one of the most influential cognitive theories of autism spectrum disorders ( asd ) highlights the primary role of deficits in executive functions ( geurts et al . 2009 ; hill 2004 ; pennington and ozonoff 1996 ; russell 1997 ) , the cognitive control processes that guide the ability to monitor ongoing performance in a dynamically changing environment . within social interactions it is necessary to select and initiate complex behaviors in response to the specific necessities of the social environment ( bachevalier and loveland 2006 ) . hence , the ability to generate appropriate responses during social interactions involves selecting the most fitting response while inhibiting those responses deemed inappropriate which is an important aspect of executive functioning . despite its suggested relevance to social functioning , executive functions are mainly studied in non - social domains ( hill 2004 ) , using tasks that focus on specific , elementary abilities such as planning behaviour and inhibitory control ( sergeant et al . findings on inhibitory control in asd are particularly mixed , with multiple reports on both deficits ( e.g. , christ et al . 2007 ; geurts et al . 2004 , 2008 ; solomon et al . 2008 ) , and attainments ( e.g. , christ et al . 2007 ; 2006 ; kana et al . 2007 ; ozonoff and jensen 1999 ; raymaekers et al . 2007 ; schmitz et al . 2006 ) , which may in part be due to differences in arousal modulation ( liss et al . 2006 ; raymaekers et al . 2004 ) . the current study will focus on the role of arousal modulation in the inhibitory control of socially relevant stimuli of children with asd . over - arousal , attained by fast presentation rates of stimuli , can cause inhibitory control deficits in participants with asd ( raymaekers et al . however , when non - social stimuli are used , these deficits are not always found in children with asd , even when fast presentation rates were used ( e.g. , christ et al . 2007 ; happ et al . 2006 ; kana et al . 2007 ; raymaekers et al . 2007 ; schmitz et al . the role of arousal modulation in inhibitory control tasks may be more clear when social stimuli are used , e.g. , emotional faces , which are known to elicit both hypo- and hyper - responsiveness in children with asd , likely due to impaired arousal modulation ( baker et al . 2008a , b ; rogers and ozonoff 2005 ; schoen et al . 2008 ) . in the current study , we investigated inhibitory control deficits in children with asd when processing socially relevant stimuli . children with high functioning autism ( hfa , including children with autism and with asperger syndrome ) were compared to typically developing control children on two experimental tasks : ( a ) a go / nogo - task with emotional stimuli presented at two different presentation rates ; and ( b ) an emotion recognition task to determine whether children with hfa have deficits in the recognition of simple emotions . we hypothesized a limited ability to inhibit responses to social stimuli in children with asd compared to controls . furthermore , we explored the effect of the presentation rate ( i.e. , arousal level ) on the ability to inhibit the prepotent motor response to these socially relevant stimuli . twenty - two children with hfa and 22 typically developing control children participated in this study . participants with hfa fulfilled established diagnostic criteria according to the dsm - iv - tr ( american psychiatric association 2000 ) , as well as the autism algorithm cut - offs on two questionnaires that assess the defining social problems of children with hfa : children s communication checklist ( ccc , bishop 1998 ) and the children s social behavior questionnaire ( csbq , luteijn et al . 2002 ) . three children were excluded from the study because they had an estimated iq below 75 as measured by the short version of the dutch wechsler intelligence scale for children ( wisc - iii ; de kort et al . therefore , eventually 18 children with a clinical diagnosis of autism ( n  =  7 ) or asperger syndrome ( n  =  11 ) aged 813  years participated in this study . one participant with hfa was on methylphenidate , but discontinued medication at least 20  h before testing allowing for a complete wash - out . all children had an estimated iq above 75 ( range hfa : 82144 ; range controls : 75154 ) . the two groups did not differ from each other with respect to age , f(1 , 40 )  <  1 , ns ,   =  .00 , fsiq , f(1 , 40 )  <  1 , ns ,   =  .01 , and gender ,  ( 1 , n  =  40 )  =  .058 , ns . as expected , the parents of the children with hfa reported more problems when compared to typically developing children on all scales of the ccc and the csbq ( see table  1 ) . the parents of the control children indicated that none of these children , or their siblings , was known with behavioural problems or a psychiatric or neurological diagnosis.table  1controls and hfa : group means and standard deviations for age , iq , and , rating scalesmeasuregroupcontrols ( n  =  22)hfa ( n  =  18)gender ( boys / girls)19/316/2msdmsdgroup comparison ( p)age10.31.410.31.6.96fsiq103.224.1108.019.0.50cccspeech output34.02.733.93.1.91syntax31.50.931.60.7.74inappropriate initiation28.21.824.13.0<.001coherence34.81.830.03.2<.001stereotyped conversation28.51.821.63.8<.001use of conversational context30.41.423.82.8<.001conversational rapport32.32.026.52.9<.001social relationships33.01.227.42.6<.001interests31.21.726.23.0<.001csbqnot optimally tuned3.73.612.24.5<.001reduced social contacts1.63.09.63.6<.001orientation problems1.21.96.93.5<.001problems in understanding1.51.48.73.5<.001stereotype behavior0.61.14.63.1<.001resistance to change0.20.53.23.1<.001total score9.08.245.311.2<.001note.ccc , children s communication checklist , csbq , children s social behavior questionnaire , fsiq , full scale iq , hfa , high functioning autism ( including children with a diagnosis of autism and asperger syndrome , see text)note that the lower the score on the ccc , the more impaired the child is , while in the csbq a higher score indicates impairment controls and hfa : group means and standard deviations for age , iq , and , rating scales note.ccc , children s communication checklist , csbq , children s social behavior questionnaire , fsiq , full scale iq , hfa , high functioning autism ( including children with a diagnosis of autism and asperger syndrome , see text ) note that the lower the score on the ccc , the more impaired the child is , while in the csbq a higher score indicates impairment emotional inhibition task . in line with raymaekers et al . ( 2004 ; 2007 ) the inhibition task was a go / nogo paradigm with two types of trials : go - trials and nogo - trials . in the middle of the computer screen there was a small square as constant fixation point . on each trial a visual stimulus , either a face with a happy expression ( go - trial ) or a face with an angry expression ( nogo - trial ) appeared for 300  ms . in a go - trial , the participants were instructed to press a response key with their index finger of their dominant hand if a face with a happy expression appeared , whereas in a nogo - trial , participants had to refrain from responding if a face with an angry expression appeared . to enhance the ecological validity of the emotional stimuli we chose emotions that promote approaching behavior in the go - trial ( happy expressions ) , and emotions that promote aversive behavior in the nogo - trial ( angry expressions , frijda 1986 ; isen 1987 ) . eight different faces were used as stimuli , taken from the karolinska directed emotional faces set which consists of 4,900 pictures of human facial expressions ( lundqvist et al . the set contains 70 actors ( 35 male , 35 female ; age range 2030  years ) each displaying seven different emotional expressions . in our selection there were equal numbers of men and women , all wearing the same plain blue grey t - shirt and each person was shot once looking happy and once looking angry . there were two conditions within this task , a fast presentation rate ( determined in a pilot study and following raymaekers et al . 2007 ) , using a 2  s interstimulus interval ( defined in terms of onset to offset ) and a slow presentation rate , using a 6  s interstimulus interval . to keep the time on task effect equal for both conditions , the fast condition consisted of 200 trials ( 160 go - trials and 40 nogo - trials ) and the slow condition consisted of 80 trials ( 64 go - trials and 16 nogo - trials ) . the duration for each condition , including instructions and practicing , was  ~10  min . hence , without instructions the condition with the 2  s interstimulus interval lasted 7.6  min , while the 6  s condition lasted 8.4  min . second , the intrasubject variability ( standard deviation of the mean reaction time of correct go - trials ) was calculated as this is also linked to arousal modulation ( raymaekers et al . the percentage of errors is the number of commission errors ( the participant responded to a nogo - trial ) divided by the total number of nogo - trials . typically , deficient inhibitory control leads to an increased error rate on nogo - trials ( casey et al . the participants had to decide whether the person on the picture displayed a happy or an angry emotion by pushing one of two buttons , namely a blue one for happy and a red one for angry . 