Category - Specific semantic deficits
- History and Development of Category-Specific Semantic Deficits.
- Sensory-Functional hypothesis.
- Domain-Specific hypothesis.
The task of explaining the organization of conceptual knowledge is both promising and difficult. It is promising because if conceptual knowledge is organized, then in principle it should be possible to form theories which would account for the nature of conceptual organization in normal brains and brains which present for cognitive deficits of one kind or another. We should think that this organization would obtain modularly; that is, we should think that conceptual knowledge should be organized according to functionally individuated cognitive mechanisms. There is reason to be wary of this promise, however. The most relevant body of possible evidence for this task spells difficulty for cognitive theorists. Subjects who present for selective deficits of semantic processing of one kind or another are notoriously difficult to explain. Cases of category-specific semantic deficits, in which individuals behave as if unable to name and/or recognize items of a particular semantic category, presently resist satisfactory explanation and therefore prevent the success of any theory of semantic architecture.
[...] It is not the case that in any given instance of category-specific deficits the error in the relevant cognitive system is either the functional semantic system or the sensory semantic system, for this presupposes both of the following: that sensory and functional information are the most essential to any category- specific deficit and that the correct identification of a given item of a given category is contingent on functional information but not sensory information, or sensory information but not functional information. [...]
[...] Given that the category ?living things' can be damaged independently of the category ?nonliving things', the plausible inference to suggest is that the semantic system is organized according to categorical schemas. However, though some suggested this hypothesis initially (for instance, Warrington, 1981), it was subsequently discarded; the interpretation of the data did not fit the notion that the organization of the semantic system reflected definite categorical boundaries. Warrington, who found reason to doubt the initial (Warrington, 1981) hypothesis that category-specific semantic deficits may result from damage to the categorical organization of the semantic system, proposed the Sensory-Functional hypothesis. [...]
[...] In this instance, Caramazza and Shelton would propose that an explanation for these types of cases (cases which subjects presented with category-specific deficits that may not count as an adaptive semantic category) can be found in the Sensory- Functional theory, such as cases in which the individual has trouble naming items of the musical instruments category, or cases in which an individual has trouble naming a specific kind of object but can depict specific visual features of that object, et cetera. [...]