Full-cue Conditions Research Articles

"Impossible" Somatosensation and the (Ir)rationality of Perception.

Impossible figures represent the world in ways it cannot be. From the work of M. C. Escher to any popular perception textbook, such experiences show how some principles of mental processing can be so entrenched and inflexible as to produce absurd and even incoherent outcomes that could not occur in reality. However, impossible experiences of this sort are mostly limited to visual perception; are there “impossible figures” for other sensory modalities? Here, we import a known magic trick into the laboratory to report and investigate an impossible experience for somatosensation—one that can be physically felt. We show that, even under full-cue conditions with objects that can be freely inspected, subjects can be made to experience a single object alone as feeling heavier than a group of objects that includes the single object as a member—an impossible and phenomenologically striking experience of weight. Moreover, we suggest that this phenomenon—a special case of the size-weight illusion—reflects a kind of “anti-Bayesian” perceptual updating that amplifies a challenge to rational models of perception and cognition.

Sustained representation of perspectival shape

Arguably the most foundational principle in perception research is that our experience of the world goes beyond the retinal image; we perceive the distal environment itself, not the proximal stimulation it causes. Shape may be the paradigm case of such "unconscious inference": When a coin is rotated in depth, we infer the circular object it truly is, discarding the perspectival ellipse projected on our eyes. But is this really the fate of such perspectival shapes? Or does a tilted coin retain an elliptical appearance even when we know it's circular? This question has generated heated debate from Locke and Hume to the present; but whereas extant arguments rely primarily on introspection, this problem is also open to empirical test. If tilted coins bear a representational similarity to elliptical objects, then a circular coin should, when rotated, impair search for a distal ellipse. Here, nine experiments demonstrate that this is so, suggesting that perspectival shapes persist in the mind far longer than traditionally assumed. Subjects saw search arrays of three-dimensional "coins," and simply had to locate a distally elliptical coin. Surprisingly, rotated circular coins slowed search for elliptical targets, even when subjects clearly knew the rotated coins were circular. This pattern arose with static and dynamic cues, couldn't be explained by strategic responding or unfamiliarity, generalized across shape classes, and occurred even with sustained viewing. Finally, these effects extended beyond artificial displays to real-world objects viewed in naturalistic, full-cue conditions. We conclude that objects have a remarkably persistent dual character: their objective shape "out there," and their perspectival shape "from here."

Blind-Walking Behavior in the Dark Affected by Previewing the Testing Space.

Visual environments affect egocentric distance perceptions in full cue conditions. In this study, the effect of three spatial layouts was tested on the perceived location of a self-illuminated single target viewed in the dark. Blind-walking (BW) estimates of target distance were underestimated in all testing spaces, as expected, but foreshortened significantly more in the shortest of the three testing rooms. Additional experiments revealed that neither changes in the perceived angle of declination nor perceived eye height were responsible for this effect. The possibility that subjects made cognitive adjustments to BW behavior to reduce physical risk was assessed by remeasuring target locations in the three different locations with magnitude estimation and by comparing the BW results obtained from subjects who had no preview of the testing space with those who had. The results support the conclusion that the effect of spatial layout is likely due to cognitive adjustments to BW behavior. The results also indicate that the perceived angle of declination is always overestimated by at least a factor of 1.5. These results can be interpreted within the context of a theory of space perception called the angular expansion theory (AET).

A construção da experiência perceptiva: o que isso quer dizer?

Classical constructivists such as Rock and Hoffman contend that the processes of perception are intelligent and construct perceptual experience by going beyond the stimulus information or by creating a percept that deviates from the physical properties of the object. On these terms, Gibson’s theory of perception is anti-constructivist. After reviewing classical constructivism, this article maintains, first, that the phenomenology of visual space shows a deviation from physical spatial properties, by being contracted in depth, even under fullcue conditions, a fact that makes trouble for Gibson’s version of direct realism. Second, independently of the first argument, it contends that perception is pervasively constructed in the sense that stimulus information must be transformed to yield perception. Accordingly, perception is radically constructed in its very bones.

Solid shape discrimination from vision and haptics: natural objects (Capsicum annuum) and Gibson’s “feelies”

A set of three experiments evaluated 96 participants' ability to visually and haptically discriminate solid object shape. In the past, some researchers have found haptic shape discrimination to be substantially inferior to visual shape discrimination, while other researchers have found haptics and vision to be essentially equivalent. A primary goal of the present study was to understand these discrepant past findings and to determine the true capabilities of the haptic system. All experiments used the same task (same vs. different shape discrimination) and stimulus objects (James Gibson's "feelies" and a set of naturally shaped objects--bell peppers). However, the methodology varied across experiments. Experiment 1 used random 3-dimensional (3-D) orientations of the stimulus objects, and the conditions were full-cue (active manipulation of objects and rotation of the visual objects in depth). Experiment 2 restricted the 3-D orientations of the stimulus objects and limited the haptic and visual information available to the participants. Experiment 3 compared restricted and full-cue conditions using random 3-D orientations. We replicated both previous findings in the current study. When we restricted visual and haptic information (and placed the stimulus objects in the same orientation on every trial), the participants' visual performance was superior to that obtained for haptics (replicating the earlier findings of Davidson et al. in Percept Psychophys 15(3):539-543, 1974). When the circumstances resembled those of ordinary life (e.g., participants able to actively manipulate objects and see them from a variety of perspectives), we found no significant difference between visual and haptic solid shape discrimination.

