the relationship between autism and imitation deficits was envisaged long time ago by ritvo and province , short after autism was originally described in the work of kanner . the imitative ability has been acknowledged to play an essential role in normal development , as it can be used by infants to acquire and master new behaviors [ 3 , 4 ] . in recent years , the relationship between autism and voluntary imitation has been investigated more systematically . in their review , for instance , williams et al .   concluded that children with an autism spectrum disorder ( asd ) are consistently impaired in performing imitative tasks relative to children with other developmental delays ( matched for chronological age , verbal iq - mental age and expressive language ( see [ 6 , 7 ] ) , or to normal controls matched for mental age [ 7 , 8 ] . asd children performed more poorly on imitation tasks than matched - to - language controls or younger children matched for receptive language and mental age , thus ruling out the interpretation that the imitation impairment is due to a linguistic deficit . neither can the imitative deficit of asd individuals be attributed to a defective gesture recognition [ 6 , 8 ] , since they recognized gestures without any trouble . moreover , asd individuals ' fine grained motor skills , even when reduced , did not correlate with their observed imitation and praxis deficits . moreover , irrespective of whether they are low or high functioning , children with autism seem to have difficulties in imitating gestures that disable children and typically developing children do not show . this finding supports the view that imitation deficits are specific to asd ( see also ) . whether the reduced ability to imitate of asd children is a true deficit or a delay in development is still under debate . this deficit seems to be already present in children as young as 20 months and is , in general , more apparent in children than in adults . consistently , an improvement in performance was observed when young asd children , with a mean age of 31 months , were retested about one year later . williams et al .   proposed that observing a meaningful ( mf ) object or gesture triggers the release of a previously rehearsed program or that observing a desired outcome might lead the observers to reach this goal by applying their own problem solving ability . hence , imitation itself would be especially required for copying meaningless ( ml ) gestures that do not have an obvious goal or associated knowledge . this would explain why in some studies asd children were reported to experience more difficulty when imitating ml compared with mf gestures involving objects [ 6 , 7 ] . it has been shown that asd children imitate goal - directed actions as well as healthy children with the same verbal mental age do . argued that the ability to imitate ( and understand ) the goal of hand actions is intact in asd children who , however , might fail to perform the imitation tasks in which they can not rely on a hand - goal strategy as in the case of ml actions . they also suggested that it is unlikely that a unique neurocognitive mechanism underlies imitative behavior in either the typical or autistic brain . consistently with this view , hamilton   put forward a dual - route model for emulation and planning versus mimicry ( ep - m model ) and proposed that the latter is impaired in children with autism . according to this model , the mirror neuron system is fractioned into an indirect , parietal route for goal emulation and planning and a direct occipitofrontal route for mimicry . in the case of the e - p route , the presence of an object or goal allows an individual to extract the teleological understanding of the action and to reconstruct the same action by his / her own means . the m - route is based on the analysis of low level kinematics of an action and allows the formation of direct associations from visual input to motor output . however , whether children with asd are able to imitate communicative gestures ( such as waving a hand for goodbye ) is still debated . communicative gestures , even though they have been included in the assessment of more than one study , have either been analysed together with other gesture types ( e.g. , ) or , when analysed as a separate class , they were found to be imitated normally . this latter result is difficult to interpret because , in addition to the instruction to imitate , participants were also provided with verbal encouragement ( e.g. , moreover , different studies used different tasks and included participants of different ages ( for children see ; for adolescents see ; for adults see ) . if , according to the ep - m model , children with autism have a selective damage to the mimicry route [ 10 , 11 ] , one would predict that they should be equally impaired at imitating novel as well as symbolic , communicative gestures . in fact , as these two types of gestures do not have an obvious outcome , children can not rely on an emulation and/or problem solving . a different set of predictions can be drawn based on a dual - route model of action imitation   ( see also [ 13 , 14 ] ) that is also consistent with the conclusions reached by williams et al . . the key feature of tessari and rumiati 's model is the presence of two different mechanisms subserving imitation : a direct route necessary for reproducing novel , ml actions , as it translates the visual input into a motor output and an indirect route that can be used only for imitating over - learned , mf actions , as it accesses the stored representations of the motor act . since both symbolic communicative ( i.e. , intransitive ) and transitive gestures ( i.e. , actions that involve the use of objects ) are already known by the subjects , imitation of either type of gestures should be comparable in terms of accuracy . after brain damage , each mechanism can be selectively impaired , giving rise to different imitation deficits affecting either known or novel actions [ 1518 ] . in particular , when the direct route is damaged , patients can not imitate novel actions , while when the indirect route is damaged , they can not use it to imitate known actions . these findings were observed when known , and novel actions were presented in separate lists .   