2.1 Participants
85 children aged between 3–5 years were recruited from the Xinhua Hospital Affiliated to Shanghai Jiaotong University, including 40 ASD children (23 ASD children with developmental delay (DD), 17 ASD children without DD), and 45 typically developing (TD) children (Fig. 1). All ASD children were evaluated and scored by experienced clinicians who specialize in identifying ASD, based on the Diagnostic and Statistical Manual of Mental Disorders (Fifth Edition, DSM-5). And ASD children scored above the threshold on both the Childhood Autism Rating Scale (CARS) and the Autism Diagnostic Observation Schedule (ADOS). Children with a history of neurological or genetic disorders, or those unable to engage in 3–5 minutes of interaction with a caregiver while wearing an EEG cap, were excluded from the study. TD children had no history of developmental disease and did not have any first-degree relatives with ASD. Caregivers of TD children were asked to complete the Chinese validated version of Social Responsiveness Scale (SRS) and only those who screened negative were included in this study. Intelligence quotient (IQ) of both ASD and TD children were assessed using the Wechsler Preschool and Primary Scale of Intelligence (WPPSI)[35]. The ASD children with DD group had Full Scale IQ (FSIQ) score at least two standard deviations below the average, while the ASD children without DD group were matched with the TD group in terms of IQ. The study was conducted in accordance with the Declaration of Helsinki, with approval from the Ethical Committee of the Xinhua Hospital Affiliated to Shanghai Jiaotong University, and in compliance with all applicable laws and regulations. Written informed consent was obtained from the children’s caregivers. All necessary biosecurity and institutional safety protocols were followed during the study.
2.2 Measures
2.2.1 Caregiver-child dyads coding
To encourage natural and spontaneous interaction between the children and their most familiar caregivers, we provided a 3–5 minutes session of free play involving puzzles and blocks [36, 37]. Caregivers and children were seated at a table and wearing EEG caps. Their interaction was recorded by a camera while EEG was captured simultaneously (see Fig. 1B). Due to potential distractions, we used the ELAN (EUDICO Linguistic Annotator) program to capture and categorize the organic and social interactions between caregivers and children in recorded videos offline and analyzed using an event-based coding system that calculated 5 behavioral indicators per second (see Supplementary). These indicators included Social Involvement of Children (SIC), Interaction Time (IT), Response of Children to Social Cues (RSC), time for Caregiver Initiated Social interactions (GIS) and time for Children Initiated Social interactions (CIS). Table S1 provides definitions and examples for each code.
2.2.2 Behavior assessment
The ADOS is a widely utilized standardized diagnostic tool for ASD in both clinical and research settings [38] by evaluating social interaction, communication, and play in individuals with high-risk ASD. To account for variability in score across different modules of the ADOS, a mapping of ADOS module total scores to Calibrated Severity Scores (CSS) has been suggested [39]. The CSS system transforms the ADOS total score into a standardized score ranging from 1 to 10, with higher scores indicating greater severity of autistic features, based on the child's actual age and language abilities. This standardized scoring system helps to provide a more accurate representation of the severity of autistic features in individuals with ASD.
The CARS [40] is a tool used to diagnose and assess the severity of ASD in children and consisted of 15 items rated on a 7-point scale from one to four; higher scores indicating a higher level of impairment. We further categorized these items into three subscales [41]: Social Impairment (SI), Negative Emotionality (NE), and Distorted Sensory Response (DSR). The criterion validity for CARS with a cut-off of 30 resulted in sensitivity of 0.86 and specificity of 0.79 [42].
The SRS is a commonly used to evaluate social deficits associated with ASD and other developmental disorders in clinical and research settings [43, 44]. The SRS provides a total score and scores on five subscales: social awareness, social cognition, social communication, social motivation, and autistic mannerisms. Multiple studies [45, 46] have reported high reliability and validity of the SRS, including the Chinese Mandarin version, which showed internal consistency for the total scale of 0.871–0.922, and test-retest reliability of 0.81–0.94. Receiver operating characteristic (ROC) analyses revealed that the SRS accurately classified 69.2–97.2% of youth with ASD [47].
2.2.3 EEG recording and pre-processing
During a 3–5 minutes free play session between caregivers and children, we recorded EEG signals using a high-density 128-channel Electrical Geodesics, Inc (EGI) system with a vertex reference (channel Cz) and a sampling rate of 1000 Hz. To ensure high-performance data, we kept impedances below 100KΩ [48]. MATLAB [49] and the EEGLab [50] toolbox were used to process offline. A bandpass filter between 0.5 and 45 Hz and a 50 Hz notch filter were consistently applied to the continuous EEG data. We retained 82 channels for analysis after excluding 46 peripheral "skirt channels" to reduce noise and muscle artifact, and interpolated any noisy electrodes [51]. EEG segments were excluded from further analysis in the following cases: when the caregiver-child interaction disengaged or when the segment contained artifacts. Afterward, 1-s epoch segments are created from the preprocessed EEG data. Independent component analysis (ICA) [52] is used to identify and eliminate eye blink, movement, and muscle activity artifacts after physically confirming artifacts rejection by visual examination. Prior to spectral analysis, the data was re-referenced to the average of the mastoids.
2.2.4 Alpha and Theta Power Spectral Density (PSD)
The power spectral density (PSD) of the theta (4–7 Hz) and alpha (8–13 Hz) frequency bands are computed for each EEG channel by applying the FFT algorithm, squaring the resulting signal to obtain amplitude, transforming the bilateral spectrum into a unilateral spectrum, and dividing it by the frequency resolution.
2.3 Statistical Analysis
The statistical analyses employed SPSS software, version 23, with the Wilcoxon rank sum test and Analysis of Variance (ANOVA) used to compare mean ± standard error of continuous variables between the ASD and TD groups. Significance level (α) was set at 0.05. Prior to analysis, behavioral data and PSD values were transformed by square root to meet normal distributional assumptions. General linear model (GLM) was used to compare groups on EEG PSD.
The application of Receiver Operating Characteristics (ROC)[53] analysis was implemented with the intent of computing the Area Under the Curve (AUC)[54], serving as a metric for the discriminative capability of behavioral indicators and PSD values in distinguishing between ASD groups and TD group. The ROC analysis, by providing sensitivity and 1 - specificity outcomes across a comprehensive range of potential thresholds, empowers the selection of a putatively "optimum" cutoff for each distinct comparative grouping. To further evaluate the diagnostic performance, we scrutinized the accuracy, sensitivity, and specificity of these behavioral indicators and PSD values within distinct ASD subgroups (i.e., ASD children with DD group, ASD children without DD group) and the TD group to explore potential discrepancies pertaining to IQ.
A series of partial Pearson correlation analyses were conducted to evaluate the dimensional relationships among EEG PSD and IQ level and behavioral indicators (SIC, IT, RSC, GIS, CIS) in all groups.