Balanced Dopamine Is Critical for Pattern Completion during Associative Memory Recall

Pattern completion, the ability to retrieve complete memories initiated by partial cues, is a critical feature of the memory process. However, little is known regarding the molecular and cellular mechanisms underlying this process. To study the role of dopamine in memory recall, we have analyzed dopamine transporter heterozygous knockout mice (DAT+/−), and found that while these mice possess normal learning, consolidation, and memory recall under full cue conditions, they exhibit specific deficits in pattern completion under partial cue condition. This form of memory recall deficit in the dopamine transporter heterozygous knockout mice can be reversed by a low dose of the dopamine antagonist haloperidol, further confirming that the inability to retrieve memory patterns is a result of dopamine imbalance. Therefore, our results reveal that a delicate control of the brain's dopamine level is critical for pattern completion during associative memory recall.

Slant perception in near space is categorically biased: Evidence for a vertical tendency

The geographical slants of hills are known to appear quite exaggerated. Here, we examine the visual and haptic perception of the geographical slant of surfaces within reach under full-cue conditions and show that the perceived orientation of even these surfaces is biased. An exaggeration with respect to deviations from horizontal is shown to be present cross-modally. Experiment 1 employed numerical estimation to show the effect for visually observed surfaces, while controlling for verbal numerical bias. Experiment 2 demonstrated that the bias is present even when manual measures show good calibration. Experiment 3 controlled for direction of gaze. Experiment 4 measured the same bias for haptic surfaces. Experiment 5 showed that the bias can also be observed using the nonnumeric task of angle bisection. These results constrain theories of geographical slant perception and appear most consistent with functional scale expansion of deviations from horizontal.

Cue use under full cue conditions cannot be inferred from use under controlled conditions

Cue use under full cue conditions cannot be inferred from use under controlled conditions

The effects of restricted viewing conditions on egocentric distance judgments

Egocentric distance perception under full-cue conditions has been shown to be accurate as revealed though visually directed action tasks. The present studies assessed the necessity of 1) binocular disparity, 2) full field of view and 3) seeing one's body standing on the ground plane, for accurate scaling of egocentric space at distances from 5 to 15 meters. An investigation of these viewing conditions is especially relevant to space perception in virtual environments in which restrictions are often present, and distance compression has been found. We provided complete pictorial depth cues (e.g., linear perspective, height in the plane, horizon ratio, familiar size) but restricted viewing conditions in a real-world egocentric distance judgment task. Participants walked to previously viewed targets on the ground plane at distances ranging from 5 to 15 meters using both direct and indirect walking tasks. The first study varied whether participants were able to view the supporting surface on which they were standing. Observers wore an occluding collar designed to block the view of their lower body and feet while viewing the target. A second study examined the influence of stereo over monocular viewing. A final study utilized three conditions varying field of view and restricting observers' ability to rotate their head. Vision was not restricted in the first condition. In the second condition, observers wore goggles to restrict field of view and could rotate their heads while viewing the target. In the third condition, observers wore the same goggles along with a cervical collar which constrained both head motion and the view of their feet on the ground. In all studies and all conditions, visually directed walking remained near veridical. These results emphasize the lack of influence of viewing restrictions on accurate egocentric distance judgments within 5 to 15 meters in the real-world and leave open the question of the factors influencing distance judgments in virtual environments.

The accuracy of metric judgements: Perception of surface normal

Observers adjusted a probe (a short rod) to appear normal to a planar surface slanted in depth. In Experiment 1, observers (N=12) performed this metric task in two conditions: with reduced cues to calibration of binocular viewing parameters and with full cues. The results provided evidence for the use of an internal working metric in metric tasks because they confirm predictions that (i) errors should be largely systematic and accounted for by assuming an inaccurate working metric and (ii) this metric should be consistent with miscalibration of relevant viewing parameters. The data support the prediction that performance errors decrease in a manner consistent with improved binocular calibration, when better cues to relevant viewing parameters are provided. We performed two additional control experiments as further tests of the binocular miscalibration account, to determine whether performance in Experiment 1 could be explained instead by the use of monocular cues. We found that monocular performance was significantly poorer than binocular performance in reduced-cue conditions (Experiment 2) and full-cue conditions (Experiment 3). These control experiments provide confirmation that binocular cues contribute to performance in the full-cue conditions of Experiment 1, and that disparity was the only effective cue to slant in reduced-cue conditions.

