Egocentric and Exocentric Spatial Judgements of Visual Displacement

The role of changes in ego- and exocentric spatial relationships on perceptual judgements about visual displacement was investigated in this study. Subjects were asked to indicate whether a dot in a test stimulus was displaced compared to a dot in a reference stimulus. Subjects were given explicit instructions to report displacement relative to themselves (egocentric) or relative to a circle surrounding the dot (exocentric). Four types of test stimuli were used in which object-circle (exocentric) and object-observer (egocentric) relations were systematically varied. It was found that for test stimuli that reveal conflicting ego- and exocentric spatial information, subjects performed poorly in both instruction conditions. This suggests that ego- and exocentric representations cannot be used independently and are probably interconnected.     

空间场景表征中的参照系选取

被试在矩形房间中从两个不同的观察点学习物体场景并在多个朝向上对物体形成的空间关系进行判断,通过控制场景中物体主要内在轴相对于环境结构（房间和地毯）的方向和被试的学习顺序,探讨被试在场景空间表征中采用何种参照系和参照系选取时的影响因素。两个实验结果发现：（1）内在参照系（intrinsic reference systems）和环境参照系均可以用于物体场景的表征,两类参照系之间的关系却是影响被试物体场景表征时参照系选取的重要因素,即当内在参照系与环境参照系方向一致时,被试无论从哪个朝向学习,都选择从垂直于内在参照系和环境参照系的朝向进行表征。反之,当二者方向不一致时,表征时参照系的选择取决于被试的学习经历;（2）无论内在参照系与环境参照系方向是否一致,物体场景本身内在结构的规则性都能够促进空间记忆,即内在结构的规则性既有助于准确编码物体的相对位置,也有助于提高空间关系判断的准确性。     

The effects of healthy aging on mental imagery as revealed by egocentric and allocentric mental spatial transformations

Previous studies suggest that mental rotation can be accomplished by using different mental spatial transformations. When adopting the allocentric transformation, individuals imagine the stimulus rotation referring to its intrinsic coordinate frame, while when adopting the egocentric transformation they rely on multisensory and sensory-motor mechanisms. However, how these mental transformations evolve during healthy aging has received little attention. Here we investigated how visual, multisensory, and sensory-motor components of mental imagery change with normal aging. Fifteen elderly and 15 young participants were asked to perform two different laterality tasks within either an allocentric or an egocentric frame of reference. Participants had to judge either the handedness of a visual hand (egocentric task) or the location of a marker placed on the left or right side of the same visual hand (allocentric task). Both left and right hands were presented at various angular departures to the left, the right, or to the center of the screen. When performing the egocentric task, elderly participants were less accurate and slower for biomechanically awkward hand postures (i.e., lateral hand orientations). Their performance also decreased when stimuli were presented laterally. The findings revealed that healthy aging is associated with a specific degradation of sensory-motor mechanisms necessary to accomplish complex effector-centered mental transformations. Moreover, failure to find a difference in judging left or right hand laterality suggests that aging does not necessarily impair non-dominant hand sensory-motor programs.     

The underestimation of egocentric distance: evidence from frontal matching tasks

There is controversy over the existence, nature, and cause of error in egocentric distance judgments. One proposal is that the systematic biases often found in explicit judgments of egocentric distance along the ground may be related to recently observed biases in the perceived declination of gaze (Durgin & Li, Attention, Perception, & Psychophysics, in press), To measure perceived egocentric distance nonverbally, observers in a field were asked to position themselves so that their distance from one of two experimenters was equal to the frontal distance between the experimenters. Observers placed themselves too far away, consistent with egocentric distance underestimation. A similar experiment was conducted with vertical frontal extents. Both experiments were replicated in panoramic virtual reality. Perceived egocentric distance was quantitatively consistent with angular bias in perceived gaze declination (1.5 gain). Finally, an exocentric distance-matching task was contrasted with a variant of the egocentric matching task. The egocentric matching data approximate a constant compression of perceived egocentric distance with a power function exponent of nearly 1; exocentric matches had an exponent of about 0.67. The divergent pattern between egocentric and exocentric matches suggests that they depend on different visual cues.     

