Emmert's law in the Ames room

The Ames distorted room illusion, in which the perceived sizes of objects placed within the room differ from their objective sizes, has been used to support arguments for indirect perception. A study is reported in which Emmert's law of the apparent size of after-images was examined in relation to the Ames room's illusory alteration of apparent and actual distances. Size judgments of afterimages projected into the Ames room were compared with control conditions in which both actual and apparent afterimage projection distances were reproduced. Results indicate that Emmert's law may not provide a simple geometrical relationship between proximal image size and actual viewing distance, and that the processes involved in making afterimage size judgments are similar to those processes involved in making size judgments of 'real world' objects.     

The Ames window illusion: perception of illusory motion by human infants

The sensitivity of human infants, 5 1/2-9 months of age, to the illusory oscillation of the Ames window was assessed in three experiments that employed some variant of the habituation-dishabituation and forced-choice preferential looking paradigms. In Experiment 1, three groups--5 1/2, 7 1/2, and 9 months of age--were given a visual choice between rotating rectangular and Ames windows after exposure to a rotating circular form. The two older groups preferred the Ames window. The results of Experiment 2 showed that this preference is not based on structural differences between the two windows. In Experiment 3, familiarization with an Ames window produced a preference for rotary motion while familiarization with a rectangular window produced a preference for oscillatory motion. These results suggest that sensitivity to the illusion emerges around 7 1/2 months of age, an outcome consistent with the emergence, at this time, of sensitivity to pictorial cues to depth.     

Perceived size and distance as a perceptual conflict between two processing modes

Three different sized squares were successively presented at the same physical distance under three observational conditions which provided different information about distance in the visual field. The 60 observers in each observational condition were asked to give verbal absolute judgments of perceived size and perceived distance for each of the squares. The results showed that in a full-cue situation a ratio of perceived absolute sizes is equal to that of the corresponding visual angles, with perceived distances appearing equal to each other; in a reduced-cue situation an object of smaller perceived size is judged to be farther away than one of larger perceived size, with the observers tending to assume the two objects as the same object or identically sized objects. These results were analyzed in terms of the perceptual conflict between primary perception and secondary perception.     

Effects of Perceived Space on Spatial Attention

Abstract—This study demonstrates that a perceptual illusion that alters the perceived length of two lines also affects spatial attention. We used a cuing method that was introduced to study space- versus object-based attention. Two parallel lines of equal length were placed so that the distance between them was equal to the length of the lines. We then added a scene with depth cues to produce a strong illusion that one line was longer than the other. The results showed that spatial attention is distributed in space as it is perceived and altered by perceptual organization. These data have implications for assumptions concerning the spatial medium that guides attention and the role of depth and distance cues in spatial orienting, as well as for understanding attentional systems related to neuropsychological functions that respond to space and objects.     

Size illusion, distance illusion, and terrestrial passage: comment on reed

Two assumptions of Reed's (1984) terrestrial passage theory are questioned. First, Reed assumes that the moon's failure to increase in visual subtense while elevating is accounted for strictly by perceptual distancing. This allows a formal account of the moon distance illusion, but at the expense of a compelling explanation of the moon size illusion. Second, in order to explain the distance illusion, Reed assumes that all objects, regardless of their perceived altitude, are perceived to start from a common point at the horizon. Several alternative application of Reed's terrestrial-passage foundation to the actual illusions are suggested.     

The misperception of rotary motion

Two principles for predicting the relative frequency of illusory reversals of rotating plane objects were derived and tested empirically. Ten objects, variously’ combining valid and confounding depth cues, were used. Predictions based on the principles were confirmed in every case. The results are offered as an improved explanation of the Ames trapezoid illusion and other illusions of rotary motion.     

Body-based perceptual rescaling revealed through the size-weight illusion

An embodied approach to the perception of spatial layout contends that the body is used as a 'perceptual ruler' with which individuals scale the perceived environmental layout. In support of this notion, previous research has shown that the perceived size of objects can be influenced by changes in the apparent size of hand. The size-weight illusion is a well known phenomenon, which occurs when people lift two objects of equal weight but differing sizes and perceive that the larger object feels lighter. Therefore, if apparent hand size influences perceived object size, it should also influence the object's perceived weight. In this study, we investigated this possibility by using perceived weight as a measure and found that changes in the apparent size of the hand influence objects' perceived weight.     

