## 2 Materials and Methods
### Participants  
A total of 60 children, either with neurotypical development (in this paper, we use the terms \"neurotypical\" and \"typically developing\" interchangeably, referring to individuals (children) without any known neurological or psychiatric conditions) (\(n=31\)) or with an ASD diagnosis (\(n=29\)), were recruited in Hungary to participate in the study. They were recruited via their parents, directly (explicitly), either into the neurotypical (NT) or into the ASD (autism) group, using web advertisements (email circulars and social media). They were all white/Caucasian and without facial artifacts (glasses, etc.). Before collecting EFE data from them, all applicants went through a clinical and psychometric assessment in order to ensure their correct placement into the ASD vs. NT groups and their intellectual abilities, being in the IQ \(>85\) region, and to collect clinical, demographic, and other background data. Autism-related symptoms were first assessed by the SCQ (Social Communication Questionnaire) [62], and then by the ADOS (Autism DiagnosticObservation Schedule) [63] and the ADI-R (Autism Diagnostic Interview--Revised) [64]. The latter two are internationally accepted standard tools for autism diagnosis. Intelligence was assessed by the Leiter-R Brief scale [65] and the level of receptive language (grammar) was assessed by the TROG-H (Test for the Reception of Grammar) [66]--the Hungarian adaptation [67]. As the recording of facial expressions was accompanied by eye tracking (although these data were not analyzed in the present study), a questionnaire was used to collect information on any potential eye or visual anomaly. General inclusion criteria comprised the following: age between 36 and 72 months, unimpaired intelligence, and receptive language (grammar). Further inclusion criteria for the NT group comprised the following: SCQ total score < 4; all ADOS and ADI-R scores below the diagnostic cutoff values. Further inclusion criteria for the ASD group comprised the following: all ADOS and ADI-R scores above the diagnostic cutoff values; a clinical diagnosis of ASD from an established diagnostic institution. Exclusion criteria were ophthalmological and neurological conditions interfering with eye tracking; any neurodevelopmental condition, except ASD in the ASD group; significant delay in language, intellectual, or motor development; being on medication influencing the central nervous system; first language being a language other than Hungarian; and any acute or chronic medical condition which might influence the relevant behaviors.  
From the total of 97 children who entered the recruitment process, 23 were excluded for not meeting some of the inclusion criteria above or meeting some of the exclusion criteria. Of the 74 children who went on to the EFE-data-collection phase, 14 were excluded from further analysis, due to either failure to collect enough data from them for analysis, or for any emerging doubt concerning the correctness of their diagnostic status (e.g., close to or above the cutoff score in ADOS or ADI-R).  
The final sample thus comprised 60 children, 31 being (neuroocognitively) typically developing and 29 having an ASD diagnosis. The two groups are well-matched with respect to IQ, receptive grammar, and their performance in the game (as indicated by number of correct (overt) mouse responses). In line with the diagnostic difference between the groups, they showed a significant difference and no overlap in their SCQ scores. There emerged a slightly significant difference in age, with small-moderate effect size; the mean age of the ASD group being higher than that of the NT group. Table 1 shows their key demographic and psychometric characteristics, and matching statistics.