Perception Of Surface Orientation Research Articles

Pedal and haptic estimates of slant suggest a common underlying representation

It is well known that people verbally exaggerate the slant of visually perceived geographical, virtual, and man-made hills. More recently it has been shown that haptic and verbal estimates of slant result in similar exaggerations, supporting the proprioception calibration hypothesis—that similar biases exist in both verbal estimates of visually perceived slant and proprioceptively perceived hand orientation. This seems to point to a common underlying representation of slant.However, it is unclear if and how manual proprioceptive estimates might be relevant for perception of ground surface slant or how this might translate to pedal perception of surface orientation. In the current work we tested whether pedal perception is systematically connected to a representational system shared by haptic and visual perception. We did this by having people orient their foot to four different orientations of a ramp (Experiment 1) or to a staircase (Experiment 2) and compared these to estimates made using a free hand measure as well as to verbal estimates. Our results show that verbal, haptic, and pedal measures of visually perceived surface orientation all result in similar estimates of slant and do so across different slanted surfaces. This suggests that verbal and haptic proprioceptive estimates tap into a representational system of visually perceived surface orientation that is relevant for walking up various surface orientations.

Estimating 3D tilt from local image cues in natural scenes.

Estimating three-dimensional (3D) surface orientation (slant and tilt) is an important first step toward estimating 3D shape. Here, we examine how three local image cues from the same location (disparity gradient, luminance gradient, and dominant texture orientation) should be combined to estimate 3D tilt in natural scenes. We collected a database of natural stereoscopic images with precisely co-registered range images that provide the ground-truth distance at each pixel location. We then analyzed the relationship between ground-truth tilt and image cue values. Our analysis is free of assumptions about the joint probability distributions and yields the Bayes optimal estimates of tilt, given the cue values. Rich results emerge: (a) typical tilt estimates are only moderately accurate and strongly influenced by the cardinal bias in the prior probability distribution; (b) when cue values are similar, or when slant is greater than 40°, estimates are substantially more accurate; (c) when luminance and texture cues agree, they often veto the disparity cue, and when they disagree, they have little effect; and (d) simplifying assumptions common in the cue combination literature is often justified for estimating tilt in natural scenes. The fact that tilt estimates are typically not very accurate is consistent with subjective impressions from viewing small patches of natural scene. The fact that estimates are substantially more accurate for a subset of image locations is also consistent with subjective impressions and with the hypothesis that perceived surface orientation, at more global scales, is achieved by interpolation or extrapolation from estimates at key locations.

Non-informative components of retinal and extra-retinal signals affect perceived surface orientation from optic flow

Non-informative components of retinal and extra-retinal signals affect perceived surface orientation from optic flow

Non-informative components of retinal and extra-retinal signals affect perceived surface orientation from optic flow

Non-informative components of retinal and extra-retinal signals affect perceived surface orientation from optic flow

Manual matching of perceived surface orientation is affected by arm posture: evidence of calibration between proprioception and visual experience in near space

Proprioception of hand orientation (orientation production using the hand) is compared with manual matching of visual orientation (visual surface matching using the hand) in two experiments. In experiment 1, using self-selected arm postures, the proportions of wrist and elbow flexion spontaneously used to orient the pitch of the hand (20 and 80%, respectively) are relatively similar across both manual matching tasks and manual orientation production tasks for most participants. Proprioceptive error closely matched perceptual biases previously reported for visual orientation perception, suggesting calibration of proprioception to visual biases. A minority of participants, who attempted to use primarily wrist flexion while holding the forearm horizontal, performed poorly at the manual matching task, consistent with proprioceptive error caused by biomechanical constraints of their self-selected posture. In experiment 2, postural choices were constrained to primarily wrist or elbow flexion without imposing biomechanical constraints (using a raised forearm). Identical relative offsets were found between the two constraint groups in manual matching and manual orientation production. The results support two claims: (1) manual orientation matching to visual surfaces is based on manual proprioception and (2) calibration between visual and proprioceptive experiences guarantees relatively accurate manual matching for surfaces within reach, despite systematic visual biases in perceived surface orientation.

