Fig. 2.

Results from Experiment 1. Perceived contrast of the center stimuli is shown separately for the (a) simultaneous and (b) sequential conditions. Observers’ estimates of the center stimulus contrast were near veridical (indicated by the dashed line). Data points reflect the apparent contrast estimates across all contrast levels, averaged over observers (N = 12), for the three different surround conditions (collinear, orthogonal, and no surround). Error bars denote ±1 SEM (note that in some cases the error bars are smaller than the data points). Schematics above the graphs illustrate the general experimental design. Normalization strength estimates (c) were derived from the normalization model. Parameter estimates illustrate the influence of the surround (collinear and orthogonal) on perceived contrast of the center stimulus for both the simultaneous and sequential conditions (see the Supplemental Material available online for additional parameter estimates). Error bars denote ±1 SEM.