No person shall practice psychology unless he has obtained a license as provided in section 20-188. The practice of psychology means the rendering of professional services under any title or description of services incorporating the words psychologist, psychological or psychology, to the public or to any public or private organization for a fee or other remuneration. Professional psychological services means the application, by persons trained in psychology, of established principles of learning, motivation, perception, thinking and emotional relationships to the assessment, diagnosis, prevention, treatment and amelioration of psychological problems or emotional or mental disorders of individuals or groups, including but not limited to counseling, guidance, psychotherapy, behavior modification and personnel evaluation, with persons or groups in the areas of work, family, school, marriage and personal relationships; measuring and testing of personality, intelligence, aptitudes, emotions, public opinion, attitudes and skills; and research relating to human behavior.