Lingering hues orient perception.

What you see is not always what you get. Consider the case of a 36-year-old woman who suffered irreversible damage to much of her primary visual cortex, a 2-millimeter-thick swatch of cells at the back of the brain that processes information taken in by the eyes. Although the woman consistently errs in describing the orientation of objects -- such as whether a rectangular block lies horizontally or vertically -- Canadian psychologists find that her visual cortex nonetheless makes accurate orientational distinctions that lie outside her conscious awareness. This helps explain why she can handily reach out and grasp a block despite her reported confusion about its orientation, maintain G. Keith Humphrey of the University of Western Ontario in London and his colleagues.

Humphrey's group tested the brain-damaged woman's unconscious perception of oientation by charting her reports of colors that linger after focusing on red and green patterns oriented in different directions. Psychologists have long noted this effect in people with normal vision. In one test, the woman -- whose color perception remained normal -- viewed two patterns that alternated every 10 seconds for 10 minutes: a circle composed of green and black vertical grates, and a circle composed of red and black horizontal grates. After a five-minute break, she looked at circles with a mix of black and white vertical grates and black and white horizontal grates. The woman reported seeing horizontal white grates as green, and vertical white grates as pink. When the experimenters rotated the circles so that the grates slanted to the left or right, the colors faded to white.

Healthy brains may employ one anatomical mechanism to assess unconsciously the orientation of objects, such as the alighnment of a block or grate, and another to make conscious judgments concerning orientation, the researchers propose in the just-received September PSYCHOLOGICAL SCIENCE.