Psychology of LanguageProf. Jon Sprouse

02.12.13:

UCICOGNITIVESCIENCES

synlab

PSYCH 150 / LIN 155

Lexical Access and the Temporal Lobe

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Stage 1: Activation of a competitor set

p kt f sθ ʃ htʃ m l

b gd v z ɮ ʔdɮ n rw

y aæ i e ɛ ɔʌ ə ou

ŋ

ð

ɪ

election

avow abuse eclipse eschew

electricity elect elector electorate

elated elapse ellipse elastic

ə l ɛ k ʃ ɪ nelection

As the physical stimuli unfolds, several potential words are activated based on their similarity to the phonetic signal.

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election

avow abuse eclipse eschew

electricity elect elector electorate

elated elapse ellipse elastic

Stage 2: Selection of the target word

p kt f sθ ʃ htʃ m l

b gd v z ɮ ʔdɮ n rw

y aæ i e ɛ ɔʌ ə ou

ŋ

ð

ɪ

ə l ɛ k ʃ ɪ nelection

The target word must then be selected from the candidate set (based on relative activation levels and other top-down information)

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Lexical access involves (at least) three neural components

p kt f

b gd

y aæ i

Phonological processing of the input (comprehension) or output (production)

So now the question is whether we can determine the cortical structures implicated in each of these components.

In this lecture we are going to use several language disorders to tease apart these components and their cortical substrates.

Stored meanings of the wordscaptain captive

Connections between the phonological processing component and the stored meanings

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Designing tasks to tap into the three neural components

of lexical access

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Word Repetition

p kt f

b gd

y aæ i

captain captive

In word repetition, the participant is asked to repeat a word: “Say brick”.

Word repetition only requires phonological processing for success.

Neither the stored meanings, nor the connection to the stored meanings is required for this task.

It is easy to see that stored meanings are not necessary to succeed at word repetition:

Can you say this word blick?

Blick is not a word in English, so it has no meaning, and therefore your ability to repeat it must be independent of meaning.

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Auditory Comprehension

p kt f

b gd

y aæ i

Auditory comprehension tasks usually ask a participant to follow a command: “Move the green square”

Notice also that there is a directional component to the connections!

Auditory Comprehension taxes all three components of the lexical access system, but only in one direction: from phonological processing to stored meanings.

Success in these tasks requires phonological processing, connections to stored meanings, and stored meanings.

captain captive

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Naming

p kt f

b gd

y aæ i

Naming tasks ask a participant to name an object: “What is this?”

Notice also that there is a directional component to the connections!

Naming tasks tax all three components of the lexical access system, but only in one direction: from stored meanings to phonological processing.

Success in these tasks requires phonological processing, connections to stored meanings, and stored meanings.

captain captive

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Comparing tasks

NamingAuditory Comprehension

Word Repetition

Phonological processing

connections

meaning

By using all three tasks, we can assess which components of the system are intact, and which may be damaged.

Basically, if a participant succeeds on one but not another, we compare the requirements of each task to better identify which component may be damaged.

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Transcortical Sensory Aphasia

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Transcortical Sensory Aphasia

NamingWord Repetition

Patients suffering from TSA clearly succeed at word repetition tasks; in fact they tend to spontaneously repeat words spoken by others.

Many patients also succeed at naming tasks.

Auditory Comprehension

Patients suffering from TSA exhibit a catastrophic loss of auditory comprehension. It is basically obliterated.

This pattern of symptoms suggests that TSA is an impairment of the directional connection between meanings and phonological processing.

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Transcortical Sensory Aphasia

www.youtube.com/watch?v=bpeZ4xm62DM

Here is the only video of TSA that I could find on the internet:

This video demonstrates the repetition abilities of this patient; however, there is no evidence of spontaneous naming in this clip.

TSA is a very rare form of aphasia, and is usually associated with other impairments, making investigation of language ability difficult.

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Artificially inducing TSA

All of the electrodes implanted in the 6 patients.

Because TSA is very rare in stroke populations, Boatman et al. 2000 attempted to artificially induce TSA symptoms in surgery patients.

