The egocentric reference for visual exploration and orientation

Clinical signs of damage to the egocentric reference system range from the inability to detect stimuli in the real environment to a defect in recovering items from an internal representation. Despite clinical dissociations, current interpretations consider all symptoms as due to a single perturbation, differentially expressed according to the medium explored (perceptual or representational). We propose an alternative account based on the functional distinction between two separate egocentric mechanisms: one allowing construction of the immediate point of view, the other extracting a required perspective within a mental representation. Support to this claim comes from recent results in the domain of navigation, showing that separate cognitive mechanisms maintain the egocentric reference when actively exploring the visual space as opposed to moving according to an internal map. These mechanisms likely follow separate developmental pathways, seemingly depend on distinct neural pathways and are used independently by healthy adults, reflecting task demands and individual cognitive style. Implications for spatial cognition and social skills are discussed.     

Spatial orientation of a limb using egocentric reference points

Testing the hypothesis that spatial localization can be based on an abstracted spatial location code, rather than on stored proprioceptive information, orientation of an unseen limb was contrasted under intra- and interlimb-movement conditions. In Experiment 1, movements were executed in the midline either vertically upward or horizontally forward in the sagittal plane. These results revealed that intralimb errors were smaller than interlimb errors only at the most distant criterion spatial targets, and it was hypothesized that positioning of a limb could be mediated by a spatial location code if spatial targets were coded in association with body reference points. Experiment 2 tested the egocentric referent hypothesis further by manipulating the availability of body-based spatial reference points under intra- and interlimb conditions. At spatial targets that could be coded in conjunction with body reference points, no difference was found between intra- and interlimb accuracy. In contrast, at spatial targets where body reference points were absent, or at least made difficult to rely on, accuracy was greater in the intralimb condition. It was concluded that spatial reference points, in this instance body-based, are necessary if the spatial positioning of a limb is to be based on the spatial location code. The data were also discussed within a more comprehensive framework of spatial frames of reference.     

Binocular distance perception: egocentric distance tasks

This study extends and tests a theory of binocular distance perception that has been shown to give a good account of performance in relative distance tasks. Here the theory is tested in two experiments in which the observer directly indicates perceived egocentric distance of targets (perceived distance from himself or herself) by means of a verbal report or manual pointing response. In the first, the distance to two targets is varied while maintaining a constant disparity between them. In the second, one target is held fixed while the distance to a second target is varied. In each case, the observer indicates the perceived distance of each target. Manual and verbal responses are found to agree with each other to within a linear transform. Both sets of data are shown to be consistent with the theory and are used to estimate the parameters of the theory. There is no other theory that predicts these results.     

The Ponzo illusion and the perception of orientation

A new theory, called the tilt constancy theory, claims that the Ponzo illusion is caused by the misperception of orientation induced by local visual cues. The theory relates the Ponzo illusion-along with the Z?llner, Poggendorff, Wündt-Hering, and cafe wall illusions-to the mechanisms that enable us to perceive stable orientations despite changes in retinal orientation or body orientation. In Experiment 1, the magnitude of the misperception of orientation was compared with the magnitude of the Ponzo illusion. In Experiment 2, predictions of the tilt constancy theory were compared with accounts based on (1) low spatial frequencies in the image, (2) memory comparisons (pool-and-store model), and (3) relative sizejudgments. In Experiment 3, predictions of the tilt constancy theory were tested against predictions of the assimilation theory of Pressey and his colleagues. In the final experiment, the orientation account was compared with theories based on linear perspective and inappropriate size constancy. The results support the tilt constancy theory.     

Absolute and relative cues for the auditory perception of egocentric distance

Three experiments were performed to examine the reverberation cue to egocentric auditory distance and to determine the extent to which such a cue could provide 'absolute', as contrasted with 'relative', information about distance. In experiment 1 independent groups of blindfolded observers (200 altogether) were presented with broadband noise from a speaker at one of five different distances (0.55 to 8 m) in a normal hard-walled room. Half of each group of observers were presented with the sound at 0 deg azimuth, followed (after a delay) by the identical sound at 90 deg azimuth. The order of presentation was reversed for the remaining observers. Perceived distance varied significantly as a function of the physical distance to the speaker, even for the first presentations. The change in the binaural information between the 0 deg and 90 deg presentations did not significantly modify the results. For both orientations, near distances were overestimated and far distances were underestimated. Experiment 2 and 3 were designed to evaluate how much prior auditory exposure to the laboratory environment was necessary. A 200 Hz square-wave signal was presented from one of three distances (1, 2, or 6 m) to observers who had either minimal room information or an exposure which included talking within the room. Perceived distance varied significantly with physical distance regardless to exposure condition.     

