The Study of Phonological Process of Persian Consonants Deletion in Speech of Educable Elementary Students With Down Syndrome Living in Tehran City, Iran

Background and Aims One of the most common language disorders in people with Down syndrome is the deletion of language sounds. This research deals with the study of the deletion phonological process in Persian language sounds, specifically consonants deletion, in the speech production of educable students with Down syndrome who study in the third to sixth grades in elementary schools, in Tehran City, Iran. This study considers the students’ ability of recognition and dominancy on the most common deleted consonants in the speech production of students within the framework of Generative Phonology School. 
Methods The statistical population of this research comprised 19 boys and 11 girls, educable students with Down syndrome, speaking only Persian language, without any vision, hearing, stuttering, reading, and writing problems at the chronological age of 11-18 years old, studying in the exceptional elementary schools in Tehran. The method of research was based on spontaneous speech of students through the naming single words of 300 simple pictures. All deleted consonants in the production of words by students were considered, and the most common deleted consonants were registered.  Then, we analyzed their ability to recognize and dominate these deleted consonants used in their writing skills. Besides, the Wepman auditory discrimination test was used to assess the students’ ability to distinguish between similar language sounds. In this descriptive-analytic study, the method of data collection was based on field research and data were statistically analyzed via the Kolmogorov-Smirnov and Wilcoxon tests, using SPSS software version 26.
Results The most common deleted consonants in the speech production of students were alveolar-liquid [r], alveolar-nasal [n], alveolar-stop [t], alveolar-liquid [l], and alveolar-stop [d]. There was no significant difference between two variables, the most deleted consonants in speech and writing (P<0.05). 
Conclusion findings showed that the educable students with Down syndrome, studying in the third to sixth grades in exceptional elementary schools in Tehran have adequate ability of realizing and dominancy on the most deleted consonants in their speech which indicates the development of phonological perception of students. Thus, the main cause of using frequently this phonological process (consonants deletion) was not phonological errors, but for the structural and functional defects in the speech production organs.