They implanted electrodes directly into the cortex of 6 patients (who were undergoing neurosurgery for epilepsy)

These electrodes delivered a small repetitive electrical current to the cortex areas between the electrode pairs.

They then tested the patients on a battery of language tasks while delivering currents to each location in an attempt to isolate the cortical locations that led to TSA-like symptoms (impaired comprehension, intact repetition and naming)

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Artificially inducing TSA

Electrode location for TSA like symptoms

Boatman et al. 2000 found that the following electrode locations lead to TSA-like symptoms: impaired comprehension with intact repetition and naming

These results accomplish two goals:

1. They establish the dissociation between the two directions of the connection between phonological processing and meaning.

2. They establish locations (for each individual) that may give rise to TSA-like symptoms.

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TSA vs M350

Locations that lead to TSA-like symptoms (Boatman et al. 2000)

Recall that the M350 indexes initial activation of lexical items: a mapping from phonological processing to meaning.

It is perhaps unsurprising that the location of M350 generators tend to overlap the location of TSA-inducing electrical interference:

Potential generators for the M350 (Pylkkanen et al. 2006)

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Anomia

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AnomiaAuditory Comprehension

Word Repetition

Patients suffering from Anomia succeed at word repetition tasks.

They also succeed at auditory comprehension.

Naming

Patients suffering from Anomia fail at naming certain objects.

This pattern of symptoms suggests that Anomia is an impairment of the directional connection between phonological processing and meanings.

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Anomia

www.youtube.com/watch?v=LWAUmsgk8eg

This is actually a pretty good example of anomic symptoms. Pay particular attention around 1:40 -- the doctor tries to give the patient a hint!

Anomia is more common than TSA, although I could only find one video of a patient suffering from anomia online:.

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Lesion sites for AnomiaAntonucci et al. 2004 investigated 8 cases of anomia (1 was an outlier, so there are 7 here). They found that the lesion site was always left temporal lobe, and that the more anterior the lesion, the worse the anomia.

anterior

posteriorLR

superior

Inferior

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Lesion sites for Anomia

In general, anomia results from diverse lesion sites across the left temporal lobe.

It is generally more inferior than superior, and more anterior lesions tend to be worse than posterior lesions.

Here I have overlaid the Anomia lesion tendencies with the induced TSA locations from Boatman et al. 2000.

This may make some sense: if we assume that meanings are distributed throughout the area, then the connections between meaning and phonological processing may also be distributed

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Category-specific AnomiaIt is relatively common for Anomia patients to demonstrate inferior performance on certain classes of nouns.

For example, Ferreira et al. 1998 report three patients who show more trouble with animals than tools.

Although rarer, there are also patients who show more trouble with tools than animal (e.g., Cappa et al. 1997).

This double dissociation suggests that living entities and inanimate objects may have distinct cortical substrates.

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Category-specific Anomia and Semantic networks

The existence of category-specific Anomia makes some sense given the semantic priming effects that we’ve already seen.

truck

fire engine

bus

vehicle

car

street

ambulance

redblue

house

fire

The spreading activation framework suggests connections between semantically related words.

Category-specific Anomia suggests geographic locality between semantically related words.

This suggests that spreading activation is indeed a physical/geographic process.

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No category-specific TSAGiven the existence of category-specific semantic organization, one might wonder whether there is category-specific phonological organization...

What this would mean in practice is that words that share phonemes would be organized together.

election

avow abuse eclipse

eschew

electricity

electorate elatedEvidence for this organization would be a category-specific version of TSA: difficulty comprehending words that share phonemes.

We have not encountered any patients with category-specific TSA, suggesting that words are not geographically organized by phoneme (but are organized by semantics). This makes some sense given the way we have conceptualized phonological processing.

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Semantic Dementia

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The picture so far

p kt f

b gd

y aæ i

lexical semantics

Anomia appears to be driven by a disruption in the connection between lexical semantics and phonological processing.

The model we’ve been using so far suggests two uni-directional connections between phonological processing and stored meanings (lexical semantics).

Transcortical Sensory Aphasia appears to be driven by a disruption in the connection between phonological processing and lexical semantics.