Short-lived effects of a visual inducer during egocentric space perception and manual behavior

A pitched visual inducer has a strong effect on the visually perceived elevation of a target in extrapersonal space, and also on the elevation of the arm when a subject points with an unseen arm to the target’s elevation. The manual effect is a systematic function of hand-to-body distance (Li and Matin Vision Research 45:533–550, 2005): When the arm is fully extended, manual responses to perceptually mislocalized luminous targets are veridical; when the arm is close to the body, gross matching errors occur. In the present experiments, we measured this hand-to-body distance effect during the presence of a pitched visual inducer and after inducer offset, using three values of hand-to-body distance (0, 40, and 70 cm) and two open-loop tasks (pointing to the perceived elevation of a target at true eye level and setting the height of the arm to match the elevation). We also measured manual behavior when subjects were instructed to point horizontally under induction and after inducer offset (no visual target at any time). In all cases, the hand-to-body distance effect disappeared shortly after inducer offset. We suggest that the rapid disappearance of the distance effect is a manifestation of processes in the dorsal visual stream that are involved in updating short-lived representations of the arm in egocentric visual perception and manual behavior.     

Intensity and reverberation as factors in the auditory perception of egocentric distance

Both auditory intensity and reverberation have previously been shown to be sufficient to produce systematically varying judgments of perceived distance when several values of the variable are presented repeatedly to the same observer. Such studies do not, however, indicate clearly whether these cues are functioning in an absolute or in a relative manner. An absolute cue to auditory distance would require that two groups presented with different values of the variable in question should report different values of perceived distance. Two experiments are reported in which intensity variation and reverberation are examined. The results showed that auditory intensity differences over a range of 20 dB did not serve as an absolute cue to auditory distance, but could serve as a strong cue to changes in such distance. A comparison of data obtained in a normally reverberatory setting (Experiment 1) and an anechoic chamber (Experiment 2) indicated that the state of reverberation could serve as an absolute cue, with greater reverberation being associated with greater perceived distances. Some of the results were discussed in terms of the possibility that the specific distance tendency (a concept developed to handle some phenomena in visual space perception) might have applicability to the study of auditory perceived distance as well.

     

Lack of degradation in visuospatial perception of line orientation after one night of sleep loss

Sleep deprivation impairs a variety of cognitive abilities including vigilance, attention, and executive function. Although sleep loss has been shown to impair tasks requiring visual attention and spatial perception, it is not clear whether these deficits are exclusively a function of reduced attention and vigilance or if there are also alterations in visuospatial perception. Visuospatial perception and sustained vigilance performance were therefore examined in 54 healthy volunteers at rested baseline and again after one night of sleep deprivation using the Judgment of Line Orientation Test and a computerized test of psychomotor vigilance. Whereas psychomotor vigilance declined significantly from baseline to sleep-deprived testing, scores on the Judgment of Line Orientation did not change significantly. Results suggest that documented performance deficits associated with sleep loss are unlikely to be the result of dysfunction within systems of the brain responsible for simple visuospatial perception and processing of line angles.     

The perception of limb orientation depends on the center of mass

Three experiments were conducted to test the hypothesis that the perception of limb orientation depends on inertial eigenvectors against the alternative that it depends on the center of mass. In all experiments, each participant pointed at visible targets with his or her occluded right arm while center-of-mass and inertial eigenvectors were manipulated independently. In Experiments 1 and 2, the arm was constrained to rotate exclusively about the shoulder, whereas in Experiment 3, the arm was allowed to rotate freely about both the shoulder and the elbow. The mechanical manipulations were applied either in the horizontal (Experiments 1 and 3) or vertical (Experiment 2) plane. Across experiments, pointing direction was affected by the center of mass and not by the inertial eigenvectors, albeit that simultaneous manipulation of both resulted in a more pronounced pointing bias than the isolated center-of-mass manipulation. These findings challenge the inertial eigenvector hypothesis and suggest that the center of mass plays a generic role in the perception of limb orientation.     

The visual perception of surface orientation from optical motion

Observers viewed monocular animations of rotating dihedral angles and were required to indicate their perceived structures by adjusting the magnitude and orientation of a stereoscopic dihedral angle. The motion displays were created by directly manipulating various aspects of the image velocity field, including the mean translation, the horizontal and vertical velocity gradients, and the manner in which these gradients changed over time. The adjusted orientation of each planar facet was decomposed into components of slant and tilt. Although the tilt component was estimated with a high degree of accuracy, the judgments of slant exhibited large systematic errors. The magnitude of perceived slant was determined primarily by the magnitude of the velocity gradient scaled by its direction. The results also indicate that higher order temporal derivatives of the moving elements had little effect on observers' judgments.     

Blur-modulated orientation perception in the rod-and-frame task

In order to assess the role of blur in a rod-and-frame task, an afocal blurring technique was developed that restricted the blur to the frame. Three levels of blur were investigated, along with a nonblurred, directly viewed frame. Results showed a significant drop in the rod-and-frame effect (RFE) with increasing blur (decreasing spatial frequency), but spatial frequencies even as low as .092 cpd failed to reduce the RFE to zero. Decreasing luminance was correlated with increased blur, but control studies showed that variation in luminance levels between .007 and .0015 cd m^?2 had no effect on RFE. The finding of a spatial frequency dependency in the rod-and-frame task permits the development of a neuropsychological theory of individual and gender differences typically found in studies of static spatial orientation.     