1998 ) were used , which were similar to the type of stimuli used in the emotional inhibition task . the task consisted of 80 trials of 16 different faces , half of which displaying a happy emotion , the other half displaying an angry emotion . after the parents filled out both questionnaires and written informed consents were obtained , the participants were tested . within the inhibition task all participants received a small gift at the end of the test session and the parents or caregivers were sent reports of the overall findings of the study . twenty - two children with hfa and 22 typically developing control children participated in this study . participants with hfa fulfilled established diagnostic criteria according to the dsm - iv - tr ( american psychiatric association 2000 ) , as well as the autism algorithm cut - offs on two questionnaires that assess the defining social problems of children with hfa : children s communication checklist ( ccc , bishop 1998 ) and the children s social behavior questionnaire ( csbq , luteijn et al . 2002 ) . three children were excluded from the study because they had an estimated iq below 75 as measured by the short version of the dutch wechsler intelligence scale for children ( wisc - iii ; de kort et al . therefore , eventually 18 children with a clinical diagnosis of autism ( n  =  7 ) or asperger syndrome ( n  =  11 ) aged 813  years participated in this study . one participant with hfa was on methylphenidate , but discontinued medication at least 20  h before testing allowing for a complete wash - out . all children had an estimated iq above 75 ( range hfa : 82144 ; range controls : 75154 ) . the two groups did not differ from each other with respect to age , f(1 , 40 )  <  1 , ns ,   =  .00 , fsiq , f(1 , 40 )  <  1 , ns ,   =  .01 , and gender ,  ( 1 , n  =  40 )  =  .058 , ns . as expected , the parents of the children with hfa reported more problems when compared to typically developing children on all scales of the ccc and the csbq ( see table  1 ) . the parents of the control children indicated that none of these children , or their siblings , was known with behavioural problems or a psychiatric or neurological diagnosis.table  1controls and hfa : group means and standard deviations for age , iq , and , rating scalesmeasuregroupcontrols ( n  =  22)hfa ( n  =  18)gender ( boys / girls)19/316/2msdmsdgroup comparison ( p)age10.31.410.31.6.96fsiq103.224.1108.019.0.50cccspeech output34.02.733.93.1.91syntax31.50.931.60.7.74inappropriate initiation28.21.824.13.0<.001coherence34.81.830.03.2<.001stereotyped conversation28.51.821.63.8<.001use of conversational context30.41.423.82.8<.001conversational rapport32.32.026.52.9<.001social relationships33.01.227.42.6<.001interests31.21.726.23.0<.001csbqnot optimally tuned3.73.612.24.5<.001reduced social contacts1.63.09.63.6<.001orientation problems1.21.96.93.5<.001problems in understanding1.51.48.73.5<.001stereotype behavior0.61.14.63.1<.001resistance to change0.20.53.23.1<.001total score9.08.245.311.2<.001note.ccc , children s communication checklist , csbq , children s social behavior questionnaire , fsiq , full scale iq , hfa , high functioning autism ( including children with a diagnosis of autism and asperger syndrome , see text)note that the lower the score on the ccc , the more impaired the child is , while in the csbq a higher score indicates impairment controls and hfa : group means and standard deviations for age , iq , and , rating scales note.ccc , children s communication checklist , csbq , children s social behavior questionnaire , fsiq , full scale iq , hfa , high functioning autism ( including children with a diagnosis of autism and asperger syndrome , see text ) note that the lower the score on the ccc , the more impaired the child is , while in the csbq a higher score indicates impairment ( 2004 ; 2007 ) the inhibition task was a go / nogo paradigm with two types of trials : go - trials and nogo - trials . in the middle of the computer screen there was a small square as constant fixation point . on each trial a visual stimulus , either a face with a happy expression ( go - trial ) or a face with an angry expression ( nogo - trial ) appeared for 300  ms . in a go - trial , the participants were instructed to press a response key with their index finger of their dominant hand if a face with a happy expression appeared , whereas in a nogo - trial , participants had to refrain from responding if a face with an angry expression appeared . to enhance the ecological validity of the emotional stimuli we chose emotions that promote approaching behavior in the go - trial ( happy expressions ) , and emotions that promote aversive behavior in the nogo - trial ( angry expressions , frijda 1986 ; isen 1987 ) . eight different faces were used as stimuli , taken from the karolinska directed emotional faces set which consists of 4,900 pictures of human facial expressions ( lundqvist et al . the set contains 70 actors ( 35 male , 35 female ; age range 2030  years ) each displaying seven different emotional expressions . in our selection there were equal numbers of men and women , all wearing the same plain blue grey t - shirt and each person was shot once looking happy and once looking angry . there were two conditions within this task , a fast presentation rate ( determined in a pilot study and following raymaekers et al . 