Distinct task-independent visual thresholds for egocentric and allocentric information pick up

The dominant view of the ventral and dorsal visual systems is that they subserve perception and action. De Wit, Van der Kamp, and Masters (2011) suggested that a more fundamental distinction might exist between the nature of information exploited by the systems. The present study distinguished between these accounts by asking participants to perform delayed matching (perception), pointing (action) and perceptual judgment responses to masked Müller-Lyer stimuli of varying length. Matching and pointing responses of participants who could not perceptually judge stimulus length at brief durations remained sensitive to veridical stimulus length (egocentric information), but not the illusion (allocentric, context-dependent information), which was effective at long durations. Distinct thresholds for egocentric and allocentric information pick up were thus evident irrespective of whether perception (matching) or action (pointing) responses were required. It was concluded that the dorsal and ventral systems may be delineated fundamentally by fast egocentric- and slower allocentric information pick up, respectively.     

Remembering object position in the absence of vision: egocentric, allocentric, and egocentric decentred frames of reference

In three experiments we examined whether memory for object locations in the peri-personal space in the absence of vision is affected by the correspondence between encoding and test either of the body position or of the reference point. In particular, the study focuses on the distinction between different spatial representations, by using a paradigm in which participants are asked to relocate objects explored haptically. Three frames of reference were systematically compared. In experiment 1, participants relocated the objects either from the same position of learning by taking as reference their own body (centred egocentric condition) or from a 90 degrees decentred position (allocentric condition). Performance was measured in terms of linear distance errors and angular distance errors. Results revealed that the allocentric condition was more difficult than the centred egocentric condition. In experiment 2, participants performed either the centred egocentric condition or a decentred egocentric condition, in which the body position during the test was the same as at encoding (egocentric) but the frame of reference was based on a point decentred by 90 degrees. The decentred egocentric condition was found to be more difficult than the centred egocentric condition. Finally, in experiment 3, participants performed in the decentred egocentric condition or the allocentric condition. Here, the allocentric condition was found to be more difficult than the decentred egocentric condition. Taken together, the results suggest that also in the peripersonal space and in the absence of vision different frames of reference can be distinguished. In particular, the decentred egocentric condition involves a frame of reference which seems to be neither allocentric nor totally egocentric.     

The relationship between allocentric and egocentric frames of reference and categorical and coordinate spatial information processing

We report two experiments on the relationship between allocentric/egocentric frames of reference and categorical/coordinate spatial relations. Jager and Postma (2003) suggest two theoretical possibilities about their relationship: categorical judgements are better when combined with an allocentric reference frame and coordinate judgements with an egocentric reference frame (interaction hypothesis); allocentric/egocentric and categorical/coordinate form independent dimensions (independence hypothesis). Participants saw stimuli comprising two vertical bars (targets), one above and the other below a horizontal bar. They had to judge whether the targets appeared on the same side (categorical) or at the same distance (coordinate) with respect either to their body-midline (egocentric) or to the centre of the horizontal bar (allocentric). The results from Experiment 1 showed a facilitation in the allocentric and categorical conditions. In line with the independence hypothesis, no interaction effect emerged. To see whether the results were affected by the visual salience of the stimuli, in Experiment 2 the luminance of the horizontal bar was reduced. As a consequence, a significant interaction effect emerged indicating that categorical judgements were more accurate than coordinate ones, and especially so in the allocentric condition. Furthermore, egocentric judgements were as accurate as allocentric ones with a specific improvement when combined with coordinate spatial relations. The data from Experiment 2 showed that the visual salience of stimuli affected the relationship between allocentric/egocentric and categorical/coordinate dimensions. This suggests that the emergence of a selective interaction between the two dimensions may be modulated by the characteristics of the task.     

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.     

