(no subject)
The New York Times
April 3, 2007
Time in the Animal Mind
By CARL ZIMMER
Humans are born time travelers. We may not be able to send our
bodies into the past or the future, at least not yet, but we can
send our minds. We can relive events that happened long ago or
envision ourselves in the future.
New studies suggest that the two directions of temporal travel are
intimately entwined in the human brain. A number of psychologists
argue that re-experiencing the past evolved in our ancestors as a
way to plan for the future and that the rise of mental time travel
was crucial to our species’ success. But some experts on animal
behavior do not think we are unique in this respect. They point to
several recent experiments suggesting that animals can visit the
past and future as well.
The first clues about the twists and turns of mental time travel
came from people with certain brain injuries that caused them to
forget autobiographical details without forgetting the information
they had picked up along the way. A man known in the scientific
literature as K.C., for instance, could play chess with no memory
of having ever played it. K.C. could remember sentences
psychologists taught him without any memory of the lessons.
K.C. had lost what psychologists now call episodic memory. Endel
Tulving, a Canadian psychologist, defined episodic memory as the
ability to recall the details of personal experiences: what
happened, where it happened, when it happened and so on.
Dr. Tulving argued that episodic memory was distinct from other
kinds of memory that did not involve personal experience. People
can remember how to get to a subway stop, for example, without
recalling the first time they were there.
Episodic memory was also unique to our species, Dr. Tulving
maintained. For one thing, he argued that episodic memory required
self-awareness. You can’t remember yourself if you don’t know you
exist. He also argued that there was no evidence animals could
recollect experiences, even if those experiences left an
impression on them.
Many animal behavior experts agreed with Dr. Tulving, even though
they had not actually run experiments testing the idea. But when
Nicola Clayton, a comparative psychologist, first heard about the
claim, she had a different reaction. "I could feel my feathers
ruffling," said Dr. Clayton, who is now at the University of
Cambridge. "I thought, hang on, that doesn’t make sense."
Dr. Clayton began to test western scrub jays to see if they met
any of the criteria for episodic memory. The jays can hide several
thousand pieces of food each year and remember the location of
each one. Dr. Clayton wondered if scrub jays simply remembered
locations, or if they remembered the experience of hiding the
food.
She ran an experiment using two kinds of food: moth larvae and
peanuts. Scrub jays prefer larvae to peanuts while the larvae are
still fresh. When the larvae are dead for a few hours, the jays
prefer peanuts. Dr. Clayton gave the birds a chance to hide both
kinds of food and then put them in another cage. She later
returned the birds to their caches, in some cases after four hours
and in other cases after five days.
The time the scrub jays spent away from their caches had a big
effect on the type of food they looked for. The birds that waited
four hours tended to dig up larvae, and the birds that had to wait
for five days passed the larvae by and dug up peanuts instead. (To
make sure they were not just picking up the smell of rotten larvae
and avoiding those spots, Dr. Clayton dumped out the caches as
soon as the birds had made them, and filled all of them with fresh
sand.)
In 1998, Dr. Clayton and her colleagues published the results of
their experiment, declaring that scrub jays met the standards for
"episodic-like" memory. Ever since, Dr. Clayton has been
investigating the memories of scrub jays more deeply. Last year,
for example, her team discovered that scrub jays not only remember
when and where they hide food, but also whether they are being
watched at the time. If one scrub jay notices another one watching
it hide food, it tends to dig up the cache later and hide it
somewhere else. Other scientists have followed Dr. Clayton’s lead
and have searched for signs of episodic-like memory in other
animals. When rats are exploring a maze, for example, they seem to
be able to recall which kinds of food they encountered along the
way. Hummingbirds seem to remember where and when they visited
individual flowers for nectar. Rhesus monkeys can remember where
they put food, but not how long ago they put it there.
Some researchers have not been persuaded by these studies,
however.
"Animals seem to be living very much in the present," said Thomas
Suddendorf, a comparative psychologist at the University of
Queensland in Australia.
