Week 1: Introduction to Cognitive Neuropsychology: The Case for Dissociations

What Is Cognitive Neuropsychology?

• A discipline within psychology that studies how cognitive processes (e.g. language, memory, reading, perception) are affected by brain injury or damage.

• Unlike general cognitive psychology (which studies typical function), this field examines breakdowns to understand normal function.

• Uses functional models (often “box and arrow” diagrams) to hypothesise how information is processed and where breakdowns occur.

• Cognitive neuropsychology = cognitive science + brain damage data.

Core Assumptions of Cognitive Neuropsychology (Caramazza, 1984, 1986)

Several key assumptions guide this discipline:

• Modularity: The cognitive system is made up of separate, specialised modules.

• Fractionation: Brain injury can selectively damage one module while leaving others intact.

• Transparency: A damaged system operates like a normal one minus the affected module (i.e., no reorganisation).

• Universality: All individuals share the same cognitive architecture, so findings from one case can apply to others.

These assumptions support the use of single-case studies, which become especially important if the universality assumption is ever questioned.

The Importance of Universality and Single-Case Studies

The assumption of universality implies that everyone processes information using the same cognitive architecture. For example, how one person reads a word is assumed to be the same for another. Therefore, if one person experiences a deficit due to brain damage, the affected cognitive process is assumed to exist in others as well.

However, if this assumption is false—if different people use different neural strategies—group studies can obscure critical insights. Averaging data across individuals might hide important individual deficits. This is why single-case studies are so powerful. They allow in-depth analysis of an individual’s unique cognitive profile and help identify specific components of the cognitive system.

For example, suppose most dyslexic individuals struggle with nonwords, but one can read nonwords yet struggles with familiar words. This unusual pattern challenges theories and suggests different systems for reading real vs. nonwords—something group data might miss.

Cognitive Models in Neuropsychology

Historically, researchers used box-and-arrow models to map out cognitive processes. Each box represents a processing stage (like word recognition), and arrows indicate the flow of information. These models are helpful for identifying where cognitive breakdowns occur.

Modern research uses connectionist models or Parallel Distributed Processing (PDP) models. These simulate networks similar to the brain’s structure. Rather than using rigid stages, information flows through interconnected units. Learning happens through experience, and damage can be simulated by deleting or weakening connections. This makes PDP models particularly useful for testing theories and simulating real-life impairments like anomia or dyslexia.

Dissociations: Key Evidence in Neuropsychology

To understand how cognitive functions are organised, researchers look for dissociations:

• Single Dissociation: One task is impaired, another is preserved—suggesting functional independence, but not definitively.

• Double Dissociation: Two patients show opposite patterns (e.g., Patient A fails Task X but does Task Y; Patient B fails Task Y but does Task X). This provides strong evidence for separate cognitive systems.

A classic example involves reading and writing. Some patients can write but not read (alexia), while others can read but not write (agraphia). This suggests distinct systems within the broader language network.

Anomia: A Case of Naming Deficits

Anomia is a language disorder where individuals struggle to retrieve the names of objects, despite knowing what they are. They may describe the object, know its use, and even recall related words—but can’t produce the exact name. It’s often described as a persistent "tip-of-the-tongue" state.

Anomia can result from failures at different stages:

1. Visual Processing Failure: The object isn’t recognised perceptually (object agnosia).

2. Semantic Degradation: The object is seen, but its meaning can’t be accessed.

3. Phonological Output Deficit: The meaning is intact, but the word can’t be retrieved or spoken.

4. Disconnection: All systems work, but they can’t communicate effectively (e.g., visual system can’t trigger the lexical system).

Identifying the precise cause is critical, as it guides targeted therapy.

Reading and Writing Disorders: The Dual Route Models

The Dual Route Model of Reading (Coltheart, 1993) explains that reading involves two pathways:

• Lexical Route: Used for recognising familiar and irregular words.

• Non-Lexical Route: Used for sounding out unfamiliar or made-up words.

When these routes are damaged, different types of dyslexia occur:

• Surface Dyslexia: Difficulty with irregular words due to impaired lexical route.

• Phonological Dyslexia: Difficulty with nonwords due to impaired non-lexical route.

Writing (spelling) also has two corresponding routes:

• Surface Dysgraphia: Phonetic spelling of irregular words due to impaired lexical spelling route.

• Phonological Dysgraphia: Inability to spell nonwords due to impaired phoneme-to-grapheme conversion.

Repetition Impairments and the Dual Route Model

Repetition tasks (e.g., saying a word someone else says) rely on both:

• Lexical Route: Uses semantic processing for known words.

• Non-Lexical Route: Converts sound directly to articulation for nonwords.

Conduction aphasia is a condition where patients can understand and speak fluently but cannot repeat nonwords—pointing to damage in the non-lexical route.

The Hickok & Poeppel Model (2004): Speech Processing Pathways

This model proposes two processing streams for speech:

• Dorsal Stream: Maps sound to motor actions—used in repetition, especially nonwords.

• Ventral Stream: Maps sound to meaning—used for comprehension and repeating familiar words.

This model parallels the visual system’s division into "what" (ventral) and "where/how" (dorsal) pathways, showing how cognitive functions are neurally distributed.

Case Study: Patient CB

CB experienced a stroke affecting the left hemisphere and additional bilateral damage. His symptoms included:

• Perfect real word repetition, but 0% for nonwords → non-lexical route damaged.

• Surface dyslexia and dysgraphia → lexical reading and writing systems impaired.

• Difficulty naming living things → semantic degradation, especially for biological categories.

• Unawareness of pronunciation errors → semantic comprehension issues.

This case illustrates how various components of the cognitive system can be selectively affected, and supports the idea of modularity and dual routes in language processing.

Comparison Table: Key "Dys-" Disorders (Language & Literacy Only)

✅ Summary:

• Dysphasia = Broad language disorder (both speaking & understanding)

• Dyslexia = Reading problem (especially with unfamiliar or irregular words)

• Dysgraphia = Writing/spelling problem (misspellings, poor letter formation)

Basic Functional Model of Naming

• Three steps:

  1. Visual Recognition (Perceptual identification)

  2. Semantic Understanding (Comprehension)

  3. Lexical Retrieval (Name production)

• Anomia: Failure in lexical retrieval (step 3), even when the object is recognized and understood.