shown to play a role incentrosome maturation [19].Identifying other targets of mitotickinases and evaluating their rolein centrosome maturation remainsa future challenge.

References1. Palazzo, R.E., Vogel, J.M.,

Schnackenberg, B.J., Hull, D.R., and Wu,X. (2000). Centrosome maturation. Curr.Top. Dev. Biol. 49, 449–470.

2. Blagden, S.P., and Glover, D.M. (2003).Polar expeditions–provisioning thecentrosome for mitosis. Nat. Cell Biol. 5,505–511.

3. Berdnik, D., and Knoblich, J.A. (2002).Drosophila Aurora-A is required forcentrosome maturation and actin-dependent asymmetric proteinlocalization during mitosis. Curr. Biol. 12,640–647.

4. Hannak, E., Kirkham, M., Hyman, A.A.,and Oegema, K. (2001). Aurora-A kinaseis required for centrosome maturation inCaenorhabditis elegans. J. Cell Biol. 155,1109–1116.

5. Kinoshita, K., Noetzel, T.L., Pelletier, L.,Mechtler, K., Drechsell, D.N., Schwager,A. et al. (2005). Aurora A phosphorylationof TACC3/Maskin is required forcentrosome-dependent microtubuleassembly in mitosis. J. Cell Biol. 170,1047-1055.

6. Barros, T.P., Kinoshita, K., Hyman, A.A.,and Raff, J.W. (2005). Aurora A activatesD-TACC/Msps complexes exclusively atcentrosomes to stabilise centrosomalMTs. J. Cell Biol. 170, 1039-1046.

7. Peset, I., Seiler, J., Sardon, T., Bejarano,L.A., Rybina, S., and Vernos I (2005).Function and regulation of Maskin, aTACC family protein, in microtubulegrowth during mitosis. J. Cell Biol. 170,1057-1066.

8. Giet, R., McLean, D., Descamps, S., Lee,M.J., Raff, J.W., Prigent, C., and Glover,

D.M. (2002). Drosophila Aurora A kinaseis required to localize D-TACC tocentrosomes and to regulate astralmicrotubules. J. Cell Biol. 156, 437–451.

9. Pascreau, G., Delcros, J.G., Cremet, J.Y.,Prigent, C., and Arlot-Bonnemains, Y.(2005). Phosphorylation of maskin byAurora-A participates in the control ofsequential protein synthesis duringXenopus laevis oocyte maturation. J.Biol. Chem. 280, 13415–13423.

10. Ohkura, H., Garcia, M.A., and Toda, T.(2001). Dis1/TOG universal microtubuleadaptors - one MAP for all? J. Cell Sci.114, 3805–3812.

11. Kinoshita, K., Habermann, B., andHyman, A.A. (2002). XMAP215: a key

component of the dynamic microtubulecytoskeleton. Trends Cell Biol. 12,267–273.

12. Brittle, A.L., and Ohkura, H. (2005). Minispindles, the XMAP215 homologue,suppresses pausing of interphasemicrotubules in Drosophila. EMBO J. 24,1387–1396.

13. Cullen, C.F., and Ohkura, H. (2001). Mspsprotein is localized to acentrosomalpoles to ensure bipolarity of Drosophilameiotic spindles. Nat. Cell Biol. 3,637–642.

14. Lee, M.J., Gergely, F., Jeffers, K., Peak-Chew, S.Y., and Raff, J.W. (2001).Msps/XMAP215 interacts with thecentrosomal protein D-TACC to regulatemicrotubule behaviour. Nat. Cell Biol. 3,643–649.

15. Tournebize, R., Popov, A., Kinoshita, K.,Ashford, A.J., Rybina, S., Pozniakovsky,A., Mayer, T.U., Walczak, C.E., Karsenti,E., and Hyman, A.A. (2000). Control ofmicrotubule dynamics by theantagonistic activities of XMAP215 andXKCM1 in Xenopus egg extracts. Nat.Cell Biol. 2, 13–19.

16. Holmfeldt, P., Stenmark, S., andGullberg, M. (2004). Differentialfunctional interplay of TOGp/XMAP215and the KinI kinesin MCAK duringinterphase and mitosis. EMBO J. 23,627–637.

