Absolute identification exposes a fundamental limit in human information processing. Recent studies have shown that this limit might be extended if participants are given sufficient opportunity to practice. An alternative explanation is that the stimuli used which vary on only one physical dimension may elicit psychological representations that vary on two (or more) dimensions. Participants may learn to take advantage of this characteristic during practice, thus improving performance. We use multi-dimensional scaling to examine this question, and conclude that despite some evidence towards the existence of two dimensions, a one dimensional account cannot be excluded.