Depth cue combination in spontaneous eye movements

Where we look when we scan visual scenes to obtain an understanding of the 3D world around us is a question of interest for both fundamental and applied research. Recently, it has been shown that depth is an important variable in driving eye movements: the directions of saccades tend to follow depth gradients (Wexler (2008), Janssen (2009)). Whether saccades are aligned with a single depth cue or a combination of depth cues is still unknown. And, in the latter case, it is interesting to ask whether saccades are based on similar combination rules as those that apply to depth perception. Moreover, these scanning eye movements across different depth planes are composed of two distinct components: conjugate shifts of gaze (saccades) and disjunctive movements changing the depth of fixation (vergence). And the same questions about the effect of depth cues still apply to vergence: various studies have reported that vergence is guided by the consciously perceived depth percept, whereas others report that vergence is based on depth cue(s). Here we studied what depth information is used to plan both saccades and vergence. We showed observers surfaces inclined in depth, in which perspective and disparity defined different plane orientations (both small (0°-45°) and large (90°,180°) conflicts). Observers' eye movements were recorded binocularly, while they scanned the surface. After the stimulus presentation, observers reported the perceived surface orientation using a joystick. We found saccade directions and perceived surface orientation use the same pattern of depth cue combination: a weighted linear cue combination for small conflicts and cue dominance for large cue conflicts. The weights assigned to each cue varied across subjects, but were strongly correlated for perception and saccades, within subjects. This correlation was maintained while manipulating cue reliability. Vergence on the other hand was dominated by the disparity cue.

Depth cue combination in spontaneous eye movements

Where we look when we scan visual scenes is an old question that continues to inspire both fundamental and applied research. Recently, it has been reported that depth is an important variable in driving eye movements: the directions of spontaneous saccades tend to follow depth gradients, or, equivalently, surface tilts (L. Jansen, S. Onat, & P. König, 2009; M. Wexler & N. Ouarti, 2008). This has been found to hold for both simple and complex scenes and for a variety of depth cues. However, it is not known whether saccades are aligned with individual depth cues, or with a combination of depth cues. If saccades do follow a combination of depth cues, then it is interesting to ask whether this combination follows the same rules as the well-studied case of depth cue combination in conscious perception. We showed subjects surfaces inclined in depth, in which perspective and binocular disparity cues specified different plane orientations, with different degrees of both small and large conflict between the two sets of cues. We recorded subjects' spontaneous saccades while they scanned the scene, as well as their reports of perceived plane orientation. We found that distributions of spontaneous saccade directions followed the same pattern of depth cue combination as perceived surface orientation: a weighted linear combination of cues for small conflicts, and cue dominance for large conflicts. The weights assigned to the cues varied considerably from one subject to the next but were strongly correlated for saccades and perception; moreover, for both perception and saccades, cue weights could be modified by manipulating cue reliability in a way compatible with Bayesian theories of optimal cue combination. We also measured vergence, which allowed us to calculate the orientation of the plane fitted to points scanned in depth. Contrary to perception and saccades, vergence was dominated by a single cue, binocular disparity.

Controlled interaction: Strategies for using virtual reality to study perception

Immersive virtual reality systems employing head-mounted displays offer great promise for the investigation of perception and action, but there are well-documented limitations to most virtual reality systems. In the present article, we suggest strategies for studying perception/action interactions that try to depend on both scale-invariant metrics (such as power function exponents) and careful consideration of the requirements of the interactions under investigation. New data concerning the effect of pincushion distortion on the perception of surface orientation are presented, as well as data documenting the perception of dynamic distortions associated with head movements with uncorrected optics. A review of several successful uses of virtual reality to study the interaction of perception and action emphasizes scale-free analysis strategies that can achieve theoretical goals while minimizing assumptions about the accuracy of virtual simulations.

Aging and the perception of surface orientation

Aging and the perception of surface orientation

The role of spatial integration in the perception of surface orientation with active touch

Vision research has shown that perception of line orientation, in the fovea area, improves with line length (Westheimer & Ley, 1997). This suggests that the visual system may use spatial integration to improve perception of orientation. In the present experiments, we investigated the role of spatial integration in the perception of surface orientation using kinesthetic and proprioceptive information from shoulder and elbow. With their left index fingers, participants actively explored virtual slanted surfaces of different lengths and orientations, and were asked to reproduce an orientation or discriminate between two orientations. Results showed that reproduction errors and discrimination thresholds improve with surface length. This suggests that the proprioceptive shoulder-elbow system may integrate redundant spatial information resulting from extended arm movements to improve orientation judgments.

Depth cues, rather than perceived depth, govern vergence

We studied the influence of perceived surface orientation on vergence accompanying a saccade while viewing an ambiguous stimulus. We used the slant rivalry stimulus, in which perspective foreshortening and disparity specified opposite surface orientations. This rivalrous configuration induces alternations of perceived surface orientation, while the slant cues remain constant. Subjects were able to voluntarily control their perceptual state while viewing the ambiguous stimulus. They were asked to make a saccade across the perceived slanted surface. Our data show that vergence responses closely approximated the vergence response predicted by the disparity cue, irrespective of voluntarily controlled perceived orientation. However, comparing the data obtained while viewing the ambiguous stimulus with data from an unambiguous stimulus condition (when disparity and perspective specified similar surface orientations) revealed an effect of perspective cues on vergence. Collectively our results show that depth cues rather than perceived depth govern vergence.

