Dolphins maintain round-the-clock visual...( Dolphins have a clever trick for ove...)

Dolphins have a clever trick for overcoming sleep deprivation. Sam Ridgway from the US Navy Marine Mammal Program explains that they are able to send half of their brains to sleep while the other half remains conscious. What is more, the mammals seem to be able to remain continually vigilant for sounds for days on end. All of this made Ridgway and his colleagues from San Diego and Tel Aviv wonder whether the dolphins' unrelenting auditory vigilance tired them and took a toll on the animals' other senses? Ridgway and his team set about testing two dolphins' acoustic and visual vigilance over a 5 day period to find out how well they functioned after days without a break. The team publish their results on May 1 2009 in the Journal of Experimental Biology at http://jeb.biologists.org.

First Ridgway and his colleagues, Mandy Keogh, Mark Todd and Tricia Kamolnick, trained two dolphins to respond to a 1.5 s beep sounded randomly against a background of 0.5 s beeps every 30 s. Ridgway explains that the sounds were low enough for the dolphins to barely notice them as they swam through their enclosure, but the animals sprung into action every time they heard the 1.5 s tone, even after listening to the sounds for 5 days without a break. Their auditory vigilance remained as sharp as it had been 5 days earlier.

Next Allen Goldblatt and Don Carder designed a visual stimulus to test the dolphins' vigilance while they continued listening to the repetitive beeps. Knowing that the dolphins' binocular vision is limited because their eyes are situated on opposite sides of their heads, Kamolnick trained one of the dolphins, SAY, to recognise two shapes (either three horizontal red bars or one vertical green bar) with her right eye before training her to recognise the same shapes with the left eye, reasoning that if half of her brain was asleep during testing, the dolphin would only see the shapes through the eye conne
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