Lesion Methods

Question 1

Agnosia

Answer 1

Loss of ability to recognise objects, people, sounds, shapes, or smells.

Inability to attach appropriate meaning to object sense-data

Many different subtypes eg finger agnosia : inability to distinguish the fingers on the hand. Result of lesions of the parietal lobe

Question 2

Aphasia

Answer 2

General term relating to a loss of language ability

Question 3

Apraxia

Answer 3

General term for disorders of action

Question 4

Amnesia

Answer 4

Lack of mnemonic abilities

Question 5

Ataxia

Answer 5

Poor coordination and unsteadiness due to failure to regulate the body’s posture and strength and direction of limb movement

Question 6

What lesions is visual agnosia associated with

Answer 6

Lesions to the left occipital and temporal lobes

Question 7

What do selective deficits tell us

Answer 7

Something about the way function is organised in the brain

Question 8

What is behavioural testing used for

Answer 8

To relate brain anatomy to behaviour and to investigate mental processes

Should tell us what functions are compromised and what functions are spared

Question 9

What causes dissociations in cognitive functions and functions of brain regions

Answer 9

Selective impairment

Question 10

Describe dissociation studies

Answer 10

Require minimum of two groups and two tasks

Comparison between patient/control groups shows deficit

Two tasks needed to determine whether a deficit is specific to a particular function, or reflects a more general impairment

Question 11

What is a single dissociation study

Answer 11

Two groups are tested on two tasks and a difference is only apparent in one task

Question 12

What are limitations of single dissociation studies

Answer 12

Differences in performance in the two tasks could be the result of differences in task difficulty

Question 13

What are double dissociations

Answer 13

One patient shows impairment in task A but not task B

Other patient shows impairment in task B but not A

Question 14

What is good about double dissociations

Answer 14

Remove the variable of task difficulty being an influence - provide evidence that there observed differences in performance reflect functional difficulties between the groups and not unequal sensitivity of the two tasks

Provide strong evidence that there are cognitive processes critical for task A that aren’t critical for task B

Question 15

Limitations of patient studies

Answer 15

Assumption of modularity

Lesions extensive and varied

Lesions anatomy inaccurate, connections not considered

Individual differences in functional anatomy

Poor temporal resolution of

Question 16

Explain assumption of modularity limitation of patient studies

Answer 16

Assumption that mental processes occur with a high degree of isolation from other mental processes

And when one area is damaged other regions don’t adapt to their function

But actually brain plasticity: brain reorganises quickly, intact regions change their behaviour. So difficult to infer function from damage region

Question 17

Explain lesions extensive and varied limitation

Answer 17

Most work done with patients who have large lesions

Lesions often damage several functional centres, so few patients with ‘pure’ deficits

Lesion size and location variable, hard to find group of similar patients. Inferences from single patients are weak

Question 18

Explain lesions anatomy inaccurate and connections not considered limitation

Answer 18

Anatomical scans show regions that are destroyed, but intact regions may not be functioning

Regions may be disconnected from other regions that provide input

Question 19

Explain individual differences in functional anatomy limitation

Answer 19

We assume that an anatomical region of the brain does the same function in all individuals

Clearly violated assumption - Wada test indicates left hemisphere predominates in language processing in most individuals

Variability of function across individuals reduces the power of group studies

Question 20

Explain poor temporal resolution and experimental control limitation

Answer 20

Even if patient studies establish which regions are necessary for a task, and its inferred cognitive processes, it is not possible to infer the stages of processing

A memory deficit may arise from a failure of encoding, retention or recall

There is no experimental control over lesion location, but animal studies using experiment ablation can provide this

Other methods over come these limitations

Question 21

Benefits of patient studies

Answer 21

Show which areas are necessary for a particular function (double dissociation)

Show cognitive, emotional, social consequences of a deficit

Cost and time effective, single case studies are possible

Can be done right to limit criticism

Question 22

What is the importance of a control group

Answer 22

Colour-coded overlays of lesions in patients with left visual field deficits show all patients have lesions in temporal-parietal junction

This region is susceptible to damage because it lies near to the blood supply

Need to include a control group of patients with right hemisphere brain damage but without VFDs

In this way we control for the effect of right - hemisphere damage and contrast only across the factor of VFD presence