EFFECTS OF GRASPING-FORM ATTITUDE ON BRIGHTNESS CONTRAST IN KOFFKA-RING TYPE PATTERNS

The purpose of this study is to examine the effects of ''grasping-form '' of non-annular test figure (TF) on simultaneous brightness contrast in Koffka-ring type patterns. To systematically manipulate the figura l unity under brightness contrast, we used a color-graphic system to i nvestigate the stimulus conditions (five degrees of separation) of the TF. Utilizing the two attitudes for grasping the TF (i.e., as a unifi ed whole or two segmented parts), seven subjects were instructed to ad just the comparison figure to match the apparent brightness of two TF sections overlapping on a black-white inducing figure with gray backgr ound. The results revealed that the magnitudes of brightness contrast (MBCs) in the TF decreased as the degree of separation decreased for b oth grasping attitudes. The average MBCs were significantly larger in the segment-grasping than in the unity-grasping, although the decrease -trait of the MBCs generally corresponded to cash other in either type of grasping-form. grasping-form. As a consequence, the grasping-form attitudes seem to represent a kind of ''image-manipulation'' by the ob servers, who may perceive the configuration of the TF at various infor mation-processing stages without being directly influenced by the TF a ppearance.