Brain LateralizationBrain Lateralization

Exploring Psychology (1)Exploring Psychology (1)

Brain Lateralization

The Unequal Specialization of the two halves of the brain

Behavioural Techniques

used to measure

Brain Lateralization

Behavioural Techniques

• Dual Task Studies/Interference Tasks

• Tachistoscopic Presentation

Interference Tasks

• Tapping

• Balancing task

Right Hand (Tapping Alone) Left Hand (Tapping Alone)

 

 

 

 

 

 

 

 

 

 Right Hand (Tapping & Reading) Left Hand (Tapping & Reading)

 

 

 

 

 

 

 

 

 

 

 

 

Whose woods these are I think I know. His house is in the village, though; He will not see me stopping here To watch his woods fill up with snow.

My little horse must think it queer To stop without a farmhouse near Between the woods and frozen lake The darkest evening of the year.

He gives his harness bells a shake To ask if there is some mistake. The only other sound's the sweep Of easy wind and downy flake.

The woods are lovely, dark, and deep, But I have promises to keep, And miles to go before I sleep, And miles to go before I sleep. Robert Frost

Right Hand (Tapping Alone) Left Hand (Tapping Alone) 

 

 

 

 

 

 Total number of Taps = Total number of Taps =

 

 

Right Hand (Tapping & Reading) Left Hand (Tapping & Reading)

 

 

 

   Total number of Taps = Total number of Taps =

 

 

 

 

 

 

 

Interference Tasks

Tapping Task

http://www.zimm-co.com/PressTheSpaceBar/pressthespacebar2000.html

Tapping Task

• Base rate of how many times a person can tap their index finger within a specified time is taken for each hand, one at a time

• Measurements taken again –

Tapping & Talking

• The tapping while simultaneously-talking-rate is compared to base rate

Tapping Task

• usually found that for most right handers talking decreases the tapping rate of the right hand more than left

(Hellige & Longstreth,

1981)

• greater interference when two activities are carried out within the same hemisphere

• greater right- than-left-hand interference indicates left hemisphere language dominance

Motor Pathway

Interference Tasks

Left Hemisphere Right Hemisphere

Right Hand

BalancingTask

• Base rate – length of time each hand can balance a dowel rod - alone

• Then, balancing in conjunction with reading

The balancing while simultaneously-reading-rate is compared to base rate for each hand

BalancingTask

• usually found that reading decreases the length of time for balancing of the right hand more than left

• greater right- than-left-hand interference indicates left hemisphere language dominance

Motor Pathway

Interference Tasks

Left Hemisphere Right Hemisphere

Right Hand

Behavioural Techniques

• Dual Task Studies/Interference Tasks

• Tachistoscopic Presentation

Tachistoscopic Presentation

Right Visual Field Advantage (RVFA) usually found for language

i.e., greater accuracy or faster Reaction Time for verbal stimuli presented in the right visual field

Language Lateralization

RVFA is taken as a Left Hemisphere advantage for Language

- due to set-up of visual pathways

Visual Pathways to Hemispheres

Dichotic Listening Technique

Dichotic Listening Technique

The simultaneous presentation of two different stimulus inputs

- one to each ear

Dichotic Listening

Broadbent (1954)

• Initially used to study attention

• The aim was to purposely divide the attention

• To provide information regarding processing capacity/limitations

Dichotic Listening

In Broadbent’s early studies

• participants heard 6 digits, 3 to each ear in simultaneous pairs:

Right Ear Left Ear6 97 52 4

• Recall 1. pair by pair (6 9, 7 5, 2 4) or2. ear by ear (672, 954)

Ear by ear recall was found to be easier & more accurate

Dichotic Listening

Broadbent’s early studies

• Broadbent concluded the ears act as separate channels, to which the person can only attend to one at a time

• But participants do recall some items from the other ear

Concluded that there is a buffer zone in which items are held until the person can get to them

Dichotic Listening

Dichotic Listening is used as a technique to measure brain lateralization

• Right Ear Advantage (REA) found for Language

Competitive stimulation causes suppression of the ipsilateral pathways (Kimura, 1961)

Auditory pathways acting as a contralateral

system

Auditory Pathways

Left Hemisphere Right Hemisphere

Contralateral

Ipsilateral

Left Ear Right Ear

Language Lateralization

Different behavioural techniques/Different routes

Same conclusion –

Left hemisphere specialized for language

Language Lateralization

Tachistoscopic presentation & Dichotic listening

What do they tell us about how the brain is organized for Language??

