Neuropsychology: Research Methods III & IV

Ref: Banich, pp. 62-99

(skim through sections on brain imaging)

Four Main Methods

Ø A. Lesion (or subtraction) method

Ø B. Experiments with intact humans

Ø C. Functional imaging studies

Ø D. Electrical recording techniques

Lesion (or Subtraction) Method

a. Observe function after damage to a structure

b. Examine damage after impairment to a function

c. Look for associations & dissociations between impairments

d. Examine in detail a known functional impairment

Some ways of using:Some ways of using:

a. Observe function after damage to a structure

animals: ablation studies

humans: observe after illness/injury

Phineas Gage:

* Known damage to frontal lobes

* Inability to plan, socially inappropriate behaviour, moodiness, capriciousness.

* Conclusion: damaged region involved in goal setting, modulation and inhibition of behaviour and emotion.

b. Examine damage after impairment to a function

Ø Broca's patient "Tan":

• Understood speech, but said only one word, "Tan”

• Post-mortem -> damage to Broca's area

Conclusion: speech production relies on Broca's areaConclusion: speech production relies on Broca's area

Ø More recent studies:

Ø use modern localisation techniques such as CAT, MRI.

b. Examine damage after impairment (cont’d)

c. Look for associations & dissociations between impairments

Ø Example of Dissociation:

Ø Patient HM: Can’t form new long-term memories

Ø BUT Normal at this task:

Repeat the following sequence of numbersRepeat the following sequence of numbers

3 7 9 1 8 43 7 9 1 8 4

ØMr. K suffered a mild stroke which affected a small region in the left parietal lobe. He made a good physical recovery, and some months later, was able to return to his previous, demanding position as a private secretary in a large corporation. He had little difficulty resuming his former duties: he was able to remember which tasks/clients he had worked with just before his illness, and had no problem learning new tasks and remembering new clients. However, he noticed a sudden difficulty with numbers. He found himself unable to accurately record numerical information given to him verbally. Also, when dialing phone numbers, he could still deal with familiar numbers, but would repeatedly make mistakes when dialing a new number for the first time.ØJK underwent further neuropsychological tests which revealed that he had a digit span of only one

c. Associations & dissociations (cont’d)

Compare to JK:Compare to JK:

c. Associations & dissociations (cont’d)

• HM & JK show opposing patterns for 2 abilities

LTM STM

HM

JK

ImpairedImpaired

IntactIntact

IntactIntact

ImpairedImpaired

c. Associations & dissociations (cont’d)

Ø -> "Double Dissociation"

• Must have:

• i. at least two individuals

• ii. at least two tasks/abilities

• iii. opposite performance on each

c. Associations & dissociations (cont’d)

• Association:

When function X is impaired, what other functions are affected ?

e.g. Mr. JK:

Does he have problems understanding language?

If so -> STM important in language comprehension.

d. Examine in detail a known functional impairment

Left Hemineglect:

A few days after suffering a mild stroke, Mrs. K began to realise things were not quite right. When she had visitors in hospital, she would often lose track of where they were in the room. She would inquire about someone's absence, only to be told that the person had not left the room, but was in fact right by her side, sitting to her left. Also, although Mrs. K normally took great care in her appearance, the nurses would often tell her that she had forgotten to brush the left side of her hair, or to apply lipstick on the left of her mouth. And finally, perhaps most troubling, she had great difficulty navigating through the corridors of the hospital to get to the bathroom. On one occasion, she was frustrated to find herself back where she started without reaching her destination:

d. Examine a known impairment (cont’d)

WC

WC

Mrs. K

d. Examine a known impairment (cont’d)

• What kinds of situations are most difficult for these individuals?

• Does the problem affect only vision, or other senses too?

• What happens when head and body are at different angles?

• What factors can help a patient attend to the left side of space?

Questions to ask:Questions to ask:

Lesion Method: Problems and Issues

Underlying assumption of this method:

performance =

normal performance – function impaired

i.e. The “subtractivity” assumption

Lesion Method: Problems and Issues

I. Compensation

II. Premorbid differences

III. Anatomical co-occurrence error

IV. The problem of group averaging

Ø i. Compensation

Ø P uses alternative strategy

Ø e.g. P with STM deficit uses visual mnemonics

Ø P with word retrieval prob. uses writing

Ø Dangers:

Ø - may underestimate importance of damaged structure/component

Ø - performance may have unusual qualitiesØ e.g. gnome -> gome

Lesion Method: Problems & Issues (cont.)

Ø ii. Premorbid differences

HM: Temporal lobe damage resulted from surgery for epilepsy.

BUT epileptics -> "atypical" brain localisation

Lesion Method: Problems & Issues (cont.)

Ø iii. Anatomical Co-occurrence Error Ø

Ø Functions appear to be associated, but this is just Ø due to anatomical proximity.

Ø e.g. Broca's aphasia:- articulation problems- problems with sentence planning

Lesion Method: Problems & Issues (cont.)

ØGroup data can reveal spurious "syndromes":

Ø

Øe.g. Broca's aphasia: articulation + central language prob's

Ø Gerstmann's syndrome: finger agnosia + agraphia + alexia

Lesion Method: Problems & Issues (cont.)

iv. The Problem of Group Averagingiv. The Problem of Group Averaging

• Group trends may not reflect each individual:

Case Task 1 Task 2 Task 31 20 75 702 25 70 803 30 80 754 75 25 755 80 30 706 70 20 807 75 80 258 70 75 309 80 70 20Average 58.3 58.3 58.3

Lesion Method: Problems & Issues (cont.)

Ø Alternative:

Ø - Present each individual separately. Ø Ø - Only report what's true for most/all individuals.

Lesion Method: Problems & Issues (cont.)

Single case studies have their own challenges:

Problem Possible solution

low power do multiple replications

atypical indiv's test as many indiv's as possible

poor replicability report all cases, as many as poss.

selective reporting report all cases, as many as poss.

Lesion Method: Problems & Issues (cont.)

B. Experiments with Intact Humans

Use existing information about brain organisation to design a study.

Example: Can take advantage of contralateral organisation of primary visual cortex:

•Visual half-field technique:

- choose a task (e.g. word naming)

- present stimulus to one half-field:

B. Experiments with Intact Humans

• +

•Visual half-field technique:

- choose a task (e.g. word naming)

- present stimulus to one half-field:

B. Experiments with Intact Humans

•CAT

Ø Which hemisphere is first to receive this stimulus?

Ø

B. Experiments with Intact Humans

Left hemisphereLeft hemisphere

Can compare RT’s to words in left vs. right visual field (e.g. lexical decision task)

Result: Words on the right approx. 100msec faster than on left.

Q: What does this tell us?

Four Main Methods

Ø A. Lesion (or subtraction) method

Ø B. Experiments with intact humans

Ø C. Functional imaging studies

Ø D. Electrical recording techniques