Study protocol The study group will be consisted of 30 ASD children (6-12 years old) who were diagnosed with ASD recruited in the Pediatric Neurology clinic at Soroka Medical Center, Beer-Sheva, Israel, and ASD centers. A convenience sample of 30 age-gender matched healthy control children (6-12 years old) will be recruited using ads and flayer in Beer-Sheva and area. Children's parents will sign the informed consent, in accordance with procedures approved by the Helsinki Ethics Committee in Soroka Medical Center. As part of the initial assessment all children including the control group subjects will undergo a complete neuro-developmental and motor screening evaluation by an experienced pediatric neurologist using the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) diagnostic criteria Children with autism have to meet Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria. ASD participants will have to communicate enough in order to cooperate and understand orders. Exclusion criteria are: ASD children who were diagnosed with neurological, orthopedic, or psychiatric diagnoses according to DSM-IV criteria that can affect motor control and postural stability; cerebral palsy; neuropathic diseases; limb fracture; head trauma during the previous year; use of any medication other than MPH during the study period; and who had an IQ score below the normal range (\<70), as assessed by the Wechsler Intelligence Scale for Children - Revised (Wisc-R) administered by a child psychologist.

Recruitment procedure ASD participants will be recruited in the children neurology department at Soroka Medical center. Control group subjects will be recruited from the community using personal contacts using ads and flayer. The PI of this project (Prof. Zamir) will not be involved in the recruitment procedure of the children's under his clinical practice.

Outcome Assessments: Postural stability Protocol The assessment procedure will be made in the ediatric Neurology clinic at Soroka Medical Center, Beer-Sheva, the parents will sign of the informed consent than the participant will be instructed to stand upright as still as possible on the force platform with the feet positioned as close as possible (heels and toes touching). A total of five 30-second quiet-standing trials will be obtained from each participant instructed to stand as still as they possibly can in two task conditions. Two minute rest break will be provided between two task conditions and thirty seconds rest breaks between the trials. The two task conditions are: (1) standing with the eyes open (EO) - standing upright viewing an "X" displayed on a screen 3 meters in front of them; (2) eyes closed (EC) - same as (1) with the eyes closed and covered by blindfolds (i.e. no visual information). (3) Same as 1 standing on foam (i.e., conflicting proprioceptive information). Balance measurements will be collected with a Kistler 9287 single force platform (Kistler Instrument Corp., Winterthur, Switzerland) that measures the time-varying displacement of the Center of pressure (CoP). The force platform data will be sampled at a frequency of 100 Hz and stored on a hard disk for later processing. Four well-established parameters of postural stability will be extracted using automatic code written in Matlab (Math Works Inc., Cambridge, MA, USA): 1) Mediolateral CoP range (mm) (ML-sway Range); 2) Anterioposterior CoP range (mm) (AP-sway Range); 3) Mean velocity of CoP sway (mm/sec); 4) Sway area (mm2) - the elliptical area of the CoP points. Lower postural stability scores indicate higher levels of postural control. Also four parameters of SDA were extracted using automatic code written in Matlab: 1) short-term diffusion coefficients in mm2s-1 (Drs); 2) long-term diffusion coefficients in mm2s-1 (Drl); 3) the Critical Time in sec (Ctr); and 4) Critical Displacement in cm (Cdr). These parameters will be computed for each subject's trials, and then averaged for each set of 5 trials to obtain an average value for each parameter and for each subject, in each experimental condition.

Gait stability protocol After a 10-minute break, gait will be measured using the narrow base walk test, modified for clinical use. Participants will be asked to walk within a narrow path (6 meters long) first without and then with a concurrent cognitive task (ST- and DT), always in the same order. The test incorporates measurement of lateral instability during gait. The width of the narrow path will be normalized to 50% of the distance between the participant's anterior superior iliac spines + the width of the subject's shoe. This produces a similar challenge for individuals with different body morphologies. The narrow path will be outlined by two narrow six meter black mattresses on the walking surface; the participants will be instructed to walk within the path without stepping on the black mattresses. All trials will be videotaped using a video-camera that was placed 2 meters in front of the walking path and 1.5 meters high to detect trial time and step errors during the test. Step error is defined as every step where the subject's shoes step outside the narrow path, touching the black mattresses outlining the sides of the narrow base walkway. test-re-test agreement of NBWT found to be high for all variables; ICC(1,2) 0.77-0.92 in ST and 0.78-0.92 in DT (unpublished data).