The types of errors may be affected by different combinations of speech sounds or different word structures. Generally speaking, distorted sounds are more frequent, meaning that the child may always pronounce the sound in that way, while omitted sounds and alternative sounds lack consistency. So, what are the tests for slurred diction? The following are the causes of slurred speech: 1. Too quiet in infancy, or lack of response to loud sounds. 2. 2. The absence of any speech sounds by the age of 2 years 3.Up to three years of age, there are still no sentences. 4.After three years of age, most of the speech is still slurred. 5.After the age of five, there are still obvious errors in speech. 6.After the age of five, the sentences still have abnormal rhythm, speed or intonation. 7.After the age of five, there are still many omissions, substitutions, or distortions in speech. 8.Speech sounds are monotonous and flat, the volume is too loud or too low, or the sound quality is too poor. 9.Speech with a pronounced nasal overtone or lack of nasal sound. 10.The older you get, the less you speak or the less clear you are.