Perception-Reaction Time

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According to scientific research, it takes the average person around 1.5 seconds to react to the previous (nonsensical) statement. Information takes time to process and the human brain takes time to react to this information. This is called the perception-reaction time (PRT) and is defined as the interval between the time where something is perceived and the time it takes to respond to it. There is no “standard” or “generally accepted” PRT and it can range anywhere from 0.15 to many seconds. The reason behind such a large range is because it can be affected by a myriad of different factors. Those factors include but are not limited to fatigue level, potential alcohol or drugs consumption, driving experiences, the familiarity of the driver with the environment, vision of the driver, weather, potential distractions and anticipation, visibility, cognitive impairment. All of these factors are known to affect cognitive response to events and our human factor experts are able to opine of the length of the expected PRT to an event based on all available information and evidence. In motor vehicle collision, the length of PRT will essentially dictate the perception-reaction distance that would make the difference between the occurrence and avoidance of an accident.

Let’s consider the example of an elderly person visiting his grandchildren out of state for the first time. He has now been driving for over 6 hours and is only 20 miles away from his final destination. He can feel the fatigue slowly impairing his senses but refuses to take a break. The roads around him are empty as he gets to an intersection. After a brief stop, he proceeds to his route and collides with a cyclist. The driver is claiming that he only saw the cyclist right before the impact happened. On the other hand, the cyclist testified that the driver made clear eye contact with him a few seconds before he proceeded to accelerate the vehicle. If the cyclist and driver made eye contact at this time, was there enough time for the driver to potentially avoid the collision? What would be the PRT of the cyclist and the driver individually? Is it possible that the driver really did not see the cyclist before accelerating his vehicle? If so, would there be enough time for the cyclist to avoid the collision? Did the driver have a longer PRT than the cyclist because of his age? What other factors could explain his slow mental processing time?

These are some of the questions that NBI’s multidisciplinary team of accidents reconstructionists, biomechanists, and human factor experts will be able to answer. Our experts are able to answer a number of questions pertaining to liability through collection and review of all the available evidence. The strength of our team comes in the multidisciplinary approach that enables the analysis of every single potentially relevant detail to your case. Our experts are also able to make use of technology to measure factors such as luminance using luminance meters and the use of the I.DRR software that allows our teams to include human factors in the process of accident reconstruction and simulations and evaluate the effect of various factors impacting cognition, perception, reaction time and behavior in the context of driving. NBI’s human factors experts are accomplished scientists with extensive knowledge in various areas of neuroscience, cognitive psychology, processing, and behaviorism providing them with a deep understanding of how the human brain functions and processes information. Our experts also have extensively published peer-reviewed research in the area of neuropsychological assessment, information processing, and cognitive impairment. This is the combination of the highest academic and research background as well as experience that makes our experts the best at opining on appropriate PRT for a range of different scenarios, environmental factors and individual’s characteristics.

Leading Experts


Felix Lee, MS, PE

Manon Limousis-Gayda, MS, CXLT