All of the six divisions of biopsychology have their shortcomings, and therefore quite often questions can only be answered through the use of several approaches, balancing out each others weak points. Consider the following 'weakness' summary of the branches of biopsychology.
The common weakness of physiological psychology and psychopharmacology is that they are limited in their dealings with human subjects because of the direct manipulation involved.
Comparative psychology does not deal directly with humans either - it studies biology of behaviour by comparing the behaviour of different species and using the findings to understand the human behaviour.
Neuropsychology's weakness is that it deals almost exclusively with case and quasiexperimental studies as it studies patients with brain damage.
The common weakness of psychophysiology and cognitive neuroscience is that they can only use noninvasive techniques with limited manipulation of the brain itself as they deal only with human subjects.
Even though the study of a wide range of organisms allows comparison of similarities and differences, other animal species cannot simply be used as a model for the study of human behavior. Therefore, for all the areas of biopsychology that cannot deal directly with human subjects, the common problem is that there is always a certain doubt about the applicability of the animal study findings to the human world.
For all the branches that deal exclusively or mostly with humans there is another problem, they are limited in the amount of brain manipulation they can use.
Clearly, two or more approaches combined, if they are selected properly, will complement one another well. Together they will be able to provide evidence for points of view that none of them could defend individually.
In most cases, being convinced by the results of one study or even of a group of studies using the same approach in biopsychology is not satisfactory. One can be more sure of the validity of conclusions when they come from convergent evidence and not from a single study.
Because of the development of data from the biological and behavioral sciences over the past 25 years, the need for the convergent-operations approach is even more necessary now than when Zing-Yang Kuo first emphasized its importance (Lickliter, 2000).
Converging operations have been made use of with various topics, such as alcohol use and abuse (Windle, 1996), aggression (Williams et al., 1996), intersensory perception (Lickliter, 2000), role of visual imagery in perception (Kosslyn et al., 1999), techniques for visualizing neurons (summarized by Pinel, 2002), Korsakoff's syndrome (summarized by Pinel, 2002), and others. Here we will present the two latter topics to show the work of converging operations in them.
Another example of the work of converging operations is in looking for a cause of Korsakoff's syndrome, a severe memory loss which is often the only disabling symptom experienced. (Pinel, 2002). Because it commonly occurs in alcoholics, the syndrome was originally believed to be caused by the toxic on the , as in the case with Jimmie G. (Pinel, 2002).
Later it was discovered that Korsakoff's syndrome is caused by thiamine () deficiency (Pinel, 2002). The syndrome occurs in malnourished persons who consume little or no alcohol. Thiamine-deprived rats showed memory loss and brain damage similar to Korsakoff's syndrome in human alcoholics. Alcohol may also have a direct toxic effect on the brain because it accelerates the brain damage in thiamine-deprived rats.
Thus, the convergent evidence here states that Korsakoff's syndrome frequently occurs in alcoholics, first, because often most of the calories they consume comes from alcohol, which lacks ; second, because alcohol interferes with metabolism of the thiamine they do consume; and third, because alcohol accelerates the brain damage produced by the lack of thiamine.
The converging operations here included: neuropsychological case reports like Jimmie G's, quasi-experiments studying alcoholics, quasi-experiments studying thiamine deficient non-alcoholics, controlled animal experiments manipulating thiamine levels and finally effects of thiamine supplementation in humans. Reaching the correct conclusion about the cause of Korsakoff's syndrome would have been impossible without the use of all of the above methods.
Strong inference
Since one cannot prove a theory, the best way to show support for a particular theory is by the method of strong inference - by disproving as many opposing to it theories as possible, while showing support for the main theory (Platt, 1964). Converging operations provide strong inference.
It is important to recognize certain challenges in following a converging-operations approach.
First, which has already been mentioned here, animal species differ from the human in radical ways. Different animal species have different ecosystems, different body structures, and different developmental . Generalizing conclusions across species requires careful and systematic analysis of the similarities and differences observed. For example, there are many the difficulties involved in trying to compare and contrast the behavior of nonhuman animal and human infants and in using observations from one species to apply inferences based on observations of another species (Lickliter, 2000).
Second, successful of a convergent-operations approach typically requires good among scientists of different areas of the field studied and overcoming the fact that "researchers in different subdisciplines often structure their questions differently, use different language for discussing similar phenomena, have different types of controls and measures, and draw from different literatures, even when investigating similar topics" (Lickliter, 2000).
And last, when going through a set of studies, it will simply take longer to get the final results on the topic studied, which will automatically multiply the financial and time involving costs of the already expensive and complicated research process. A project, which would potentially cost significantly more and would take significantly longer than another one, may not get chosen by some researchers, at least some of the time.
Conclusion
"The fish trap exists because of the fish.
Once you've gotten the fish you can forget the trap.
The rabbit snare exists because of the rabbit.
Once you've gotten the rabbit, you can forget the snare.
Words exist because of meaning.
Once you've gotten the meaning, you can forget the words."
- Chuang-tzu
Progress in biopsychology typically comes from convergent evidence. Despite the difficulties, a convergent-operations approach creates a broader perspective in than a more traditional single-method or species-specific approach and helps to identify theories and principles in psychology that could be generalized to different species and populations. (Lickliter, 2000).
The strength of biopsychology is in the diversity of its methods and approaches, and, as a field, it is built on converging operations.
