Hammerhead sharks may have human-grade vision with one major blind spot

2935553971_b4c86cf410.jpgA new study conducted in Florida has given scientists reason to believe that hammerhead sharks may have vision comparable to that of humans. The researchers measured electrical activity in the eyes of half a dozen sharks from three different hammerhead species. They then put electrodes under the sharks' corneas and recorded electrical activity while shining lights in horizontal and vertical arcs around each eye. Compared to normal-headed sharks, the hammerheads had three times the visual overlap — that's what creates stereo vision and depth perception in animals with eyes that face forward. This, of course, helps them be faster and more efficient at hunting prey. But there's a catch: because their eyes are so far apart, hammerheads have these giant blind spots right in the middle of their head. As study leader Michelle McComb put it in an interview with National Geographic:
There's actually been anecdotal claims by divers that they see little fish schooling right in front of the hammerheads' heads. It's like the fish are swimming by and saying, Ha, ha, ha, you can't see me!
Hammerhead sharks have "human" vision [National Geographic] Image via Eric Charlton's Flickr

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  1. But how do the fish know the shark can’t see them? There ought to be a Ph.D. lurking somewhere in there, if you could see it.

  2. First, you would have to check that this was nonrandom behavior. Ask IF the fish know the shark can’t see them before asking HOW they know.

  3. Correlation is not causation. Fish were noted swimming in front of the center of Hammerhead sharks because all of the fish that were swimming to either side had already been eaten.

  4. Just for the sake of accuracy, the sentence in the BB article should read (without the brackets): “The researchers measured electrical activity in the eyes of half a dozen sharks from three different hammerhead species < > electrodes under the sharks’ corneas and recording electrical activity while shining lights in horizontal and vertical arcs around each eye.

    Also, upon comparing this article and the National Geographic article it cites with the original published study in the Journal of Experimental Biology, I find it interesting how popular media outlets feel compelled to have “hooks” in the article’s title, even if they are completely misleading. The original study does not say that sharks have “human grade vision”, only that, like humans (and many, many other predator species) hammerheads have overlapping visual fields which could be useful for generating binocular vision. This is a far cry from saying that their vision is human like. For comparison, the article states that hammerheads have up to ~48 degrees of binocular overlap, while (from a quick google survey) hawks have between 30-40 degrees, cats ~100 degrees and humans ~120-140 degrees.

    I’m all for making science accessible to everyone, and I laud people who do so. However, I think more care should be taken to look at original sources rather than news articles about news articles about the original study. I also think this process could be facilitated by making more original research open access, but that’s another story…

  5. Oops, I guess I should have previewed my prior comment: The first sentence should read: “The researchers measured electrical activity in the eyes of half a dozen sharks from three different hammerhead species BY PUTTING electrodes under the sharks’ corneas and recording electrical activity while shining lights in horizontal and vertical arcs around each eye.

  6. I agree namnezia.

    Sophisticated retinas are not enough for human-grade vision, you need to back it up with the processing and recognition ability of the human visual cortex. It even appears that the surface area of the human visual cortex alone is larger than the entire surface area of the shark brain.

    Another media science article hook fail.

  7. I have read the article based on the Hammerhead sharks and their Human grade vision and the new factor of the major blind spot.Sophisticated retinas are not enough for human-grade vision.As it is seems to be the great news the sharks have capability to compare the human beings in the terms of the pure vision.It is not possible for the all different species of the sharks.I like the post very much as it contain informative knowledge.

  8. Ampullae of lorenzini ARE cool! Lots of other species develop these sensory adaptations that allow them to sense “extra” things. Some snakes have infrared-sensing ‘pit organs’ that allow them to sense heat emitted by predators, as do some bats. Alligators have special little sense organs on their chins to sense ripples in the surface water. Many of these extra sensory organs evolved from systems normally devoted to sensing touch in the skin and use similar neural pathways. Evolutionary diversity is quite cool.

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