Perceptual reference points for form and orientation in young infants: anchors or magnets?

In some domains, certain stimuli are especially salient and efficiently encoded and are referred to as reference points. One current issue concerns whether reference points are associated with regions of increased or decreased discriminability and function as either perceptual anchors or magnets. In two experiments utilizing the familiarization/novelty-preference procedure, the question of whether 3- to 4-month-old infants' representations of form and orientation information are structured by perceptual reference points and whether such reference points serve as anchors or magnets is examined. In Experiment 1, infants displayed above-chance discrimination performance for pairs of form stimuli that were equivalently distinct on a physical basis, but only when one member of each pair was a "good" form (i.e., diamond, square, or triangle). In Experiment 2, infants displayed above-chance discrimination performance for pairs of stimuli differing by 7.5 degrees of orientation, but only when one member of each pair was either horizontal or vertical. The combined results from the two experiments suggest that "simple" gestalts and main axes (i.e., horizontal and vertical) serve as perceptual anchors in young infants' representations of form and orientation information.     

Identification of symmetry: Effects of stimulus orientation and head position

It has been argued that the perceptual advantage of symmetry depends upon the essentially symmetrical properties of the visual system. According to this explanation, the ease of identification of symmetries about different axes of orientation should decrease with increasing distance from the vertical: Reaction times to vertical symmetry should be faster than those to diagonal symmetry, which in turn should be faster than those to horizontal symmetry. Previous research demonstrating this pattern of responding employed stimuli with linear axes. In the present study, the subjects viewed tachistoscopically presented symmetrical and asymmetrical dot patterns (which had no explicit axes) in one of three head positions: upright, 45 deg left, and 45 deg right. The subjects’ performance failed to support the structural explanation: Identification of symmetry is equivalently fast for vertical and horizontal; vertical and horizontal show strong advantages over obliques, and this general advantage follows retinal coordinates. Findings are discussed in light of alternative theories of symmetry processing.     

Einstein’s jacket: Evidence for long-term perceptual specificity in mental imagery

To what extent are visual fantasies constrained by our perceptual experience of the real world? Our study exploits the fact that people’s knowledge of the appearance of individuals from the early 20th Century (e.g., Albert Einstein, Winston Churchill) derives predominantly from viewing black-and-white media images. An initial experiment shows that mental imagery for individuals from this period are experienced as significantly less colourful than imagery for individuals from the era of colour media. A second experiment manipulated whether participants were instructed to explicitly imagine using colour or not (i.e., “imagine Albert Einstein wearing a green jacket” vs. “imagine Albert Einstein wearing a jacket”). Results show that colour manipulation only influences imagery for black-and-white era individuals, with no comparable effect on imagery for colour era individuals. This finding is replicated in a third experiment that includes an additional control condition of imagining generic characters (i.e., “Imagine a knight wearing a cloak” vs. “imagine a knight wearing a red cloak”). Again, only imagery for black-and-white era individuals is affected by the colour manipulation. Overall these results provide evidence for long-term perceptual specificity effects in mental imagery. We argue that visual fantasies can be constrained by surface features of underlying representations in memory, even when imagining something we have never directly perceived.     

Reconstruction from the mental image

In three experiments young children were asked to reconstruct an array of objects after they had imagined its appearance following either a rotation of the array or a change in their own position (Huttenlocher & Presson, 1973). In reconstructing arrays, subjects first positioned that object which would be most prominent to an observer following the imagined transformation. Surprisingly, this occurred even when subjects made an egocentric error by reconstructing a copy of the original array. Hence young children, although apparently egocentric, can imagine themselves in a new position with a new perspective. The mental operations which underlie imagined spatial transformations are discussed in light of the results.     

