Patient A speaks fluently but cannot understand speech. Patient B produces only agrammatic, halting speech but understands sentences reasonably well. This pattern constitutes:
AA single dissociation suggesting that production and comprehension draw on the same underlying system.
BA double dissociation providing evidence that production and comprehension are implemented by separable neural systems.
CA clinical paradox that contradicts the localizationist approach to language entirely.
DA pattern explained by lesion size rather than lesion location.
A double dissociation exists when Patient A has deficit X but not Y, and Patient B has deficit Y but not X. Here, fluent production with impaired comprehension (Wernicke-type) and impaired production with preserved comprehension (Broca-type) constitute exactly this pattern. This is stronger evidence for separable systems than a single dissociation, because it controls for the possibility that one task is simply harder than the other.
Question 2 Multiple Choice
An agrammatic patient correctly understands 'The cat chased the dog' but fails on 'The cat was chased by the dog.' This selective impairment most directly suggests:
AThe patient has lost access to the word meanings of 'cat' and 'dog' in passive constructions.
BSyntactic movement operations are neurally and cognitively separable from lexical access.
CThe patient's comprehension is entirely unaffected and only production is impaired.
DPassive constructions are universally more difficult regardless of brain structure.
The patient can access word meanings (knows 'cat,' 'dog,' 'chase') and understands canonical word-order sentences. What fails is the ability to process syntactic movement — the reordering of thematic roles in passive constructions. This dissociation between syntactic processing and lexical access provides behavioral evidence that these are neurally separable operations, supporting theoretical claims in linguistics that syntactic structure is cognitively real and distinct from the lexicon.
Question 3 True / False
Double dissociation is a stronger methodological tool than single dissociation for inferring separate cognitive systems, because it controls for the possibility that one task is simply harder than the other.
TTrue
FFalse
Answer: True
A single dissociation (A impaired on task X, intact on Y) could occur simply because X is harder — brain damage degrades performance on the harder task first. A double dissociation (A impaired on X but not Y; B impaired on Y but not X) cannot be explained by a single difficulty dimension, because the pattern reverses across patients. This is why double dissociations are considered strong evidence for independent cognitive and neural subsystems in neuropsychology.
Question 4 True / False
Modern neuroimaging has confirmed the classical Wernicke-Geschwind model, showing that Broca's area is exclusively dedicated to speech production and Wernicke's area exclusively to comprehension.
TTrue
FFalse
Answer: False
Modern neuroimaging shows both regions are involved in both production and comprehension, just with different profiles. The current model is one of distributed fronto-temporal-parietal networks with dorsal and ventral processing streams. Different aphasic syndromes arise from damage to different nodes or connections within this network — not because each syndrome corresponds to one discrete area, but because different network disruptions impair different computations.
Question 5 Short Answer
Why is the study of aphasic patients particularly valuable for testing theoretical claims in linguistics, such as whether syntactic structure is cognitively real and distinct from the lexicon?
Think about your answer, then reveal below.
Model answer: Healthy speakers cannot demonstrate selective linguistic impairment — you cannot ask someone to lose only their syntactic processing while retaining lexical access. Aphasic patients provide natural experiments where brain damage selectively disrupts specific subsystems. If damage produces failure on sentences requiring syntactic movement (passives, object-relative clauses) while leaving word-meaning access intact, this behavioral evidence shows that syntactic operations are neurally and cognitively separable from lexical access. This kind of evidence is impossible to obtain from healthy speakers and provides a uniquely powerful test of theoretical linguistic claims.
This is why neurolinguistics and cognitive neuropsychology have been so productive for theoretical linguistics: patient data offers a natural experimental manipulation of cognitive architecture that would be unethical and impossible to produce artificially.