Comparing visual perception on conventional cabinet tachistoscopes and computer monitor tachistoscopes

Abstract

Computer monitor-based tachistoscopes (using a cathode ray tube, CRT)and conventional tachistoscopes differ in experimental control over stimulus continuity, duration, and timing accuracy. This study evaluated the perception of visual stimuli presented with the two different types of devices. An experiment was conducted to compare recognition of visuospatial stimuli (random shapes) presented laterally and centrally in the visual fields for short exposure durations (14, 29, and 43 msec), first with one device and then with another. Results indicated that the subjects' error rates and laterality patterns were similar on both types of tachistoscopes. It was concluded that perception of visual stimuli presented as continuous images on a conventional tachistoscope may be equivalent to perception of visual stimuli presented as pulsating Images on a CRT. Further studies are needed using other types of visual materials to determine the range of visual stimuli for which both types of tachistoscopes measure equivalent perceptual processes.Tachistoscopic presentation ofvisual stimuli is an important technique used by psychologists to study cognitive and neuropsychological functions. Computer-based tachistoscopes using the computer's monitor for stimulus presentation have virtually replaced conventional cabinet and projection tachistoscopes as the means ofpresenting stimuli. However, due to the nature ofthe raster-scan cathode ray tube (CRT) display employed in most computer monitors, stimuli presented on those monitors have certain fundamental differences from those presented on conventional tachistoscopes. These differences may have particular implications for (I) studies employing brief exposure durations, (2) studies attempting to determine visual thresholds or critical interstimulus intervals, and (3) perceptuallaterality studies. The purpose ofthe present study was twofold. First, we sought to review the different properties ofthe two types oftachistoscopic presentation methods and to evaluate their limitations. Second, we determined experimentally the extent to which these differences would affect subjects' perception of stimuli that were presented centrally and in the lateral visual fields for brief exposure durations. TACHISTOSCOPIC PRESENTATION METHODS AND THEIR LIMITATIONS Artifacts of CRT ImagesThe image on a CRT consists of glowing regions of phosphor energized by electrons. In the raster-scan CRT used in most computer monitors, an electron beam (or group ofthree beams for most color monitors) scans the entire phosphor-coated screen in aseries ofparallellines that form the raster. The electron beam is tumed on, energizing the phosphor, when passing a point where the screen is to glow, and tumed off where it is to stay dark. This raster-scan process takes about 35 usec per line in a common video graphics array (VGA) monitor, completely refreshing the screen in about 13-17 msec, depending on the monitor and controller card in use.Typically, each point of energized phosphor glows for less than I msec. The raster s...

Full-screen ultrafast video modes over-clocked by simple VESA routines and registers reprogramming under MS-DOS

“…As has been pointed out by some authors (Bridgeman, 1998;Hutner et al, 1999), the persistence of the monitor's phosphor should be taken into account. Thus, if the persistence of the monitor's phosphor is longer than the refresh interval, the shortest stimulus duration is decided by the monitor's phosphor, no matter which refresh rate is provided by this method.…”

“…Thus, if the persistence of the monitor's phosphor is longer than the refresh interval, the shortest stimulus duration is decided by the monitor's phosphor, no matter which refresh rate is provided by this method. However, typical monitors have fast decay phosphors, and the persistence time is less than 4 msec (Bridgeman, 1998), or on the order of 0.2-0.6 msec (Hutner et al, 1999). Then, the shortest stimulus duration is decided by this method if the final refresh rate is below 250 Hz.…”

“…Researchers have put much effort into this issue (Bokhorst, 1995;Diesch, 1994;Hutner, Duboff, Oscar-Berman, & Mueller, 1999;McKinney, MacCormac, & Welsh-Bohmer, 1999;Myors, 1998Myors, , 1999a. The key problem is the refresh cycle of the video card, which is 60 Hz under standard VGA 640 3 480 mode.…”

“…This problem becomes extremely significant if two stimuli are desired to be displayed at the same time, one at the top part of the screen and the other at the bottom part of the screen. The gap will be above 10 msec, if the stimuli are small and near the edge of the screen (Hutner et al, 1999).…”

Development of a light-emitting diode tachistoscope

“…[5][6][7] To display images in their entirety, stimulus exposures must be multiples of the refresh rate, placing physical limits on the durations that can be achieved. However, as with their predecessors they also are compromised, particularly for short exposures.…”