Accurate motion-produced distance and direction under systematically distorted perception

Abstract:  We report the visually directed actions of soccer players. After perceiving the location of a target on their left side at the starting point and traveling toward the ball without seeing the target, the players could kick the ball accurately (Experiment 2). In contrast, if they were verbally asked the direction of the target in a similar situation, the perceived direction was systematically distorted (Experiment 3). Our major concern in explaining the distorted perception was whether the egocentric distance before locomotion was perceived accurately or not, and whether the updating of the target location during locomotion was accurate or not. Combining these two possibilities, there should be four hypotheses, each of which assumes either: (1) accurate egocentric distance and accurate updating, (2) inaccurate egocentric distance and accurate updating, (3) accurate egocentric distance and inaccurate updating, or (4) inaccurate egocentric distance and inaccurate updating. Based on these hypotheses, we conducted four simulations, which revealed that the combination of the perception of the accurate egocentric distance and the distorted updating that substituted the constant function for the sine function produced not only a good r ², but also three kinds of interactions obtained in Experiment 3. Why did the players, based on their distorted perception, perform accurately? We would like to suggest that through perceptual learning they might acquire a perceptual-motor relation as the inverse function of the physical-perceptual relation.     

Investigating the Relation between Imagery and Perception: Evidence from Face Priming

The relation between imagery and perception was investigated in face priming. Two experiments are reported in which subjects either saw or imagined the faces of celebrities. They were later given a speeded perceptual test (familiarity judgement to pictures of celebrities) or a speeded imagery test (in which they were told the names of celebrities and asked to make a decision about their appearance). Seeing faces primed the perceptual test, and imaging faces primed the imagery test; however, there was no priming between seeing and imaging faces. These results show that perception and imagery can be dissociated in normal subjects. In two further experiments, we examined the effects of imaging faces on a subsequent face-naming task and on a task requiring familiarity judgements to partial faces. Both these tasks were facilitated by prior imaging of faces. These results are discussed in relation to those of McDermott & Roediger (1994), who found that imagery promoted object priming in a perceptual test involving naming partial line drawings. The implications for models of face recognition are also discussed.     

Isolating observer-based reference directions in human spatial memory: head, body, and the self-to-array axis

Several lines of research have suggested the importance of egocentric reference systems for determining how the spatial properties of one's environment are mentally organized. Yet relatively little is known about the bases for egocentric reference systems in human spatial memory. In three experiments, we examine the relative importance of observer-based reference directions in human memory by controlling the orientation of head and body during acquisition. Experiment 1 suggests that spatial memory is organized by a head-aligned reference direction; however, Experiment 2 shows that a body-aligned reference direction can be more influential than a head-aligned direction when the axis defined by the relative positions of the observer and the learned environment (the "self-to-array" axis) is properly controlled. A third experiment shows that the self-to-array axis is distinct from - and can dominate - retina, head, and body-based egocentric reference systems.     

Spatial frameworks in imagined navigation

The spatial framework model proposes that people use the extensions of their body axes as a reference frame for encoding spatial layouts in memory, and that the physical and functional properties of our bodies and the world determine the accessibility of egocentric locations from memory representations. The present experiment provides evidence that spatial framework results can be obtained even with perceptual scenes that contain no objects to be held in memory. Using a paradigm in which participants interpreted direction and distance information to follow a mental path within a checkerboard grid, the present study shows that spatial framework results are obtained when reasoning occurs from a perspective that is misaligned with respect to the physical reference frame of the participant. The theoretical implications of these results are discussed.     

Systems of Spatial Reference in Human Memory

Seven experiments examined the spatial reference systems used in memory to represent the locations of objects in the environment. Participants learned the locations of common objects in a room and then made judgments of relative direction using their memories of the layout (e.g., "Imagine you are standing at the shoe, facing the lamp; point to the clock"). The experiments manipulated the number of views that observers were allowed to experience, the presence or absence of local and global reference systems (e.g., a rectangular mat on which objects were placed and the walls of the room, respectively), and the congruence of local and global reference systems. Judgments of relative direction were more accurate for imagined headings parallel to study views than for imagined headings parallel to novel views, even with up to three study views. However, study views misaligned with salient reference systems in the environment were not strongly represented if they were experienced in the context of aligned views. Novel views aligned with a local reference system were, under certain conditions, easier to imagine than were novel views misaligned with the local reference system. We propose that learning and remembering the spatial structure of the surrounding environment involves interpreting the layout in terms of a spatial reference system. This reference system is imposed on the environment but defined by egocentric experience.     

