However, psychology, even scientific psychology, presents falsifiability challenges not evident in the natural scientists. Some scientists might argue that Freud has been shown to be a poor theorist, given what has been revealed about the brain since Popper's day. If a depressive shows no improvement after years of Freudian therapy, but does show improvement after taking Prozac, that could be said to prove Freud wrong. Unfortunately, so many other external factors can affect a person's mood it is hard to attribute a single cause to a person's remission. It could be the drug or other conditions in the individual's environment. While large drug trials try to use large sample sizes as a way of reducing the influence of extraneous variables as well as use control groups who receive a placebo, the less observable and testable the phenomenon, the more difficult it is to measure. Even attempts to demonstrate improvement of children on an academic test after being prepared for the exam are contentious in terms of their ability to be externally validated. Tests of mood or psychological health are even more difficult to construct. Almost no conceivable ethical scientific test could confirm a broad-based psychological theory with the same level of falsifiability as a law of physics, given the levels of controls that would have to be imposed upon the human subjects.
Neuroscience is far easier to subject to the falsifiability test than psychological theories. For example, stroke victims with damage to critical brain areas have shown consistent cognitive deficits in certain behaviors pertaining to movement and behavior, demonstrating the link between body and mind, and how the physical body impacts consciousness and personality. The finding that the left hemisphere of the brain tends to control functions related to language, and the right spatial relationships has been verified by numerous scientific studies upon victims with impaired cognitive functions confined to one area. For example one study of individuals with brain damage, one group with exclusively left brain damage and the other with right brain damage were asked to copy the same complex figure. The results suggested that: "constructional function is not localized separately in each hemisphere in each individual, but is generally localized contralateral to the localization of language function (mostly the right hemisphere); and (2) language and constructional functions are localized in the same hemisphere only in exceptional cases" (Yukiko 2006, p.181). The ability to compare the two groups allowed the thesis of confined hemispheric activity to be falsifiable. But only the discipline of neuroscience (versus social psychology) can usually construct such biologically-oriented tests.
"To be falsifiable a theory must have two properties. It must provide a way to determine the status of its theoretical entities…it must say how those theoretical entities interact and explain various events" (Good and bad theories, 2007, on Philosophy). Psychology is a discipline that encompasses both biology and anecdotal evidence. It is both research-based yet also exists in a hands-on clinical setting, where therapists may tailor their approach to the needs of the client, rather than a theory. For clinicians to apply falsifiability to every technique they deploy with patients might not be possible or even desirable. But the examination of falsifiable scientific theories is required to understand how the biology of the brain works, the efficacy of certain psychotropic drugs, and also the validity of certain clinical treatments.
Cohen, Patricia. (2007). Freud is widely taught at universities, except in the psychology department. The New York Times. Retrieved April 3, 2010 at http://www.nytimes.com/2007/11/25/weekinreview/25cohen.htm
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Yukiko, Sato, Kojima Tomoyuki, Kato Masahiro. (2006). Brain hemispheric damage and constructional disorders: From the standpoint of hemispheric lateralization. Japan Journal of Logopedics and Phoniatrics, 47 (2): 181-187.