1,721,115 research outputs found
The perceptual expansion of a filled area depends on textural characteristics
No full textAccording to the Oppel-Kundt illusion, a filled space appears larger than an empty one. In the present research we studied how textural characteristics affect the perceived size of two-dimensional patterns. We investigated the perceived extension of square textures by manipulating spatial frequency and filling microelements' numerosity. Subjects compared the test stimuli with a uniform gray square varied in size and performed the task both with the adjustment and the constant stimuli methods. An illusory increment of area extension was generally found with textured stimuli. The illusory effect increased with spatial frequency and decreased with the microelements' number, indicating an independent processing of these two basic properties. Moreover, the smaller effect found when spatial frequency extraction became harder, confirmed that the illusion involves spatial frequency processing. Finally, the reduced overestimation of areas observed with a weaker subparts' articulation confirmed the relevance of clear distinguishable micropatterns at the basis of the phenomenon. Those results demonstrate the influence of textural statistical properties on perceiving the size of a visual object
The riddle of the rotating-tilted-lines illusion
No full textGori and Hamburger (2006, Perception 35 853-857) devised a new visual illusion of relative motion elicited by the observer's motion. We propose that the systematic error of direction discrimination found by Lorenceau et al (1993, Vision Research 33 1207-1217) can explain this illusion. The neural correlate of such a systematic error with respect to the two types of neurons in the primary visual cortex, namely end-stopped and contour cells, is discussed
How the visual aspects can be crucial in reading acquisition: the intriguing case of crowding and developmental dyslexia
Full text linkDevelopmental dyslexia (DD) is the most common neurodevelopmental disorder (about 10% of children across cultures) characterized by severe difficulties in learning to read. According to the dominant view, DD is considered a phonological processing impairment that might be linked to a cross-modal, letter-to-speech sound integration deficit. However, new theories-supported by consistent data-suggest that mild deficits in low-level visual and auditory processing can lead to DD. This evidence supports the probabilistic and multifactorial approach for DD. Among others, an interesting visual deficit that is often associated with DD is excessive visual crowding. Crowding is defined as difficulty in the ability to recognize objects when surrounded by similar items. Crowding, typically observed in peripheral vision, could be modulated by attentional processes. The direct consequence of stronger crowding on reading is the inability to recognize letters when they are surrounded by other letters. This problem directly translates to reading at a slower speed and being more prone to making errors while reading. Our aim is to review the literature supporting the important role of crowding in DD. Moreover, we are interested in proposing new possible studies in order to clarify whether the observed excessive crowding could be a cause rather than an effect of DD. Finally, we also suggest possible remediation and even prevention programs that could be based on reducing the crowding in children with or at risk for DD without involving any phonological or orthographic training
Perceptual learning as a possible new approach for remediation and prevention of developmental dyslexia
No full textLearning to read is extremely difficult for about 10% of children across cultures because they are affected by developmental dyslexia (DD). According to the dominant view, DD is considered an auditory-phonological processing deficit. However, accumulating evidence from developmental and clinical vision science, suggests that the basic cross-modal letter-to-speech sound integration deficit in DD might arise from a mild atypical development of the magnocellular-dorsal pathway which also contains the main fronto-parietal attentional network. Letters have to be precisely selected from irrelevant and cluttering letters by rapid orienting of visual attention before the correct letter-to-speech sound integration applies. Our aim is to review the literature supporting a possible role of perceptual learning (PL) in helping to solve the puzzle called DD. PL is defined as improvement of perceptual skills with practice. Based on the previous literature showing how PL is able to selectively change visual abilities, we here propose to use PL to improve the impaired visual functions characterizing DD and, in particular, the visual deficits that could be developmentally related to an early magnocellular-dorsal pathway and selective attention dysfunction. The crucial visual attention deficits that are causally linked to DD could be, indeed, strongly reduced by training the magnocellular-dorsal pathway with the PL, and learning to read for children with DD would not be anymore such a difficult task. This new remediation approach - not involving any phonological or orthographic training - could be also used to develop new prevention programs for pre-reading children at DD risk
Mathematical analysis of the Accordion Grating illusion: a differential geometry approach to introduce the 3D aperture problem
