The attenuation of perceived image smear during saccades.

The perception of image smear for a target flashed during a saccade is attenuated if the target remains visible after the eye movement ends, a result that has been attributed to backward masking. In this experiment, normal observers matched the length of perceived smear in two conditions that were designed to produce comparable retinal stimulation and, therefore, similar amounts of masking. In the saccade condition, a small stationary bright dot was illuminated for 5-640 ms, starting near the onset of a horizontal saccade. In the fixation condition, the bright dot moved right or left at 50, 100, or 200 degrees s-1 while the observer viewed a stationary target and, thereafter, remained stationary. As expected, in the saccade condition perceived smear first increased and then decreased as the duration of the flashed dot extended beyond the duration of the eye movement. However, perceived smear was substantially greater in the fixation condition for stimulus durations that were longer than the period of dot motion. Under the conditions of our experiment, the attenuation of perceived image smear during saccades is attributable primarily to the operation of an extraretinal eye movement signal, rather than to backward masking.