, 1949). However, little is known about how this occurs in real-world navigation or how it may have evolved. We manipulated the most commonly navigated surfaces with a non-intuitive cost derived from evolved navigation theory. Observers in realistic settings unknowingly overestimated horizontal distances that contained a risk of falling and did so by the relative degree of falling risk. This manipulation produced previously unknown, large magnitude illusions in everyday vision in the environments most commonly navigated by humans. These results bear upon predictions from multiple fundamental theories of visual cognition.

Visual Field Dependence as a Navigational Strategy

Visual perception is an important component of environmental navigation. Previous research has revealed large individual differences in navigational strategies (i.e., the body’s kinesthetic and embodied approach to movement) and the perception of environmental surfaces (via distance estimations), but little research has investigated the potential relationship between these sources of individual variation. An important navigational strategy is the interaction between reliance on visual cues and vestibular or proprioceptive cues. We investigated the role of this navigational strategy in the perception of environmental surfaces. The results supported three embodied evolutionary predictions: Individuals who were most reliant on visual context (1) overestimated vertical surfaces significantly more, and (2) feared falling significantly more, than did those who were least reliant on visual context; and (3) all individuals had roughly accurate horizontal distance estimates, regardless of their navigational strategy. These are among the first data to suggest that individual differences in perception are closely related to the individual differences in navigation that derive from navigational risks. Variable navigational strategies may reflect variable capacities to perceive and navigate the environment.

Learning and exposure affect environmental perception less than evolutionary navigation costs.

Most behaviors are conditional upon successful navigation of the environment, which depends upon distance perception learned over repeated trials. Unfortunately, we understand little about how learning affects distance perception–especially in the most common human navigational scenario, that of adult navigation in familiar environments. Further, dominant theories predict mutually exclusive effects of learning on distance perception, especially when the risks or costs of navigation differ. We tested these competing predictions in four experiments in which we also presented evolutionarily relevant navigation costs. Methods included within- and between-subjects comparisons and longitudinal designs in laboratory and real-world settings. Data suggested that adult distance estimation rapidly reflects evolutionarily relevant navigation costs and repeated exposure does little to change this. Human distance perception may have evolved to reflect navigation costs quickly and reliably in order to provide a stable signal to other behaviors and with little regard for objective accuracy.

Preference for the nearer of otherwise equivalent navigational goals quantifies behavioral motivation and natural selection.

Navigation and environmental perception precede most actions in mobile organisms. Navigation is based upon the fundamental assumption of a ubiquitous Preference for the Nearest of otherwise equivalent navigational goals (PfN). However, the magnitude and triggers for PfN are unknown and there is no clear evidence that PfN exists. I tested for PfN in human participants on a retrieval task. Results of these experiments provide the first evidence for PfN. Further, these data quantify the three primary PfN triggers and provide an experimental structure for using PfN as a behavioral metric across domains. Surprisingly, PfN exists at a high, but not universal, magnitude. Further, PfN derives most from the absolute distance to the farthest of multiple goals (df), with little influence of the distance to the nearest goal (dn). These data provide previously unavailable quantification of behavioral motivation across species and may provide a measurable index of selection. These methods hold particular import for behavioral modification because proximity is a powerful determinant of decision outcomes across most behaviors.

Evolved navigation theory and the plateau illusion.

Most people anecdotally feel that the distance extending toward a cliff or slope appears shorter than the same distance extending away from it. This odd impression persists, despite the distance being equal across both conditions and humans encountering such a scenario daily in the navigation of stairs, slopes, curbs, and vertical surfaces protected by handrails. We tested three sets of competing predictions about this previously uninvestigated phenomenon. Data from two experiments coincided with the well-established predictions from evolved navigation theory. Contrary to anecdotal expectations, observers perceive the distance extending toward the edge of a steep slope to be longer than the distance extending away from it. We title this the plateau illusion and suggest that it may be an embodied process that arose over evolutionary time in response to navigation risks.