http://www.newscientist.com/news/news.jsp?id=ns99992960
Sea lion scores top for memory
19:00 23 October 02
Exclusive from New Scientist Print Edition
California sea lions may have the best memory of all non-human creatures.
A female called Rio that learned a trick involving letters and numbers
could still perform it 10 years later - even though she hadn't performed
the trick in the intervening period.
(Image: T. KYRIACCOU/REX IMAGES)
Learning concepts such as "sameness" - when one letter or number matches
another, for example - is thought to require sophisticated brain
processing. So scientists expect animals to have trouble retaining the
ability over long periods unless they are given repeated reminders of the
rules. Primates like the rhesus macaque have been found to have
impressive long-term memories, but Rio trumped them all. Colleen Kastak
and Ronald Schusterman, marine biologists at the University of
California, Santa Cruz, began training her in 1991. They started by
holding up a card with a number or letter on. Rio was then shown a card
bearing the same symbol and another card with a different symbol. If she
picked the matching symbol, she was rewarded with a fish. In 2001, the
researchers tested Rio again, this time using numbers and letters not
used in the previous test. She was just as good at the test as before.
Although her 10 year performance is unequalled by any other species, no
animal apart from Rio has been tested after such a long gap.
Because the symbols used were different this time, it proved Rio had
remembered and was capable of applying the concept of "sameness" to new
situations, rather than just recalling matches between familiar numbers
and letters. In a second test, the researchers taught Rio to distinguish
between numbers and letters. They showed her two cards at a time, one of
a letter and the other, a number from a set of 10 letters and numbers.
When she picked numbers she got a fish. When tested a year later, Kastak
and Schusterman found Rio remembered how to separate the symbols into
letters and numbers. Kastak says their impressive memory could help sea
lions recognise different categories of prey that are only present at
certain times of the year.
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