Ontological issues in distance perception: Cue use under full cue conditions cannot be inferred from use under controlled conditions

Phosphorescent square tiles (arranged to yield a single image size) were viewed in the dark by 56 monocular observers who utilized a chinrest. The targets were placed at one of three horizontal distances and at one of three eye heights, allowing us to study the relative effect of height in the visual field (HVF) and sagittal distance on observers' verbal reports of the horizontal distance at which the object lay (near, middle, or far). In Experiment 1, we found that reports covaried primarily with HVF and, as predicted, they exhibited a weak paradoxical inverse relation with horizontal distance. In a second and third experiment, a visible surface was placed under the targets at the three eye heights in both dark and fully lighted conditions. In this situation, the inverse distance relation disappeared, and HVF no longer influenced the judgments of most observers. The results show that information projected from relevant support surfaces is essential for veridical information about object distance. These results raise fundamental issues for perceptual researchers regarding how to decide when a cue has been properly delineated, given the assumption that the relation between a cue and what it specifies is probabilistic.

Dissociation between Visual Perception of Allocentric Distance and Visually Directed Walking of its Extent

Walking without vision to previously viewed targets was compared with visual perception of allocentric distance in two experiments. Experimental evidence had shown that physically equal distances in a sagittal plane on the ground were perceptually underestimated as compared with those in a frontoparallel plane, even under full-cue conditions. In spite of this perceptual anisotropy of space, Loomis et al (1992 Journal of Experimental Psychology. Human Perception and Performance 18 906-921) found that subjects could match both types of distances in a blind-walking task. In experiment 1 of the present study, subjects were required to reproduce the extent of allocentric distance between two targets by either walking towards the targets, or by walking in a direction incompatible with the locations of the targets. The latter condition required subjects to derive an accurate allocentric distance from information based on the perceived locations of the two targets. The walked distance in the two conditions was almost identical whether the two targets were presented in depth (depth-presentation condition) or in the frontoparallel plane (width-presentation condition). The results of a perceptual-matching task showed that the depth distances had to be much greater than the width distances in order to be judged to be equal in length (depth compression). In experiment 2, subjects were required to reproduce the extent of allocentric distance from the viewing point by blindly walking in a direction other than toward the targets. The walked distance in the depth-presentation condition was shorter than that in the width-presentation condition. This anisotropy in motor responses, however, was mainly caused by apparent overestimation of length oriented in width, not by depth compression. In addition, the walked distances were much better scaled than those in experiment 1. These results suggest that the perceptual and motor systems share a common representation of the location of targets, whereas a dissociation in allocentric distance exists between the two systems in full-cue conditions.

Depth-dependent contrast gain-control

Contrast adaptation that was limited to a small region of the peripheral retina was induced as observers viewed a multiple depth-plane textured surface. The small region undergoing contrast adaptation was present only in one depth-plane to determine whether contrast gain-control is depth-dependent. After adaptation, observers performed a contrast-matching task in both the adapted and a non-adapted depth-plane to measure the magnitude and spatial specificity of contrast adaptation. Results indicated that contrast adaptation was depth-dependent under full-cue (disparity, linear perspective, texture gradient) conditions; there was a highly significant change in contrast gain in the depth-plane of adaptation and no significant gain change in the unadapted depth-plane. A second experiment showed that under some monocular viewing conditions a similar change in contrast gain was present in the adapted depth-plane despite the absence of disparity information for depth. Two control experiments with no-depth displays showed that contrast adaptation can also be texture- and location-dependent, but the magnitude of these effects was significantly smaller than the depth-dependent effect. These results demonstrate that mechanisms of contrast adaptation are conditioned by 3-D and 2-D viewing contexts.

Pappus in optical space.

Optical space differs from physical space. The structure of optical space has generally been assumed to be metrical. In contradistinction, we do not assume any metric, but only incidence relations (i.e., we assume that optical points and lines exist and that two points define a unique line, and two lines a unique point). (The incidence relations have generally been assumed implicitly by earlier authors.) The condition that makes such an incidence structure into a projective space is the Pappus condition. The Pappus condition describes a projective relation between three collinear triples of points, whose validity can--in principle--be verified empirically. The Pappus condition is a necessary condition for optical space to be a homogeneous space (Lobatchevski hyperbolic or Riemann elliptic space) as assumed by, for example, the well-known Luneburg theory. We test the Pappus condition in a full-cue situation (open field, broad daylight, distances of up to 20 m, visual fields of up to 160 degrees diameter). We found that although optical space is definitely not veridical, even under full-cue conditions, violations of the Pappus condition are the exception. Apparently optical space is not totally different from a homogeneous space, although it is in no way close to Euclidean.

