Cognitive Psychology: Semantic Memory (Concepts and Knowledge)

Summary

Dr. Gilchrist introduces semantic memory and how we organize concepts and categories. He explains the hierarchical network model (Collins & Quillian), including cognitive economy and category levels—superordinate, basic, subordinate—and how verification time varies. He highlights problems like typicality and fuzzy category boundaries, then presents the spreading-activation model (Collins & Loftus) to explain semantic relatedness and priming. Finally, he describes the perceptual–functional theory (Farah & McClelland), which emphasizes visual features for living things and functional features for artifacts, supported by neuropsychological evidence of category-specific deficits. He asks students to draw a prototypical dog before Wednesday for the upcoming lesson on prototypes and exemplars.

Takeaways

• 🧠 Semantic memory stores our general knowledge and facts about the world and language, distinct from episodic memory which holds personal experiences with identifiable sources.
• 📚 Concepts are mental representations that help us categorize objects or ideas (e.g., what it means to be a dog or a teacher).
• 🔍 Categories are groups of related objects, and researchers often study them using methods like sentence verification and relatedness judgments.
• 🌳 The Hierarchical Network Model (Collins & Quillian, 1969) organizes semantic memory into nodes connected by levels, with general properties stored higher up and specific ones lower down.
• ⚖️ The principle of cognitive economy ensures that shared properties (like all animals breathing) are stored only once at the highest applicable category level.
• 🐦 Categories can be organized into three levels: superordinate (general, e.g., animal), basic (common, e.g., bird), and subordinate (specific, e.g., canary). Basic-level categories are usually learned first and used most often.
• ⏱️ Verification time increases the more levels you traverse in the hierarchy—verifying 'a canary is an animal' takes longer than 'a bird is an animal'.
• 🐧 Typicality effects challenge the hierarchical model—people verify typical members (like robins) faster than atypical ones (like penguins), even when both are at the same categorical level.
• 🕸️ The Spreading Activation Model (Collins & Loftus, 1975) replaced the strict hierarchy with a web-like network where activation spreads to related concepts based on closeness and association strength.
• 🔥 This spreading activation explains phenomena like typicality effects and semantic priming—thinking of 'red' makes you faster to recall related words like 'fire' or 'cherry'.
• ⚙️ The Perceptual-Functional Theory (Farah & McClelland, 1991) suggests living things are categorized based on visual/perceptual features, while non-living objects rely more on functional/use-based properties.
• 🧩 Neuropsychological evidence supports this distinction—damage to temporal regions affects recognition of living things, while damage to parietal and frontal areas impairs recognition of non-living objects.

Q & A

What is semantic memory, and how does it differ from episodic memory?

Semantic memory refers to our general knowledge and facts about the world, including concepts, language, and factual information. It differs from episodic memory because semantic memory lacks a specific source—people usually can’t recall where or when they learned a fact, while episodic memory involves recalling specific personal experiences tied to time and place.

What is a concept in cognitive psychology?

A concept is a mental representation that allows us to categorize and think about a class of objects, ideas, or events. For example, the concept of 'dog' includes all the mental associations and attributes that define what we consider a dog.

How do researchers determine how well an object fits into a category?

Researchers use methods such as sentence verification (e.g., verifying that 'an apple is a fruit') and relatedness judgments (e.g., assessing how closely related 'chair' and 'stool' are) to determine how strongly an object belongs to a category.

What is the Hierarchical Network Model proposed by Collins and Quillian (1969)?

The Hierarchical Network Model suggests that semantic memory is organized in a hierarchy of interconnected nodes representing concepts. Each node stores information, and properties common to all items in a category are stored at the highest relevant level to achieve cognitive economy.

What is the principle of cognitive economy in the Hierarchical Model?

The principle of cognitive economy states that shared properties of concepts should be stored only once at the highest possible hierarchical level. For example, 'breathes' is stored under 'animal' rather than repeated under 'bird' or 'fish'.

What are the three categorical levels described in the Hierarchical Model?

The three categorical levels are: (1) superordinate (broad categories like 'animal'), (2) basic (more specific categories like 'bird'), and (3) subordinate (very specific categories like 'canary' or 'ostrich'). Basic-level categories are typically the first learned and most commonly used.

What is one major limitation of the Hierarchical Model?

A key limitation is that it fails to account for familiarity and typicality effects. People verify sentences about familiar or typical examples (like 'a robin is a bird') faster than atypical ones (like 'a penguin is a bird'), even though both should take the same time according to the model.

What is the Spreading Activation Model proposed by Collins and Loftus (1975)?

The Spreading Activation Model describes semantic memory as a web of interconnected nodes, where activation of one concept spreads to related concepts. The closer two concepts are in this network, the stronger their semantic relationship, which helps explain typicality and priming effects.

How does the Spreading Activation Model explain semantic priming?

When a concept like 'red' is activated, related concepts such as 'fire engine', 'cherry', or 'rose' also receive activation, making them easier and faster to recall or recognize. This is known as semantic priming.

What is the Perceptual-Functional Theory proposed by Farah and McClelland (1991)?

The Perceptual-Functional Theory suggests that living things are primarily represented by perceptual (visual) features like color and shape, while non-living things are represented by functional properties—how they are used. Brain damage studies support this distinction, showing category-specific deficits.

What neuropsychological evidence supports the Perceptual-Functional Theory?

Patients with brain damage often show category-specific deficits: damage to temporal regions (e.g., inferior temporal cortex) tends to impair recognition of living things, while damage to posterior frontal or parietal areas affects recognition of non-living objects, consistent with perceptual and functional processing differences.

Why did Dr. Gilchrist ask students to draw a prototypical dog?

Dr. Gilchrist asked students to draw a prototypical dog to illustrate how people form mental representations or prototypes of concepts. The exercise helps explore how prototypes reflect typical features we associate with a category, such as 'dog'.