In Stereo: Hammerhead Sharks Have Human-Like Vision
Sharks and humans seem more and more alike with each new scientific find. Not only do some sharks have hunting patterns that resemble those of serial killers, but now scientists have discovered that the hammerhead shark’s distinctive head shape allows it to see like a human.
Binocular vision occurs when the fields of two eyes overlap, allowing the accurate perception of depth and distance. It is especially important for predators which need to judge the distance to their prey [BBC News]. Researcher Stephen Kajiura, a sensory biologist, suggests that the stereo vision helps the sharks hunt prey like squid that dart around in three dimensions. The wide set eyes also allow the sharks to see through 360 degrees of vision, according to the researchers, who published their findings in The Journal of Experimental Biology.
Scientists have debated the significance of the hammerheads’ odd shape for centuries, according to lead researcher Michelle McComb. Earlier theories suggested that the head aids swimming by producing hydrodynamic lift, or improves smell by increasing the distance between nostrils, or produces better vision. But other researchers had argued that the placement of the eyes must make it hard for the shark to look forward, and thus would prevent the two fields of vision from overlapping. To test the vision theory, researchers examined different hammerhead species individually by placing sensors on [each] shark’s skin to measure its brain activity, specifically testing whether the animal would react to beams of light shone from different locations around the tank. By doing so, they could measure each shark’s field of vision [BBC News]. Their results confirm that the sharks have anterior binocular vision, meaning they can see directly ahead, that the two eyes’ fields of vision overlap, and that they can judge the distance of their prey.
The hammerhead does have a large blind spot in the center directly in front of its head, but because it swings its head from side to side while swimming, it can see through 360 degrees—not only in front and behind them, but also above and below their heads.
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Image: flickr / suneko