The results of several experiments are reported most of which suggest that there is an optimum density for weight discrimination. This density corresponds to the “non-illusory” density, as determined by the density at which a visible weight is correctly matched with a hidden weight. The greater the illusion (whether of heaviness or lightness) the poorer the discrimination.
It is pointed out that similar changes in discrimination occur as a result of peripheral sensory adaptation in many modalities; but that the size-weight illusion, and the associated discrimination changes, must be due to a central scaling process. A theoretical model is suggested.
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