Why Can't I Spot Four-Leaf Clovers? Q. My wife easily finds four-leaf clovers, standing up. I never can, even on hands and knees. A. The standard strategy involves pattern recognition, "finding a square in a sea of triangles," said Dr. Marc J. Dinkin, director of neuro-ophthalmology at NewYork-Presbyterian Hospital/Weill Cornell Medical Center. A complex neural network is involved, he said. First, the viewer must have the visual acuity and the sensitivity to color and contrast to perceive leaves as separate objects, or at least see the usual white lines perpendicular to each leaf's axis. Assuming the retina and optic nerve are healthy, these functions are likely intact, so why does he have trouble spotting those lucky leaves? Dr. Dinkin asked. The answer may lie in his visual cortex. Once information from retinal cells reaches the visual cortex in the brain's occipital lobe, it is parsed and sent to centers with specific cells for various orientations of lines. In combination, they detect shapes. From there, information about objects and patterns is forwarded to the temporal lobe, for comparison with known images. Absent serious brain damage, Dr. Dinkin said, the primary issues are probably attention and technique. Attention is crucial, focusing only on key shapes and ignoring superfluous details. As for technique, he said pawing on hands and knees may be doomed to fail; standing back and scanning is more effective, and speed probably improves with practice.