Figure 2.

Noise paradigm for quantifying limits of local and global processing of orientation. (a) Stimuli contain a Gaussian range of orientations, and subjects judge whether the overall orientation is clockwise or anti-clockwise (in this case, clockwise) of a reference orientation (here, vertical). The inset to the lower-right shows a model observer limited by the local precision with which it can estimate the orientation of each element (σ_loc) and by the global number of samples it can average (N_glo). (b) Sample psychometric function collected with various offsets of the mean orientation; the slope of this function is our performance estimate. (c) Such noise experiments involve estimating such thresholds as a function of the range of orientations present. Data can then be modeled (using the boxed equation) to yield estimates of local and global limits on performance. The two dashed lines show the signatures of poorer local or global processing.