The goal of this observational study is to assess the effectiveness of a machine-assisted system for early screening of autism. The main questions it aims to answer are:

• Does the machine-assisted system including 5 main behavioral paradigms identify toddlers with autism from those with other neurodevelopmental disorders and typical development?
• Are there any differences in the early symptoms of autism among toddlers over the whole mainland China? Participants will receive some developmental and social communicational evaluations for clinical diagnoses. They will also receive the behavior evaluations of the machine-assisted system. The above evaluations will be performed just once.

The current study is a diagnostic accuracy study. In total, 1000 Toddlers with autism spectrum disorder, global developmental delay, language disorder, and typical development (n=250 for each group) will be recruited in this study. The gold standard of the diagnosis of autism spectrum disorder will be the clinical diagnosis from developmental and behavioral pediatricians, and the diagnoses will be confirmed by Autism Diagnostic Observation Schedule-2nd edition and Griffiths Development Scales-Chinese edition(GDS-C). The diagnostic accuracy of the machine-assisted system for early screening of autism will be evaluated.

ASD group：

Inclusion Criteria:

1. Children diagnosed with ASD according to a clinical judgement based on the criteria of ASD in DSM-5 and further confirmed with ADOS-2;
2. Ages 1.5-2.5 years;
3. Parents/caregivers understand the content of the study and agree to participate in.

GDD group：

Inclusion Criteria:

1. Age 1.5-2.5 years, gestational age 37-42 weeks, birth weight 2500-4000g;
2. Clinically diagnosed with GDD (Global Developmental Delay) according to the DSM-V diagnostic criteria, with a Griffiths Development Scales-Chinese edition(GDS-C) assessment showing a Developmental Quotient (DQ) ≤75 in two or more domains;
3. Those who did not meet the initial screening positivity criteria for ASD (Autism Spectrum Disorder) using M-CHAT-R/F.

LD group：

Inclusion Criteria:

1. Age 1.5-2.5 years, gestational age 37-42 weeks, birth weight 2500-4000 g;
2. Clinically diagnosed with LD (Language Disorder) according to the DSM-V diagnostic criteria, with a Developmental Quotient (DQ) ≤75 in the language domain of the Griffiths Development Scales-Chinese edition(GDS-C) and DQ >75 in all other domains;
3. Those who did not meet the initial screening positivity criteria for ASD (Autism Spectrum Disorder) assessed by M-CHAT-R/F

Exclusion Criteria for ASD, GDD, and LD groups:

1. Rett Syndrome, Fragile X Syndrome, Angelman Syndrome, Prader-Willi Syndrome, tuberous sclerosis, and other syndromes caused by known genetic defects or inherited metabolic diseases;
2. Children with brain injuries, specific chronic or congenital diseases.
3. The gestational age is less than 37 weeks, or the birth weight is lower than 2500g.

TD group：

Inclusion Criteria:

1. Healthy, typically developing toddlers aged 1.5-2.5 years ;
2. gestational age of 37-42 weeks, birth weight of 2500-4000 g;
3. Developmental Quotients(DQs) are greater than 75 in all domains of theGriffiths Development Scales-Chinese edition(GDS-C);
4. Screened negative by M-CHAT-R/F screening for autism spectrum disorder (ASD).

Exclusion Criteria:

Children with neurodevelopmental disorders (e.g., developmental delay, language impairment), neurological conditions (e.g., epilepsy, tuberous sclerosis), or other severe chronic diseases were excluded.

The diagnostic accuracy study will be performed in children with ASD, GDD, LD, and healthy, typically developing children aged between 1.5 to 2.5 years old.