PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 14978579

[Illusions: a window into perception].

Marcus Vinícius C Baldo·Hamilton Haddad
View original source ↗Export metadata ↓

Abstract

Perception is the active construction of a neural state that correlates with biologically relevant elements present in the environment. This correlation, far from affording a one-to-one mapping, nonetheless guides our actions towards adaptive behaviors, thus being forged under evolutionary constraints. Since the construction of a percept is an intrinsically ambiguous process, perceptual discrepancies can arise from identical stimulation patterns. The recognition of these discrepancies is termed illusion, which originates, however, from the same physiological mechanisms that ordinarily lead to standard perception. Emanating from different sources, such as optical, sensory and cognitive factors, visual illusions are useful tools in accessing the physiological basis of perceptual processes and their interaction with motor planning and execution. Here we examine the biological roots of visual illusions and their interplay with some neurobiological, philosophical and esthetical issues.

Explore related subjects

Form PerceptionHumansOptical IllusionsPattern Recognition, VisualPsychophysicsVisual CortexEnglish AbstractJournal Article

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Marcus Vinícius C Baldo, Hamilton Haddad. 2004-02-16. [Illusions: a window into perception].. https://doi.org/10.1590/s1516-44462003000600003

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2005

A long-distance stereoscopic detector for partially occluding surfaces.

An external noise technique was used to investigate the stereoscopic process that generates an illusory phantom occluder from binocularly unmatched elements. Observers were required to identify the quadrant in which a binocularly defined target was presented. We had three targets: (a) two vertical binocular bars with the unmatched portions arranged to induce a stable phantom occluder (valid), (b) the same stimuli except the image for the left eye was switched with that for the right eye therefore not inducing a stable occluder (invalid), and (c) a single binocular bar with the same unmatched portion (single-bar). For each target, the luminance contrast of the signal required for 75% correct responses was measured at four levels of external interocular noise. Contrast thresholds were found to be lower for the valid target than for both the invalid and the single-bar targets. The results suggest that the visual system has a stereoscopic detector that responds to stimuli that meet a long-distance requirement for the perception of partially occluding surfaces.

Form Perception↗
PubMed2005

Haptic feature extraction.

This study examined the process by which the shape of a haptically explored object is synthesized from the geometric characteristics of simpler constituent elements, such as arcs and ellipses. Subjects traced the outlines of virtual objects by means of whole arm movements. Each object consisted of the union of a large central ellipse and two smaller circles, extending upward and outward from the top left and right sides of the base. The sizes of the two circles and the eccentricity of the elliptical base were varied. After exploring the object's contour in the absence of vision, subjects reproduced the sensed shape by means of freehand drawing. Speed and force were modulated during the exploratory phase in a manner that suggested that subjects reacted to rather than predicted changes in curvature. Also, subjects typically devoted more time to exploring the part of the contour encompassing the two smaller circles. During drawing, individual features of the explored shape were reproduced with varying degrees of fidelity. Aspects related to the size and location of the smaller circles were reproduced better than was the eccentricity of the ellipse forming the base. Since subjects spent proportionally less time exploring the base, these results suggest that subjects selectively focused attention to regions of high spatial contrast and that the exploratory strategy introduced distortions in the haptically sensed shapes.

Form Perception↗
PubMed2005

The spatial frequency and orientation selectivity of the mechanisms that extract motion-defined contours.

The human visual system can undertake a specialized form of motion integration, one that enables the presence of extended spatial contours to be disambiguated from their backgrounds. We have shown previously that the visual system can selectively integrate local motion signals when their directions are along spatial contours and its efficiency is inversely related to the curvature of the contour involved (Ledgeway, T., & Hess, R. F. (2002). Vision Research, 42, 653-659). This integration primarily involves the direction, rather than the speed, of local motion signals. In the present study, we sought to investigate both the spatial frequency and orientation tuning of this specialized contour integration process, using a path detection paradigm. The results show that the tuning for spatial frequency is very broad, in line with previous studies that have examined this issue. In contrast, the orientation selectivity of the mechanism mediating contour extraction under these conditions is relatively narrowband. Thus, spatial frequency but not orientation pooling appears to take place prior to the extraction of motion-defined contours, a situation that is different from that previously shown for spatial contours composed of static, oriented elements.

Form Perception↗