severely stutter. Stutterers commonly report dramatically increased fluency when talking in unison with another speaker, copying another's speech, whispering, singing, and acting or when talking to pets, young children, or themselves. Other situations, such as public speaking and speaking on the telephone, are often greatly feared, and increased stuttering is reported. Feelings and attitudes Stuttering could have a significant negative cognitive and affective impact on the person who stutters. It has been described in terms of the analogy to an iceberg, with the immediately visible and audible symptoms of stuttering above the waterline and a broader set of symptoms such as negative emotions hidden below the surface. Feelings of embarrassment, shame, frustration, fear, anger, and guilt are frequent in people who stutter, and may actually increase tension and effort, leading to increased stuttering. With time, continued exposure to difficult speaking experiences may crystallize into a negative self-concept and self-image. Many perceive stutterers as less intelligent due to their disfluency; however, as a group, individuals who stutter tend to be of above average intelligence. People who stutter may project their attitudes onto others, believing that the others think them nervous or stupid. Such negative feelings and attitudes may need to be a major focus of a treatment program. Many people who stutter report a high emotional cost, including jobs or promotions not received, as well as relationships broken or not pursued. Fluency and disfluency Linguistic tasks can invoke speech disfluency. People who stutter may experience varying disfluency. Tasks that trigger disfluency usually require a controlled-language processing, which involves linguistic planning. In stuttering, it is seen that many individuals do not demonstrate disfluencies when it comes to tasks that allow for automatic processing without substantial planning. For example, singing "Happy Birthday" or other relatively common, repeated linguistic discourses, could be fluid in people who stutter. Tasks like this reduce semantic, syntactic, and prosodic planning, whereas spontaneous, "controlled" speech or reading aloud requires thoughts to transform into linguistic material and thereafter syntax and prosody. Some researchers hypothesize that controlled-language activated circuitry consistently does not function properly in people who stutter, whereas people who do not stutter only sometimes display disfluent speech and abnormal circuitry. Associated conditions Stuttering co-occurs with other learning disorders. These associated disabilities include: Attention deficit hyperactivity disorder (ADHD): A disorder characterized by problems sustaining attention, hyperactivity, or acting impulsively. The prevalence of ADHD in school-aged children who stutter is .