No full textWhen an observer moves towards a square-wave grating display, a non-rigid distortion of the pattern occurs in which the stripes bulge and expand perpendicularly to their orientation; these effects reverse when the observer moves away. Such distortions present a new problem beyond the classical aperture problem faced by visual motion detectors, one we describe as a 3D aperture problem as it incorporates depth signals. We applied differential geometry to obtain a closed form solution to characterize the fluid distortion of the stripes. Our solution replicates the perceptual distortions and enabled us to design a nulling experiment to distinguish our 3D aperture solution from other candidate mechanisms (see Gori et al. (in this issue)). We suggest that our approach may generalize to other motion illusions visible in 2D displays
A new psychophysical estimation of the receptive field size
No full textWhen a line extends beyond the width of an aperture, its direction of motion cannot be detected correctly. Only the component of motion perpendicular to the line is detectable (aperture problem). Early visual areas face the same aperture problem because receptive field sizes are relatively small. The susceptibility of early visual areas to the aperture problem opens an opportunity to measure the aperture width of a receptive field psychophysically that can be used to estimate the receptive field size. We found an already established visual illusion (the rotating tilted lines illusion or RTLI) can be used to measure the aperture size and hence estimate the receptive field size. To estimate the receptive field size, we conducted a psychophysical experiment in which the radii and tilted line length of RTLI were systematically changed. Our psychophysical estimation of receptive field size strongly corresponds with the previous measures of receptive field size using electrophysiological and fMRI methods
Detection vs. grouping thresholds for elements differing in spacing, size and luminance. An alternative approach towards the psychophysics of Gestalten
No full textThree experiments were performed to compare thresholds for the detection of non-uniformity in spacing, size and luminance with thresholds for grouping. In the first experiment a row of 12 black equi-spaced dots was used and the spacing after the 3rd, 6th, and 9th dot increased in random steps to determine the threshold at which the observer detected an irregularity in the size of the gaps. Thereafter, spacing in the same locations was increased further to find the threshold at which the observer perceived four groups of three dots each (triplets). In the second experiment, empty circles were used instead of dots and the diameter of the circles in the first and second triplet increased until the difference in size gave rise either to a detection or grouping response. In the third experiment, the dots in the second and fourth triplet were increased in luminance. The aim again was to compare the difference in brightness required for detection or grouping, respectively. Results demonstrate that the threshold for perceiving stimuli as irregularly spaced or dissimilar in size or brightness is much smaller than the threshold for grouping. In order to perceive stimuli as grouped, stimulus differences had to be 5.2 times (for dot spacing), 7.4 times (for size) and 6.6 times (for luminance) larger than for detection. Two control experiments demonstrated that the difference between the two kinds of thresholds persisted even when only two gaps were used instead of three and when gap position was randomized
A new set of illusions: the dynamic luminance-gradient illusion and the breathing light illusion
No full textA novel set of illusions that break brightness constancy and size constancy at the same time is reported. The illusions occur when observers move towards or away from these patterns. Many variations of these phenomena and a possible explanation are discussed. We introduce here a new set of illusions that show illusory variances in brightness and also in size of the stimuli. During the 2006 meeting of the Vision Sciences Society (VSS), Alan Stubbs showed his illusions, created in Maine, USA, in the 'Best Visual Illusion of the Year Contest', hosted by the Neural Correlate Society, while Simone Gori showed his illusions, created in Germany, during the VSS 'Demo Night'. Although the patterns were different and Stubbs stressed more the illusory variance in luminance while Gori stressed more the illusory variance of the size, the two phenomena were actually very related to each other and they also have common origins. After this meeting the two authors decided to work on this new set of illusions together. This article is the result of their efforts
Visual Illusions: An Interesting Tool to Investigate Developmental Dyslexia and Autism Spectrum Disorder
Full text linkA visual illusion refers to a percept that is different in some aspect from the physical stimulus. Illusions are a powerful non-invasive tool for understanding the neurobiology of vision, telling us, indirectly, how the brain processes visual stimuli. There are some neurodevelopmental disorders characterized by visual deficits. Surprisingly, just a few studies investigated illusory perception in clinical populations. Our aim is to review the literature supporting a possible role for visual illusions in helping us understand the visual deficits in developmental dyslexia and autism spectrum disorder. Future studies could develop new tools - based on visual illusions - to identify an early risk for neurodevelopmental disorders. © 2016 Gori, Molteni and Facoetti
- …
