Abstract
Six subjects on a building roof viewed the outside terrain through a projection device which superposed a full horizon moon on that view. Subjects judged the size of the moon in various scenery configurations by adjusting a comparison disc while accommodation measurements were taken using a laser optometer. Results showed a strong correlation between mean accommodative states and size judgments during the day and a weaker correlation at night. Accommodation responses were not identical to all scenes and as accommodation shifted inward, the judged size of the moon decreased. “Night myopia” was also clearly evident. The relatively nearer accommodation responses and smaller size judgments of the isolated zenith-type moon as compared to the horizon moon suggests that the moon illusion is mediated by the accommodation mechanism. The results are discussed in connection with a similar study by Iavecchia, Iavecchia and Roscoe, and differences in the mean “dark focus” of accommodation between the two groups are related to the findings.
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