Dr. Suddendorf argues that a scrub jay could remember type of food
along with the location of a cache without having a sense or
memory of self. "Information is not really what characterizes
mental time travel," Dr. Suddendorf said. "I know that in 1967 in
Sweden my mom gave birth to me, but that doesn’t mean I can travel
back to that time and experience that event."
Episodic memory also depends on many other faculties that have
only been clearly documented in the human mind, Dr. Suddendorf
argues. He said he believes it evolved after our ancestors
branched off from other apes. The advantage lay not in knowing the
past, however, but in providing "an advantage for predicting the
future," he said.
Recent brain scanning studies support Dr. Suddendorf’s link
between the past and future. Daniel Schacter, a psychologist, and
his colleagues at Harvard University recently studied how brains
function as people think about past experiences and imagine future
ones. Constructing an episodic memory causes a distinctive network
of brain regions to become active. As a person then adds details
to the memory, the network changes, as some regions quiet down and
others fire up.
The researchers then had their subjects think about themselves in
the future. Many parts of the episodic memory network became
active again.
Dr. Suddendorf argues that these overlapping networks for mental
time travel evolved at least 1.6 million years ago. He points to
stone tools hominids made at that time. Paleoanthropologists have
determined that the tools were moved many miles from where they
were made.
"If you’ve just eaten, the only reason you’re going to take a tool
with you is if you anticipate using it in the future," he said.
Dr. Suddendorf has roused comparative psychologists to action --
"like a red rag to a bull," as one comparative psychologist, Sara
Shettleworth of the University of Toronto, put it. They have been
looking for evidence that animals can also plan for the future.
Some studies suggest not. Cebus monkeys, for example, will eat
until they are stuffed and throw the rest of the food out of their
cage, despite the fact that they will not have food the next
morning.
But in other studies, animals show more promise. "We tested
squirrel monkeys to see if they could anticipate the future, and
to our surprise it looks like they could," said Dr. William
Roberts, a comparative psychologist at the University of Western
Ontario. He and his colleagues ran a test in which they offered
squirrel monkeys a choice between one piece of date or four. Not
surprisingly, the monkeys took four.
But the scientists then began to take away water from the monkeys
before they offered the choice. If the monkeys took four pieces,
the scientists kept the water away for three hours. If the monkeys
took one, the scientists returned the water in half an hour. The
monkeys learned to choose one date. Even though they were not
thirsty at the time, they anticipated becoming thirsty in the
future. (If the scientists stopped withholding water, the monkeys
went back to picking four pieces of dates instead of one.)
Dr. Clayton recently tested her scrub jays for foresight. She and
her colleagues put the birds in three adjoining compartments for
six days. Each morning the birds were shut for two hours in one of
two rooms. In one room they got nothing to eat. In the other room,
they got powdered pine nuts (the scrub jays can eat the powder,
but they cannot cache it). For the rest of the day, each bird
could move around all three rooms and enjoy more powdered nuts.
On the seventh day, the scientists switched the powdered pine nuts
with real ones. If the birds were so inclined, they could cache
the pine nuts in ice cube trays the scientists put in the two
morning rooms. "If I’m a bird, what I could do is take some of the
provisions and hide it in there so that if I do wake up there in
the morning, I can get my own breakfast," Dr. Clayton said.
Dr. Clayton found that the birds put over three times more pine
nuts in the no-breakfast room than in the breakfast room. She
argues that the results mean that birds can take action for their
future needs, knowing what they’ll need and where they’ll need it.
Other experts on animal behavior say that the study is
compelling. Even Dr. Suddendorf, who has been so critical of
previous studies, is intrigued by Dr. Clayton’s results. He said
he wonders how long the birds can plan ahead: "Can they do this
for an event next week or next month like humans can? Is it
limited to caching, to just food?"
"It’s good to see people waking up to this," Dr. Suddendorf
said. "In five years the picture is going to look a lot
clearer. The future looks bright for research on the future."
