Inverse discrimination time as a perceptual distance for alphabetic characters

Reaction times to discriminate lower‐case letters were collected in an experiment. The inverse discrimination times were used to build metrics on the space of letters. These metrics were found to be significantly correlated with various well‐known letter confusability measures, and a meaningful dimensional analysis of the alphabet was performed. This methodology is mathematically well founded, it requires fewer data than common methods, and it appears to be highly sensitive to visual similarity between letters, which allows visual letter features to be effectively analysed.