This study investigated how the variations of width-ratios of the gray test figure (TF) to the inducing figure (IF) in slanted stripe-patterns of Koffka-ring type influenced the shift of simultaneous brightness/hue assimilation and contrast. Subjects estimated the appearances of gray TFs in the five TF-to-IF width-ratios of stripes on the display using black-white (Experiment 1) and red-green (Experiment 2) IF-presentations. The results revealed that the magnitudes of brightness and hue contrasts in the TF increased as the TF-to-IF width-ratio decreased. A significant assimilation was not observed in the mean magnitudes of TF-appearance in the width-variations of stimulus-patterns. Consequently, the stimulus-patterns used in this study seemed to cause the subjects to perceive the brightness and hue contrasts throughout the width-variation. However, the tendency to assimilation in the larger TF-to-IF width-ratio was observed by the subjects who were more attentive to the pattern-location in their viewing style. Therefore, it may be postulated that the contrast is primarily affected by sensory (bottom-up) factors while the assimilation is affected by cognitive (top-down) factors in the brightness and hue information-processing.

Key words: Koffka-ring type stripe-pattern, assimilation and contrast, effects of width-variation, viewing-attitude