Hierarchical organisation in perception of orientation

According to Rock [1990, in The Legacy of Solomon Asch (Hillsdale, NJ: Lawrence Erlbaum Associates)], hierarchical organisation of perception describes cases in which the orientation of an object is affected by the immediately surrounding elements in the visual field. Various experiments were performed to study the hierarchical organisation of orientation perception. In most of them the rod-and-frame-illusion (RFI: change of the apparent vertical measured on a central rod surrounded by a tilted frame) was measured in the presence/absence of a second inner frame. The first three experiments showed that, when the inner frame is vertical, the direction and size of the illusion are consistent with expectancies based on the hierarchical organisation hypothesis. An analysis of published and unpublished data collected on a large number of subjects showed that orientational hierarchical effects are independent from the absolute size of the RFI. In experiments 4 to 7 we examined the perceptual conditions of the inner stimulus (enclosure, orientation, and presence of luminance borders) critical for obtaining a hierarchical organisation effect. Although an inner vertical square was effective in reducing the illusion (experiment 3), an inner circle enclosing the rod was ineffective (experiment 4). This indicates that definite orientation is necessary to modulate the illusion. However, orientational information provided by a vertical or horizontal rectangle presented near the rod, but not enclosing it, did not modulate the RFI (experiment 5). This suggests that the presence of a figure with oriented contours enclosing the rod is critical. In experiments 6 and 7 we studied whether the presence of luminance borders is important or whether the inner upright square might be effective also if made of subjective contours. When the subjective contour figure was salient and the observers perceived it clearly, its effectiveness in modulating the RFI was comparable to that observed with luminance borders.     

The role of balance dynamics in the active perception of orientation.

The Stoffregen and Riccio (1988) hypothesis that perceived orientation is determined primarily by balance dynamics was tested. Perception of orientation was evaluated in the context of a task that required Ss to control the roll orientation of a device in which they were seated. The device's direction of balance was manipulated across trials and thus was independent of gravity. Eighteen Ss participated in the investigation. After each trial, Ss estimated their mean tilt with respect to upright. Correlations of perceived tilt with tilt from balance were consistently higher than the correlations with gravity tilt. The dominance of balance over gravity depended on the magnitude of tilt from balance.     

The beholder's share in the perception of orientation of 2-D shapes

A considerable amount of research demonstrates that people perceive cardinal orientations (horizontal and vertical) more accurately than other orientations; this is termed the oblique effect. We investigated the interaction of this effect with the degree of elongation of the stimulus. Our stimuli were ellipses with a wide range of aspect ratios, varying from a circle (aspect ratio = 1) to a line (aspect ratio = 123.5). The task was to set a probe line in the same orientation as the long axis of the ellipse. In our first experiment, we determined that performance is degraded as the aspect ratio decreases; furthermore, the bias and response variability are linearly related to a transformation of aspect ratio (roundness). We found significant individual differences; the results show high within-subjects correlations and low between-subjects correlations. In our second experiment, we had observers judge the orientation of circles randomly mixed in with ellipses of low aspect ratio. The observers demonstrated intrinsic preferences and generated reproducible distributions of orientation settings with idiosyncratic profiles. These distributions predict the influence on the response to ellipses with an aspect ratio higher than one and can be considered as the beholder's share in the perception of shape orientation.     

The effect of spatial orientation on the perception of moving tactile stimuli

Previous studies have shown that the perception of spatial patterns, such as letters, presented to the hand is affected by the spatial orientation of the hand. The present study investigated how the perception of direction of motion across the fingerpads changes with the position of the hand in space. The moving stimuli were generated on two displays. In one condition, the displays were placed horizontally in front of the subject, with the subject’s thumb (target site) and index finger (nontarget site) placed flat on the displays. In a second condition, the displays were vertically oriented and gripped between the thumb and index finger. Using a selective-attention paradigm in which subjects are instructed to respond only to the direction of motion at the target site, performance was still affected by the direction of motion at the nontarget site. Changing the orientation of the displays changed the effectiveness of the nontarget in interfering with the identification of the target movement. Nontarget stimuli that produced no interference in the horizontal orientation did so in the vertical, and vice versa. It appears that subjects are not using the local direction of movement across the fingerpads to judge the relative direction of movement at the two sites; rather, they are using the external direction of movement.     

The egocentric nature of procedural justice: Social value orientation as moderator of reactions to decision-making procedures

In four studies, the authors investigated the individual-oriented versus social-oriented nature of procedural justice effects by comparing fairness-based responses to decision-making procedures among proself versus prosocial oriented individuals. In Studies 1 through 3, we measured participants’ social value orientation and manipulated whether or not they were granted or denied voice in a decision-making process. Results consistently revealed that the effects of voice versus no-voice on fairness-based perceptions, emotions, and behavioral intentions were significantly more pronounced for individuals with proself orientations than for individuals with prosocial orientations. These findings were extended in Study 4, a field study in which perceived procedural justice was a stronger predictor of satisfaction and organizational citizenship behaviors among proselfs than among prosocials. These findings suggest that procedural justice effects can be accounted for by self-oriented motives or needs, rather than prosocial motives that are often conceptualized as being associated with justice.