2007 ) , using a 2  s interstimulus interval ( defined in terms of onset to offset ) and a slow presentation rate , using a 6  s interstimulus interval . to keep the time on task effect equal for both conditions , the fast condition consisted of 200 trials ( 160 go - trials and 40 nogo - trials ) and the slow condition consisted of 80 trials ( 64 go - trials and 16 nogo - trials ) . the duration for each condition , including instructions and practicing , was  ~10  min . hence , without instructions the condition with the 2  s interstimulus interval lasted 7.6  min , while the 6  s condition lasted 8.4  min . second , the intrasubject variability ( standard deviation of the mean reaction time of correct go - trials ) was calculated as this is also linked to arousal modulation ( raymaekers et al . the percentage of errors is the number of commission errors ( the participant responded to a nogo - trial ) divided by the total number of nogo - trials . typically , deficient inhibitory control leads to an increased error rate on nogo - trials ( casey et al . the participants had to decide whether the person on the picture displayed a happy or an angry emotion by pushing one of two buttons , namely a blue one for happy and a red one for angry . 1998 ) were used , which were similar to the type of stimuli used in the emotional inhibition task . the task consisted of 80 trials of 16 different faces , half of which displaying a happy emotion , the other half displaying an angry emotion . after the parents filled out both questionnaires and written informed consents were obtained , the participants were tested . within the inhibition task the order of two presentation rates were counterbalanced across the participants . all participants received a small gift at the end of the test session and the parents or caregivers were sent reports of the overall findings of the study . all children were faster and less variable in the fast presentation rate compared to the slow condition , respectively f ( 1 , 38 )  =  74.07 , p  <  .001 ,   =  .66 and f ( 1 , 38 )  =  10.00 , p  <  .005 ,   =  .21 . in their overall performance children with hfa could not be differentiated from control children on response speed , f ( 1 , 38 )  =  2.59 , ns ,   =  .06 , however , the responses of the children with hfa were more variable than the control children , f ( 1 , 38 )  =  4.09 , p  <  .05 , a group  *  presentation rate interaction , f ( 1 , 38 )  =  7.00 , p  <  .02 ,   =  .16 ( see table  2 ) , indicated a different effect of presentation rate on response speed in hfa and controls . while the fast presentation rate elicited similar mean reaction times in both groups ( ns ) , the slow presentation rate elicited slower responses in the hfa than in the control group , p  <  .05 . there was no differential effect of presentation rate on intrasubject variability for the two groups , f ( 1 , 38 )  =  3.36 , ns ,   =  .08.table  2group means and standard deviations for the emotional inhibition task for controls and participants with hfameasuregroupcontrolshfafast ( 2  s isi)slow ( 6  s isi)fast ( 2  s isi)slow ( 6  s isi)msdmsdmsdmsdmrt446.680.3510.687.6476.2129.4597.0168.3sd mrt125.742.33134.245.2151.263.0183.190.0% errors10.36.010.25.412.75.111.35.0note.hfa , high functioning autism ( including children with a diagnosis of autism and asperger syndrome , see text ) , isi , inter stimulus interval , mrt , mean reaction time , sd , standard deviation group means and standard deviations for the emotional inhibition task for controls and participants with hfa note.hfa , high functioning autism ( including children with a diagnosis of autism and asperger syndrome , see text ) , isi , inter stimulus interval , mrt , mean reaction time , sd , standard deviation percentage errors ( inhibitory control ) : all children made less errors when the presentation rate was slow than when the presentation rate was fast , f ( 1 , 38 )  =  6.96 , p  <  .02 ,   =  .16 , but no group , f  <  1 , ns , =  .01 , nor interaction effects , f ( 1 , 38 )  =  1.08 , ns ,   =  .03 , were found . there were no group differences in the recognition of happy or angry faces on the emotion recognition task ( response speed : group , f ( 1 , 38 )  =  2.88 , ns ,   =  .07 ; group  *  emotion , f ( 1 , 38 )  =  2.52 , ns ,   =  .06 : accuracy : group , f ( 1 , 38 )  =  1.18 , ns ,   =  .03 , group * emotion , f  <  1 , ns ,   =  .02 . ) . the current results suggest that children with hfa are able to exert adequate inhibitory control when processing facial expressions , which is in line with most former studies that used neutral stimuli ( e.g. , christ et al . 