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Neurological mechanisms for the formation of concepts and categorization

Although we previously emphasized the differences between strictly defined and vague concepts, studies conducted at the neurological level show that there are important differences between the vague concepts themselves. In particular, concepts related to animals and related to objects created by humans are apparently stored in various parts of the neural system of the brain. Some evidence of this was given by us when discussing perception in chapter 5. At the same time, we noted that there are patients who have impaired ability to recognize animal images with a relatively normal ability to recognize artificially created objects, such as tools, but at the same time there are patients with opposite pattern of disturbances. Recent studies show that effects that extend to images also apply to words. Many patients who have lost the ability to name images of objects presented to them also cannot say what the corresponding words mean. So, for example, a patient who could not name the giraffe depicted in the photograph also could not say anything about giraffes when the word "giraffe" was called to him. The fact that this violation applies to words and images also indicates that this violation is related to concepts: the patient partially lost the concept of “giraffe” (Farah & McClelland, 1991).

Other studies have focused on categorization processes. One of the directions of such studies shows that other parts of the brain participate in determining the similarity between the object and the prototype of the concept than in determining the similarity between the object and the instances stored in memory. These studies are based on the following considerations: instance processing involves extracting individual examples from long-term memory; as we know from chapter 8, such extraction is possible due to the structures of the median parietal lobes. Consequently, a patient with injuries in these areas of the brain will be unable to efficiently categorize objects based on a process involving specimen processing, although the ability of such a patient to use prototypes may remain normal. This is precisely what the research results indicate.

In one such study, patients suffering from damage to the median temporal lobes, as well as normal subjects, were tested using two different tasks. In one task, study participants were required to learn how to sort point patterns into two categories (see examples in Fig. 9.6); in another assignment, subjects were required to learn how to sort pictures into two categories corresponding to two different authors. Independent evidence showed that only the second task required the extraction of copies from memory. Patients mastered the concepts associated with point patterns as easily as healthy participants, but they performed much worse than healthy participants with a task involving mastering concepts related to paintings (Kolodny, 1994).



Fig. 9.6.

Examples of point patterns used in categorization studies in patients with amnesia

. After individuals have learned that all training samples belong to the same category, they have to decide whether test samples belong to the same category (adapted from: Squire & Knowlton, 1995).



This suggests that the use of instances is determined by brain structures mediating long-term memory, while the use of prototypes for categorization should be determined by other structures.
In another study, a patient was studied who was practically unable to transfer any information to long-term memory, but successfully coped with tasks involving point patterns. Thus, it is obvious that prototype-based categorization is independent of structures mediating long-term memory (Squire & Knowlton, 1995).

The foregoing indicates that there are neurological differences between categorization based on prototypes and categorization based on stored instances. What about rule-based categorization? One recent study shows that the use of rules involves neural structures other than similarity-based processes. Two groups of subjects were trained to categorize imaginary animals into two categories, according to whether these animals were from Venus or from Saturn. One group of subjects was trained to categorize based on complex rules, for example: “This is an animal from Venus if it has antenna-like ears, a curly tail and hooves on its legs; otherwise it is an animal from Saturn. " Another group was trained to categorize animals, relying only on memory. (The first time they saw the animal, they were left to guess where it came from, but in subsequent attempts they had to remember which category it belonged to.) Then the participants of both groups were presented with images of new animals, and while they were categorizing, their brain was scanned. The group trained to categorize animals according to the rules continued to do so in the same way, however, the group trained to categorize animals from memory had to extract information on the most preserved copies in memory and assign the new animal to the category to which this instance.

In the memory group, most of the brain regions that were activated during the task belonged to the visual cortex in the occipital part of the brain. These data are consistent with the assumption that subjects from this group relied on extracting visual information about the specimens. The subjects from the memory group also showed activation in the occipital part of the brain, however, they also had activation of some frontal areas of the brain. These areas are often affected in patients who have difficulty completing tasks involving the use of rules. Consequently, rule-based categorization includes neural networks other than similarity-based categorization (Smith, Patalano, & Jonides, 1998).

The described studies are another example of the interaction between the biological and psychological approach to the study of the categorization phenomenon. Thus, studies have shown that categorization processes, considered as different at the psychological level, such as the use of instances and the use of rules, include various mechanisms of brain functioning. In this example, a pattern manifests itself with which we have already repeatedly met throughout the previous chapters: the distinction is first made at the psychological level, and then the fact that it also extends to the biological level is demonstrated.
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