What term describes the involuntary, singular preoccupation with a specific thought or concern?

The term that describes an involuntary, singular preoccupation with a specific thought or concern is perseveration. This psychological phenomenon can manifest in various contexts, often seen in individuals with certain mental health conditions, where they repeatedly return to the same idea or thought, despite the situation's demands or the presence of new information.

Perseveration differs from other cognitive processes such as tangential thinking, which refers to a train of thought that veers off topic and does not return to the main subject. Thought-blocking, on the other hand, describes a situation where an individual suddenly stops speaking or loses their thought, often temporarily. Finally, word salad involves a jumble of words or disconnected phrases that do not form coherent statements, which is not indicative of focused preoccupation but rather disorganized thought processes. Thus, the definition of perseveration accurately encapsulates the concept of being fixated on a specific thought or concern.