Final answer:
Flat affect is an example of negative symptoms of psychological disorders like schizophrenia and reflects a diminished emotional expression, different from hallucinations or disorganized speech which are 'positive symptoms.'
Step-by-step explanation:
Among the options given, c. Flat affect is an example of negative symptoms of a psychological disorder, particularly as seen in conditions such as schizophrenia. Negative symptoms are characteristics that are diminished from the individual's personality or capabilities, rather than additional experiences or behaviors that are gained. These can include a lack of emotional expression, a reduction in the ability to experience pleasure (anhedonia), and a decrease in the motivation to engage in goal-directed behavior. Unlike hallucinations or disorganized speech, which are considered positive symptoms because they represent an excess or distortion of normal functions, flat affect represents a reduction or loss of normal functions.