Abstract

People tend to perceive a vertical line to be longer than the same size of horizontal line (the horizontal-vertical illusion; HVI). We asked whether the configuration of a form could have an effect on HVI, using the method of adjustment where participants adjusted the length of one (horizontal or vertical) line to be equal to that of the other line. In the first experiment, when '⊥' -like and 'ㅏ' -like figures with varying division positions were introduced, the total amount of HVI changed with the division position (so-called bisection effect; BE). The amount of pure HVI (with BE subtracted) was less in the '⊥' type figures than in the 'ㅏ' type figures. Trend analysis on the HVI of '⊥' type figures showed that BE had a quadratic component, which we thought was a reflection of configural effect of a whole form. In the second experiment with a rectangular or a cross, HVI was less in these good configurations than in the 'ㄴ' type figures. In the third experiment, we divided each of the above good configurations into two separate 'ㄴ' type figures and observed less HVI with the divided patterns than with the 'ㄴ' figure. But the effect size was small. It was concluded that configuration could have an effect on HVI and some of its effect could result from the multiple comparison pairs belonging to the configuration. Configurational aspects and anchorage effect in size judgment were discussed.