This paper examines the psychological validity of hierarchies in consonantal features based on analyses of naturally occurring speech errors in Mandarin spoken in Taiwan. Differences in consonant pairs that interacted in speech errors involve five features: place, voice onset time, continuancy, frication, and nasality in different proportions. Most errors involve consonant pairs differing in only one feature, and there is a monotonic decrease as the number of feature differences increases. This suggests that consonant similarity in terms of shared features affects the frequency with which two segments are mutually involved in speech errors. Place of articulation is the feature most often violated in speech errors whereas nasality is violated the least often. Such a hierarchy of feature distribution may have some cross-linguistic validity and can be partially explained in Optimality Theory in which faithfulness to manner is ranked higher than faithfulness to place predicting more error violations in place features.