UM INVARIANTE NO CONTROLE DA PERCEPÇÃO E AÇÃO EM TAREFAS DE BISSECÇÃO (original) (raw)
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Perceptual constancy in judgments of egocentric distance: prevailing binocular information
Arquivos Brasileiros De Oftalmologia, 2003
Binocular cues were considered the prevailing information on specifying depth since the beginning of vision research. In the present study, two perceptual responses, the classical verbal report and a more recent method, open-loop walking, were used to assess the role of binocular information for egocentric distance perception. In two cue conditions environments, full- and reduced-cue, observers judged and walked egocentric distances of stimuli presented at eye-level, under binocular or monocular viewing. Results indicated perceptual constancy for open-loop walking and binocular responses, as well as poor performances under strong degradation on visual information (reduced-cue under monocular viewing), thus presenting evidence to support the fundamental role of binocular information on perception of egocentric distances. Besides that, visually directed actions could be adequate measures of perceived distance, with a better reliability than verbal report, since they were quite free of intrusion of inferential processes and perceptual tendencies. In addition, reduced head movements, side-to-side as well as back and forth deflexion movements, could have contributed to a near perfect coupling between binocular disparity information and open-loop walking responses.
Perception-action interaction and bissection
2004
Several studies using visually directed actions as indicators of perceived distance showed that people could accurately walk toward targets far up to 22m. Those results, summed up to those related to perceptual measures of perceived distance, showed that those responses were controlled by a single internal variable, namely visually perceived location. In the present study, we compared performance in bisection tasks, performed by open-loop walking or by perceptual matching. Observers (N=20) walked toward or adjust a pointer to the mean point of an egocentric distance (5, 10 or 15m), under binocular viewing. Results indicated accuracy on both responses, with no reliable differences between them, supporting the hypothesis of a single internal variable controlling action and perception. This invariant may be determined by a weighted set of sources of information.
Distance perception in a natural outdoor setting: is there adevelopmental trend to overconstancy?
The Spanish Journal of Psychology, 2006
The main purpose of the present study was to investigate whether in natural environment, using very large physical distances, there is a trend to overconstancy for distance estimates during development. One hundred and twenty-nine children aged 5 to 13 years old and twenty-one adults (in a control group), participated as observers. The observer's task was to bisect egocentric distances, ranging from 1.0 to 296.0 m, presented in a large open field. The analyses focused on two parameters, constant errors and variable errors, such as measuring accuracy and precision, respectively. A third analysis focused on the developmental pattern of shifts in constancy as a function of age and range of distances. Constant error analysis showed that there are two relevant parameters for accuracy, age, and range of distances. For short distances, there are three developmental stages: 5-7 years, when children have unstable responses, 7-11, underconstancy, and 13 to adulthood, when accuracy is reached. For large distances, there is a two-stage development: 5-11 years, with severe underconstancy, and beyond this age, with mild underconstancy. Variable errors analyses indicate that precision is noted for 7 year-old children, independently of the range of distances. The constancy analyses indicated that there is a shift from constancy (or slightly overconstancy) to underconstancy as a function of physical distance for all age groups. The age difference is noted in the magnitude of underconstancy that occurs in larger distances, where adults presented lower levels of underconstancy than children. The present data were interpreted as due to a developmental change in cognitive processing rather than to changes in visual space perception.
Peripersonal perception in action
Synthese, 2021
Philosophy of perception is guilty of focusing on the perception of far space, neglecting the possibility that the perception of the space immediately surrounding the body, which is known as peripersonal space, displays different properties. Peripersonal space is the space in which the world is literally at hand for interaction. It is also the space in which the world can become threatening and dangerous, requiring protective behaviours. Recent research in cognitive neuroscience has yielded a vast array of discoveries on the multisensory and sensorimotor specificities of the processing of peripersonal space. Yet very little has been done on their philosophical implications. Here I will raise the following question: in what manner does the visual experience of a big rock close to my foot differ from the visual experience of the moon in the sky?
Distance from a stimulus, stimulus size and orientation with respect to the observer are relevant metric properties of visual space. However, whether and how these metrics are related to each other is not well known. Some studies have shown that estimates of egocentric distances are usually more accurate than judgments of exocentric distances, suggesting that there is dissociation between ‘localization’ judgments and ‘size’ judgments. Other investigations have revealed that the orientation of the stimulus influences the accuracy of size estimations. To better understand the relationships between these metric properties of visual space, we conducted an experiment to compare size perception as a function of orientation from viewer egocentric and exocentric frames of reference (FoR). Observers were instructed to draw two circles on a screen by clicking with a mouse when the screen was positioned on either the frontoparallel plane or the ground plane. From an egocentric FoR, egocentric distance and direction were processed asymmetrically, as knowledge of the particular combination of both size and orientation was always needed to compute visual direction. However, in terms of the accuracy of size estimates (S0/S) from an exocentric FoR, size and orientation were independent for all conditions. Therefore, the orientation did not need to be computed in order to compute the size. Regarding exocentric direction or orientation (α0/α), size and orientation were only dependent when the two points were presented successively. In conclusion, these findings suggest that orientation and distance always interact and that distance, visual direction or orientation require an egocentric cue.
The Spanish Journal of Psychology, 2006
The aim of this study is twofold: on the one hand, to determine how visual space, as assessed by exocentric distance estimates, is related to physical space. On the other hand, to determine the structure of visual space as assessed by exocentric distance estimates. Visual space was measured in three environments: (a) points located in a 2-D frontoparallel plane, covering a range of distances of 20 cm; (b) stakes placed in a 3-D virtual space (range ≈ 330 mm); and (c) stakes in a 3-D outdoors open field (range = 45 m). Observers made matching judgments of distances between all possible pairs of stimuli, obtained from 16 stimuli (in a regular squared 4 × 4 matrix). Two parameters from Stevens' power law informed us about the distortion of visual space: its exponent and its coefficient of determination (R2). The results showed a ranking of the magnitude of the distortions found in each experimental environment, and also provided information about the efficacy of available visual cues of spatial layout. Furthermore, our data are in agreement with previous findings showing systematic perceptual errors, such as the further the stimuli, the larger the distortion of the area subtended by perceived distances between stimuli. Additionally, we measured the magnitude of distortion of visual space relative to physical space by a parameter of multidimensional scaling analyses, the RMSE. From these results, the magnitude of such distortions can be ranked, and the utility or efficacy of the available visual cues informing about the space layout can also be inferred.
Egocentric and Exocentric Spatial Judgements of Visual Displacement
The Quarterly Journal of Experimental Psychology A, 1999
The role of changes in ego-and exocentric spatial relationships on perceptual judgem ents about visual displacement was investig ated 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 con¯icting ego-and exocentric spatial information, subjects performed poorly in both instruction conditio ns. This suggests that ego-and exocentric representations cannot be used indepen dently and are probably interconnected.