Performance in discriminating rotated 'same' patterns from 'different' patterns may decrease with rotation angle up to about 90° and then increase with angle up to 180°. This anomalously improved performance under 180° pattern rotation or point-inversion can be explained by assuming that patterns are internally represented in terms of local features and their spatial-order relations ('left of', 'above', etc.), and that, in pattern comparison, an efficient internal sense-reversal operation

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... (transforming 'left of' to 'right of ', etc.). Previous experiments suggested that local features and spatial relations could not be efficiently separated in some pattern-comparison tasks. This hypothesis was tested by measuring 'same-different' discrimination performance under four transformations: point-inversion i 1 of the whole pattern, pointinversion lF of local features alone, point-inversion lp of local-feature positions alone, and identity transformation Id. The results suggested that internal sense-reversal operations could be applied selectively and efficiently, provided that local features were well separated. Under this condition performances for lF and l were about the same whereas performance for lp was significantly worse, the latter performance resulting possibly from an attempt to apply internal global and local sense-reversal operations serially.