Language Lateralization

RVFA & REA are taken as a Left Hemisphere advantage for Language

What about the Right Hemisphere?

Strict Localization Model (Moscovitch 1973)

Left Ear/VF Right Ear/VF

Left Hemisphere Right Hemisphere

Efficiency Model (Moscovitch 1973)

Left Ear/VF Right Ear/VF

Left Hemisphere Right Hemisphere

Hand Preference

& Brain Lateralization

Hand Preference and Cerebral Asymmetry

Right handers

- most left hemisphere dominant for language

Left handers

- c. 75% left hemisphere dominant for language

- remainder have a bilateral organization

Handedness & Cerebral Asymmetry

Right Handers Left Handers

Lateralization of Bilateral Organization

Language of Language

Incidence of Hand Preference

10% Left handed

• Generation• Culture

Hand Preference

Measurement

Measurement of Hand Preference

• Hand used for writing

• Most widely used measure now:

Edinburgh Handedness Inventory (EHI) (Oldfield, 1971)

Measurement of Hand Preference

Edinburgh Handedness Inventory

(EHI)

EDINBURGH HANDEDNESS INVENTORY (Oldfield, 1971)Please indicate your preferences in the use of hands in the following activitie by putting + in the appropriate column.Where the preference is so strong that you would never try to use the other hand unless absolutely forced to, put ++. Ifin any case you are really indifferent put + in both columns.

Some of the activities require both hands. In these cases the part of the task, or object, for which hand preference is wanted isindicated in brackets.

Left

Right

1 Writing

2 Drawing

3 Throwing

4 Scissors

5 Toothbrush

6 Knife (without fork)

7 Spoon

8 Broom (upper hand)

9 Striking match (match)

10 Opening box (lid)

Edinburgh Handedness Inventory (EHI) (Oldfield, 1971)

EHI Scoring

The laterality Quotient for the EHI is derived in the following way:

• Add the number of +’s getting a total for each column

• Subtract the sum for the left hand column from that for the right hand column

• Divide the obtained difference by the sum of both columns

• Multiply the resulting ratio by 100

Right Column – Left Column X 100 = Laterality Quotient R Col + L Col

• The EHI provides a score which ranges from +100 to -100

(Right handed (Left handed for all items) for all items)

Edinburgh Handedness Inventory (EHI)

• Measures degree of hand preference

• Provides a hand preference score

• EHI scores range from

+100 (Strongly Right Handed)

to

-100 (Strongly Left Handed)

Degree of Handedness

Strong Left Strong Right

Handers Handers

Weak Left Weak Right

Handers Handers

-100 -50 0 +50 +100

Hand Preference Measurement

• Other Hand Preference Measures

(e.g., Annett’s Hand Preference Measure)

• Carry out tasks

Degree of Hand Preference

• Forced to use right hand

• Handicap – broken arm

• Family Handedness

• Genetics – biologically related

Handedness & Cerebral Asymmetry

Strong Left & Weak Left &

Right Handers Right Handers

Lateralization of Bilateral Organization

Language of Language

Hand Preference

Familial Sinistrality

Presence of left handers in one’s family

Brain Lateralization

– outweigh own hand preference?

Familial Sinistrality

Left Hander - with FS

Left Hander - with No FS

Right Hander - with FS

Right Hander - with No FS

Cerebral Asymmetry Worksheet

1. Define cerebral asymmetry

2. Name 3 behavioural techniques used to measure cerebral asymmetry

3. Briefly describe the rationale behind one of these techniques

4. What are the advantages of a behavioural technique over other types of techniques?

5. Calculate your direction and degree of hand preference using the Edinburgh Handedness Inventory (Oldfield, 1971).

EHI = R column – L column X 100 = Rc + Lc

direction =degree =

6. Is a strong hand preference associated with: -Weak brain lateralization

-Strong brain lateralization

-No cerebral lateralization

Brain Lateralization and Ability

A Lateralized or more Bilateral

organization best??

Brain Lateralization

Why be Lateralized for functioning?

- Asymmetrical versus a Symmetrical

brain