Semantic memory

[1] This general knowledge (word meanings, concepts, facts, and ideas) is intertwined in experience and dependent on culture.

Tulving's proposal of this distinction was widely accepted, primarily because it allowed the separate conceptualization of world knowledge.

A grounded simulation approach refers to context-specific re-activations that integrate the important features of episodic experience into a current depiction.

Some accounts of category-specific semantic deficits that are amodal remain even though researchers are beginning to find support for theories in which knowledge is tied to modality-specific brain regions.

[14] This study[15] was not created to solely provide evidence for the distinction of semantic and episodic memory stores.

According to this theory, brains are able to associate specific information with other disparate ideas despite not having unique memories that correspond to when that knowledge was stored in the first place.

There are still a number of memory phenomena for which TLC has no account, including why people are able to respond quickly to obviously false questions (like "is a chicken a meteor?")

[36] The adaptive control of thought (ACT)[37] (and later ACT-R (Adaptive Control of Thought-Rational)[38]) theory of cognition represents declarative memory (of which semantic memory is a part) as "chunks", which consist of a label, a set of defined relationships to other chunks (e.g., "this is a _", or "this has a _"), and any number of chunk-specific properties.

[39] Some models characterize the acquisition of semantic information as a form of statistical inference from a set of discrete experiences, distributed across a number of contexts.

HAL computes an NxN matrix, where N is the number of words in its lexicon, using a 10-word reading frame that moves incrementally through a corpus of text.

Like SAM, any time two words are simultaneously in the frame, the association between them is increased, that is, the corresponding cell in the NxN matrix is incremented.

[47] Neuroimaging evidence suggests that left hippocampal areas show an increase in activity during semantic memory tasks.

For instance, Lambon Ralph, Lowe, & Rogers (2007) found that category-specific impairments can occur where patients have different knowledge deficits for one semantic category over another, depending on location and type of damage.

[48] Category-specific impairments might indicate that knowledge may rely differentially upon sensory and motor properties encoded in separate areas (Farah and McClelland, 1991).

In many cases, there is a point where one domain is better than the other (such as the representation of living and nonliving things over feature and conceptual relationships or vice versa).

Additionally, deficits in semantic memory as a result of herpes simplex virus encephalitis tend to have more category-specific impairments.

[48] Other disorders that affect semantic memory, such as Alzheimer's disease, has been observed clinically as errors in naming, recognizing, or describing objects.

[52] Theories on category-specific semantic deficits tend to fall into two different groups based on their underlying principles.

These theories assume that natural selective pressures have caused neural circuits specific to certain domains to be formed, and that these are dedicated to problem-solving and survival.

[54] It is fairly rare for patients with semantic dementia to develop category specific impairments, though there have been documented cases of it occurring.

[54] With Alzheimer's disease in particular, interactions with semantic memory produce different patterns in deficits between patients and categories over time which is caused by distorted representations in the brain.

In one case study, a patient underwent surgery to remove an aneurysm, and the surgeon had to clip the anterior communicating artery which resulted in basal forebrain and fornix lesions.

However, after the operation and the lesions developed, the patient reported difficulty with naming and identifying objects, recognition tasks, and comprehension.

Every lesion is different, but in this case study researchers suggested that the semantic deficits presented themselves as a result of disconnection of the temporal lobe.

The findings led to the conclusion that any type of lesion in the temporal lobe, depending on severity and location, has the potential to cause semantic deficits.

It has been concluded that there are significant gender differences when it comes to category-specific semantic deficits, and that the patient will tend to be impaired in categories that had less existing knowledge to begin with.

[61] Positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) allow cognitive neuroscientists to explore different hypotheses concerning the neural network organization of semantic memory.

[62] A developing theory is that semantic memory, like perception, can be subdivided into types of visual information—color, size, form, and motion.

[63] Neuroimaging studies suggest a large, distributed network of semantic representations that are organized minimally by attribute, and perhaps additionally by category.

Other areas, such as more anterior regions of temporal cortex, may be involved in the representation of nonperceptual (e.g. verbal) conceptual knowledge, perhaps in some categorically-organized fashion.