Cognitive Neuroscience (Laterality)

Question 1

What is Laterality?

Answer 1

The idea that two cerebral hemispheres have separate functions- this leads to the notion that two different minds control our behaviour

Question 2

What are the functions of the left and right hemisphere?

Answer 2

the left hemipshere appears to be dominant in language and in memory whilst the right hemisphere more actively involved in tasks concerning creativity, emotions and musical patterns.

Question 3

What are the 8 studies that shed important light on lateralisation?

Answer 3

Kimura (1960)
Cutting (1973) 
Schwartz and Tallal (1980) 
Penfield 
Zatorre (1992/1995) 
Hugdhal (1999) 
Rimol (2005) 
Shytyrov (2005)

Question 4

In Shwartz and Tallal’s (1980) study, they highlight that evidence regarding lateralisation of language comes from what research?

Answer 4

Observations of patients with unilateral brain lesions, Dichotic listening tests and Evoked potential procedures.

Question 5

What did Kimura 1960 report regarding dichotic listening?

Answer 5

She found that dichotic listening studies produce an REA and that this is due to the ‘ localisation of speech and language processing in the dominant left hemisphere of the cerebral cortex’

Question 6

What is REA??

Answer 6

It was found from dichotic listening studies and means that , for most right handers, verbal information is reported more accurately when information is presented to the right ear and non verbal information is more accurately reported when presented in the left ear (Hugdahl and Asbjornsen 2000)

Question 7

What do findings from REA reflect?

Answer 7

1. That there is a behavioural laterality of speech perception.
2. That the left hemisphere is involved in speech at the cortical level.
3. that faster and more neural connections from right auditory inputs to central auditory pathways in the left hemisphere.

Question 8

What did Penfield do and consequently find regarding laterality?

Answer 8

He removed the cortical regions where the abnormal neural discharge originated for people with epilepsy, when doing this he had to stimulate the brain in different places and found that stimulation of the left hemisphere can block the ability to speak whilst the stimulation of the right hemisphere rarely does.

Question 9

What was Zatorre’s (1992/1995) PET study- What did he find?

Answer 9

There were 3 conditions- people listened to burst of noise, listened to words and listened to speech sounds.

He found that the degree of asymmetry and regional location vary as a function of the input and task.

( listening to noise = activation of primary auditory cortex in RH and LH, listening to words= activation in secondary auditory association cortex in both hemispheres (but greater in LH, and discriminating speech sounds activated the interior frontal areas of premotor cortex in the LH )

Question 10

How do the findings of the brain stimulation studies and the behavioural tests differ?

Why might this difference exist?

Answer 10

The result of the dichotic listening studies show a right ear advantage of words in 80% of right handed participants but brain stimulation show language represented in the left hemisphere in more than 98% of right handers.

May be due to behavioural tests measuring multiple things and behavioural stratagies can be employed e.g paying attention to a particular ear.

Question 11

What is the argument for whether language may not be lateralised?

Answer 11

It may infact be speech sounds (temporal acoustic cues) that are lateralised rather than language itself. e.g plosives with rapidly changing temporal cues processed on the left rather than the language itself.

Question 12

What did Cutting 1973 find regarding his dichotic listening study ?

Answer 12

He used stop consonants, liquids and vowels as different conditions of dichotic listening. He found that the largest REA is produced when stop consonants are presented in pairs dichotically , liquids had a less strong REA and vowels did not show any REA.

Question 13

What does Cutting 1973 support the idea of?

Answer 13

all three of his conditions had different rates of acoustic change and temporal cues therefore it may support the idea that REA may be due to acoustic change rather than linguistics ( language itself not lateralised but acoustic change)

Question 14

Explain Hugdahl (1999) study?

Answer 14

PET scan used in dichotic listening test (present CV syllables to one ear and musical instrument to the other ear) and measured changes in distribution of blood flow

Found that though both syllables and instruments activated in the RH and LH (in the superior temporal gyri) overall, the CV syllables had a greater LH activation.

Question 15

What did Rimol 2005’s method?

Answer 15

studied sub-syllabic speech units in the posteior temporal lobe. used fMRI to study the activation of CV syllables, consonants and noise in 17 men with a REA - wanted to find out if isolated stop consonants evoke a specific neuronal response.

Question 16

What did Rimol 2005 find?

Answer 16

that both consonants and CV syllables produced a leftward lateralisation (more so than noise) however, consonants are even more prominant in leftward lateralisation than syllables.

Question 17

What are the implications of Rimol 2005 study?

Answer 17

it challanges traditions ideas of speech perception where lateralisation was seen as an indicated that speech was ‘special’ and thus would be expected to become more leftward lateralised as it moved from consonants to syllables to words.

Question 18

What did Shytyrov (2005) find in contrast to the idea that leftward lateralisation is due to the processing of rapidly changing stimuli?

Answer 18

found that neither psychical properties nor phoneme status are sufficient for laterality. In order to elicit left lateralised cortical activation in normal right handed individuals, a rapidly changing spectrally rich sound needs to be placed in context of frequently encountered language elements (words).

Question 19

What are the implications of Shytyrovs (2005) findings?

Answer 19

1. Language laterality is bound to the processing of sounds as meaningful units.
2. linked to the process of learning and memory formations rather than their physical or phonological properties.

Question 20

What are the main two alternate theories to laterality?

Answer 20

The acoustic laterality theory= physical properties of speech sounds are essential factors determining laterality to the left

The phonological laterality theory= claims that non speech and speech sounds are processed independently of each other and that there exists a specialised speech processing module in the cortex.