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Purpose: A recent hypothesis ascribes dyslexia to a perceptual anchoring deficit. Supporting results have so far been obtained only in children with dyslexia and additional learning difficulties, but the hypothesis has been argued to apply to all individuals with dyslexia. Method: The authors measured auditory frequency discrimination thresholds in 54 young adults (native speakers of Dutch; 25 individuals with dyslexia; 29 age- and education-matched controls), with a 2-alternative forced-choice staircase paradigm. There were 2 conditions: 1 in which 1 tone in each pair had a fixed frequency across trials (standard), and 1 in which both tones varied in frequency (no standard). Presence of a standard stimulus allows the creation of a stimulus-specific representation in short-term memory (perceptual anchor). Results: The standard condition yielded significantly lower discrimination thresholds in both controls and individuals with dyslexia; both groups benefited equally from the presence of an invariant stimulus. Conclusion: There is no difference between this group of adults with dyslexia and controls in their capacity to form a perceptual anchor. The implication is that an anchoring deficit cannot be generalized to all cases of dyslexia. Key Words: dyslexia, auditory processing, short-term memory, There is broad agreement that dyslexia is associated with poor phonological processing (Lyon, Shaywitz, & Shaywitz, 2003; Vellutino, Fletcher, Snowling, & Scanlon, 2004), but the nature and cause of this [...]

In this paper a haptic matching task is used to analyze haptic spatial processing. In various conditions, blindfolded participants were asked to make a test bar parallel to a reference bar. This always resulted in large bur systematic deviations. It will be shown that the results can be described with a model in which an egocentric reference frame biases the participants' settings: What a participant haptically perceives as parallel is a weighted average of parallel in allocentric space and parallel in egocentric space. The basis of the egocentric reference frame is uncertain. There is strong evidence that at least a hand-centred reference frame is involved, but possibly a body-centred reference frame also plays a role. Dans cet article, une tache de correspondance haptique est utilisee pour analyser le traitement haptique de l'espace. On a demande a des participants auxquels on avait bande les yeux. de faire un test de barre parallele a une barre de reference. Cela a toujours donne des deviations importantes mais systematiques. Nous allons montrer que les resultats peuvent etre decrits au moyen d'un modele ou un cadre de reference egocentrique fausse les reglages du participant. Ce qu'un sujet percoit de facon haptique comme etant parallele est une moyenne ponderee du parallelisme dans l'espace allocentrique et du parallelisme dans l'espace egocentrique. Le fondement du cadre de reference egocentrique est incertain. Il existe de fortes indications a l'effet qu'au moins un cadre de reference centre sur les mains est en jeu, mais qu't,n cadre de reference axe sur le corps joue possiblement un role aussi.

Highlights are due to specular reflection and cause the lustrous or mirrorlike appearance of many material surfaces. We investigated in detail the structure of highlight patterns that are due to material surface roughness. We interpret results in terms of a simple model of a random Gaussian surface. The model's prediction corresponds with the microscopic measurement within a factor of 2. The method allows one to rank generally the roughness of the surfaces of the fruit samples by purely optical means. This simple procedure for estimating surface roughness from images has implications for visual perception and graphic rendering. OCIS codes: 100.3010, 120.5700, 120.6650, 240.5770, 240.6700, 330.4060.

The authors investigated how well participants were able to locate the singular point in an expanding or rotating flow field. The participants' responses gave insight into the magnitude and direction of possible deviations from the veridical point and into the reproducibility of the participants' answers. The stimulus window was circular with a radius of 10 [degrees]. The performance of the participants improved with increasing expansion or rotation of the stimulus. When either the outer rim or the central part of the stimulus was blocked out, performance was not affected when singular points were inside the visible part of the stimulus. Singular points that were outside the visible part of the stimulus, however, were judged to be closer to the rim of the visible part than they actually were. Performance deteriorated with increasing eccentricity of the entire stimulus area (up to 20 [degrees], keeping the field size constant), whereas it was not affected by the eccentricity of the singular point within the stimulus. A drastic limitation of the presentation period had only a quantitative effect on performance.

The authors report on different methods to probe the structure of visually perceived surfaces in 3 dimensions. The surfaces are specified by patterns of shading with Lambertian and specular components, which deform over time and over stereoscopic views. Five observers performed 2 probe tasks, 1 involving the adjustment of a punctate probe so as to be on the apparent surface and the other involving the adjustment of a small gauge figure that indicates surface attitude. The authors found that these rather different methods yielded essentially identical depth maps up to linear transformations and that the observers all deviate slightly from veridicality in basically identical ways. The nature of this deviation appears to be correlated with the rough topography of the specularities.

Observers' perceptions of a male and a female torso were investigated using monocular and stereoscopic images under varying conditions of illumination. Observers judged the shapes of these torsos by adjusting a gauge figure to estimate the local slant and tilt at numerous probe points arranged in a lattice over the torso's surface. The results revealed that the judged surfaces in the monocular and stereoscopic conditions were related by an affine stretching transformation in depth that accounted for approximately 95% of the between-condition variance. There was also a strong affine component between the judgments obtained for the different illumination directions, although a further analysis of the residuals indicated that changing the direction of illumination influenced perceived structure in a piecewise manner.