Perceived azimuth direction is exaggerated: Converging evidence from explicit and implicit measures

Abstract

Recent observations suggest that perceived visual direction in the sagittal plane (angular direction in elevation, both upward and downward from eye level) is exaggerated. Foley, Ribeiro-Filho, and Da Silva's (2004) study of perceived size of exocentric ground extent implies that perceived angular direction in azimuth may also be exaggerated. In the present study, we directly examined whether perceived azimuth direction is overestimated. In Experiment 1, numeric estimates of azimuth direction (−48° to 48° relative to straight ahead) were obtained. The results showed a linear exaggeration in perceived azimuth direction with a gain of about 1.26. In Experiment 2, a perceptual extent-matching task served as an implicit measure of perceived azimuth direction. Participants matched an egocentric distance in one direction to a frontal extent in nearly the opposite direction. The angular biases implied by the matching data well replicated Foley et al.'s finding and were also fairly consistent with the azimuth bias function found in Experiment 1, although a slight overall shift was observed between the results of the two experiments. Experiment 3, in which half the observers were tilted sideways while making frontal/depth extent comparisons, suggested that the discrepancy between the results of Experiment 1 and 2 can partially be explained by a retinal horizontal vertical illusion affecting distance estimation tasks. Overall the present study provides converging evidence to suggest that the perception of azimuth direction is overestimated.

Large perceptual distortions of locomotor action space occur in ground-based coordinates: Angular expansion and the large-scale horizontal-vertical illusion.

“…This is because the magnitude of the allocentric component for the three larger poles (i.e., 1.2 or ~20%) is quantitatively consistent with prior estimates of the difference in gain between the angular expansion gain for perceived elevation (1.5; Durgin & Li, 2011) and the angular expansion gain for perceived azimuth measured when the retinotopic HVI is taken into account (1.25; Li & Durgin, in press). That is, 1.5 divided by 1.25 equals 1.2, which predicts a 20% overestimation of height compared to width.…”

“…Asymmetric directional distortions can be used to quantitatively model downhill slope exaggeration (Li & Durgin, 2009), as well as a variety of ground-extent anisotropies (Durgin & Li, 2011, Foley et al, 2004; Li et al, 2011; Li et al, 2013; Li & Durgin, in press). Thus, the present study used mathematical modeling based on non-verbal techniques of parameter estimation to extend the explanatory scope of the AEH to the large-scale HVI.…”

“…The magnitude of the outdoor version of the illusion has been reported to be as high as 25% for large objects. We hypothesized that the magnitude of the large-scale object illusion may correspond to the quantitative difference between angular expansion gains measured for left/right (azimuthal) direction (1.2–1.3; Foley et al, 2004; Li & Durgin, in press; Li et al, 2013) and for up/down (elevation) direction (1.5; Durgin & Li, 2011). …”

Do Explicit Estimates of Angular Declination Become Ungrounded in the Presence of a Ground Plane?

“…In the present experiment, we presented a fixed reference ball at the top of a narrow pole that was positioned either very close, in depth, to the farthest ground target or far beyond it. If the distance in depth between the target and the reference is what primarily produces contamination, then angular estimates for the farthest targets (smallest angles) should differ as a function of the whether the 3D distance to the reference ball is small or large (see also Li & Durgin, 2016 , for a similar effect in judgments of azimuth).…”

Differential Angular Expansion in Perceived Direction in Azimuth and Elevation Are Yoked to the Presence of a Perceived Ground Plane

“…He observed that the perceived visual angle for large-scale vertical extents was greater than that for horizontal extents in a manner that might account for the large-scale horizontal-vertical illusion (HVI) [2,3,4]; Li and Durgin discovered that exaggeration in downhill slant perception was amplified by conditions that yoked it to an exaggerated perception of downward gaze direction or angular declination [5]. Durgin and Li ultimately showed that these exaggerations in perceived angular declination could quantitatively account for long-standing observations of explicit ground distance underestimation [6,7,8]. Indeed, Foley and colleagues [9] had interpreted underestimates of ground distance using the assumption that the effective (but not perceived) angular size of the ground extents, from the point of observation, was differentially exaggerated in azimuth and in elevation.…”