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 on a number of factors, but mainly on the dog’s visual abilities. If we reduce the events that we see on the TV screen to their simplest form, the motion that we see really becomes a changing 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 a constant, unchanging illumination. A fluorescent light, for instance, seems to be glowing continually 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 test dogs using this same task. On average, Beagles are able to see flicker rates up to 75 Hz—about 50 percent faster than the flicker rate that humans can resolve.
The fact that dogs have better flicker perception than humans have is consistent with the data suggesting that they perceive motion better than people do. It also answers a commonly asked question: Why do the majority of dogs seem uninterested in the images on television—even when those images are of dogs? The answer is that the image on a raster television screen is updated and redrawn 60 times per second. Since this rate is above a human’s flicker resolution ability of 55 Hz, the image appears continuous and successive images blend smoothly together. Given that dogs can resolve flickers at 75 Hz, to dogs a TV screen probably appears to be rapidly flickering, making the images appear less real and thus causing many dogs not to direct much attention to them. Even so, some dogs seem to ignore the apparent flickering of the television and respond to dogs and other moving images on the TV screen if they’re 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 increasing reports of pet dogs who are very interested when a nature show contains 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 distinction really is a testimony to how well dogs see and accurately interpret moving images. On seeing a cartoon canine, a dog recognizes that the figure is moving, but the movements of an animated figure are not a precise rendering of the pattern of movements of a live animal. Therefore, the dog sees something moving but recognizes that it is not a dog or any other real animal of interest.
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