604 Child Development a航ents wit ative response on a pde variety ke d that er h play infan s.For consin ort Test (Mine ple human infants and pre 1982 Knight,Hillyar the same that was 1981 sly rewarded bu Task (Shallic (D )and tasks that p uire on,Buc They have a strong to ndency ided by ass ples The Ho y rev a data hat d1 er ed theB error.Dur atal de ermr ility may be in the ssively d t 4 are ace Com anng the 1987. m man and that br out this ab d ad have at the le hun t at th d thos lesi CO behave as do that the sity Eeoee yatt出 on wo ld be m beha be pre ta on ativ aved nse events Th ure a ront be c may ere why tone, onse rat than ex ognition tha 1a6 aPP Di time ,1975 the ele also explain why ntal ca e outside rld and to b I0 tests (e.g. Hebb 939 nt(For excellent dis ide ion ance of shortterm life. The be avior o he of see ter,1980.1985 pro foll e ha the man infa to behave of hu with pretr e t or on monkeys long after it has 1985 1987；Jacob 6).By virtue of the ems to re tations for the time n ces observe a re information about the location of coul 604 ChUd Dev^opment Our results estaUished that AB, like de￾layed response, is impaired selectively by dorsolateial prefronttJ lesions in adult rhesus monkeys, and that die pattem of erTors dis￾played by the operated monkeys closely re￾sembles that exhibited by human infants. For example, human in&nts and i^efrontal mon￾keys are nearly always correct when the ob￾ject is hidden in the same location that was previously rewarded but perfimn near chance when the position is reversed (Diamond, 1985; Diamond & Goldman-Bakic, 1983). They have a strong tendency to repeat the previously rewarded response and are strongly guided by associative principles. The selection of a previously reiOTirded response rather than one glided by updated visual data is temied the J ^ error. During postaatal de￾velopment, progressively longer delays be￾tween hiding and response are required to elicit this error in children (Diamond, 1985). Gomparing the human and monkey data, we were able to demonstrate diat the brain￾lesioned adult monkeys behave at the level of 7V'2-9-month-old human in^ts, making the AB error widi delays of 2-5 sec. Nomial mon￾keys and those with lesions of die posterior parietal cortex behave as do 12-month-old hu￾man infente, who perform correctly at these delays. On die basis of their common depen￾dence on prefrontal cortex Mid on what we know and can dieorize about prefrontal cor￾tex, we conclude that bodi ddayed response and AB tasks measure a common jmwess— die emergence of representational memory. This capacity may be considered a building block, if not a comerstone, of cognitive devel￾opment in man. Moreover, "object perma￾nance"—the recognition that an otgect has continuity in time and space when not in tjteuj—must depend on die elemental capac￾ity to form representations of the outside world and to base responses on those repre￾sentations In die absence of the objects diey represent. (For excellent discussion of die re￾levance of short-term memory processing to the temporal o^jaaization of behavior, see Fuster, 1980, 1985.) Representational processes disaUow in￾appropriate responses.—A cardinal feature of die behavior of human infents and of hunians and monkeys with prefrontal lesions is the strong tendency to persevenUfi a particul^ re￾sponse long after it has ceased to be ^propri￾ate. For example, a monkey with a prefroatal lesion, unlike a nramal monkey, seems to re￾spond to the first food well &at catches its eye or to die just previously reinforced position radier than on the basis of recendy observed informadon about the location of the reward. Patients with frc»ital lobe damage are simi￾larly perseverative, exhibiting impairments on a wide variety of tests that require suppres￾sion of prept^nt responses (or responses to distracting stimulation), including the Wis￾consin Gard Sort Test (Milner, 1963, 1964), tests of selective attention (Kni^t, Hillyard, & Neville, 198?* «ni ^ Hillyard, Woods, & Neville, 1^0, 1981), die Stroop Test (Perret, 1974), the Tower of London Task (Slu^ice, 19^), and tasks that require inhibition of pre￾potent responses (Guitton, Buchtel, & Doug￾las, 1982, 1^5). Some have considered per￾severation as a primary deficit attiibuteble to damage to the orbital prefrontal cortex (Fus￾ter, 1985; Mishkin, 1964). However, I have argued feat perseveratiw behavior and dis￾tractability may be secondary consequences of file more fundamental impairment in the mechanism by which symbolic rei»esenta￾tions are accessed and held "on line" to guide a response (Goldman-RaJdc, 1987). It seems possible diat witfiout diis ability, an organism would be virtually compelled to respond refexively to stimuli present in the environ￾ment at the time of resp<mse or on the basis of prepotent response tendMicies. Further, it is easy to envision that die intensity and sa￾lience of stimulalion would be important fac￾tors goveming b^avior under such circum￾stances. In acMition, behavior mi£^t be regulated largely by associative c(mditioning to events that occurred in close temporal proximity. The sparing of associative memory after prefrontal irqury may help to explain why human ii^iits diaracteristically repeat a previously rewarded response rather dian ex￾ecute a new more apEHK^riate response in Piaget's AB paaK^m (Diamond, 1^ ; Uz￾giris & Hunt, WfS). It may also explain why frontal lobe p(#^ s can have an average store of feotual iralc^iw&on suid perform wdl on conventional IQ tests (e.g., Hebb, 1939) but be grossly deficient in how they utilize dieir representational knowfedge to guide behav￾ior in everyday life. "Hie behavior of such pa￾tients, and to some extent of hum^i infiunts, is fragmented, la^b g clear direction and ejffies￾sively controH^ by extemal stimulafeon. It foUows diat die prefrontal ccatex may be nec￾essary to overricte the teiwiency to behave stricdy on die basis of reinibrcemeat or on the basis of stirou^rtkm pre&eirt at the mome^ of response (Fuster, 1985; Goldman-R^c, 1987; ]acdbsen, 1936). By virtue o£&€ sii^u￾lar process of wcffkiag memory, die jjirefrontal cortex nuiin^iiis access to internalized tepre￾sentsrtiCTis for die time necessary to craniate a response or response sequence, tlie emer￾gence of this capacity in postnatal life could