17. Gard, D.L., and Kirschner, M.W. (1987). Amicrotubule-associated protein fromXenopus eggs that specifically promotesassembly at the plus-end. J. Cell Biol.105, 2203–2215.

18. Gergely, F., Draviam, V.M., and Raff,J.W. (2003). The ch-TOG/XMAP215protein is essential for spindle poleorganization in human somatic cells.Genes Dev. 17, 336–341.

19. do Carmo Avides, A.M., Tavares, A., andGlover, D.M. (2001). Polo kinase and Aspare needed to promote the mitoticorganizing activity of centrosomes. Nat.Cell Biol. 3, 421–424.

Wellcome Trust Centre for Cell Biology,Institute of Cell Biology, School ofBiological Sciences, The University ofEdinburgh, Edinburgh EH9 3JR, UK.

DOI: 10.1016/j.cub.2005.10.022

Current Biology Vol 15 No 21R882

Figure 2. The function of Aurora A phosphorylation of TACC.

Microtubules (black lines) with minus ends focused at the centrosome (blue) and plusends extending away. Phosphorylation by Aurora A (Aur A) recruits TACC, andconsequentially its binding partner Msps/XMAP215 to the centrosome in mitosis. Whatis the function of the complex once at the centrosome? Targeting ofTACC–Msps/XMAP215 to the centrosome may enhance the activity of Msps/XMAP215in stabilising microtubule plus ends (1). In another model, the phosphorylation at serine863/626 is proposed to allow the complex to stabilise the minus ends of microtubulesnucleated at the centrosome (2).

1

2

Aur ATACC

Msps/XMAP215

TACC

Msps/XMAP215

PPP

TACC

Msps/XMAP215

TACC

Msps/XMAP215

PPP

Current Biology

Lauren Stewart1 and Vincent Walsh2

The extent to which perceptualand cognitive capacities areinnate and the extent to whichthey are shaped by theenvironment has long been amatter of debate. Two of themajor test beds for establishing

where the line between nature andnurture should lie have beenstudies of the effects ofdeprivation on the development ofperceptual abilities in animals [1],and of language learning abilitiesin humans [2–4].

Perhaps one of the mostextreme positions on this matterwas held by the German Emperor,

Infant Learning: Music and theBaby Brain

When it comes to listening to music, infants literally have a more openmind than their parents. Studies which investigate listening behaviourof babies and adults have shown that, as we learn to discriminate themusical sounds in our own environment, we become less sensitive tothose of other cultures.

Frederick II (1194–1250). Hebelieved that children raised insilence would grow up speakingGerman. Intent on proving thatGerman was God’s naturallanguage, he tested this theory byraising children in silence, butfound that the children did notacquire any language at all. In hisdefence, he did have ahypothesis, but his error was inemploying a total rather than apartial deprivation design.

Fortunately, nature aboundswith partial deprivationexperiments which provide a moreethically constrained approach forasking questions concerning theextent to which our perceptualabilities are shaped by theenvironment. For instance, allchildren grow up hearing thesounds of the dominant languagefrom their own environment ratherthan the sounds of any other ofthe world’s languages. The workof Werker and colleagues [3,4] hasshown that infants start life withthe potential to acquire anylanguage. They showed that up tothe age of six months, Canadianinfants raised in their Englishspeaking homes can discriminatebetween different sounds withinthe Hindi language, even thoughthese same differences areimperceptible to Canadian adults.By the end of the child’s first year,however, the speech sounds intheir own environment havebegun to shape their perceptualabilities and their phoneticperception is transformed from‘universal’ to ‘language-specific’[3,4]. They are now better atdiscriminating between thesounds of their own languagethan those of another tongue. Thisis the first stage of becoming anative speaker — accurateperception of speech soundsprecedes learning to producethem.

Just as different languageshave both universal and culturallyspecific features, so too doesmusic. Even in this world ofmusical pluralism one canexperience music of differentcultures as alien. While differentlanguages use different sets ofphonemes, the music of differentcultures uses different musicalscales and different ways of

grouping events in time. Evidencehas recently emerged thatperceptual abilities are shaped byregularities in one’s musical, aswell as one’s linguisticenvironment. By measuringperceptual discrimination ofnative and non-native sounds, inboth infants and in adults, Lynchet al. [5] showed that infants havecomparable pitch discriminationabilities in native and foreignmelodic contexts, whereas adultsexhibit superior skills when themelodic context is drawn fromtheir own culture. Hannon andTrehub [6,7] have now examinedperception of musical rhythm ininfants and adults.

