We have all done this. While driving down the road, perhaps on a mountain path, you round a corner, and suddenly there is an obstacle, such as a boulder or another car in your path. In order to avoid crashing, a plan must be made quickly, requiring both visual and motor controls. Do you slam on the brakes, or perform dangerous swerve in order to avoid the object before you? Reacting immediately gives you sufficient time to perform an action, but extra information is lost to choose which action is best. For example, say you immediately decide to swerve to avoid the car in front of you, but as you swerve into the other lane, you realize there is another car coming in the opposite direction. If a bit more time were taken to observe the situation, you probably would have chosen to slam the brakes instead. On the contrary, the more time you spend before acting allows you to gather greater sensory information, aiding you in making a wiser motor action, but as a consequence, there is less time to perform your decided action. Although so much is going on, we perform these actions automatically.
Peter Battaglia and Paul Schrater have researched this very phenomenon. In their study, they allowed participants to control the time spent on looking and the time spent on action so they could visual accuracy for motor accuracy as needed. To do this, participants were placed in front of a computer with a touch screen. They were instructed to put their finger on a start button, which made a target appear on the screen, and glide the finger over to the target before a timer ran out. The computer recorded the time spent on sensory input (how much time between touching the start button and initially moving the finger) and the time spent on motor action (how much time between the initial finger movement and hitting the target). Upon starting the simulation, dots began appeared on the screen, representing new visual information, until the movement for the target was initiated. Different trials were performed where varied amounts of dots were originally placed on the screen before the trial began. Afterwards they quantified the results of low medium and high dot density.
The results showed that when there were more dots on the screen initially, the participant spent more time viewing before making that first movement. How does this apply to us? Basically, when we have to make quick motor decisions, our brains will automatically balance time spent viewing the situation and the time before initially making an action, based on how much sensory input is around. The more sensory input, the longer the brain takes to make a motor decision. So, if you were to round a corner on the road and see a car in the path while there is a lot of visual input, such as pedestrians, traffic lights, and bikers, it will take more time for to make a motor decision than if the road was empty. This balance between visual accuracy and motor accuracy exists inherently in everyone, allowing us to make the best decision possible when little time is available.
Battaglia, P., and P. Schrater. 2007. Humans trade off viewing time and movement duration to improve visuomotor accuracy in a fast reaching task. The Journal of Neuroscience. 27: 6984-6994.