Developmental trends in the adherence of perception to Weber's law

Weber’s law, a basic psychophysical principle by which sensitivity to changes along a given physical dimension decreases when stimulus intensity increases, characterizes human adults' perception for virtually all sensory dimensions. Nevertheless, the developmental trajectory of its validity in perception has not yet been tested. Here we investigated how early in childhood perception becomes adherent to Weber’s law (i.e. minimum detectable increment in stimulus magnitude increases proportionally with stimulus magnitude). Children aged 5-10 and adults were asked to perceptually estimate the size of discs varying in radius. The just noticeable difference (JND) for a given size was determined in the method of adjustment by the variance of the estimations. JND increased with object size in accord with Weber’s law at all ages tested. However, while for adults JND increased linearly with stimulus magnitudes, young children exhibited a quadratic trend in the increment in JND with stimulus magnitude. The results thus document a fundamental difference in the way visual information is encoded by the developing perceptual system compared to the matured one, even at a very basic level of processing. We also showed that, similar to adults, visually-guided action in children violated Weber’s law, providing the first clear evidence for an early emergence of the dissociation between vision for perception and vision for action in children.