April 3, 2007
Time in the Animal Mind
By CARL ZIMMER
Humans are born time travelers. We may not be able to send our
bodies into the past or the future, at least not yet, but we can
send our minds. We can relive events that happened long ago or
envision ourselves in the future.
New studies suggest that the two directions of temporal travel are
intimately entwined in the human brain. A number of psychologists
argue that re-experiencing the past evolved in our ancestors as a
way to plan for the future and that the rise of mental time travel
was crucial to our species’ success. But some experts on animal
behavior do not think we are unique in this respect. They point to
several recent experiments suggesting that animals can visit the
past and future as well.
The first clues about the twists and turns of mental time travel
came from people with certain brain injuries that caused them to
forget autobiographical details without forgetting the information
they had picked up along the way. A man known in the scientific
literature as K.C., for instance, could play chess with no memory
of having ever played it. K.C. could remember sentences
psychologists taught him without any memory of the lessons.
K.C. had lost what psychologists now call episodic memory. Endel
Tulving, a Canadian psychologist, defined episodic memory as the
ability to recall the details of personal experiences: what
happened, where it happened, when it happened and so on.
Dr. Tulving argued that episodic memory was distinct from other
kinds of memory that did not involve personal experience. People
can remember how to get to a subway stop, for example, without
recalling the first time they were there.
Episodic memory was also unique to our species, Dr. Tulving
maintained. For one thing, he argued that episodic memory required
self-awareness. You can’t remember yourself if you don’t know you
exist. He also argued that there was no evidence animals could
recollect experiences, even if those experiences left an
impression on them.
Many animal behavior experts agreed with Dr. Tulving, even though
they had not actually run experiments testing the idea. But when
Nicola Clayton, a comparative psychologist, first heard about the
claim, she had a different reaction. "I could feel my feathers
ruffling," said Dr. Clayton, who is now at the University of
Cambridge. "I thought, hang on, that doesn’t make sense."
Dr. Clayton began to test western scrub jays to see if they met
any of the criteria for episodic memory. The jays can hide several
thousand pieces of food each year and remember the location of
each one. Dr. Clayton wondered if scrub jays simply remembered
locations, or if they remembered the experience of hiding the
food.
She ran an experiment using two kinds of food: moth larvae and
peanuts. Scrub jays prefer larvae to peanuts while the larvae are
still fresh. When the larvae are dead for a few hours, the jays
prefer peanuts. Dr. Clayton gave the birds a chance to hide both
kinds of food and then put them in another cage. She later
returned the birds to their caches, in some cases after four hours
and in other cases after five days.
The time the scrub jays spent away from their caches had a big
effect on the type of food they looked for. The birds that waited
four hours tended to dig up larvae, and the birds that had to wait
for five days passed the larvae by and dug up peanuts instead. (To
make sure they were not just picking up the smell of rotten larvae
and avoiding those spots, Dr. Clayton dumped out the caches as
soon as the birds had made them, and filled all of them with fresh
sand.)
In 1998, Dr. Clayton and her colleagues published the results of
their experiment, declaring that scrub jays met the standards for
"episodic-like" memory. Ever since, Dr. Clayton has been
investigating the memories of scrub jays more deeply. Last year,
for example, her team discovered that scrub jays not only remember
when and where they hide food, but also whether they are being
watched at the time. If one scrub jay notices another one watching
it hide food, it tends to dig up the cache later and hide it
somewhere else. Other scientists have followed Dr. Clayton’s lead
and have searched for signs of episodic-like memory in other
animals. When rats are exploring a maze, for example, they seem to
be able to recall which kinds of food they encountered along the
way. Hummingbirds seem to remember where and when they visited
individual flowers for nectar. Rhesus monkeys can remember where
they put food, but not how long ago they put it there.
Some researchers have not been persuaded by these studies,
however.
"Animals seem to be living very much in the present," said Thomas
Suddendorf, a comparative psychologist at the University of
Queensland in Australia.
