What is the reference in reference repulsion?

Reference repulsion is a mechanism posited to explain systematic biases of direction judgment of single drifting dot displays (Rauber and Treue, 1998 Perception 27 393-402). Rauber and Treue obtained systematic but, surprisingly, very different effects depending upon whether standard and comparison stimuli were presented simultaneously or successively. Successive effects were described as exhibiting repulsion from both vertical and horizontal cardinal axes, whereas simultaneous effects showed repulsion from horizontal only. We contend that the proposed mechanism makes no testable predictions because the so-called reference can only be specified a posteriori, a fact acknowledged by Rauber and Treue. We attempted to replicate Rauber and Treue's experiments, but we obtained no systematic biases of direction judgment. Comparisons across several studies suggest that errors in direction judgments of single drifting dot patterns vary widely in magnitude and direction, as might be expected with what are essentially baseline or pretest measures. In our view, reference repulsion describes neither a real perceptual mechanism nor a predictable pattern of direction misjudgments.