Schematic diagrams of stimulus and task procedure.

<p><b>(a)</b> A target letter was viewed through an aperture with varying sizes (in diameter) ranging from 1.2° to 9° in diameter. The numbers in the parentheses indicate the aperture sizes as percentages of the area of the circle containing the stimulus target. The size of the target image was 4° of visual angle. <b>(b)</b> At the beginning of each trial, participants were instructed to fixate on a central dot on the display screen to make sure that the aperture always appears on the center of a target image. A participant’s task was to identify the target stimulus as quickly and accurately as possible. Participants freely moved the viewing window over the target image via a gaze-contingent display until they could recognize the target identity. Participants pressed space bar as soon as they recognized its identity. Then, participants reported the target identity by clicking one of 26-letter images or 26-face names response keys forming a clock face. This measurement was repeated for three different blur levels, including no blur.