Low perceptual sensitivity to altered video speed in viewing a soccer match

Abstract

When watching videos, our sense of reality is continuously challenged. How much can a fundamental dimension of experience such as visual flow be modified before breaking the perception of real time? Here we found a remarkable indifference to speed manipulations applied to a popular video content, a soccer match. In a condition that mimicked real-life TV watching, none of 100 naïve observers spontaneously noticed speed alterations up/down to 12%, even when asked to report motion anomalies, and showed very low sensitivity to video speed changes (Just Noticeable Difference, JND = 18%). When tested with a constant-stimuli speed discrimination task, JND was still high, though much reduced (9%). The presence of the original voice-over with compensation for pitch did not affect perceptual performance. Thus, our results document a rather broad tolerance to speed manipulations in video viewing, even under attentive scrutiny. This finding may have important implications. For example, it can validate video compression strategies based on sub-threshold temporal squeezing. This way, a soccer match can last only 80 min and still be perceived as natural. More generally, knowing the boundaries of natural speed perception may help to optimize the flow of artificial visual stimuli which increasingly surround us.We are almost literally immersed in an artificial visual world, made in large part by motion pictures. How robust is our sense of reality with such pervasive technologies? For example, how well can we detect speed alterations in a video clip? The availability of videos, videogames and virtual reality systems, through which a variety of arbitrarily altered worlds can be experienced, calls for an appraisal of the boundaries within which video speed can be manipulated without conflicting with perception. However, although much effort has been devoted to studying motion perception 1,2 , how we perceive the speed of real-life scenes is still largely unknown, due especially to stimulus complexity and the presence of cognitive, higher-order factors 3-5 . Here we have addressed natural speed perception by measuring the detectability of speed alterations applied to a soccer match video clip. ResultsRetrospective noticing. In the first experiment we used a rather ecological setting, with observers watching a 10-minute video clip of a soccer match without any specific task. They viewed it only once and were told that at the end they would have to answer questions concerning the match, aimed to assess attention and memory capabilities. Observers were divided into five groups (N = 25 each), and each group watched the video clip at a different speed (0.88x, 0.96x, 1.00x, 1.04x and 1.12x, where 1.00x is the original video speed -30 fps; see Methods). The original audio track with voice commentary was pitch-compensated to avoid distortions when the video was played at a different speed. In general, observers were quite compliant, as suggested by self-reported attention measures (mental concentration: 60%, event-following: 81%). By contras...

Speed Biases With Real-Life Video Clips

“…However, the effects of auditory stimulation on visual motion perception are less obvious, and depend on the experimental conditions (e.g., Sekuler et al, 1997 ; Watanabe and Shimojo, 2001 ; Alais and Burr, 2004 ; Grassi and Casco, 2010 ). Indeed, coupled with our previous evidence of a lack of effect of voice-over on video speed perception (de’Sperati and Baud Bovy, 2017 ), the present results suggest that arbitrary soundtracks, while likely contributing a variety of efficacious emotional surrounds, do not slow-down or speed-up perceived reality in a video. One reason may be that arbitrary soundtracks do not admit an even loose audio-visual binding (Parise et al, 2013 ), thus dissipating the cross-modal integration potential of the auditory channel.…”

“…In this and our previous study (de’Sperati and Baud Bovy, 2017 ), we refer to video clip speed although technically we did not implement a gradual speed change but only discrete removal or insertion of single video frames at proper time positions. That this choice was meant to prevent video quality deterioration, as a gradual frame rate change obtained by disabling synchronization with vertical retrace signal could introduce tearing, and interpolation could generate the impression of unnatural motion.…”

“…Yet, videos might easily fool us. For example, we recently showed that observers fail to notice large speed manipulations when viewing a soccer match video clip (de’Sperati and Baud Bovy, 2017 ). In that study, we also 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.…”

Cortical Resonance to Visible and Invisible Visual Rhythms

“…The capability of judging the correct speed of a dynamic scene in a video clip is surprisingly poor. We have recently shown that (i) speeding up a soccer match video by as much as 12% goes completely undetected [1]; (ii) there are systematic biases in judging the correct video speed, often consisting of speed underestimation [2]; and (iii) 6-7-year-old children judge videos to be slower, as compared to older children and adults [3]. Thus, it appears that there is a mechanism in the brain that implicitly codes a subjective "right" speed of events.…”

Who Has Done It? Exploring Gaze Agency in Obsessive-Compulsive Checkers

“…Recently, Gregori Grgič et al ( 2016 ) suggested a new tool to assess “gaze agency”, defined as the “sense of gaze-operated self-agency in non-social context”, that is, the awareness to cause something in the environment through the movements of our eyes. Basically, their approach consisted of pairing a novel task for spontaneous agency discovery and a psychophysical task for explicit agency monitoring, both based on eye movements (for this kind of dual-task approach see also de’Sperati and Baud Bovy, 2017 ). It should be noted that in our daily life we do not use our eyes to physically modify the environment, although with gaze-operated devices this might soon become a widespread reality.…”