2007 ; happ et al . 2007 ; raymaekers et al . 2007 ; schmitz et al . 2006 ) . despite their equal accuracy , children with hfa responded disproportionably slower than controls in the slow , but not in the fast presentation rate condition . this slowness is generally not related to inhibitory control deficits per se ( casey et al . 1997 ) , and could not be attributed to the inability to recognize simple emotions . in line with raymaekers et al . ( 2004 ) we found that presentation rate affected children with hfa differently than typically developing children , however , our pattern of findings differs from the earlier reported pattern . ( 2004 ) showed that on a neutral inhibitory control task adults with asd were more impaired ( as reflected by accuracy measures ) when the presentation rate was fast , while we found that children with hfa were more impaired when the presentation rate was slow ( as reflected by response speed measures ) . among others , the two studies differed in the timing of the fast presentation rates and in the age of the participants . in a study in children with hfa , with a similar fast presentation rate as in the current study , raymaekers et al . ( 2007 ) could not replicate the former adult pattern of findings ( raymaekers et al . this suggests that the effect of presentation rate is both age and stimulus dependent , as in children the presentation rate only seems to influence performance when emotional stimuli are used . the current findings , including the enhanced response time variability , suggest a lack of efficient arousal modulation , motivation , or reduced attention ( e.g. , garretson et al . 1990 ) in children with hfa . when stimuli are presented at a slow pace it might be harder to sustain attention or to keep a sufficient amount of motivation . we tried to eliminate sustained attention as a confounding factor to keep the time on task exactly the same in both presentation rate conditions and by counterbalancing this presentation rate ( see also christ et al . 2007 ) . however , it is still possible that the children with hfa were less motivated and put in less effort when the presentation rate was slow . whether this is especially the case when although one might interpret these findings as evidence for under - arousal in children with hfa when confronted with facial expressions , we believe that replication studies ( in which psycho physiological measures , such as heart rate variability or skin conductance , of arousal are included ; see also geurts et al . a potential confound of the experimental set up might be the choice to include emotions with response tendencies in line with the requested action in the emotional inhibition task . however , reversing the instruction by requesting responses to angry expressions and no responses to happy expressions could introduce an additional inhibition element to the task , above the inhibitory control that is inherent to the go / nogo - task . , we show that even when more socially relevant stimuli are used children with hfa do not show inhibitory control deficits . however , motivation and/or arousal might be a factor that influences the processing of socially relevant stimuli as slow presentation rates resulted in more profound performance decrements in children with hfa as compared to typically developing children . how and when motivation plays a role in children with hfa needs to be addressed in future research as this might give us insight in how we can motivate children with hfa in such a way that in daily life their performances increase .
the current study explored whether inhibitory control deficits in high functioning autism ( hfa ) emerged when socially relevant stimuli were used and whether arousal level affected the performance . 
 a go / nogo paradigm , with socially relevant stimuli and varying presentation rates , was applied in 18 children with hfa ( including children with autism or asperger syndrome ) and 22 typically developing children ( aged 813  years ) . 
 children with hfa did not show inhibitory control deficits compared to the control group , but their performance deteriorated in the slow presentation rate condition . 
 findings were unrelated to children s abilities to recognize emotions . 
 hence , rather than a core deficit in inhibitory control , low arousal level in response to social stimuli might influence the responses given by children with hfa .