Fig. 1.

Eight Gabor letters. The letters of the IndyEighteen alphabet are composed of Gabors. Each of the 18 possible Gabors is oriented ±45° from vertical and is at one of nine locations in a 3 × 3 grid. When a right-tilted and a left-tilted Gabor coincide, they form a plaid, but vision still responds to them independently. We suppose that the Gabors are detected independently, so that each Gabor is a feature. With two orientations and nine locations, there are 18 possible Gabors, i.e., features. The eight letters displayed here are a randomly selected subset of the 2¹⁸ letters in the whole alphabet. Note that within this subset, some features are common to many letters (e.g., six of the eight letters contain a right-tilted Gabor at the top right corner), whereas some features are common to just a few (e.g., two of the eight letters contain a right-tilted Gabor at the bottom left position).