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September 18, 2007

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Built-in brain “templates” may clue tots to threats

Sept. 18, 2007
Special to World Science  

The baby’s moth­er said that as far as she knew, the five-month-old had never seen a spi­der. Yet some­how, a sim­ple black-on-white draw­ing of a spi­der seemed to grab its at­ten­tion in a way oth­er pic­tures could­n’t.

Such scenes re­peat­ed them­selves again and again in re­cent ex­pe­ri­ments by Da­vid Rak­i­son of Carnegie-Mellon Un­ivers­ity in Pitts­burgh, Penn., and Jaime Der­rin­ger of the Un­ivers­ity of Min­ne­so­ta in Min­ne­ap­o­lis, Minn.

The Black Wid­ow, one of a very few poi­son­ous spi­ders in the Unit­ed States. (Cour­te­sy U.S. Nat'l Park Serv­ice)

Many peo­ple re­gard snakes and spi­ders with a pe­cu­liar ter­ror, or fascina­t­ion, start­ing from a ten­der age. Re­search­ers have sug­gested these fears might be root­ed in our ev­o­lu­tion­ary past, when such ver­min were a per­en­ni­al threat. 

But is this so? And if so, just how do we learn to fear these an­i­mals?

Rakison and Derringer say their study with in­fants sug­gests the new­born brain pro­vides chil­dren with bas­ic sketches, or “per­cep­tual tem­plates,” of some things that may be rel­e­vant to them in life. An­i­mals to avoid, such as spi­ders and snakes, for ex­am­ple. More spec­u­la­tive­ly, per­haps even things to grav­i­tate to­ward—for in­stance, peo­ple with a cer­tain range of body mea­sure­ments as sex­u­al part­ners.

In the case of dan­ger­ous an­i­mals, such sketches may serve to help the child learn to dread the crea­tures, Rak­i­son said. “We’re not say­ing ba­bies are born with a fear of spi­ders,” he ex­plained. But the mech­an­ism may pre­dis­pose them “to learn about spi­ders in a dif­fer­ent way than they would learn about dogs or cats, say.”

We may al­so have these “per­cep­tual tem­plates” for dan­ger­ous crea­tures be­sides spi­ders and snakes, but early find­ings sug­gest the tem­plates ex­ist for at least these two groups, he added. Most spi­ders aren’t poi­son­ous, he ac­knowl­edged; but a large frac­tion of them are poi­son­ous in Af­ri­ca, where early hu­mans evolved. The find­ings, he added, sup­port the the­o­ry that ev­o­lu­tion pre­pares us to pay at­ten­tion to some spe­cif­ic threats.

Ev­o­lu­tion oc­curs when an or­gan­ism gets more chances to re­pro­duce than oth­ers do be­cause it has more ad­van­ta­geous genes. The re­sult is that the ben­e­fi­cial genes spread through­out a popula­t­ion, while less help­ful ones, for si­m­i­lar rea­sons, die out. Cease­less repe­ti­tions of this pro­cess can gen­er­ate en­tirely new spe­cies.

Rak­i­son and Der­rin­ger rea­soned that a hu­man an­ces­tor with a gene that let her learn to fear spi­ders soon af­ter birth, might have sur­vived long­er than oth­ers. Even a five-percent in­crease in sur­viv­al chances would lead such a gene to spread through a popula­t­ion in “20 or 30 genera­t­ions,” Rak­i­son said.

Images si­mi­lar to this one cap­tured infants' at­ten­tion in a study.

In their stu­dy, Rak­i­son and Der­rin­ger sat 16 five-month-old ba­bies on their par­ents’ laps and showed them three sim­ple, sche­mat­ic pic­tures. One de­picted a spi­der; a sec­ond, the same spi­der with its legs point­ed in un­nat­u­ral di­rec­tions, so that the ob­vi­ous spi­der re­sem­blance was lost; and third, the same spi­der with its body parts to­tally scram­bled.

The in­fants looked at the normal spi­der for about 24 sec­onds on av­er­age, com­pared to 16 or 17 sec­onds for the oth­er images, the re­search­ers found. 

The find­ings sug­gest “in­fants may pos­sess a rep­re­senta­t­ion for spi­ders that in­cor­po­rates their bas­ic struc­ture and con­fi­gura­t­ion,” they wrote, de­tail­ing their find­ings in the Sept. 6 ad­vance on­line is­sue of the re­search jour­nal Cog­ni­tion. Such im­ages may help a child learn to quickly as­so­ci­ate the crea­ture with dan­ger by watch­ing en­coun­ters be­tween mem­bers of its own spe­cies, and the an­i­mal, they added.