Ordinal depth information from accommodation?

The ability to judge egocentric distance was assessed in two groups of six observers using a manual pointing task. The purpose of the study was to determine the extent to which blur-driven accommodation can provide information on target distance in the absence of any retinal cues to distance. Observers were extremely accurate when carrying out the pointing task in a ‘fullcue’ condition. In contrast, observers were extremely poor at carrying out the task when accommodation was the only distance cue available. Responses on individual trials bore little relationship to the actual target distance in any of the observers. On the other hand, accommodation weakly biased the mean responses in some observers. This bias appears to be due to the observers' effective use of accommodation to determine whether the target presented in one trial was nearer or further away than the target presented in the previous trial. Accommodation therefore appears to provide ordinal information, although the distance signal may actually arise from accommodation-driven vergence. The poverty of accommodation as a source of metric information was highlighted in a second group of observers who all demonstrated a strong bias when perceiving distance in the presence of an initially ambiguous retinal cue. It is concluded that accommodation can act as a source of ordinal distance information in the absence of other cues to distance but the contribution of accommodation to normal distance perception in full-cue conditions is questioned.

Cues to Viewing Distance for Stereoscopic Depth Constancy

A veridical estimate of viewing distance is required in order to determine the metric structure of objects from binocular stereopsis. One example of a judgment of metric structure, which we used in our experiment, is the apparently circular cylinder task (E B Johnston, 1991 Vision Research 31 1351-1360). Most studies report underconstancy in this task when the stimulus is defined purely by binocular disparities. We examined the effect of two factors on performance: (i) the richness of the cues to viewing distance (using either a naturalistic setting with many cues to viewing distance or a condition in which the room and the monitors were obscured from view), and (ii) the range of stimulus disparities (cylinder depths) presented during an experimental run. We tested both experienced subjects (who had performed the task many times before under full-cue conditions) and naïve subjects. Depth constancy was reduced for the naïve subjects (from 62% to 46%) when the position of the monitors was obscured. Under similar conditions, the experienced subjects showed no reduction in constancy. In a second experiment, using a forced-choice method of constant stimuli, we found that depth constancy was reduced from 64% to 23% in naïve subjects and from 77% to 55% in experienced subjects when the same set of images was presented at all viewing distances rather than using a set of stimulus disparities proportional to the correct setting. One possible explanation of these results is that, under reduced-cue conditions, the range of disparities presented is used by the visual system as a cue to viewing distance.

The visual perception of three-dimensional length.

A set of 4 experiments evaluated observers' sensitivity to three-dimensional (3-D) length, using both discrimination and adjustment paradigms with computer-generated optical patterns and real objects viewed directly in a natural environment. Although observers were highly sensitive to small differences in two-dimensional length for line segments presented in the frontoparallel plane, their discrimination thresholds increased by an order of magnitude when the line segments were presented at random orientations in 3-D space. There were also large failures of constancy, such that the perception of 3-D length varied systematically with viewing distance, even under full-cue conditions.

The Visual Discrimination of Relative Surface Orientation

In a series of three experiments, observers' discrimination thresholds for relative surface orientation were measured under full cue conditions, in which surfaces were specified by multiple sources of optical information including shading, texture, motion, and binocular disparity. The results revealed that observers' sensitivity to relative surface orientation varies for different types of structural configuration. Weber fractions were approximately 8% for planar patches connected to form a dihedral angle. They increased to 11% for planar patches that were spatially separated, and jumped to over 26% for patches that were part of a smoothly curved surface.

Distortions of Three-Dimensional Space in the Perceptual Analysis of Motion and Stereo

A fundamental issue in the study of human vision is the accuracy with which observers can perceive the three-dimensional structures of objects in the environment. The formal mapping from physical to perceived space is considered as a geometric transformation, and the literature is reviewed to identify which aspects of object structure are systematically distorted by this transformation and which ones remain invariant. In the perceptual analysis of several different sources of optical information, including motion and stereo, both individually and in combination, there is a consistent pattern of results to indicate that perceived depth intervals are scaled differently from comparable intervals in either horizontal or vertical directions. These and other findings provide strong evidence that the relationship between physical and perceived space is noneuclidean, and that the three-dimensional structures of objects can appear systematically distorted even when viewed under full cue conditions.

Familiar size and judgments of distance: Effects of response mode

Two methods of assessing the perceived egocentric distance of a familiar object presented under full-cue conditions were compared. Familiar size modified verbal estimates of distance but did not affect ratio distance judgments, a less direct measure of perceived distance. In addition, familiar size failed to affect size estimates of an unfamiliar target present in the visual field. These results are consistent with the claim that many of the reported findings indicating an effect of familiar size on direct scalar judgments of egocentric distance may represent a cognitive rather than a perceptual response of the distance of the familiar target.