LITERATURE REVIEW The Ebbinghaus illusion was discovered by Hermann Ebbinghaus, a psychologist whom studied the psychology of memory (Martinez-Conde & Macknik, 2010, p. 2). The Ebbinghaus illusion got its name after: b.) a.) The target size difference at which observers made size discrimination errors significantly varied over participant group in the Ponzo illusion, F(4,95)=11.285; p<0.001, Müller-Lyer illusion, F (4,95)=11.005; p<0.001, and Kanisza-occlusion illusion, F(4,95)=2.581; p=0.042, but only approached significance for the Ebbinghaus illusion, F(4,84)=2.214; p=0.074. This assumption seems reasonable since the smallest size difference that we tested (e.g., 0.0716 deg) corresponded to Vernier thresholds for comparing elements at separations between 5.0 and 12 deg (Levi, Klein & Yap, 1988; Levi & Klein, 1990; Palomares, et al., 2005) and to normal letter acuity at fixation (e.g. These results suggest that ability of normal adults to discriminate objects with a size difference of 0.0357 deg was not reliably better than chance. The classic evidence of WS visuospatial deficits has been from visuomotor tasks, which requires extensive spatial working memory, considerable coordination between visual and motor systems (Farran & Jarrold, 2003), and/or sustained attentional switching between local and global spatial information (Pani, et al., 1999). Levi & Klein, 1991). Ebbinghaus illusion and, correspondingly, greater accuracy at discriminating the real sizes of stimuli in this task relative to UK and Japanese participants. 1We broadly define integration as the combination or coordination of separate elements into a unified group. On the other hand, WS individuals can use grouping properties to facilitate search, suggesting that they can implicitly perceive global organization (Pani, Mervis & Robinson, 1999). performed an experiment in which subjects had to judge which of two central target disks was larger (or smaller), and then they had to grasp that disk. Bihrle AM, Bellugi U, Delis D, Marks S. Seeing either the forest or the trees: dissociation in visuospatial processing. In one randomly selected trial within a pair of trials the longer line was on the right and on the other trial it was on the left. Kaldy Z, Kovacs I. 3d), while its prevalence increased with age (Fig. Hess R, Field D. Integration of contours: new insights. The raw scores correspond to those of normal 8 year-olds (verbal) and 6.5 year olds (matrices) at the 50th percentile. (d) Crucially, geometric means of difference ratios (size difference illusion/size difference baseline), which represent the illusion magnitude, were not reliably different between normal adults and WS participants. The position of the inducing context was constant as described in Section 2.2 (Stimuli). 3b). Experiments have shown that, while adult subjects perceive the center circles as differing in size, they reach out to grasp the circle accurately. haptic information. An NIH fellowship (NS047979) to MP, NIH (NS050876), NSF (0117744) and March of Dimes (04-46 and 01-87) grants to BL, and a JHU undergraduate research award to CO funded this research. What do most people do in the Ebbinghaus illusion? The Ebbinghaus illusion is the phenomenon that a central circle surrounded by large circular flankers is perceived to be smaller than a similar central circle surrounded by small flankers. Thus, the extent to which WS individuals have impaired visuospatial integration is still unsettled. We thank the Williams Syndrome Association, our participants and their families, Gitana Chunyo for help in testing participants and Jim Hoffman for comments on earlier drafts of this manuscript. For lines, we found that 13 out of 23 people correctly discriminated length (one-tailed sign test, p=0.3388). Mirages, for example, is an optical illusion in which the image of the distant object, as a ship, oasis, or water on the dry road ahead or is made to appear nearby. Consistent with our results on perception of contextual illusions, Grice et al. improved performance is due to enhanced expectations as is theorized in Chauvel’s (2014) study, or not. 6The Ebbinghaus illusion might be different from the other illusions we studied. The Ebbinghaus illusion was discovered by the German psychologist Hermann Ebbinghaus (1850–1909).The illusion was popularized by Edward B. Titchener in a 1901 textbook, in English, which is why the illusion is sometimes called "Titchener circles". 