@inproceedings{Itti_etal99arvo,
  author = {L. Itti and J. Braun and C. Koch},
  title = {Contrast Discrimination can Explain Orientation Discrimination},
  volume = {40},
  number = {4},
  pages = {3016},
  month = {Mar},
  year = {1999},
  abstract = {Purpose: Many current early vision models consist of a population of noisy orientation-selective filters, followed by noiseless central decision. It has been argued (Bowne, Vis Res 1990;30:449-61) that all such models, with noise only at the sensory level (filters), cannot explain the differential dependence of contrast and orientation discrimination thresholds on stimulus contrast (Delta_c propto c^-0.4 versus Delta_theta propto c^-0.1, c>0.1). Most current models indeed predict improvement with contrast at the same rate for Delta_c/c and Delta_theta, both resulting from an overall improvement in signal-to-noise ratio with stimulus contrast. One way to reconcile both observations is to assume additional, task-dependent noise at the central decision stage (Bowne, 1990). Here, we argue that this apparent contradiction constitutes further evidence for a certain type of non-linear interactions among filters (``divisive inhibition'', also known as ``Heeger normalization''). [[[FIGURE]]] Results: A model with noiseless decision was able to simultaneously account for both observations (figure) by implementing strong non-linear excitatory and inhibitory interactions between filters tuned to similar orientations. Resulting from the interactions, the orientation tuning bandwidth of the filters broadened by 25\% as c increased from 0.01 to 0.99, which partially canceled the improvement of Delta_theta with c, but did not affect Delta_c/c. Conclusion: ad hoc task-dependent central noise is unnecessary provided that filters interact. Far from constituting a weakness of current spatial vision models, the differential contrast dependence of different types of thresholds corroborates the current views as to the nature of interactions between filters.},
  booktitle = {Investigative Ophthalmology and Visual Science (Proc. ARVO 1999)},
  type = {mod;psy},
  file = {http://iLab.usc.edu/publications/doc/Itti_etal99arvo.pdf},
  review = {abs/conf},
}