Hannon and Trehub [6,7] usedpreferential looking to testwhether infants could discriminaterhythmic changes in native (in thiscase Western) and foreign (in thiscase Balkan) contexts: if an infantis presented with a stimulus anumber of times, a change in thestimulus will, if recognized, causethe infant to spend longer lookingat the source of the stimulus(hence the term preferentiallooking). The authors measuredlooking behaviour when a changein metre was introduced, either toBalkan music or to Westernmusic. In musical terms, metre isthe underlying pulse thatdifferentiates, for instance, a waltz(one, two, three, one, two, three)from a march (one, two, three,four, one, two, three, four). InBalkan music, the metre is morecomplex, commonly consisting ofcycles of five or seven pulseswhich give the music a distinctlyirregular feel. Hannon and Trehub[6,7] played rhythms with eitherBalkan or Western metres toinfants at 6 months or 12 monthsold and to Canadian adults.

The question was whetherinfants would spot theintroduction of a change in bothtypes of metre or whether theywould only notice the change inthe metre of their native culture.Hannon and Trehub [6,7] foundthat, while six months old infantsresponded to the introduction of achange to either the Balkan or theWestern metre, twelve month oldinfants could only spot the changein their native, Western, metre.However, after a limited amount of

exposure to Balkan music — twohours per day for two weeks —the 12 month old infants started toexhibit the same perceptualabilities as the younger subjects.Adults, on the other hand, failedto achieve native-like perceptionof Balkan metre after two weeksof listening (but see experiment 3of [7] for an intriguing twist).

Echoing the claims of FrederickII, several modern day composersand musicologists contest thatthe Western musical system isthe most natural one. But thiswould predict that our nervoussystems are, regardless of ourmusical environment, moreattuned to this system than otheralternative ones. The work ofHannon and Trehub [6,7] providescompelling evidence to thecontrary: as far as the brain isconcerned, the most naturalmusical system is that which youhave grown up hearing [2,8].

It is worth considering why thebrain loses the ability todiscriminate sounds. What couldbe the possible value of losing anability? We can gain an insightinto this by considering what abrain is for. We do not merelyreact to the outside world, wepredict the state of the outsideworld based on previousexperience. And we can bestpredict the future state of theworld by accurately sensing andencoding its present and paststates. This leads to thedevelopment of specificperceptual and neuralsensitivities. Kittens reared withexposure to, for instance, onlyvertical edges never learn toperceive horizontal edges, nor doneurons in their visual cortexacquire any sensitivity tohorizontal lines [9]. A kitten in avertical world has no need tomake predictions about horizontallines, just as children reared in anentirely English-speakingenvironment have no need tomake predictions about thesounds that are unique to theHindi language.

This view has been formalisedby the work of Saffran andcolleagues [10,11]. Using stringsof words and tones with infants asyoung as 8 months, they askedhow much of our abilities are

Dispatch R883

hardwired and independent of theenvironment and how much theyare dependent on incominginformation. Infants aresophisticated learners and itseems that, in language andmusic, their perceptual abilitiesare driven by innate mechanismsand learning by experience [8]. Inboth domains their learning isdriven by the ability to extractstatistical regularity from stimuli.Their responses to strings ofwords and sounds depend on theprobability that one element of astring will follow another based onprevious experience. In otherwords, it seems that the infantsare making statistical inferencesregarding the external world.What we now need to know is theextent to which the algorithms forextracting these regularities andbuilding predictions are similar oreven shared at some stages ofdevelopment across domainssuch as music and language.

The issue is a deep one: Wemake predictions about visualobjects, about others’ emotionalresponses, about speech, musicand the movement of objects inthe world. The ground has shifted,then, from thinking abouthardwired knowledge to thinkingabout hardwired ways of

acquiring knowledge. Whetheradults can recapture the earlypower of these learningmechanisms or whether moredeveloped mechanisms can beadapted to learn things in differentways is also a question opened bythis line of work.