in the present study , we aimed to clarify how high - functioning autistic ( hfa ) children imitated different types of actions ( i.e. , known mf symbolic communicative , pantomime of object use , and novel ml actions ) and to test which of the available models best accounts for their impaired - preserved imitative pattern . importantly , we consider that investigating imitation performance in asd is highly valuable as it allows testing current theoretical models of imitation . thirteen high - functioning children with autism ( m = 7.31 years old , sd = 1.79 ; all males ) and 14 typically developing children ( m = 7.00 years old , sd = 1.71 ; all males ) participated in the study . age did not differ between the two groups ( t(26 ) = 0.46 , p > 0.1 ) . all children were right - handed ( average on the percentage of right hand use hfa : m = 90.91% , sd = 15.02 , controls : m = 89.89% , sd = 16.62 ) . all autistic participants were clinically diagnosed as having a pervasive development disorder  not otherwise specified  according to dsm - iv . none of the patients had comorbid attention deficit and hyperactivity disorder ( adhd ) , seizure disturbance , or any other associated disorder known to cause autism . high - functioning autistic participants were selected if they had a full scale iq > 70 and they scored above threshold for autistic spectrum disorder on the children autistic rating scale ( cars ) or ados ( see table 1 ) . children with autism typically , developing children were recruited from local schools and were administered an intelligence scale ( wisc , verbal subscale ) by the experimenter . ethical permission for the study was granted by sissa ethical committee , and informed consent was given by one parent of each child . stimuli consisted of five sets of 12 simple , nonsequential gestures each . of these , three sets included mf gestures : 12 transitive gestures without objects like , for instance , pretending to pour from an imagined bottle ( all taken from ) , 12 intransitive symbolic gestures like , for instance , waving goodbye , ( all taken from ) , and 12 transitive gestures performed with an object like , for instance , pouring from a real bottle . the remaining two sets included 24 meaningless ( ml ) gestures , obtained by modifying the relationship between hand , arm , and trunk of the mf transitive and intransitive gestures . each action was displayed up to two times for 3 seconds on a computer screen using presentation software ( neurobs ) . all actions were modelled by a female adult using her right hand arm ; subjects were only given the instruction  do what she does  without mentioning the hand they should use . when performing the gestures , the model kept the gaze fixed straight ahead , thus avoiding confound effects regarding the possibility of reading intentions from gaze . participants ' performance was video - recorded and scored offline by a rater , blind to the predictions of the study and to group membership , who was instructed to code each action using a 3-point scale system : 0 for totally incorrect , 1 partially correct , and 2 for correct imitation . for the partially incorrect imitative performance , the rater was asked to code the errors with one of 15 a priori defined error - types ( see the appendix ) and report the hand used in each trial . participants could begin the experimental session either with mf ( 3 blocks ) or ml gestures ( 2 blocks ) , and this order was counterbalanced across participants . an additional rater scored the performance of approximately 30% of the participants , and a good interraters agreement was obtained ( cohen 's kappa = 0.65 , s.e . two types of assessment were carried out in order to ascertain what participants knew about the intransitive and transitive gestures employed in the study . for the symbolic intransitive actions , participants were asked to say whether they knew the meaning of each action ( n = 12 ) ; for the transitive gestures , participants were presented with the corresponding object and asked to demonstrate how it is normally used . this latter task allowed us also to evaluate participants ' hand dominance , given that no instructions were provided to the children as to which hand they should use with the object placed on the table in front of them . the order of the imitative tasks and of the knowledge assessment tasks was counterbalanced across subjects . for each participant , mf ( transitive or intransitive ) gestures that were not recognized were not included in the analysis . hfa children were able to recognize on average 74.36% ( sd = 14.22 ) and control children 85.61% ( sd = 5.16 ) of the intransitive gestures . hfa children were able to demonstrate the use of objects ( transitive actions ) on average 98.71% ( sd = 3.13 ) and control children 100% . a repeated - measures anova on percentage of imitative correct responses with meaning ( ml , mf ) and context ( transitive , intransitive ) as within - subjects independent variables and with group ( hfa , controls ) as a between - subjects variable ( see figure 1 ) was performed . overall , the hfa group imitated more poorly ( m = 73.26 , se = 3.96 ) than the control group ( m = 90.10 , se = 3.82 ) ; meaningful actions ( m = 89.10 , se = 2.22 ) were performed better than meaningless ( m = 74.28 , se = 3.54 ) , and the accuracy with intransitive actions ( m = 82.33 , se = 2.72 ) and transitive actions was comparable ( m = 81.01 , se = 3.32 ) . main effects of group and meaning were found to be significant ( f(1 , 26 ) = 9.355 , p = 0.005 ; f(1 , 26 ) = 45.84 , p < 0.001 , resp . ) but not the main effect of context ( f(1 , 26 ) = 0.26 , p > 0.05 ) . as predicted , the two - way interactions group  meaning ( f(1 , 26 ) = 6.21 , p < 0.05 ) were significant but not the two - way interaction group  context ( f(1 , 26 ) = 0.26 , p > 0.05 ) nor the 3-way interaction ( group  context  meaning : f(1 , 26 ) = 0.35 , p > 0.05 ) . context  meaning interactions were also found significant ( f(1 , 26 ) = 14.59 , p = 0.001 resp . ) . in order to better understand the interactions , we performed subsequent post hoc analysis . as to the meaning  group interaction , no differences were found between hfa and control children in imitation of mf actions ( tukey , p > 0.1 ) , whereas differences were found for imitation of ml actions ( tukey , p < 0.05 ) . the difference between imitation of mf and ml actions is driven mostly by hfa children who imitated ml actions more poorly ( tukey , p < 0.001 ) . control children imitated mf actions somewhat better than ml actions ( tukey , p = 0.024 , see figure 1 ) . regarding the context  meaning interaction , no significant differences were found in imitating transitive and intransitive ml actions ( tukey , p > 0.1 ) , while intransitive mf actions were found to be better imitated than transitive mf actions ( tukey , p = 0.019 ) . however , the context  meaning interaction seems to be mostly driven by differences in imitating intransitive actions : imitation of intransitive mf actions and imitation of intransitive ml actions were highly significant ( tukey , p < 0.001 ) ( with bonferroni correction for p values ) . the two groups did not significantly differ as far as imitation of actions involving real objects was concerned ( f(1 , 26 ) = 1.59 , p > 0.05 ) . importantly , we found no significant correlation between individual iq quotients and the imitative performance on neither ml actions ( r = 0.34 , p > 0.05 ) nor mf actions ( r = 0.32 , p > 0.05 ) . in order to assess whether children iq level influenced their individual imitative performance , we computed an analysis of covariance ( ancova ) with group ( hfa , controls ) and iq scores as predictors . the covariate variable ( iq ) was standardized prior to performing the analysis , by centering the mean ( see ) . consistent with the correlational analysis , we found that overall iq level did not influence participants imitative performance ( f(1 , 24 ) = 2.362 , p > 0.1 ) , not even when the meaning of actions was taken into account ( iq  meaning interaction : f(1 , 24 ) = 0.232 , p > 0.6 ) . we correlated the performance on imitation of mf and ml actions , regardless of whether they were transitive or intransitive , with the age of the control participants and of the hfa children , respectively ( see figure 2 ) . we found that the imitative performance of the control group on ml actions ( but not that of meaningful actions , r = 0.51 , p > 0.05 ) significantly correlated with increasing subjects ' age ( r = 0.56 , p < 0.05 ) , while the imitative performance of the hfa group on either type of gestures significantly correlated with their increasing age ( mf : r = 0.72 , p < 0.05 ; ml : r = 0.79 , p < 0.001 ) . due to a clear outlier in the control group ( a child with 4 years old ) , we have recalculated the correlations regarding the control group excluding this participant . in contrast with the hfa group , the results show now that neither the performance of ml actions nor of mf actions correlated with the age of participants ( mf : r = 0.06 , p > 0.55 ; ml : r = 0.29 , p > 0.05 ) . participants could imitate a gesture by selecting the same limb used by the model ( i.e. , anatomical imitation ) or by using the one on the same side of the model 's body as if they were looking in a mirror ( i.e. , specular imitation ) . it has often been claimed that typically developing children at a young age tend to prefer specular over anatomical imitation and that the preference becomes apparent when they are about 12 years old . which kind of imitation asd children prefer is still not clear . in one study , unlike controls , adults with autism did not benefit from viewing other person 's mirror - image movements , while in another one , both control and asd children showed a preference for mirror imitation of hand actions . in these studies , since the model performed the action using the left hand in half of the trials while the imitator tended to use predominantly the dominant right hand , it is difficult to establish whether participants preferred the specular to the anatomical imitation .  
 figure 3 plots the percentage of trials in which participants used the left hand ( specular imitation ) to imitate the different types of gestures . although the autistic group made more use than the control group of specular imitation in all imitative tasks , on the mann - whitney u test for independent samples , no significant differences were found between the two groups on imitation of transitive ( u = 0.46 , p > 0.1 ) and intransitive ml gestures ( u = 0.20 , p > 0.1 ) , transitive with ( u = 1.6 , p > 0.1 ) and without ( u = 0.23 , p > 0.1 ) the actual object at hand , and intransitive mf gestures ( u = 0.41 , p > 0.1 ) . in the current study we aimed to understand whether children with autism have a generalized deficit in imitating all gesture types or they only fail with object nonrelated gestures . we therefore tested a sample of high - functioning children with a clinical diagnosis of autism and an age - matched sample of typically developing children for their ability to imitate either novel or known gestures . gestures could , or could not , involve the presence of an object ( transitive or intransitive ) . in agreement with williams et