The relationship between allocentric and egocentric frames of reference and categorical and coordinate spatial information processing

We report two experiments on the relationship between allocentric/egocentric frames of reference and categorical/coordinate spatial relations. Jager and Postma (2003) suggest two theoretical possibilities about their relationship: categorical judgements are better when combined with an allocentric reference frame and coordinate judgements with an egocentric reference frame (interaction hypothesis); allocentric/egocentric and categorical/coordinate form independent dimensions (independence hypothesis). Participants saw stimuli comprising two vertical bars (targets), one above and the other below a horizontal bar. They had to judge whether the targets appeared on the same side (categorical) or at the same distance (coordinate) with respect either to their body-midline (egocentric) or to the centre of the horizontal bar (allocentric). The results from Experiment 1 showed a facilitation in the allocentric and categorical conditions. In line with the independence hypothesis, no interaction effect emerged. To see whether the results were affected by the visual salience of the stimuli, in Experiment 2 the luminance of the horizontal bar was reduced. As a consequence, a significant interaction effect emerged indicating that categorical judgements were more accurate than coordinate ones, and especially so in the allocentric condition. Furthermore, egocentric judgements were as accurate as allocentric ones with a specific improvement when combined with coordinate spatial relations. The data from Experiment 2 showed that the visual salience of stimuli affected the relationship between allocentric/egocentric and categorical/coordinate dimensions. This suggests that the emergence of a selective interaction between the two dimensions may be modulated by the characteristics of the task.     

The availability versus the use of partial information: Multiple levels of selective processing between perception and action

Temporal overlap of cognitive processes occurs when partial information about a stimulus activates associated responses before the stimulus has been fully identified. Recent evidence obtained with psychophysiological measures suggests that such overlap sometimes does, and sometimes does not occur. In this contribution, we argue that in order to understand why, we have to distinguish between selection of partial information for perception and selection of partial information for control over activation of responses. We discuss several mechanisms and factors that may modulate the temporal overlap of mental processes because they selectively influence the perceptual availability or the use of partial information.     

Identifying the information for the visual perception of relative phase

The production and perception of coordinated rhythmic movement are very specifically structured. For production and perception, 0 degree mean relative phase is stable, 180 degrees is less stable, and no other state is stable without training. It has been hypothesized that perceptual stability characteristics underpin the movement stability characteristics, which has led to the development of a phase-driven oscillator model (e.g., Bingham, 2004a, 2004b). In the present study, a novel perturbation method was used to explore the identity of the perceptual information being used in rhythmic movement tasks. In the three conditions, relative position, relative speed, and frequency (variables motivated by the model) were selectively perturbed. Ten participants performed a judgment task to identify 0 degree or 180 degrees under these perturbation conditions, and 8 participants who had been trained to visually discriminate 90 degrees performed the task with perturbed 90 degrees displays. Discrimination of 0 degree and 180 degrees was unperturbed in 7 out of the 10 participants, but discrimination of 90 degrees was completely disrupted by the position perturbation and was made noisy by the frequency perturbation. We concluded that (1) the information used by most observers to perceive relative phase at 0 degree and 180 degrees was relative direction and (2) becoming an expert perceiver of 90 degrees entails learning a new variable composed of position and speed.     

Lateralization of egocentric and allocentric spatial processing after parietal brain lesions

The purpose of this paper was to verify whether left and right parietal brain lesions may selectively impair egocentric and allocentric processing of spatial information in near/far spaces. Two Right-Brain-Damaged (RBD), 2 Left-Brain-Damaged (LBD) patients (not affected by neglect or language disturbances) and eight normal controls were submitted to the Ego-Allo Task requiring distance judgments computed according to egocentric or allocentric frames of reference in near/far spaces. Subjects also completed a general neuropsychological assessment and the following visuospatial tasks: reproduction of the Rey-Osterreith figure, line length judgement, point position identification, mental rotation, mental construction, line length memory, line length inference, Corsi block-tapping task. LBD patients presented difficulties in both egocentric and allocentric processing, whereas RBD patients dropped in egocentric but not in allocentric judgements, and in near but not far space. Further, RBD patients dropped in perceptually comparing linear distances, whereas LBD patients failed in memory for distances. The overall pattern of results suggests that the right hemisphere is specialized in processing metric information according to egocentric frames of reference. The data are interpreted according to a theoretical model that highlights the close link between egocentric processing and perceptual control of action.     