The sci­en­tists re­peat­ed the tests in sev­er­al dif­fer­ent ways to at­tempt to rule out oth­er ex­plana­t­ions. For in­stance, they tried it again with a flow­er pic­ture. But ba­bies showed no par­tic­u­lar in­clina­t­ion to look at a nor­mal flow­er more than a scram­bled one.

The find­ings are part of a larg­er body of new re­search sug­gesting that in gen­er­al, the new­born brain is­n’t a “blank slate,” de­void of any thoughts or ten­den­cies, as a ven­er­a­ble phil­o­soph­i­cal no­tion holds. 

A 2006 study pub­lished in the re­search jour­nal Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ces sug­gested that hu­mans in­her­it­ed some bas­ic spa­tial rea­son­ing abil­i­ties from their ape-like an­ces­tors. In a study pub­lished in this week’s early on­line edi­tion of the same jour­nal, Pe­ter Frans­son of the Karolin­ska In­sti­tute in Stock­holm, Swe­den, and col­leagues probed the is­sue with brain scans. They found that rest­ing, prem­a­ture ba­bies showed net­works of spon­ta­ne­ous ac­ti­vity in brain ar­eas that in adults are as­so­ci­ated with see­ing, hear­ing and mov­ing.

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The baby’s mother said the five-month-old had seen few or no spiders before. Yet somehow, a simple black-on-white drawing of a spider seemed to grab its attention in a way other pictures couldn’t. Such scenes repeated themselves again and again in recent experiments by David Rakison of Carnegie-Mellon University in Pittsburgh, Penn., and Jaime Derringer of the University of Minnesota in Minneapolis, Minn. Many people regard snakes and spiders with a peculiar terror, or fascination, starting from a tender age. Researchers have suggested these fears might be rooted in our evolutionary past, when such vermin were a perennial threat. But is this so? And if so, just how do we learn to fear these animals? Scientists at Carnegie-Mellon say their study with infants suggests the newborn brain provides children with basic sketches, or “perceptual templates,” of some things that may be relevant to them in life. Animals to avoid, such as spiders and snakes, for example. More speculatively, perhaps even things to gravitate toward—for instance, people with a certain range of body measurements as sexual partners. In the case of dangerous animals, such sketches may serve to help the child learn to dread the creatures, Rakison said. “We’re not saying babies are born with a fear of spiders,” he explained. But the mechanism may predispose them “to learn about spiders in a different way than they would learn about dogs or cats, say.” We may also have these “perceptual templates” for dangerous creatures besides spiders and snakes, but early findings suggest the templates exist for at least these two groups, he added. Most spiders aren’t poisonous, he acknowledged; but a large fraction of them are poisonous in Africa, where early humans evolved. The findings, he added, support the theory that evolution prepares us to pay attention to some specific threats. Evolution occurs when an organism gets more chances to reproduce than others do because it has more advantageous genes. The result is that the beneficial genes spread throughout a population, while less helpful ones, for similar reasons, die out. Ceaseless repetitions of this process can generate entirely new species. Rakison and Derringer reasoned that a human ancestor with a gene that let her learn to fear spiders soon after birth, might have survived longer than others. Even a five-percent increase in survival chances would lead such a gene to spread through a population in “20 or 30 generations,” Rakison said. In their study, Rakison and Derringer sat 16 five-month-old babies on their parents’ laps and showed them three simple, schematic pictures. One depicted a spider; a second, the same spider with its legs pointed in unnatural directions, so that the obvious spider resemblance was lost; and third, the same spider with its body parts totally scrambled. The infants looked at the spider for about 24 seconds on average, compared to 16 or 17 seconds for the other pictures, the researchers found. The findings suggest “infants may possess a representation for spiders that incorporates their basic structure and configuration,” the researchers wrote, detailing their findings in the Sept. 6 advance online issue of the research journal Cognition. Such images may help a child learn to quickly associate the creature with danger by watching encounters between members of its own species, and the animal, they added. The scientists repeated the tests in several different ways to attempt to rule out other explanations. For instance, they tried it again with a flower picture. But babies showed no particular inclination to look at a normal flower more than a scrambled one. The findings are part of a larger body of research suggesting that in general, the newborn brain isn’t a “blank slate,” devoid of any thoughts or tendencies, as a venerable philosophical notion holds. A 2006 study published in the research journal pnas suggested that humans inherited some basic spatial reasoning abilities from their ape-like ancestors. In a study published in this week’s early online edition of the same journal, Peter Fransson of the Karolinska Institute in Stockholm, Sweden, and colleagues probed the issue with brain scans. They found that resting, premature babies showed networks of spontaneous activity in brain areas that in adults are associated with seeing, hearing and moving.