al . view , we found that , relative to control children , high - functioning autistic children were more impaired in imitating novel than known actions . in addition , we found that the imitative performance of either group of participants was not dependent on whether the gesture implied the use of an object or not ( transitive versus symbolic communicative ) , as both mf transitive and symbolic communicative gestures were imitated equally well by both groups . in particular , the finding that imitation of object - related actions as well as symbolic communicative gestures is preserved in asd children is inconsistent with the hypothesis put forward by hamilton . according to this author 's proposal , children with autism are able to imitate only gestures that imply the use of an object ( or include a clear goal ) as its presence allows the emulation of the action instead of mimicry . an individual emulates an observed action by first extracting the goal of the action and then planning and reconstructing it by its own means . the fact that hfa and control children imitate equally well mf actions that do not have an object associated ( i.e. , symbolic communicative gestures ) challenges the view that autistic children are only able to emulate . the finding that , in hfa children , imitation of both transitive and intransitive mf actions is intact while imitation of ml actions is impaired strongly suggests that they suffer from a selective damage to one of the two putative mechanisms for action imitation hypothesised by tessari and rumiati : the direct route . the access to the representational system for actions stored in memory appears to be intact in these children . our results could possibly have useful implications for an early diagnose of the disorder , in that , we suggest that only the use of ml actions is appropriate for assessing imitation skills . due to several factors , the diagnosis of autism is still often made quite belatedly ( around 6 years of age ) because it is based on the assessment of language skills that do not develop before the first year of life . our study suggests that testing imitation could be used for identifying the eventual presence of the disorder without having to wait for the emergence of linguistic abilities , particularly in high - functioning children . the fact that hfa children imitated mf actions that convey a communicative meaning just like the control group did is apparently in contrast with the view that autism is primarily associated with social deficits ( e.g. , ) . according to this position , and in contrast to our data , it should be expected that the stimuli that pose difficulties for autistic children are those that carry emotional or social content . although any type of imitation procedure involves the interaction between the child and another person , not all imitation procedures seem to be impaired in asd children . what is striking about our results is that , while the gestures that explicitly carried social or communicative content were correctly imitated by the asd children , the gestures that did not have any special social content were not correctly imitated . as imitation processes have been acknowledged to play an important role in empathy , for they promote shared mutuality in social interactions and force social bonding , the social deficits in autism , such as poor interaction with others or retraction from social interaction , might be secondary to and develop as in consequence of the imitation deficit described in asd . regarding imitation of both ml and mf gestures , the accuracy of autistic children tended to improve with participant 's increasing age . the recovery of symptoms in asd has long been debated and mechanisms that might promote it have been systematically scrutinized ( see   for a review ) . although our results can not be taken as definitive evidence , they are in agreement with the hypothesis that the imitative asd children 's difficulties might not represent a true deviance but rather a delay in development , as they ameliorate as children get older . therefore , the imitative deficit could be expected to back down as the child gets older . in the present study , we evaluated the ability to imitate of high - functioning autistic children using a voluntary imitation procedure rather than an automatic imitation paradigm ( see e.g. , ) , whereby participants show a facilitation effect ( shorter reaction times , rt ) when executing a prefixed movement at the same time as they observe the same movement ( compatible trials ) ; in contrast , observing a movement incompatible with the preinstructed one leads to an interference ( longer rt ) . this paradigm has been suggested to tap the mirror neuron system in humans ; as performance on it has been found to be preserved in asd , it is not clear whether asd individual performs poorly on imitation tasks due to a malfunctioning mirror neuron system . although we do not directly tackle automatic imitation in the present study , we predict that an abnormal mirror neuron system would affect primarily actions that are already present in one 's own repertoire ( known actions ) . we failed to find any difference between specular and anatomical imitation . in approximately half of the trials , participants did prefer to imitate with their nondominant hand , mirroring the observed movement . overall , our results suggest that , for both autistic and typically developing children , imitating an observed movement in a specular manner might be beneficial . in conclusion , our main findings on the imitative performance of hfa children inform us of a dissociation between imitation of mf actions and imitation of ml novel actions . this fact is rather suggestive of a preserved indirect memory - based mechanism to imitation together with a potentially malfunctioning direct route to imitation .