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Many people report that their dogs completely ignore what is visible on television, while others report that their dogs are often captivated by events on the TV screen. Whether or not a dog pays attention to a program on television depends upon a number of factors. However, it mostly depends upon the dog's visual abilities. If we reduce the events that we see on the TV screen to its simplest form, the motion that we see really becomes a moving pattern of light across the retina in our eye.
At the level of single cells on the retina, a moving target appears to be a flicker. As the image of the target passes over a visual receptor in the eye and then moves on, it causes a momentary increase or decrease in brightness. For this reason, behavioral researchers often use an individual's ability to see a flickering target as a measure of not only the speed at which the visual system can record events, but also of the efficiency of motion perception.
To measure flicker sensitivity, an individual looks at a lighted panel. If the rate of flickering is very fast there is "flicker fusion" and the panel looks the same as if it were continuously illuminated. A fluorescent light, for instance, seems to be glowing continuously with a uniform light, but it is actually flashing at a rate of 120 times (cycles of light and dark) per second. In the laboratory, the ability to resolve flicker is measured by slowing the flicker rate until the person begins to see the light flutter.
When humans are tested on this task, the average person can't see any flickering much above a speed of 55 cycles per second, or about half the rate that fluorescent lamps normally flash. (Technically the number of cycles per second is referred to as Hertz, abbreviated Hz.) It is possible to teach dogs to do this same task. When this is done with beagles, they are able to see flicker rates up to 75 Hz on average, which is around 50 percent faster flashing than humans can resolve.
The fact that dogs have better flicker perception than humans is consistent with the data that suggests that they have better motion perception ability than people. It also answers a commonly asked question as to why the majority of dogs don't seem to be interested in the images on the television-even when those images are of dogs. The image on a standard television screen is updated and redrawn 60 times per second. Since this is above a human's flicker resolution ability of 55 Hz, the image appears continuous and the gradually changing images give us the illusion that it is continuous.
Because dogs can resolve flickers at 75 Hz, a TV screen probably appears to be rapidly flickering to dogs. This rapid flicker will make the images appear to be less real, and thus many dogs do not direct much attention to it. Even so, it is true that some dogs ignore the apparent flickering of the television and seem to respond to dogs and other interesting images on the TV screen if they are interesting enough. However, changes in technology are beginning to change the number of dogs that watch TV. High-resolution digital screens are refreshed at a much higher rate so even for dogs there is less flicker, and we are getting more reports of pet dogs who are very interested when various nature shows containing images of animals moving.
Still, people are sometimes surprised to find that although their dog responds when there is a dog on the screen, or perhaps some other animal running swiftly, it does not respond to cartoon images of dogs. This really is a testimony to how good a dog's ability is to see and accurately interpret moving images. When a dog sees a cartoon canine he recognizes that it is moving, but the movements of an animated figure are not a precise rendering of the pattern of movements of a live animal. Therefore he sees something moving, but it is not a dog or any other real animal of interest.
Stanley Coren is the author of many books, including Born to Bark, The Modern Dog, Why Do Dogs Have Wet Noses? The Pawprints of History, and more.
Copyright SC Psychological Enterprises Ltd. May not be reprinted or reposted without permission.
