Position discrimination may be better than detection.

@article{Allik1982PositionDM,
  title={Position discrimination may be better than detection.},
  author={J{\"u}ri Allik and Ehtibar N. Dzhafarov and M Rauk},
  journal={Vision research},
  year={1982},
  volume={22 8},
  pages={1079-81}
}