Structuralism and Functionalism played pivotal roles in shaping the early development of psychology as a science. Structuralism, as the first formal school of psychology, established a foundation for scientific inquiry into the human mind. It introduced the technique of introspection, which, despite its limitations, was a significant attempt at employing systematic methods to study mental processes. This approach encouraged subsequent psychologists to seek more objective and reliable methods of study, paving the way for the development of various psychological research techniques.

Functionalism, on the other hand, expanded the scope of psychology beyond the structure of mental processes to include their functions and purposes. It stressed the importance of understanding how mental processes aid in adapting to the environment. This perspective brought a practical dimension to psychological studies, encouraging the application of psychological knowledge in areas like education, industry, and clinical settings. Additionally, Functionalism’s emphasis on the evolutionary aspects of mental processes laid the groundwork for future perspectives like evolutionary psychology. Overall, both Structuralism and Functionalism significantly contributed to establishing psychology as a science, each introducing key concepts and methods that influenced its subsequent evolution.

The decline of Behaviorism as the dominant perspective in psychology was due to several factors, including its limitations in explaining complex human behaviors and the rise of new psychological perspectives. One of the primary criticisms of Behaviorism was its focus solely on observable behavior while neglecting internal mental processes. This approach was seen as too reductionist, as it failed to account for cognitive processes like thinking, reasoning, and memory, which are crucial in understanding human behavior.

The emergence of the cognitive revolution in the 1950s and 60s was a significant factor in the decline of Behaviorism. Cognitive psychology, with its emphasis on internal mental processes, provided a more comprehensive framework for understanding human behavior. It introduced concepts such as information processing, memory systems, and problem-solving, which were not adequately addressed by Behaviorism.

Additionally, the inability of Behaviorism to explain phenomena like language acquisition and creativity, which involve complex cognitive processes, further highlighted its limitations. The rise of humanistic psychology, which emphasized personal growth and human potential, also challenged the deterministic view of Behaviorism, advocating for a more holistic approach to understanding human behavior.

As a result of these developments, psychology gradually shifted from Behaviorism to more integrative approaches that considered both observable behavior and internal mental processes, leading to the rich and diverse field that psychology is today.

The early theoretical perspectives in psychology, particularly Structuralism and Functionalism, had a profound influence on the development of modern cognitive psychology. Structuralism's emphasis on the components of consciousness laid the groundwork for the future exploration of mental processes. Although the method of introspection used in Structuralism was later criticized for its lack of scientific rigor, the fundamental idea of analyzing mental processes was a precursor to cognitive psychology's focus on understanding internal mental states.

Functionalism's contribution was in its emphasis on the purpose and function of mental processes, which resonated with the cognitive approach. Cognitive psychology, which emerged in the mid-20th century, expanded on this idea by exploring how mental processes like perception, memory, and thinking function in the context of information processing and adaptation to the environment.

Furthermore, the decline of Behaviorism and its emphasis on observable behavior paved the way for the cognitive revolution. This shift brought attention back to the internal mental processes that Behaviorism had neglected, aligning with the initial interest of Structuralism and Functionalism in understanding the workings of the mind.

In summary, the early theoretical perspectives provided the conceptual foundation upon which cognitive psychology built its principles, leading to a more comprehensive and nuanced understanding of the human mind and behavior.

The introspective method used in Structuralism faced several key criticisms, primarily due to its subjective nature and lack of scientific rigor. First, introspection relied heavily on the individual's personal experience and self-reporting, which introduced a high degree of subjectivity. This made it difficult to verify and replicate findings, as different individuals might have varying interpretations and responses to the same stimulus.

Another criticism was the lack of objectivity and measurable data. Unlike other scientific fields, where observations can be quantified and independently verified, introspection did not allow for such empirical validation. This made it challenging to develop universally accepted findings or theories based on introspective methods.

Furthermore, introspection was criticized for its limited scope, as it was only applicable to conscious experiences. It failed to account for unconscious processes, which later theories, such as Freud's psychoanalysis, suggested played a significant role in human behavior and mental processes. The inability of introspection to explore these unconscious elements further highlighted its limitations as a comprehensive method for studying the mind. These criticisms eventually led to the decline of Structuralism and the rise of new psychological approaches that emphasized more objective and quantifiable methods.

Functionalism significantly contributed to the development of applied psychology by expanding the focus of psychological study from theoretical analysis to practical application. This perspective emphasized understanding the purpose and role of mental processes in adapting to the environment, thus fostering a more practical approach to psychological research.

Functionalism's broader scope of study, which included emotions, habits, and the overall adaptability of mental processes, opened up new areas for application. For instance, it influenced educational psychology through its emphasis on how mental processes aid in learning and adapting to educational environments. This led to the development of teaching methods and educational systems that catered to varying learning styles and cognitive processes.

In industrial and organizational psychology, Functionalist principles helped in understanding worker behavior, motivation, and productivity, leading to more effective management practices and work environments. Similarly, in clinical psychology, the Functionalism approach contributed to understanding how mental processes relate to coping mechanisms and psychological disorders, aiding in the development of treatment methods.

Overall, Functionalism's influence was crucial in moving psychology beyond theoretical constructs to real-world applications, laying the groundwork for the various specialized fields within applied psychology.