Abstract
BackgroundIn visual psychophysics, precise display timing, particularly for brief stimulus presentations, is often required. The aim of this study was to systematically review the commonly applied methods for the computation of stimulus durations in psychophysical experiments and to contrast them with the true luminance signals of stimuli on computer displays.Methodology/Principal FindingsIn a first step, we systematically scanned the citation index Web of Science for studies with experiments with stimulus presentations for brief durations. Articles which appeared between 2003 and 2009 in three different journals were taken into account if they contained experiments with stimuli presented for less than 50 milliseconds. The 79 articles that matched these criteria were reviewed for their method of calculating stimulus durations. For those 75 studies where the method was either given or could be inferred, stimulus durations were calculated by the sum of frames (SOF) method. In a second step, we describe the luminance signal properties of the two monitor technologies which were used in the reviewed studies, namely cathode ray tube (CRT) and liquid crystal display (LCD) monitors. We show that SOF is inappropriate for brief stimulus presentations on both of these technologies. In extreme cases, SOF specifications and true stimulus durations are even unrelated. Furthermore, the luminance signals of the two monitor technologies are so fundamentally different that the duration of briefly presented stimuli cannot be calculated by a single method for both technologies. Statistics over stimulus durations given in the reviewed studies are discussed with respect to different duration calculation methods.Conclusions/SignificanceThe SOF method for duration specification which was clearly dominating in the reviewed studies leads to serious misspecifications particularly for brief stimulus presentations. We strongly discourage its use for brief stimulus presentations on CRT and LCD monitors.
Highlights
Motivation and Scope Precise timing of visual stimuli can be a requirement for experiments in psychology
323 studies were discarded because after reviewing the full text it appeared that the experiments described in them did not make use of stimulus durations, onset asynchronies, or interstimulus intervals of less than 50 ms
This systematic review shows that the sum of frames (SOF) method is the clearly dominating measure to specify the durations of stimuli even for brief presentations
Summary
Motivation and Scope Precise timing of visual stimuli can be a requirement for experiments in psychology. In rapid serial visual presentation paradigms, the onsets and offsets of the single stimuli need to be known and controlled for exactly to study perceptual phenomena like repetition blindness [1] or the attentional blink [2] Another widely used technique is visual masking [3] in which the visibility of a briefly presented target stimulus is impaired by a masking stimulus presented in close spatiotemporal proximity. This paradigm, which is used in many experimental situations in psychophysics and visual neuroscience, requires brief stimulus presenations and precise timing for the stimuli themselves and for the temporal distances between their presentations. The aim of this study was to systematically review the commonly applied methods for the computation of stimulus durations in psychophysical experiments and to contrast them with the true luminance signals of stimuli on computer displays
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