Neurobiology

Margaret S. Livingstone, Ph.D.

Professor of Neurobiology

We are interested in how cells in the visual system process information. Previous emphasis in the lab was on the parallel processing of different kinds of visual information: form, color, depth, and movement. We discovered an interdigitating and highly specific connectivity between functionally distinct regions in V1 and V2 (Livingstone and Hubel, 1984, 1987).

Presently we have become more interested in how each of these variables is coded by cells in visual cortex. We developed a method for high-resolution receptive-field mapping in alert animals, and have used this technique to explore color perception, stereopsis and direction selectivity in primate V1, MT, V4, and IT. We have further developed this method to allow us to to look at interactions between stimuli (second-order interactions). These maps allow us to see how stimuli are integrated by single cells.

This figure shows the spatial organization of L and M cone inputs to four color opponent cells in V1.

We used this technique in MT, an extrastriate visual-motion area, and found that we can see subunit structure in MT cells, which shows us how cells at one stage integrate information from previous stages. This technique is nice because it makes no assumptions about the structure or function of these complicated receptive fields, but it yields rich information about how they process visual stimuli. A longer-term goal is to use this mapping technique in other extrastriate visual areas to explore still more complex receptive fields, looking at color and form processing. Doris Tsao has recently begun studying the mechanisms of face selectivity by combining single-unit recording with function MRI.

A side interest in the lab is to use what we know about vision to understand some of the discoveries artists have made about how we see. The separate processing of color and form information has a parallel in artists' idea that color and luminance play very different roles in art (Livingstone, Vision and Art, Abrams Press, 2002). The elusive quality of the Mona Lisa's smile can be explained by the fact that her smile is almost entirely in low spatial frequencies, and so is seen best by your peripheral vision (Science, 290, 1299). These three images show her face filtered to show selectively lowest (left) low (middle) and high (right) spatial frequencies.

So when you look at her eyes or the background, you see a smile like the one on the left, or in the middle, and you think she is smiling. But when you look directly at her mouth, it looks more like the panel on the right, and her smile seems to vanish. The fact that the degree of her smile varies so much with gaze angle makes her expression dynamic, and the fact that her smile vanishes when you look directly at it, makes it seem elusive.

Bevil Conway and I recently began looking at depth perception in artists, because poor depth perception might be an asset in a profession where the goal is to flatten a 3-D scene onto a canvas. We found evidence that a surprisingly large number of talented artists, including Rembrandt, might be stereoblind (Livingstone and Conway, 2004).  In the etching below you can see that Rembrandt portrayed himself as strabismic (with misaligned eyes).  If this were the case in only one or two of his self portraits, or if he also showed other subjects with misaligned eyes, we wouldn’t think anything of it, but Rembrandt most of the time portrays himself, but not other subjects, as wall-eyed, and the outward deviating eye is reversed in his paintings compared with his etchings (think about it!)