Seeing big things: overestimation of heights is greater for real objects than for objects in pictures

In six experiments we demonstrate that the vertical-horizontal illusion that is evoked when viewing photographs and line drawings is relatively small, whereas the magnitude of this illusion when large objects are viewed is at least twice as great. Furthermore, we show that the illusion is due more to vertical overestimation than horizontal underestimation. The lack of a difference in vertical overestimation between pictures and line drawings suggests that vertical overestimation in pictures depends solely on the perceived physical size of the projection on the picture surface, rather than on what is apparent about an object's represented size. The vertical-horizontal illusion is influenced by perceived physical size. It is greater when viewing large objects than small pictures of these same objects, even when visual angles are equated.     

The open-object illusion: size perception is greatly influenced by object boundaries

This study presents a new powerful visual illusion, in which simple “open” objects—ones with missing boundaries—are perceived as bigger than the same size, fully “closed” objects. In a series of experiments that employed a continuous-response adjustment procedure, it was found that the lack of vertical boundaries inflated the perceived width of an object, whereas the lack of horizontal boundaries inflated its perceived length. The effect was highly robust and it was replicated across different stimulus types and experimental parameters, with almost all observers exhibiting a strong effect. In contrast to the overestimation of the size of an object due to missing boundaries, the inclusion of inner boundaries within an object caused observers to underestimate its size, suggesting that filled space sometimes shrinks, rather than inflates, the perceived size of an object. The open-object illusion bears practical implications for graphics and design as well as important theoretical implications. Specifically, it indicates that the perception of an object’s area is not veridical but rather critically depends on contour closure. It is suggested that the visual system extends the missing boundaries of open contour objects, which results in an overestimation of the object’s size.     

Overestimation of the projected size of objects on the surface of mirrors and windows

Four experiments investigated judgments of the size of projections of objects on the glass surface of mirrors and windows. The authors tested different ways of explaining the task to overcome the difficulty that people had in understanding what the projection was, and they varied the distance of the observer and the object to the mirror or window and varied the size of the mirror. The authors compared estimations of projected size with estimations of the physical size of the object that produced the projection. For both mirrors and windows, observers accurately judged the physical size of objects but greatly overestimated the projected size of the same objects. Indeed, judgments of projected size were more similar to physical than to projected size. People were also questioned verbally about their knowledge of projected size relative to physical size. The errors produced for these conceptual questions were similar to those found in the perceptual estimation tasks. Together, these results suggest that projections of objects on mirrors and windows are treated in the same way and that observers cannot perceive such projections as distal objects.     

Objects, raised lines, and the haptic horizontal-vertical illusion

Experiments were conducted to determine whether the haptic horizontal-vertical illusion occurs with solid, three-dimensional objects as well as with tangible lines. The objects consisted of round or square bases, with dowel rods projecting above them at heights equal to the widths of the horizontal bases. A negative illusion, with overestimation of horizontals, was found with free haptic exploration, but not with tracing with the fingertip. The negative illusion occurred when subjects felt wooden Ls and inverted Ts with a grasping, pincers motion of the index finger and thumb. The presence or absence of illusory misperception was dependent upon exploration strategy, since the negative illusion vanished with finger tracing. A negative illusion was also found when subjects adjusted a vertical dowel so that it was judged to be equal in extent to a round or square base. A general overestimation of judged size derived from the pincers response measure, but was not found with the use of a tangible ruler. Comparable illusory results are most likely when drawings and objects promote similar haptic scanning methods. The results were consistent with the idea that the orientation of an edge or line is more important than whether one explores a tangible line or a three-dimensional object.     

