Assimilative hue shifts in color depend on bar width

Hue shifts were measured in isoluminant color gratings whose bar width was varied from 2′ to 20′ of visual angle. Subjects matched the hues in each grating with individual Munsell swatches. Hue shifts were largest for bar widths of 2′; however, they depended on the color combination used. Green and red shifted toward (i.e., assimilated with) whatever second grating color they were paired with. Blue, on the other hand, assimilated with red and with yellow, but remained relatively unchanged when combined with green. Yellow shifted only minimally, regardless of the second grating color. Hue shifts decreased with increasing stripe width and disappeared between 4.5′ and 7.5′. Compared with the assimilative hue shifts, color contrast effects were slight or absent. These results cannot be attributed merely to chromatic aberration, macular pigment, eye movements, or field size.