Figure 4.

Comparison of the effects of crowding and attentional load on judgment of mean orientation. (a–c) Three subjects’ mean-orientation discrimination thresholds are plotted as a function of the orientation variability of the stimulus, under four experimental conditions (indicated by the legend). Fits of the noise model to the crowded (dashed lines) and attentional-load conditions (thicker lines) are also shown with corresponding estimates of local noise (s) and global sampling (n) listed in the legend box. Note that the addition of attentional load, to crowded or uncrowded conditions, has the effect of shifting data upward on log-log axes. Crowding, by contrast selectively impairs performance only at low levels of orientation variability. (d–g) Summarizes these findings for all observers. Crowding reduces subjects’ local precision i.e. at estimating the orientation of individual elements, while attentional load reduces the number of elements they effectively pool to make their judgment.