What of the adults in Hannonand Trehub’s experiment [7]?Would they have learned like the12 month olds if they just hadmore time, or had they missed acritical time window after whichthey could not use the samelearning mechanism? Again ahalfway house might be the rightplace to stop: it may not be thatthe window is slammed shut, butthat the adults continue to usepredictive learning mechanismsonly on a different, usually lessrich and more fixed body of neuralrepresentations than are availableto children. Adults can learn, ofcourse, but they have toovercome the limitations set bytheir early experience andsubsequent neural sensitivities.Balkan dance classes are nowopen for enrolment.

References1. Hubel, D.H., and Wiesel, T.N. (1963).

Receptive fields of cells in striate cortexof the very young, visually inexperiencedkittens. J. Neurophysiol. 26,994–1002.

2. Kuhl, P.K. (1994). Learning andrepresentation in speech and language.Curr. Opin. Neurobiol. 5, 812–822.

3. Werker, J.F., and Tees, R.C. (1984).Cross-language speech perception:Evidence for perceptual reorganisationduring the first year of life. Infant Behav.Dev. 7, 49–63.

4. Werker, J.F., and Lalonde, C.E. (1988).Cross-language speech perception:initial capabilities and developmentalchange. Dev. Psychol. 24, 672–683.

5. Lynch, M.P., Eilers, R.E., Oller, D.K., andUrbano, R.C. (1990). Innateness,experience, and music perception.Psychol. Sci. 1, 272–276.

6. Hannon, E.E., and Trehub, S.E. (2005).Metrical categories in infancy andadulthood. Psychol. Sci. 16, 48–55.

7. Hannon, E.E., and Trehub, S.E. (2005).Tuning in to musical rhythms: Infantslearn more readily than adults. Proc.Natl. Acad. Sci. USA 102, 12639–12643.

8. Streeter, L.A. (1976). Languageperception of two month old infantsshows effects of both innatemechanisms and experience. Nature259, 39–41.

9. Hirsch, H.V., and Spinelli, D.N. (1970).Visual experience modifies distribution ofhorizontally and vertically orientedreceptive fields in cats. Science 168,869–871.

10. Saffran, J.A., Aslin, R.N., and Newport,E.L. (1996). Statistical learning by eightmonth old infants. Science 274,1926–1928.

11. Saffran, J.A., Johnson, E.K., Aslin, R.N.,and Newport, E.L. (1999). Statisticallearning of tone sequences by humaninfants and adults. Cognition 70, 27–52.

1University of Newcastle and WellcomeDepartment of Imaging Neuroscience,University College London, London, UK.2Institute of Cognitive Neuroscienceand Department of Psychology,University College London, London, UK.

DOI: 10.1016/j.cub.2005.10.019

Current Biology Vol 15 No 21R884

Adam Clark Arcadi

Human language exhibits manyunique features compared withthe communication systems ofother animals. The most obviousof these is its expressive power— the grammatical structure oflanguage permits an infinitenumber of meaningful utterances[1]. Language behavior dependson the ability to model the mentalstates of conspecifics [2]. And theability to produce and processspeech involves specialized oro-

facial, respiratory and perceptualabilities [3]. But these potentiallyunique features are alsosupported by capacities thatshow continuities with otherspecies. For example, membersof some species partitioncontinuous acoustic variationcategorically, exhibit lateralizationin perceptual processing, requireauditory feedback to learnspecies-specific vocalizations,engage in timed vocalinteractions, vary call productiondepending on their audience, and

encode information aboutexternal events in their calls [4].

Tracing the evolution oflanguage requires clarifying thenature of continuities betweenhuman and nonhuman cognitivestructures and communicationsystems in order to specify likelypathways by which language’sunique features could haveemerged [5]. One intriguingresearch area, explored bySlocombe and Zuberbühler [6] in arecent issue of Current Biology,concerns the possibility that someanimal signals refer to objects orevents external to the signaler, andmay therefore be similar to words.The first evidence of suchreferential potential came from theobservation that wild vervetmonkeys (Cercopithecus aethiops)produce acoustically distinct alarmcalls in response to their threemost important predators —

Language Evolution: What DoChimpanzees Have to Say?

Although unique in important ways, language shares some propertieswith other animal communication systems. Comparative analyses ofnonhuman primate vocalizations can shed light on the evolution oflanguage’s special features.