Visual working memory contains a representation of certain image statistics (Victor & Conte, 2004), in addition to a pixel-by-pixel representation. Here, we show that the representation of statistics is more stable in time (up to 3000 ms) than the pixel-by-pixel representation, especially for changes in luminance and local high-order statistics, and is not affected by visual masking. Bilaterally symmetric arrays and arrays with local correlations are more readily encoded than random ones, but a change in the presence of bilateral symmetry, per se, contributes only modestly to the ability to detect that an array has changed.