lateralization

Question 1

What is cerebral lateralization?

Answer 1

The idea that one hemisphere performs certain functions more efficiently or dominantly than the other, such as the left hemisphere being dominant for language. It reflects hemispheric specialization rather than absolute separation.

Question 2

What are commissures?

Answer 2

Bundles of axons that physically connect the left and right hemispheres, allowing direct communication between them. Humans have five commissures, and they transfer sensory, cognitive, and motor information across hemispheres.

Question 3

What is the largest commissure?

Answer 3

The corpus callosum, which carries the majority of interhemispheric communication.

Question 4

What did Paul Broca discover in his research on aphasia?

Answer 4

Broca found that patients with expressive aphasia consistently had damage in the left hemisphere of the inferior prefrontal cortex. This region became known as Broca’s area and is responsible for the motor production of speech.

Question 5

What did early research on apraxia reveal about lateralization?

Answer 5

That apraxia is linked to damage in the left hemisphere even though apraxia usually affects both sides of the body. Voluntary movements that require attention are impaired, while spontaneous or automatic movements remain intact.

Question 6

Why did Myers and Sperry design split-brain cat studies?

Answer 6

To determine whether learning in one hemisphere transfers to the other and to test the necessity of commissures for interhemispheric transfer of learned information.

Question 7

What was the purpose of cutting both the commissures and the optic chiasm in the cats?

Answer 7

Cutting the commissures isolated the hemispheres. Cutting the optic chiasm ensured each eye sent visual information to only one hemisphere, allowing full experimental control over which hemisphere was trained.

Question 8

What happened in normal cats when trained on a visual discrimination task using only one eye?

Answer 8

After learning the task with one eye patched, the cats immediately performed at a hundred percent when the patch was switched to the other eye. This showed that intact commissures allowed rapid transfer of learned information between hemispheres.

Question 9

What happened when split-brain cats learned the task with one eye patched?

Answer 9

When the patch was switched to the untrained eye, performance fell to chance level, and the task had to be relearned by the other hemisphere. Learning no longer transferred once commissures were severed.

Question 10

What did Myers and Sperry conclude about hemispheric functioning from the cat experiment?

Answer 10

That information learned in one hemisphere is normally shared with the other through commissures, and when commissures are cut, each hemisphere learns and stores information independently, functioning almost like two separate brains.

Question 11

What is commissurotomy in humans and why is it performed?

Answer 11

A surgical procedure that cuts the corpus callosum and sometimes other major commissures to treat severe epilepsy that does not respond to medication. The goal is to prevent seizures from spreading between hemispheres, reducing severity and frequency.

Question 12

What were the clinical outcomes of commissurotomy?

Answer 12

The therapeutic benefits were often greater than expected, with many patients experiencing dramatic reductions in major convulsions or complete stopping of generalized seizures.

Question 13

Why is the optic chiasm left intact in human split-brain surgery?

Answer 13

Because the purpose of clinical surgery is not to isolate sensory input, but to stop seizure spread while preserving normal visual experience. Keeping the optic chiasm intact maintains normal binocular vision and routine visual functioning.

Question 14

What visual information crosses at the optic chiasm?

Answer 14

Information from the nasal halves of each retina crosses to the opposite hemisphere, ensuring each hemisphere receives information from the contralateral visual field.

Question 15

How do researchers present visual stimuli to only one hemisphere in human split-brain patients?

Answer 15

The patient fixates on the center of a screen, and stimuli are flashed for a tenth of a second to either the left or right visual field. The brief timing prevents the eyes from moving, ensuring the stimulus travels only to the contralateral hemisphere.

Question 16

Which hemisphere receives information from the left visual field?

Answer 16

The right hemisphere.

Question 17

Which hemisphere receives information from the right visual field?

Answer 17

The left hemisphere.

Question 18

How do researchers test tactile abilities in split-brain patients?

Answer 18

By placing objects under a ledge where neither hand can be seen. This prevents the left hemisphere from visually monitoring what the left hand is doing and isolates the motor control of each hemisphere.

Question 19

What can the left hemisphere do when it receives information?

Answer 19

It can speak, name objects, understand language syntax, and guide the right hand to choose or identify objects. When an item is presented to the right visual field or right hand, the patient can verbally identify it.

Question 20

What happens when the right hemisphere receives information?

Answer 20

The patient verbally reports seeing nothing, because the right hemisphere lacks speech production. However, the left hand, controlled by the right hemisphere, can correctly select or identify the object by pointing or touching.

Question 21

What happens when different stimuli are flashed to each visual field at the same time?

Answer 21

Each hemisphere processes its own image independently. The left hemisphere verbally reports only what it saw, while the hands retrieve different objects, reflecting two separate streams of consciousness.

Question 22

What is the helping-hand phenomenon?

Answer 22

When the right hand, controlled by the left hemisphere, begins to choose the wrong object, the left hand, controlled by the right hemisphere, reaches over and corrects the right hand.

Question 23

What do chimeric figure tests reveal in split-brain patients?

Answer 23

When shown a face composed of two different halves, each hemisphere completes its own version. The patient verbally describes the face seen by the left hemisphere, but the left hand points to the face seen by the right hemisphere, demonstrating independent perception.

Question 24

What is cross-cuing in split-brain patients?

Answer 24

An indirect form of communication where one hemisphere generates a visible or behavioral cue that the other hemisphere interprets. For example, the right hemisphere may trigger a frown or head shake to signal the left hemisphere that it answered incorrectly.

Question 25

Can some information still pass between hemispheres after commissurotomy?

Answer 25

Yes. Complete independence is not guaranteed. Some transfer can occur depending on surgical method, age, time since surgery, and task type. Indirect cues and subcortical pathways may also allow partial communication.

Question 26

Does emotional information transfer across hemispheres after split-brain surgery?

Answer 26

Yes. Emotional reactions, such as smiling or fear responses, cross easily even when the left hemisphere does not know the cause of the emotion.

Question 27

When are both hemispheres likely to be recruited in split-brain patients?

Answer 27

As task difficulty increases, especially for complex cognitive operations requiring greater processing capacity.

Question 28

What abilities show dominance or specialization in the left hemisphere?

Answer 28

Speech production, syntax, verbal memory, analytical reasoning, sequential processing, language rules, and greater activation during complex motor tasks for the ipsilateral hand.

Question 29

What abilities show dominance or specialization in the right hemisphere?

Answer 29

Emotional processing, identifying facial expressions, spatial ability, mental imagery, holistic processing, musical melody perception, and memory for nonverbal material.

Question 30

Which hemisphere is superior for spatial tasks such as mental rotation or unfolding shapes?

Answer 30

The right hemisphere.

Question 31

What did Levy’s mental block unfolding studies show?

Answer 31

The right hemisphere solves spatial tasks rapidly, silently, and accurately, while the left hemisphere struggles, often relying on slow verbal strategies and showing hesitation.

Question 32

What is the modern perspective on hemispheric lateralization?

Answer 32

It focuses on individual cognitive processes rather than broad categories. Complex abilities like language or spatial reasoning contain many subcomponents that may be lateralized differently across hemispheres.

Question 33

Why is the older view of hemisphere specialization considered inaccurate?

Answer 33

Because it grouped entire abilities under one hemisphere, ignoring that many components of those abilities are actually distributed across both hemispheres. The right hemisphere contributes to speech perception and word meaning even though the left hemisphere dominates language production.