Attenuation of alignment effect with exocentric encoding of location

An object's location is best retrieved from the orientation in which it was learned. Otherwise, retrieval necessitates a mental effort to restore the original perspective. In this case there is a cost to speed and accuracy of location responses known as the alignment effect. We hypothesised that one can attenuate this alignment effect by systematically referring objects in an exocentric frame of reference during learning. Sixteen male students were asked to learn the location of five objects disposed in a totally new environment either by locating the objects in an egocentric or in an exocentric spatial frame of reference. After the learning phase, the participants were asked to imagine orienting themselves to an object in the scene and to point to another object. The analysis of pointing accuracy, orientation, and pointing times showed that the performances of participants engaged in the exocentric condition remained insensitive to the augmentation of the angle between their actual position on the path and the imagined orientation. On the other hand, the participants engaged in egocentric learning were disoriented when the difference between their actual orientation and the imagined orientation was great. We conclude that when an object's location is intentionally referred to in an exocentric reference frame, alignment effect can be significantly reduced.     

Neural correlates of the first-person-perspective

Human self-consciousness depends on the metarepresentation of mental and bodily states as one's own mental and bodily states. First-person-perspective taking is not sufficient, but necessary for human self-consciousness. To assign a first-person-perspective is to center one's own multimodal experiential space upon one's own body, thus operating in an egocentric reference frame. The brain regions involved in assigning first-person-perspective comprise medial prefrontal, medial parietal and lateral temporoparietal cortex. These empirical findings complement recent neurobiologically oriented theories of self-consciousness which focus on the relation between the subject and his/her environment by supplying a neural basis for its key components.     

Frames of reference in spatial memories acquired from language

Four experiments examined reference systems in spatial memories acquired from language. Participants read narratives that located 4 objects in canonical (front, back, left, right) or noncanonical (left front, right front, left back, right back) positions around them. Participants' focus of attention was first set on each of the 4 objects, and then they were asked to report the name of the object at the location indicated by a direction word or an iconic arrow. The results indicated that spatial memories were represented in terms of intrinsic (object-to-object) reference systems, which were selected using egocentric cues (e.g., alignment with body axes). Results also indicated that linguistic direction cues were comprehended in terms of egocentric reference systems, whereas iconic arrows were not.     

Disowning one's seen real body during an out-of-body illusion

Under normal circumstances, we experience that our center of awareness is located behind our eyes and inside our own body. To learn more about the perceptual processes that underlie this tight coupling between the spatial dimensions of our consciously perceived self and our physical body, we conducted a series of experiments using an 'out-of-body illusion'. In this illusion, the conscious sense of self is displaced in the testing room by experimental manipulation of the congruency of visual and tactile information and a change in the visual perspective. We demonstrate that when healthy individuals experience that they are located in a different place from their real body, they disown this body and no longer perceive it as part of themselves. Our findings are important because they reveal a relationship between the representation of self-location in the local environment and the multisensory representation of one's own body.     

Imagined body orientation and perception of the visual vertical

The existence of body orientation mental imagery was tested by examining whether self roll tilt imagery affects the subjective visual vertical (SVV). Twenty healthy subjects judged the orientation of a dim luminous bar with respect to gravitational vertical, while normally seated in complete darkness with their head firmly restrained earth vertically. SVV was measured in three conditions: a reference condition with no imagery, and a left and a right imagery condition, during which the bar orientation was to be judged while the subjects imagine themselves roll-tilted towards left or right, respectively. The imagined roll tilts were of the same magnitude as roll tilts which generally induce an E- effect, i.e., an SVV lean toward the side opposite to those of body tilt. If imagery and perception of self roll tilt share common processes, self roll tilt imagery should induce an E-like effect. Results show an imagery- induced E-like effect, which strongly supports the idea that humans can perform mental imagery of body orientation about gravity. Received: 4 April 2000 / Accepted: 1 September 2000