Is there a language disorder that appears to be a complete disruption of lexical semantics?

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Semantic DementiaWord RepetitionPatients suffering from Semantic Dementia are

successful at word repetition.

NamingAuditory Comprehension

However, they have problems both comprehending and naming certain words, but not others.

This pattern of symptoms suggests that the meanings of certain words are lost.

This suggests that phonological processing is spared in Semantic Dementia

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SD is a progressive deterioration of the temporal lobe

Semantic Dementia is a form of progressive fronto-temporal degeneration that targets the left anterior lobe more than the right anterior lobe, and tends to target the inferior portions more than the superior portions. It tends to begin in the temporal pole (blue area) and progress over time (yellow area)

SD is often contrasted with Alzheimer’s Disease, which is a progressive degenerative disease that tends to target parietal-temporal areas (blue areas), although it can also involve frontal areas as well.

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Video of Semantic Dementia

www.youtube.com/watch?v=fkKrsbwQvrE

Semantic Dementia is relatively rare, especially compared to Alzheimer’s. This is the only video I could find on the internet:

The early stages of SD are generally characterized by what appears to be word loss (similar to anomia), but upon closer inspection it turns out that the patients do not even know the concepts underlying the objects.

This patient appears to have progressed further toward some general symptoms of dementia.

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Semantic versus Episodic Memory

Semantic Dementia is characterized by a loss of semantic memory: knowledge of concepts themselves.

Alzheimer’s Disease is characterized by a loss of episodic memory: memory of events.

However, both are progressive diseases that lead to degeneration of much of the cortex and ultimately death.

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The picture so far

p kt f

b gd

y aæ i

lexical semantics

Anomia appears to be driven by a disruption in the connection between lexical semantics and phonological processing.

The model we’ve been using so far suggests two uni-directional connections between phonological processing and stored meanings (lexical semantics).

Transcortical Sensory Aphasia appears to be driven by a disruption in the connection between phonological processing and lexical semantics.

Semantic Dementia appears to be a loss of the concepts underlying the meanings of words.

Is there a disorder that targets phonological processing directly?

30

Wernicke’s Aphasia

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Naming

Wernicke’s AphasiaAuditory Comprehension

Word Repetition

In patients suffering from Wernicke’s aphasia, all three tasks are impaired.

This pattern could suggest a catastrophic loss of language ability, but these patients do speak in what appear to be complete, grammatical sentences. But the sentences don’t make any sense, and may not even be composed of real words!

This suggests an impairment of phonological processing, which would then affect both comprehension and production of speech.

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Video of Wernicke’s Aphasia

www.medclip.com/index.php?page=videos&section=view&vid_id=103628

Wernicke’s aphasia was first identified by Carl Wernicke in the late 1800s (~1874):

Wernicke’s aphasia is sometimes called fluent aphasia because they appear to produce fully grammatical sentences (albeit meaningless). It is also sometimes called receptive aphasia because of the difficulties in comprehension.

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Wernicke’s area

Wernicke’s aphasia tends to be caused by damage to an area of the superior temporal gyrus appropriately named Wernicke’s area, first identified by Carl Wernicke during postmortem examinations of patients demonstrating the symptoms of Wernicke’s aphasia.

Boatman et al. 2000 were also able to induce the symptoms of Wernicke’s aphasia with electrical interference at these electrode locations.

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Lexical access and language disorders

p kt f

b gd

y aæ i

lexical semantics

Semantic Dementia appears to be a loss of the concepts underlying the meanings of words.

Anomia appears to be driven by a disruption in the connection between lexical semantics and phonological processing.

The model we’ve been using so far suggests two uni-directional connections between phonological processing and stored meanings (lexical semantics).

Transcortical Sensory Aphasia appears to be driven by a disruption in the connection between phonological processing and lexical semantics.

Wernicke’s Aphasia appears to be driven by a disruption in phonological processing.

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TSA

Lexical access and the temporal lobe

p kt f

b gd

y aæ i

lexical semantics

anomia

Wernicke’saphasia

semanticdementia

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