Roles of egocentric and allocentric spatial representations in locomotion and reorientation

Four experiments investigated the nature of spatial representations used in locomotion. Participants learned the layout of several objects and then pointed to the objects while blindfolded in 3 conditions: before turning (baseline), after turning to a new heading (updating), and after disorientation (disorientation). The internal consistency of pointing in the disorientation condition was relatively high and equivalent to that in the baseline and updating conditions, when the layout had salient intrinsic axes and the participants learned the locations of the objects on the periphery of the layout. The internal consistency of pointing was disrupted by disorientation when participants learned the locations of objects while standing amid them and the layout did not have salient intrinsic axes. It was also observed that many participants retrieved spatial relations after disorientation from the original learning heading. These results indicate that people form an allocentric representation of object-to-object spatial relations when they learn the layout of a novel environment and use that representation to locate objects around them. Egocentric representations may be used to locate objects when allocentric representations are not of high fidelity.     

Orientational manoeuvres in the dark: dissociating allocentric and egocentric influences on spatial memory

Subjects in a darkroom saw an array of five phosphorescent objects on a circular table and, after a short delay, indicated which object had been moved. During the delay the subject, the table or a phosphorescent landmark external to the array was moved (a rotation about the centre of the table) either alone or together. The subject then had to indicate which one of the five objects had been moved. A fully factorial design was used to detect the use of three types of representations of object location: (i) visual snapshots; (ii) egocentric representations updated by self-motion; and (iii) representations relative to the external cue. Improved performance was seen whenever the test array was oriented consistently with any of these stored representations. The influence of representations (i) and (ii) replicates previous work. The influence of representation (iii) is a novel finding which implies that allocentric representations play a role in spatial memory, even over short distances and times. The effect of the external cue was greater when initially experienced as stable. Females out-performed males except when the array was consistent with self-motion but not visual snapshots. These results enable a simple egocentric model of spatial memory to be extended to address large-scale navigation, including the effects of allocentric knowledge, landmark stability and gender.     

Developmental time course of the acquisition of sequential egocentric and allocentric navigation strategies

Navigation in a complex environment can rely on the use of different spatial strategies. We have focused on the employment of “allocentric” (i.e., encoding interrelationships among environmental cues, movements, and the location of the goal) and “sequential egocentric” (i.e., sequences of body turns associated with specific choice points) strategies during navigation. To investigate the developmental pattern of these two strategies in school-aged children, we used a virtual reality paradigm in which the spontaneous or imposed use of both strategies could be assessed. Our results showed an increase in spontaneous use of the allocentric strategy and also an increase in reliance on environmental landmarks with age. Although a majority of the children spontaneously used the sequential egocentric strategy, all age groups performed above chance when the allocentric strategy was imposed. Altogether, our findings suggest that young children are able to employ an allocentric strategy but that the nature of this allocentric strategy changes progressively in a complex cognitive representation between 5 and 10 years of age.     

Searching for the minimal essential information for skilled perception and action

