Delboeuf錯視における判断順序効果

Apparent size of circles in the Delboeuf configuration was judged under variation of their diameters and compared to that of circle singletons of equivalent diameter. The primary purpose of the study was to investigate the effect of judgment order on the perceived size, i.e. starting with either inner or outer circle. In addition，we compared the measured strength of the illusion as obtained by two different methods - category rating and magnitude estimation. We found that the circle judged first had an assimilative effect on the apparent size of the subsequently judged circle，with the amount of the effect being contingent on diameter ratio and diameter difference of the constituent circles. Moreover，assimilation of the inner circle was more pronounced than that of the outer circle. The judgment-order effect may be accounted for by attentional mechanisms: if the outer circle is judged first，spatial span of attention is large，so that the inner circle falls in the span. Conversely，if the inner circle is judged initially，spatial span of attention is too small to take up the outer circle. The amount of illusion was greater when judged using magnitude estimation than category rating， conceivably due to a coarser internal mapping at the latter procedure.