a radial motion bias

Beardsley S. A., Vaina L. A. (2005). Psychophysical evidence for a radial motion bias in complex motion discrimination. Vision Research, 45, 1569–1586.
PubMed
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Burr D. C., Badcock D. R., Ross J. (2001). Cardinal axes for radial and circular motion, revealed by summation and by masking. Vision Research, 41, 473–481.
PubMed

Reverse Hierarchy Theory

Ahissar, M. & Hochstein, S. (2004). The reverse hierarchy theory of visual perceptual learning. TRENDS in Cognitive Sciences 8(10): 457-464

Ahissar, M. & Hochstein, S. (1997). Task difficulty and the specificity of perceptual learning. Nature 387:401–406.

pdf etc.