Summary A common concern for both cognitive/computational and ecological/dynamical models of human motor control is the isolation of the minimal essential information needed to support skilled perception and action. In perception isolating essential features of the optic flow field, which are reliably informative regarding the nature of current events, from nonessential features provides a valuable step towards understanding how the computational complexity of perceptual information processing may be reduced to manageable levels and how relatively direct linkages of low dimensionality may be established between information and control variables. Likewise, in the study of action, discrimination of the movement features that remain immutable (invariant?) across changes in task conditions from the variables that are situationally determined provides a principled insight into the structural framework upon which skilled movement is built. Controversy abounds, however, in the study of perception and action as to whether features isolated as informative and immutable are centrally represented (in the form of a template or program) or are rather directly picked up (in the case of perceptual variables) or are simply an emergent consequence of the underlying dynamics (in the case of action variables). In this paper some examples of putative minimal essential information sources in perception and action are provided, strategies for uncovering such sources are discussed, and attention is directed, with the use of some recent data collected on natural skills, to some systematic expert-novice differences in the utilization of essential information and control variables. Expert-novice differences are highlighted because of the insight they may provide regarding the nature of perceptual-motor skill acquisition.     

Vision for perception and vision for action: normal and unusual development

Evidence suggests that visual processing is divided into the dorsal ('how') and ventral ('what') streams. We examined the normal development of these streams and their breakdown under neurological deficit by comparing performance of normally developing children and Williams syndrome individuals on two tasks: a visually guided action ('how') task, in which participants posted a card into an oriented slot, and a perception ('what') task, in which they matched a card to the slot's orientation. Results showed that all groups performed worse on the action task than the perception task, but the disparity was more pronounced in WS individuals and in normal 3-4-year-olds than in older children. These findings suggest that the 'how' system may be relatively slow to develop and more vulnerable to breakdown than the 'what' system.     

The contributions of egocentric and allocentric reference frames in haptic spatial tasks

The influence of egocentric and allocentric reference frames on performance in haptic spatial tasks, was tested in three conditions. Blindfolded subjects had to make two bars haptically parallel, perpendicular or mirrored in the midsagittal plane. The hypothesis is that the contributions of egocentric and allocentric reference frames are combined, resulting in settings that lie in between the allo-representation and the ego-representation. This leads to different predictions for the outcome of different conditions. All findings were consistent with the hypothesis. In addition, for subjects with large deviations a reversal of the oblique effect was found once again, which provides extra support for the hypothesis.     

Development of egocentric and allocentric spatial representations from childhood to elderly age

Spatial reference frames are fundamental to represent the position of objects or places. Although research has reported changes in spatial memory abilities during childhood and elderly age, no study has assessed reference frames processing during the entire lifespan using the same task. Here, we aimed at providing some preliminary data on the capacity to process reference frames in 283 healthy participants from 6 to 89 years of age. A spatial memory task requiring egocentric/allocentric verbal judgments about objects in peri-/extrapersonal space was used. The main goals were: (1) tracing a baseline of the normal process of development of these spatial components; (2) clarifying if reference frames are differently vulnerable to age-related effects. Results showed a symmetry between children of 6–7 years and older people of 80–89 years who were slower and less accurate than all other age groups. As regards processing time, age had a strong effect on the allocentric component, especially in extrapersonal space, with a longer time in 6- to 7-year-old children and 80- to 89-year-old adults. The egocentric component looked less affected by aging. Regarding the level of spatial ability (accuracy), the allocentric ability appeared less sensitive to age-related variations, whereas the egocentric ability progressively improved from 8 years and declined from 60 years. The symmetry in processing time and level of spatial ability is discussed in relation to the development of executive functions and to the structural and functional changes due to incomplete maturation (in youngest children) and deterioration (in oldest adults) of underlying cerebral areas.     

Voluntary head movement and allocentric perception of space

Although visual input is egocentric, at least some visual perceptions and representations are allocentric, that is, independent of the observer's vantage point or motion. Three experiments investigated the visual perception of three-dimensional object motion during voluntary and involuntary motion in human subjects. The results show that the motor command contributes to the objective perception of space: Observers are more likely to apply, consciously and unconsciously, spatial criteria relative to an allocentric frame of reference when they are executing voluntary head movements than while they are undergoing similar involuntary displacements (which lead to a more egocentric bias). Furthermore, details of the motor command are crucial to spatial vision, as allocentric bias decreases or disappears when self-motion and motor command do not match.