Dr. Suddendorf argues that a scrub jay could remember type of food
along with the location of a cache without having a sense or
memory of self. "Information is not really what characterizes
mental time travel," Dr. Suddendorf said. "I know that in 1967 in
Sweden my mom gave birth to me, but that doesn’t mean I can travel
back to that time and experience that event."
Episodic memory also depends on many other faculties that have
only been clearly documented in the human mind, Dr. Suddendorf
argues. He said he believes it evolved after our ancestors
branched off from other apes. The advantage lay not in knowing the
past, however, but in providing "an advantage for predicting the
future," he said.
Recent brain scanning studies support Dr. Suddendorf’s link
between the past and future. Daniel Schacter, a psychologist, and
his colleagues at Harvard University recently studied how brains
function as people think about past experiences and imagine future
ones. Constructing an episodic memory causes a distinctive network
of brain regions to become active. As a person then adds details
to the memory, the network changes, as some regions quiet down and
others fire up.
The researchers then had their subjects think about themselves in
the future. Many parts of the episodic memory network became
active again.
Dr. Suddendorf argues that these overlapping networks for mental
time travel evolved at least 1.6 million years ago. He points to
stone tools hominids made at that time. Paleoanthropologists have
determined that the tools were moved many miles from where they
were made.
"If you’ve just eaten, the only reason you’re going to take a tool
with you is if you anticipate using it in the future," he said.
Dr. Suddendorf has roused comparative psychologists to action --
"like a red rag to a bull," as one comparative psychologist, Sara
Shettleworth of the University of Toronto, put it. They have been
looking for evidence that animals can also plan for the future.
Some studies suggest not. Cebus monkeys, for example, will eat
until they are stuffed and throw the rest of the food out of their
cage, despite the fact that they will not have food the next
morning.
But in other studies, animals show more promise. "We tested
squirrel monkeys to see if they could anticipate the future, and
to our surprise it looks like they could," said Dr. William
Roberts, a comparative psychologist at the University of Western
Ontario. He and his colleagues ran a test in which they offered
squirrel monkeys a choice between one piece of date or four. Not
surprisingly, the monkeys took four.
But the scientists then began to take away water from the monkeys
before they offered the choice. If the monkeys took four pieces,
the scientists kept the water away for three hours. If the monkeys
took one, the scientists returned the water in half an hour. The
monkeys learned to choose one date. Even though they were not
thirsty at the time, they anticipated becoming thirsty in the
future. (If the scientists stopped withholding water, the monkeys
went back to picking four pieces of dates instead of one.)
Dr. Clayton recently tested her scrub jays for foresight. She and
her colleagues put the birds in three adjoining compartments for
six days. Each morning the birds were shut for two hours in one of
two rooms. In one room they got nothing to eat. In the other room,
they got powdered pine nuts (the scrub jays can eat the powder,
but they cannot cache it). For the rest of the day, each bird
could move around all three rooms and enjoy more powdered nuts.
On the seventh day, the scientists switched the powdered pine nuts
with real ones. If the birds were so inclined, they could cache
the pine nuts in ice cube trays the scientists put in the two
morning rooms. "If I’m a bird, what I could do is take some of the
provisions and hide it in there so that if I do wake up there in
the morning, I can get my own breakfast," Dr. Clayton said.
Dr. Clayton found that the birds put over three times more pine
nuts in the no-breakfast room than in the breakfast room. She
argues that the results mean that birds can take action for their
future needs, knowing what they’ll need and where they’ll need it.
Other experts on animal behavior say that the study is
compelling. Even Dr. Suddendorf, who has been so critical of
previous studies, is intrigued by Dr. Clayton’s results. He said
he wonders how long the birds can plan ahead: "Can they do this
for an event next week or next month like humans can? Is it
limited to caching, to just food?"
"It’s good to see people waking up to this," Dr. Suddendorf
said. "In five years the picture is going to look a lot
clearer. The future looks bright for research on the future."