Video Dating...Spider Style

When a tiny jumping spider gets tired of jumping, it may be able to relax in a decidedly human way - by watching television. Animal behaviorist David Clark of the University of Cincinnati has found that, unlike some animals, the jumping spider can perceive smooth motion in televised images, a discovery that could lead to new information about how the animals communicate.

Our talent for comprehending television pictures is determined by our ability to view a succession of still pictures and be tricked into stringing them together into a moving image. This can be accomplished only if there are enough pictures flashing by in any given instant. To perceive seamless motion, the average person needs between 16 and 55 images a second, a figure comfortably below a television’s rate of 60 pictures a second.

The nonhuman eye, however, is tougher to fool: using brain electrodes, researchers have found that some animals, such as pigeons and bees, need hundreds of pictures a second before perceiving smooth, fluid motion. But other animals - chickens, chimps, cats and some lizards among them - do fall below the 60-frames-a-second rate, joining humans in the faunal kingdom’s great potential television audience.

What’s never been clear, however, is whether animals that are able to perceive motion on a two-dimensional screen can understand the images they see. Clark, working with behavioral ecologist George Uetz, decided to explore the question.

"I could have worked with a number of animals for this study," Clark says. "But I chose spiders because they have good vision and communicate with each other almost entirely by visual displays. Also, I had hundreds of them on hand."

Clark built a tiny viewing chamber and equipped it with a pair of Sony Watchman television sets. He then placed his eight-legged subjects inside the chamber and showed them images of different spider-salient stimuli, such as potential mates. In most cases the response was dramatic.

Spiders shown images of crickets went into a characteristic stalk-and-attack posture, sometimes ignoring real crickets displayed elsewhere in the chamber. When presented with a threatening image of a larger species of jumping spider, the animals either rose up on their legs in an aggressive display or retreated. In a third experiment subjects responded to videos of potential mates by waving their legs or rotating their bodies - classic courtship gestures. In some cases different images were shown on each television to see which elicited the greatest response.

The implications of this research go beyond providing entertainment to arachnids. "Using video manipulation," says Clark, "I can exaggerate pieces of the televised creature’s anatomy, change its color or alter the sequences of its behavior. All this allows me to determine which features the subject is responding to. Knowing how a spider distinguishes a threat from a mate from a meal has tremendous potential in helping us learn how these animals see their world."

The preceding article was reprinted with permission from Discover magazine. Will Ostrow 1991 Discover Publications.