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Size constancy fails below half a degree

J Ross, B Jenkins, J R Johnstone

    Nature
    |January 31, 1980
    PubMed
    Summary
    This summary is machine-generated.

    Size constancy, the perception of object size despite changing image size with distance, has limits. This study shows size constancy holds for image sizes above 0.5 degrees, breaking down below this threshold.

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    Area of Science:

    • Visual Perception
    • Psychophysics
    • Cognitive Science

    Background:

    • Size constancy is the perceptual phenomenon where objects appear to maintain their size despite changes in the size of their retinal image as distance varies.
    • The limits of size constancy are known, with examples like people appearing small when viewed from great heights.

    Purpose of the Study:

    • To investigate the threshold at which size constancy breaks down.
    • To determine the minimum image size required for accurate size scaling with distance.

    Main Methods:

    • Observing various objects at different distances, including the Moon.
    • Utilizing after-images to assess perceived size.
    • Measuring image size in degrees of visual angle.

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    Main Results:

    • Size constancy was demonstrated to hold when the image size was greater than half a degree (0.5°).
    • Size constancy was found to break down when the image size was less than half a degree.
    • Image size is scaled for perceived distance only when the image size exceeds the 0.5° threshold.

    Conclusions:

    • A critical threshold of 0.5° for image size exists for the successful operation of size constancy.
    • Visual perception relies on image size relative to distance, with a minimum angular size necessary for accurate interpretation.