The participants included three groups: patients with MDD (n=37, 54.05% female, mean age: 28.17, SD: 2.27), patients with SAD (n=35, 54.28% female, mean age: 27.49, SD: 2.06) and HC group (n=35, 48.57% females, mean age: 28.38, SD: 3.41). Patients with MDD and SAD were recruited from four psychological services clinics in Sari, Iran. Patients were diagnosed with MDD or SAD according to the Structured Clinical Interview for DSM-IV for Axis I Disorders (SCID-I) .
Exclusion criteria for the two patient groups were the following: a) any current or past diagnosis of a psychotic disorder, b) autism spectrum or any developmental disorders, c) bipolar disorder and/or d) any neurological diseases such as epilepsy, Parkinson's disease, or severe head injury. Individuals were also excluded if they had any substance abuse issues history during the preceding six months. Patients in the SAD group were excluded if they had any history of major depression, and in the MDD group, patients were excluded if they had a history of SAD.
The healthy control (HC) group was recruited from the Islamic Azad University in Sari, Iran. None of the participants in the HC group had a history of any DSM-IV Axis I or Axis II disorders as verified with SCID-I, a brain injury, neurological diseases, and/or evidence of current or past substance abuse.
All participants were included if they had the following criteria: a) at least 20 years old, b) able to understand the experimental procedure, and c) had normal visual and auditory senses.
2.2. Clinical assessment
For both patient groups, diagnoses were established by the Persian version of Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I) . All participants completed the Persian version of Beck Depression Inventory-II (BDI-II)  and the Persian version of the Beck Anxiety Inventory (BAI)  to assess the severity of depression and anxiety symptoms, respectively. The BDI is a 21-item self-report measure developed to assess the attitudes and clinical symptoms in both depressed and non-depressed psychiatric patients . The BAI is a 21-item self-report measure, which evaluates the severity of anxiety symptoms . In previous studies, the Persian versions of the BDI-II and the BAI had good psychometric properties  . We also employed the Wechsler Adult Intelligence Scale-Revised Version (WAIS-R)  to assess overall intellectual functioning.
2.3. TOM tasks
2.3.1. Reading in the mind of the eyes Task
To measure mental state decoding, we utilized the Reading in the Mind of the Eyes test (RMET),  translated into Persian . The RMET consists of 36 black-and-white photographs of eyes of the same size (15cm×6cm). Three mental states are presented (i.e., neutral, negative, and positive), and the participant is asked to select the option which could best represent the mental state of the picture. Moreover, as a control task, volunteers were required to express their opinions on the gender of each picture (i.e., gender recognition). There was no time limit for answering questions, and the total score was calculated based on the total participant’s correct response to each picture; the highest score a participant could acquire was 36. Following the studies of Harkness et al.  and Richman & Unoka , three subscales were also calculated based upon the value of each mental state (i.e., 8 positive, 12 negative, and 16 neutral). Previous studies have indicated attentional bias to negative stimuli in depressed individuals  ; therefore, in this study, we used such scoring for accurate differentiation of the three groups in discrimination of positive and negative mental states.
2.3.2. Faux Pas Task
The faux pas task was assessed mental states reasoning. The test composed of 20 short stories; half of them included a faux pas while the other half were control stories. According to Baron-Cohen et al. , a Faux Pas occurs when a speaker says something without considering if it is something that the listener might not want to hear or know with negative consequences often (See Appendix 1). There were no time limits, and therefore, to understand the story entirely, volunteers could read it repeatedly. At the end of every story, there were two faux pas questions together with two control ones. The faux pas questions were about the main character’s intentions and were designed to assess thorough understanding as to whether or not they could recognize that a faux pas had occurred in the story.
The control questions aimed to check the reader’s full comprehension of the story. In the Faux Pas Task, participants who answered “yes” to the first question (e.g., In the story you just read, has there been a faux pas and/or an embarrassing mistake in a social situation?) were required to answer the next faux pas question; meanwhile, in the stories involving a faux pas, one score was saved for each correct response. In case the subject’s answer to the first question was “no”, they were not asked the following question; however, all participants were required to answer two control questions, even if their answers to the first question had been negative. Ultimately, 20 was the maximum score a participant could achieve on the Faux Pas Questions, and 40 on the control ones.
Following a brief description of the study, participants provided written informed consent. Then, all participants underwent a demographic questionnaire and the SCID-I. Next, they were dividied between tasks: half of the participants completed RMET before Faux Pas, and the other half first completed Faux Pas then RMET.. After the ToM tasks, participants completed the BAI and BDI-II. All tasks were administered in a single session and lasted approximately 120 minutes. The ethics committee of the Faculty of Psychology and Education of Shahid Beheshti University approved the procedure.
2.5. Statistical analysis
All statistical analyses were performed using SPSS 23. We computed frequency and mean scores for the participants’ demographic and clinical data. Before using parametric tests, we used Kolmogorov–Smirnov and Levene's tests to assess normality and homogeneity of variance for demographic, clinical, and ToM tasks scores. A Pearson's Chi-squared test was performed to analyze the sex ratio of the groups and a parametric one-way analysis of variance (ANOVA) was employed for index age, educational level, IQ, and clinical measures (BDI-II and BAI). Two one-way multivariate analysis of variance (MANOVA) with post-hoc Tukey comparisons were used to compare groups in decoding ToM (RMET and its subscales) and reasoning ToM (Faux pas and gender recognition). Disorder type (SAD, MDD or HC) was included as an independent variable; RMET and Faux-pas scores as dependent variables. For all analyses, the level of statistical significance was set at P < 0.05.