Note on duration of stimulus exposure in experiments on covert scanning of laterally shown targets

Prevention of contamination by eye movements is on methodological requirement in the choice of an exposure time in experiments on the covert scanning of stimuli, tachistoscopically exposed laterally. The use of measures of eye movement latency to set upper limits for exposure intervals seems questionable because latency does not index the total time (minimally, 200 msec.) required to obtain information through an eye movement. The foregoing requirement, however, is only one consideration in selection of an exposure time. Since covert encoding processes can only function while the stimulus is on and during the after-stimulation, duration of exposure delimits the operating time of these processes. Choice of an interval, therefore, should establish the setting required to study those aspects of covert scanning of experimental interest.