The Effect of a Central Task on Luminance Thresholds for Peripherally Presented Stimuli

The effect of a central task on peripheral vision was investigated by obtaining luminance thresholds for stimuli presented from 20° to 90° in the periphery. A control group observed a steady foveal fixation light. For the two experimental groups, the fixation light was interrupted periodically and the subject was required to maintain illumination of the light by pressing a button. Interruption rates of 15 and 53 times per minute were investigated. The control condition with the steady fixation light produced the lowest thresholds. For the interrupted conditions, thresholds were higher for the near periphery but differences disappeared in the far periphery. Luminance threshold values were generally highest for the 15-per-minute interrupted group. The results are interpreted as reflecting the effect of an attention-demanding central task on the size of the functional visual field.