Influence of visually induced expectation on perceived motor effort: A visual-proprioceptive interaction at the Santa Cruz Mystery Spot

It is known that dense objects seem heavier than larger, less dense objects of the same weight. We have investigated a related illusion, in which visual context biases the apparent weight of a single object. The apparatus is a cabin on a steep hillside near Santa Cruz, CA, tilted 17° from vertical. From its ceiling hangs a weight on a chain. The cabin’s tilt makes the weight appear suspended at an angle. Pushing the weight toward the visually based vertical is perceived as difficult, whereas pushing it away from the visual vertical is perceived as easy. Seven subjects pushed the weight in both directions, judging required effort on a double-anchored 1–10 scale. All experienced the effort illusion, with no significant subject effect. When subjects’ eyes were closed, the effect was smaller but still present. Apparently proprioceptive and skin inputs, equal for both directions, are ignored or underweighted as visually based expectations influence perceived effort.     

An empirical test of formal equivalence between Emmert's law and the size-distance invariance hypothesis

Emmert's law and the size-distance invariance hypothesis have been said to be formally equivalent, provided that Emmert's law means that the perceived size of an afterimage is proportional to the perceived distance of the projected surface of the afterimage. However, there have been very few studies that have attempted to verify this formal equivalence empirically. We measured both the perceived size and distance of afterimages and real objects with the same proximal size. Nineteen participants projected afterimages of 1 deg in visual angle on the wall located at distances of 1 to 23 meters from the participants. They also observed real objects, disc-shaped and made from a sheet of Styrofoam board, with the same proximal size as that of the afterimages, which were located at the same physical distances as those of the wall on which the afterimages were projected. Each participant reproduced the apparent sizes of the afterimages and real objects using the reproduction method and estimated the apparent distances using the magnitude estimation method. When the mean apparent sizes of the afterimages and real objects, represented as a function of apparent distance, were fitted to a linear function, the slopes for the afterimages and real objects did not differ significantly. These results are interpreted as evidence for the formal equivalence of Emmert's law and the size-distance invariance hypothesis.     

A Müller-Lyer-type illusion of egocentric distance with 3D convex and concave objects

An illusion of egocentric distance with concave and convex objects at a distance of 135 cm is reported. When the centre of a concave object was viewed with both eyes its surface appeared nearer than the centre of the surface of a convex object at the same distance. The distortion was about two per cent of the viewing distance with right-angle objects and about five per cent with hemicylindrical objects. The distortion was slightly reduced when size cues for distance were attached to the surfaces of the objects, absent with monocular viewing, greater with convex than with concave objects, and occurred with the generally convex surface of a model human face. Possible explanations of the findings are discussed.     

An airplane illusion: apparent velocity determined by apparent distance

When a small drone plane appears to be a normal-sized airplane, it appears to be very far away and moving too fast. This is the airplane illusion. In the illusory situation, familiar size determines the apparent size and distance of the plane. It sets the depth for the frontal-plane component of the perceived motion and the relative depth difference for the motion-in-depth component. Because these perceived distances are very large, the perceived velocities are very large in the respective directions. Cognition can override familiarity and produce a veridical perception of the drone.     

Seeing the body distorts tactile size perception

Vision of the body modulates somatosensation, even when entirely non-informative about stimulation. For example, seeing the body increases tactile spatial acuity, but reduces acute pain. While previous results demonstrate that vision of the body modulates somatosensory sensitivity, it is unknown whether vision also affects metric properties of touch, and if so how. This study investigated how non-informative vision of the body modulates tactile size perception. We used the mirror box illusion to induce the illusion that participants were directly seeing their stimulated left hand, though they actually saw their reflected right hand. We manipulated whether participants: (a) had the illusion of directly seeing their stimulated left hand, (b) had the illusion of seeing a non-body object at the same location, or (c) looked directly at their non-stimulated right-hand. Participants made verbal estimates of the perceived distance between two tactile stimuli presented simultaneously to the dorsum of the left hand, either 20, 30, or 40 mm apart. Vision of the body significantly reduced the perceived size of touch, compared to vision of the object or of the contralateral hand. In contrast, no apparent changes of perceived hand size were found. These results show that seeing the body distorts tactile size perception.     

