Figure 2.

Context has little effect on contrast discrimination. Each panel shows threshold contrast increment c_t, versus pedestal contrast c, in a different context. Error bars contain 95% confidence intervals. All curves adhere to a transducer model of contrast discrimination (Foley 1994), in which $(a{(c+c_t)}^p/(b^{p-q}+{(c+c_t)}^{p-q}))-(a{c}^p/(b^{p-q}+c^{p-q}))=1$. Baseline values (solid curves) for JAS are: a=19, b=0.044, p=3.6 and q=0.7; for CG: a=11, b=0.056, p=3.6 and q=0.5. When p was allowed to vary with the surround orientation, a slightly but significantly better fit (dotted curves) was obtained for each observer.