4One-way ANOVAs for the Ponzo and Müller-Lyer illusions approached significant levels (p<0.10). comparing a single line and a line with arrowheads) increased the number of young children who had biased responses for choosing targets with inducing context. In the best-known version of the illusion, two circles of identical size are placed near to each other, and one is surrounded by large circles while the other is surrounded by small circles. These surrounded the target circles whose location was held constant throughout the trials. Shape perception reduces activity in human primary visual cortex. Illusion Optics. chance performance). The illusion is based on relative size perception and discovered by a German psychologist at the end of the 19th century. Participants indicated which target line was longer or which circle was larger, by pointing. Moreover, these results suggest that implicit and non-implicit integration of spatial information have different vulnerabilities in abnormal development. The WS group had average raw KBIT scores of 37 (range of 23 to 50) for verbal and 19 (range of 14 to 24) for the matrices components. 2), and were printed via laser printer on 8.5 × 11-inch white letter paper2. For the Ebbinghaus illusion the larger target circle is on left for the expansive trial, and on the right for the compressive trial. (2010) showed that children were less susceptible to this illusion than adults. Tukey post hoc analyses indicate that the size difference at which 3–4 year olds made errors was significantly larger than those at which 5–6, 7–10 year olds and normal adults made errors in the Ponzo illusion. Since participants were forced to choose which target was longer or bigger, they could make correct guesses at the smallest size difference we tested, which could result in no error for a condition. In order to determine whether size discrimination and illusion susceptibility were related to the hallmark impairment in block construction tasks and measures of verbal and non-verbal abilities, we carried out a subset of correlations on scores of WS participants. The perception of Gestalt grouping by shape appears by 6–7 months of age while grouping by luminance appears by 3–4 months of age, suggesting that different perceptual grouping abilities have varied developmental onsets (Quinn, Bhatt, Brush, Grimes & Sharpnack, 2002). These findings show that WS individuals may have functional implicit processes of grouping and visuospatial integration, even though they are impaired in explicit representation of spatial relationships. What illusion is being studied. Here, we introduce a novel variant of this illusion called the Dynamic Ebbinghaus illusion in which the size and eccentricity of the surrounding inducers modulates dynamically over time. In the Müller-Lyer illusion, most people make which line too short? The correlations between DAS block construction scores and size discrimination in the baseline conditions of the Ponzo (n=16; Pearson r=−0.414; p=0.111) and Kanisza-occlusion (n=16; Pearson r=−0.428; p=0.059) were negative, which suggest that better block construction skills may be associated with better size discrimination skills. Meyer-Lindenberg A, Kohn P, Mervis CB, Kippenhan JS, Olsen RK, Morris CA, Berman KF. b.) Across all four illusions, the distributions between normal adults and WS individuals highly overlap, and are not significantly different (see text for details). In a separate procedure, we asked normal adults to discriminate line lengths or circle diameters that were different by 0.0357 deg (i.e., half of the smallest size difference in the main experiment), which is below hyperacuity thresholds for similar inter-target separations (e.g. Letter case and text legibility in normal and low vision. For example, when asked to draw a Navon figure (Fig. 3c). 3a). When the horizontal rectangles were equal in length, the one that passed in front of its inducer appeared longer (Fig. For example, for the Müller-Lyer illusion the inducer that tends to lead to a “larger” response (i.e., the inward-pointing arrowheads) was always on the right. Jordan H, Reiss JE, Hoffman JE, Landau B. 3c). Anatomical studies also indicate reduced overall brain volume with disproportionate reduction in grey matter in the thalamus and V1 (Reiss, Eckert, Rose, Karchemskiy, Kesler, Chang, Reynolds, Kwon & Galaburda, 2004). [2,3]). All t-tests had p-values >0.05. Global spatial organization by individuals with Williams Syndrome. EBBINGHAUS ILLUSION IN TOUCH AS EVIDENCE FOR THE TWO STREAM PERCEPTION-ACTION HYPOTHESIS By Erin Renee Smith The Ebbinghaus Illusion (also known as Titchener's circles) is a classic visual illusion. In non-critical or expansive trials (Fig. Model and copies by WS participants (age in years; months). 3b). We asked if people with Williams Syndrome (WS), a rare genetic disorder that results in severely impaired global visuospatial construction abilities, are also susceptible to the context of visual illusions.
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