The "top-down" effects of grasping-form on simultaneous contrasts.

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To examine the top-down effects on simultaneous contrasts under various stimulus conditions, we measured the magnitudes of hue and brightness contrasts (MHCs and MBCs) by manipulating subjects' attitudes and experiences on visual perception. First, we arranged the subjects' experimental literacy to identify the difference between hue/brightness contrast and assimilation in the perception of Koffka-ring type patterns ("striped" patterns). Results revealed that the subjects, who knew the transition from "contrast" to "assimilation" when the test figure (TF) made wider than the inducing figure (IF), reported typical transition in the MHCs and MBCs under the increasing ratio of striped TF to IF.Furthermore, the subjects' experimental literacy was tailored to examine the relationship between the hue contrast and the similarity of TF's geometrical row-patterns (for instance, gray circle on red IF vs.gray square on green IF). Further results indicated that the subjects, who were well versed in the relationship between the TF's pattern and the hue contrast, positively responded to the existence of the significant relationship between the TF's figural similarity and the MHCs. In conclusion, the top-down (grasping) attitudes adopted by the subjects generate the different effect even on the more peripheral or sensitive phenomena such as simultaneous contrast. To further elaborate the top-down effects on simultaneous contrast, we need more intensive studies using more developed experimental conditions.