Hefting for a maximum distance throw: a smart perceptual mechanism

Objects for throwing to a maximum distance were selected by hefting objects varying in size and weight. Preferred weights increased with size reproducing size-weight illusion scaling between weight and volume. In maximum distance throws, preferred objects were thrown the farthest. Throwing was related to hefting as a smart perceptual mechanism. Two strategies for conveying high kinetic energy to projectiles were investigated by studying the kinematics of hefting light, preferred, and heavy objects. Changes in tendon lengths occurring when objects of varying size were grasped corresponded to changes in stiffness at the wrist. Hefting with preferred objects produced an invariant phase between the wrist and elbow. This result corresponded to an optimal relation at peak kinetic energy for the hefting. A paradigm for the study of perceptual properties was compared to size-weight illusion methodology.     

The role of expectancies in the size-weight illusion: A review of theoretical and empirical arguments and a new explanation

The size–weight illusion (SWI) refers to the phenomenon that objects that are objectively equal in weight but different in size or volume are perceived to differ in weight, such that smaller objects feel heavier than larger ones. This article reviews studies trying to support three different viewpoints with respect to the role of expectancies in causing the SWI. The first viewpoint argues for a crucial role; the second admits a role, yet without seeing consequences for sensorimotor processes; and the third denies any causal role for expectancies at all. A new explanation of the SWI is proposed that can integrate the different arguments. A distinctive feature of the new explanation is that it recognizes the causal influence of expectancies, yet combines this with certain reactive and direct behavioral consequences of perceiving size differences that are independent of experience-based expectancies, and that normally result in the adaptive application of forces to lift or handle differently sized objects. The new account explains why the illusion is associated with the repeated generation of inappropriate lifting forces (which can, however, be modified through extensive training), as well as why it depends on continuous visual exposure to size cues, appears at an early age, and is cognitively impenetrable.     

The nature of adaptation in distance perception based on oculomotor cues

In previous work by the senior authors, brief adaptation to glasses that changed the accommodation and convergence with which objects were seen resulted in large alterations in size perception. Here, two further effects of such adaptation are reported: alterations in stereoscopic depth perception and a change when distance is represented by a response of S’s arm. We believe that the three effects are manifestations of one primary effect, an alteration of the relation between accommodation and convergence on the one hand and the distance they represent in the nervous system (registered distance) on the other. This view was supported by the results of two experiments, each of which demonstrated that the alterations in stereoscopic depth perception could be obtained after adaptation periods which had provided no opportunity to use stereoscopic vision, and that the adaptation effect was larger for depth perception than for size perception when it was obtained under the same conditions; the latter finding was expected if both effects resulted from the same change in registered distance. In three of the five experiments here reported, the variety of cues that could represent veridical distance during the adaptation period was limited. In one condition of adaptation, only the pattern of growth of the retinal images of objects that S approached and the kinesthetic cues for S’s locomotion served as cues to veridical distance. In two other conditions S remained immobile. In one of these, only the perspective distortion in the projection of the scene that S viewed mediated veridical distance, and in the other one familiar objects of normal size were successively illuminated in an otherwise totally dark field, conditions from which opportunities to use stereoscopic vision were again absent. After exposure to each of these adaptation conditions, adaptive changes in perceived size and larger ones in perceived stereoscopic depth were obtained. Because we found that familiar size may serve as the sole indicator of veridical distance in an adaptation process, we concluded that it can function as a perceptual as distinguished from an inferential cue to distance.     

Brightness contrast effects in a pupillometric experiment

The effect of depth displacement of test bars from the induction wedge of the Ponzo illusion was investigated in two experiments. Either two wedges of opposite orientation were presented simultaneously, one at a near and the other at a far distance, or only one wedge was presented at either the near or the far distance. The test bars were stereoscopically either in the plane of the wedge or displaced from the wedge in distance. When the two wedges were presented simultaneously, the direction of the Ponzo illusion was determined by the wedge at the same perceived distance as the test bars. When only one wedge was present, stereoscopic displacement of the bars in front of, but not behind, the wedge decreased the magnitude of the illusion. The results are interpreted in terms of the adjacency principle.