The effect of perceived surface orientation on perceived surface albedo in binocularly viewed scenes.

We examined how observers discount perceived surface orientation in estimating perceived albedo (lightness). Observers viewed complex rendered scenes binocularly. The orientation of a test patch was defined by depth cues of binocular disparity and linear perspective. On each trial, observers first estimated the orientation of the test patch in the scene by means of a gradient probe and then matched its perceived albedo to a reference scale. We found that observers' perception of orientation was nearly veridical and that they substantially discounted perceived orientation in estimating perceived albedo.

Measuring perceived 3D shape at multiple spatial scales.

We present and test a novel multiscale representation of perceived 3D surface orientation: the orientation path. Using a multiscale probe, we measure perceived surface orientation at multiple spatial scales; linking the measurements for a given surface location yields that location's orientation path. The multiscale data obtained show that observers consistently see different surface orientations at different spatial scales. We demonstrate that such multiscale data can reveal multiscale differences between observers' percepts of a stimulus and the stimulus geometry. We also demonstrate the use of the orientation path in evaluating the multiscale effects of adding a depth cue to a 3D display.

Perceiving surface slant from deformation of optic flow.

Perceived surface orientation and angular velocity were investigated for orthographic projections of 3-D rotating random-dot planes. It was found that (a) tilt was accurately perceived and (b) slant and angular velocity were systematically misperceived. It was hypothesized that these misperceptions are the product of a heuristic analysis based on the deformation, one of the differential invariants of the first-order optic flow. According to this heuristic, surface attitude and angular velocity are recovered by determining the magnitudes of these parameters that most likely produce the deformation of the velocity field, under the assumption that all slant and angular velocity magnitudes have the same a priori probability. The results of the present investigation support this hypothesis. Residual orientation anisotropies not accounted for by the proposed heuristic were also found.

The Dominance of Static Depth Cues over Motion Parallax in the Perception of Surface Orientation

Under polar projection (the natural projection for visual scenes) motion parallax is a powerful cue specifying relative depth. For small-field stimuli, it is ambiguous in the sense that a concave surface can be perceived as convex and deforming. By contrast, concavity/convexity of wide-field surfaces is unambiguously perceived. This led us to hypothesise a critical role of the 3-D rigidity constraint for large visual scenes in motion (Dijkstra et al, 1995 Vision Research35 453 – 462). To examine this hypothesis, we exposed subjects to planes inclined in space, and asked them to report the tilt (direction of inclination). Depth was specified either by motion parallax (MP, the surface oscillated around a frontoparallel axis) or by static perspective cues (SP, orthogonal square grids drawn on the plane). At ECVP95, we had reported a predominance of SP over MP when the tilts specified by these two cues ( tMP and tSP respectively) differed (1995 Perception24 Supplement, 137). Since these results were obtained for fast movements (oscillation frequency for MP: 3.6 Hz), we extended our investigation to a slower frequency (0.5 Hz) which is more likely to be involved during natural head-movements. We found that: (i) errors in tilt reports were larger for MP than for SP, and decreased with increasing field-size; (ii) in the case of conflict ( tMP= tSP±90°), the reported tilt was either tMP or tSP, rather than an average of these two values; (iii) in this case, tilt was most often reported according to SP, rather than to MP cues; this effect occurred even when the accuracies for the two individual cues were similar. Therefore, in a conflict situation between MP and SP, surface orientation is reported according to a winner-take-all rule, which is largely in favour of static grid-cues. Hence, even for wide-field movements, the image contrast distribution can lead the visual system to prefer an unrigid, rather than rigid, solution to the 3-D shape-from-motion problem.

The perception of surface orientation from multiple sources of optical information

An orientation matching task was used to evaluate observers' sensitivity to local surface orientation at designated probe points on randomly shaped 3-D objects that were optically defined by texture, lambertian shading, or specular highlights. These surfaces could be stationary or in motion, and they could be viewed either monocularly or stereoscopically, in all possible combinations. It was found that the deformations of shading and/or highlights (either over time or between the two eyes' views) produced levels of performance similar to those obtained for the optical deformations of textured surfaces. These findings suggest that the human visual system utilizes a much richer array of optical information to support its perception of shape than is typically appreciated.