Tuesday, March 1, 2011

Flicker Refresh Rate or Why a Dog Can Turn on a Dime

Much has been written about canine vision, but I encountered a new aspect yesterday while reading Alexandra Horowitz's Inside of a Dog, "flicker refresh rate."  Basically, it is the rate at which at new image forms on the retina of the eye.  For people, the rate is around 60 hertz, or if you equate it to motion picture film, 60 frames per second.  At that rate, we perceive a series of still frames as being in smooth, continuous motion.  Below that rate and we perceive a flickering of the images.

A dog has a flicker refresh rate of 70-80 hertz.  Ms Horowitz (and others) go on to discuss what this means in terms of what a dog sees on a non-digital tv and how it perceives fluorescent lights.  However, they fail to tell us why a higher refresh rate is of value to a dog.  I did a little Googling this morning, but everything I came up with concerned dogs and how a tv image appeared to them.

I finally happened upon an article by Don Glass describing the even higher refresh rate of birds, 100 hertz and more depending upon the species.  The higher refresh rate enables them to fly through the woods at high speed and not crash into branches.  It enables large flocks to change direction abruptly and in unison.  For hawks, it allows them to detect the motion of prey while they are flying.  

The higher refresh rate of my canine teammate helps to explain how she can process the change of direction cues I give even as she is running full speed ahead into a tunnel or over a jump.  The trick is learning to give these subtle cues at the right time, and training the dog that we want them to finish the current obstacle but we will be changing direction.  For me learning to give the cues soon enough is by far the harder task.

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