Abstract
We live almost literally immersed in an artificial visual world, especially motion pictures. In this exploratory study, we asked whether the best speed for reproducing a video is its original, shooting speed. By using adjustment and double staircase methods, we examined speed biases in viewing real-life video clips in three experiments, and assessed their robustness by manipulating visual and auditory factors. With the tested stimuli (short clips of human motion, mixed human-physical motion, physical motion and ego-motion), speed underestimation was the rule rather than the exception, although it depended largely on clip content, ranging on average from 2% (ego-motion) to 32% (physical motion). Manipulating display size or adding arbitrary soundtracks did not modify these speed biases. Estimated speed was not correlated with estimated duration of these same video clips. These results indicate that the sense of speed for real-life video clips can be systematically biased, independently of the impression of elapsed time. Measuring subjective visual tempo may integrate traditional methods that assess time perception: speed biases may be exploited to develop a simple, objective test of reality flow, to be used for example in clinical and developmental contexts. From the perspective of video media, measuring speed biases may help to optimize video reproduction speed and validate “natural” video compression techniques based on sub-threshold temporal squeezing.
Highlights
Motion pictures—videos—are becoming pervasive in our everyday life
The mean adjustment rates over the entire trial duration were quite similar across display sizes and repetitions, the only statistically significant effect being the video clip main factor (F(3,33) = 5.680, p = 0.003, η2 = 0.341)
The largest systematic speed error was found with physical motion (C3, water waves, point of subjective equality (PSE) = 25%), and smaller errors were found with human motion (C1, jumping man, PSE = 9%), ego-motion (C4, walking in the crowd, PSE = 4%), and mixed human-and-physical motion (C2, foot dribbling, PSE = 3%)
Summary
We found a small but reliable tendency toward speed underestimation, which suggests that the best speed for reproducing a video may not be its original shooting speed. This may sound rather counterintuitive, as we tend to implicitly assume that shooting speed and reproduction speed should coincide, for otherwise motion rendering would be sub-optimal or even artifactual. This may sound rather counterintuitive, as we tend to implicitly assume that shooting speed and reproduction speed should coincide, for otherwise motion rendering would be sub-optimal or even artifactual1
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