3. Semantic Memory and the Meaning of Words

What are word meanings linked to?

• the orthographic form

• the phonological form

• conceptual and world knowledge

what is a concept?

concepts involve a collection of features

What is involved in hierarchically structured models of conceptual representation? (Collins & Quinlan 1969)

• organisation based on basic level categories and superordinate categories. Evidence for this came from category verification tasks:

• “A canary is an animal” Vs.  “A canary is a bird” (Yes or no?) Reaction times increased as a function of nodes going up in the hierarchy

• But this model did not explain why “A penguin is a bird” took longer than other cases.

What is involved in prototype models of conceptual representations?

• concepts made of frequent/typical features of typical category members

• graded internal structure as a function of similarity to prototype

• Prototype models explained that because they noted that the similarity to the prototype was an essential aspect in categorising (i.e., determining category membership).

  • So whales and penguins are not very similar to the prototype of mammals & birds respectively and share features with fish. This makes it more difficult to decide which category they belong to.

What is involved in embodied concepts as a cognitive theory of conceptual representations?

• grounding concepts in body actions and perception (sensory-motor features)

• JUG → perceptual simulations (shape, size) + actions it affords (drinking, grabbing, pouring); activates planning/ execution structures

• Motor cortex is organised somatotopically according to the body part controlled. 

• Imaging studies indicate that when people observe actions or perform actions, similar brain regions are active as a function of body part involved (e.g., mouth, hand, foot). Language can elicit similar activity, suggesting that motor aspects of actions are activated when processing language and action verbs, in particular.

What was found regarding distribution of meaning?

• first observed neural activity of individual moving mouth, hand and foot

• then showed related action words: lick, pick, kick

• overlapping activation with the movement regions when just words shown

• activating motor plans common in experience

What was found when individuals in the scanner are asked to name pictures, view pictures, match pictures and answer questions about objects/animals?

• common activations across tasks with same animal and objects

What is involved in distributed models of semantic memory in the brain?

• concepts: distributed networks organised around sensory-motor function

• networks of features make up categories/concepts

• no single meaning centre

What was the double dissociation found with patient JRB and another regarding category specific impairments?

• JRB: difficulty understanding and naming some categories

• other patients showed the opposite pattern

• struggles naming living things but not non-living things

• living things tend to be known for their sensory-perceptual properties (e.g., shape)

• non-living things tend to have more functional properties (actions and uses)

How can patient JRB’s type of impairment be explained?

• damage to category knowledge (as in hierarchical models) top node: living vs. non-living

• selective damage to sensory-features → knowledge representations are clustered (as in distributed models)

What is a brief overview of Semantic Dementia?

• affects the anterior temporal lobe and leads to non-category specific semantic impairments

• inconsistent with distributed view of semantic features

• greater damage to the ATL on the left than the right

What kinds of deficits are seen with semantic dementia?

Deficit appears multi-modal (not specific to a sensory input modality)

• impairment in recognition and understanding of auditory or visual words and objects

• impaired recognition when objects are cued by smell or touch

• not category-specific, not restricted to a feature type

relatively preserved:

• grammar (syntax)

• ‘episodic’ memory for events

• spatial & geographical knowledge

• IQ

How does Hodges study of picture naming in semantic dementia support the hierarchical model?

• progressively lose more specific knowledge of concepts

In semantic dementia what are other factors that affect retention or loss of meaning?

1. familiarity/frequency: how often objects are seen and their names are heard or read in everyday life

2. age of acquisition: whether objects and their names are learned in early childhood or later childhood/adulthood

What did Mummery et al find about classification in semantic dementia: is this a bird?

• much better at typical features, and some patients will say butterflies are birds

• the typicality of concepts and features plays a role, as in prototype theories

How can we explain semantic dementia? How is it consistent with the evidence showing brain activation for specific features?

• the temporal pole form a modality-independent hub where features of meaning (appearance, sound, feel, use, etc.) are brought together from different sites

What is involved in semantic selection beyond the ideas of individual concepts?

• the brain not only activates multiple distributed features of concepts but also needs to select which features are relevant for the context

• in language understanding and in most communicative goal-oriented tasks

What is involved in the case of ambiguity in selecting the right interpretation?

• gennari et al 2007

• showed ambiguous vs unambiguous words in context

• in minimal phrases

• inferior frontal gyrus

• posterior middle temporal gyrus

• more activation in these regions for ambiguous cases

• these two regions: ambiguity resolution in language

What are these regions associated with in semantic/conceptual representations and processing?:

• anterior temporal lobe

• inferior frontal gyrus

• posterior middle temporal gyrus

distributed meaning and regions associated with retrieval and selection of context-relevant features