The progress of scientific discoveries made Descartes' theories seem more superstitious than based on facts and they soon disappeared. Materialistic theories began to flourish in the mid-20th century, and behaviorism was among them. This theory stated that the science of psychology is more interested in finding a pattern of stimulus and response. According to Watson and Skinner, behavior is shaped by the physical inputs that humans receive, and humans' private mental states are irrelevant. Behaviorism also did not last long and was soon replaced by “cognitivism” which was part of the investigative research methods of psychology. Another theory put forward was the "Mind-Brain Identity Theory" which stated that the mental events experienced by humans are neurological rather than behavioral or spectral. Introspection is considered an internal process since the activation of neurons is in no way connected to inputs from the body. Activation of neurons can be considered as a type further divided into different types of tokens. The type-token identity theory is that when an individual is in pain, a particular type of neuron fires, while the token-token identity states that each instance of physical pain is identical to a particular physical state and is