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Carl E. Granrud, Melissa A. Granrud; Perception of the Ponzo illusion: A lifespan study. Journal of Vision 2004;4(8):757. doi: 10.1167/4.8.757.
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Leibowitz and Judisch (1967) reported that 5-year-old children do not perceive the Ponzo illusion, and that perception of this illusion declines substantially beyond about 50 years of age. More recent findings suggest that 5-year-olds perceive the Ponzo illusion, and that perception of this illusion may remain constant across the lifespan. However, studies have obtained inconsistent results, and the data on developmental changes in perception of the Ponzo illusion, particularly in late adulthood, are inconclusive. We tested three age groups: 4 to 5 years, 20 to 30 years, and 80 to 90 years of age (n = 20 in each age group). Participants viewed two versions of the Ponzo illusion, one at a time, on a laptop computer, and used the computer's touch pad to adjust each version's basal line to match the length of its apical line. Participants completed 4 practice trials and 10 test trials with each version of the illusion. They also completed a control task for each version of the illusion, in which they matched the lines' lengths without the illusion-inducing context present. This task ensured that every participant understood the study's instructions, could perform the task, and had adequate visual acuity to judge line length. All three age groups perceived both versions of the Ponzo illusion. Mean illusion magnitudes for the 4- to 5-, 20- to 30-, and 80- to 90-year-old groups were 12.5%, 9.5%, and 11.8%, respectively, for one version of the illusion and 8.4%, 9.3%, and 7.3%, respectively, for the other version. One-sample t tests revealed that all six means differed significantly from zero (p < .001 for all tests). One-way ANOVAs found no significant differences between the age groups for either version of the illusion (p > .05 for both analyses). Our study found no evidence of age-related changes in perception of the Ponzo illusion, and our results clearly indicate that this illusion is perceived by 4- to 5-year-old children and 80- to 90-year-old adults.
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