Summary: A new study reports the adaptation effect relies upon a person’s perceived norms about how fast an object would normally move being altered by short burst of exposure to different speeds.
Source: University of Lincoln.
Football officials watching slow-motion clips or drivers changing from motorways to 30mph zones could be unconsciously mis-judging speed – and the motivations behind a person’s movements – because their perceptions of ‘normal’ have been altered by recent experiences, new research has found.
Vision science researchers tested whether exposure to slow-motion footage of people either running in a marathon or walking would alter their perception of real-life movement, and found that after viewing the footage for a short while, participants judged normal-speed playback as too fast, and it had to be slowed down in order to appear ‘normal’.
The opposite effect occurred after viewing fast movements, meaning that judgements of speed are unconsciously influenced by previously viewed speeds. Vision scientists said the so-called ‘adaptation effect’ is down to a person’s own perceived ‘norms’ about how fast something would usually move being altered by relatively short periods of exposure to different speeds.
For example, people viewing repeated play-back clips of football games or races – in either slow-motion or fast-forward – would begin to view the altered footage as natural behavior, so decisions based on video reviews to determine premeditated fouling or feigning injury could be negatively impacted.
Researchers said drivers could also experience a similar thing – called velocity re-normalisation – which would alter their perception of speed so that when they moved from high-speed conditions to slower zones, it would take time to adjust because faster speeds would feel more normal. This is down to the brain continuously compensating for changes in the driver’s visual stimulation.
The study, funded by the Economic and Social Research Council UK, was led George Mather, a Professor of Vision Science at the University of Lincoln, UK.
Professor Mather said: “The speed at which people move – their gestures or walking pace – carries important social cues about the meaning and intent behind their actions or their emotional state and temperament.
“Eyebrows, for instance, can say a great deal. A rapid flick is a common form of greeting, while a slow rise and fall can indicate surprise or fear, and the speed at which a person walks is slower when that person is feeling sad rather than happy.
“This research has some quite interesting implications. This season the Football Association will review video footage of fouls in football matches in order to decide whether a player intended to deceive the referee by feigning injury or pretending to have been fouled. If these reviews involve repeated viewing of slow-motion replays, the findings may well be affected due to the ‘adaptation effect’ we reported.
“In another context, after you have driven along a motorway at 70mph for a while, you may have had the experience that upon leaving the motorway it is easy to misjudge slow speeds and so approach the exit too fast. This may occur because, perceptually, 70mph becomes ‘normal’ speed after spending some time on the motorway, so 30mph on the slip road appears slower than it appears while driving in a city.
Funding: The research was supported by the Economic and Social Research Council.
Source: Cerri Evans – University of Lincoln
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Full open access research for “Visual adaptation alters the apparent speed of real-world actions” by George Mather, Rebecca J. Sharman & Todd Parsons in Scientific Reports. Published online July 27 2017 doi:10.1038/s41598-017-06841-5
Visual adaptation alters the apparent speed of real-world actions
The apparent physical speed of an object in the field of view remains constant despite variations in retinal velocity due to viewing conditions (velocity constancy). For example, people and cars appear to move across the field of view at the same objective speed regardless of distance. In this study a series of experiments investigated the visual processes underpinning judgements of objective speed using an adaptation paradigm and video recordings of natural human locomotion. Viewing a video played in slow-motion for 30 seconds caused participants to perceive subsequently viewed clips played at standard speed as too fast, so playback had to be slowed down in order for it to appear natural; conversely after viewing fast-forward videos for 30 seconds, playback had to be speeded up in order to appear natural. The perceived speed of locomotion shifted towards the speed depicted in the adapting video (‘re-normalisation’). Results were qualitatively different from those obtained in previously reported studies of retinal velocity adaptation. Adapting videos that were scrambled to remove recognizable human figures or coherent motion caused significant, though smaller shifts in apparent locomotion speed, indicating that both low-level and high-level visual properties of the adapting stimulus contributed to the changes in apparent speed.
“Visual adaptation alters the apparent speed of real-world actions” by George Mather, Rebecca J. Sharman & Todd Parsons in Scientific Reports. Published online July 27 2017 doi:10.1038/s41598-017-06841-5