Laterality Flashcards
How long ago did Homo erectus exist? How does it differ from Homo habilus?
Between 2 million and 800 000 years. It was taller and less robust than homo habilus
What was the difference in relative brain size between homo habilus and homo erectus?
Homo erectus had a much larger relative brain size, as the capability of the brain was growing in order to carry out more complex tasks
Give 2 reasons why there were larger groups or communities of homo erectus when compared to its predecessors?
Co-operative hunting and infant care
What are the characteristics of homo sapiens?
800 000 years ago - present, taller and less robust, final and dramatic increase in brain size
What evidence has been found of Neanderthal dextrality?
Asymmetrical dental wear - neanderthals would hold meat between their left hand and teeth, and cut with their right hand - sometimes leaving marks on their teeth, all in the same direction
Which two characteristics have been around since Australopithecus Africanus?
Bipedalism e.g. walking upright, and frontal and occipital petalia
At what stage of hominid evolution is the enlarged broca’s area identified?
Homo habilus
At what stage of hominid evolution did dextrality emerge?
Homo habilus
At what stage of hominid evolution did complex social structures emerge?
Homo erectus
What did Corballis propose about gesture?
- That gesture preceded speaking in homo habilus due to a high larynx
- that primate vocalisations have a limited range and are not volitional
- humans use gesture
What is the significance of mirror neurons?
They could be the key to understanding intention - Area F5 (same area as Broca’s area in humans) activated when monkey reaches for a peanut and when other monkeys or human reaches for a peanut
What are some characteristics of our earliest bipedal ancestors in relation to mirror neurons?
- bilateral mirror neuron centres
- LH specialisation for vocalisation - not speech, just making simple noises
- little or no hand preference
What happens to mirror neurons post homo habilus?
- vocalisations become attached to gestures
- mirror neurons become specialised in LH
- emergence of broca’s area
- right hand becomes dominant for tool use and gestures
What is the McGurk effect?
When the lip movements of a person are inconsistent with a sound, humans mishear it
How do the sensory/primary areas of our brain develop?
They seem to myelinate earlier, and tend not to be lateralised e.g. there’s no difference in basic vision between LH and RH side
How do the association areas of our brain develop?
They myelinate later and tend to become lateralised - suggests that lateralisation might develop fairly late
How does the corpus callossum develop over time?
A very large increase from infancy to adulthood in relative size. Due to its importance in lateralisation, this supports the argument that lateralisation might develop fairly late
What did Bates discover about the effect of unilateral lesions?
For children, there were no asymmetrical effects of lesions depending on RHD or LHD
For adults, LHD associated with a much greater rate of errors when compared to RHD
This suggests that children’s brain are different to adult’s brains in terms of lateralisation
What did Lenneberg propose on the subject of development of laterality?
That the brain is not lateralised at birth and lateralisation develops with age
What was discovered about the sizes of left and right temporal planum in adults and infants?
The temporal planum was found to be larger on the left than the right for both infants and adults, suggesting that laterality could be innate
What did Hepper (1991) find in relation to foetal thumb sucking?
92% suck their right thumb - irrespective of foetal position or gestational age
100% of children who sucked their right thumb went on to be dextral
66% of children who sucked their left thumb went on to be sinistral
What did Holowka and Petitto (2002) find in relation to infant mouth openings?
- RH dominant for smiling: expression of emotion
- LH dominant for babbling: verbal expression
- results similar to those of adults
What did Molfese (1975) find in relation to wave forms for speech and mechanical sounds?
Speech - larger AER’s (more processing) in LH, more pronounced for children
Mechanical - larger AER’s (more processing) in RH, more pronounced for children
Shows that functional lateralisation is present in early infancy
What is dichotic listening?
Assessing which side of the brain people use for language - present separate material simultaneously to both ears and ask subject which sound they heard
What does Kimura’s dichotic listening model suggest?
Kimura suggested that the dichotic procedure suppressed ipsilateral pathways and accuentated contralateral pathways
What is the direct access model? (Kimura)
The direct access model suggests that right ear stimuli have direct access to LH language processes. Left ear stimuli goes to RH then must cross over to LH.
How did Entus (1977) test for dichotic listening in infants?
Entus attempted to elicit a sucking response in response to interesting sounds while infant sucking on an electric dummy
Explain habituation and dishabituation
If someone gets bored with a stimulus, they have habituated. If a new stimulus is presented and that person shows interest in the new stimulus, they have dishabituated. If the person does not dishabituate, they have not detected the change
What did Entus find with his infant habituation study?
Dishabituation is stronger for the right ear compared to the left - suggesting that the infant noticed a change more when the sounds heard with the right ear were changed.
In the Entus study, how did the results differ for musical stimuli?
Dishabituation is stronger for the left ear compared to the right - suggesting that dishabituation is dependent upon stimulus type
What are Broca’s area and Wernicke’s area?
Broca’s area is the name for the area of the brain concerned with language production
Wernicke’s area is the name for the area of the brain concerned with language comprehension
What were the findings of the Wood study on child and adult laterality? (2004)
- children have more variable laterality scores
- no evidence that LH dominance increases either from childhood to adulthood, or within childhood itself
What did the Holland study find?
- language lateralisation does increase with age
- the bias toward left hemisphere activation at Broca’s area becomes stronger as age increased
Why do children with unilateral lesions recover?
Brain plasticity - not lack of lateralisation
What are some negative outcomes in differences in laterality?
Early death, dyslexia, stuttering, schizophrenia & schizotypy
What are some positive outcomes in differences in laterality?
Enhanced spatial/artistic ability
Intellectual ability/giftedness
What are two possible explanations for the findings of Porac and Coren? (1981)
The elimination hypothesis (left handers dying earlier) and modification hypothesis (change in educational methods over time)
What did Hughahl (1993) find when investigating the elimination and modification hypotheses?
That the percentage of left handers decreased with age, and the number of switchers increased with age, supporting the modification hypothesis
What characteristics did Samuel Orton suggest that dyslexics have? What name did he give the condition?
- mirror reversal problems
- able to mirror write
- weak or reversed hand preference
Strephosymbolia (twisted symbols)
Explain strephosymbolia
- LH sees word normally, RH sees word mirror reversed
- Dyslexics have a developmental delay in hemispheric asymmetry
- Hemispheric suppression causes mirror reversed projection of text to become dominant
What is the main problem with Orton’s theory?
How the visual system actually works e.g. LH and RB project identical images on slightly different angles
What did Hughahl find in his experiment on dyslexic children? (2003)
Temporal planum size associated with ear asymmetry for dyslexics, but not controls
No structural or functional asymmetry between groups
Define stuttering
The repetition (audible or silent) or whole words or parts of words within a sentence
What did Orton suggest the cause for stuttering was?
He suggested that speech control was bilateral, and the LH dominance was replaced by competition from both hemispheres
What did the Foundas (2004) study on stuttering find?
For both groups, 64% left TP > right TP
What were the effects of delayed auditory feedback in the Foundas study? (2004)
- for the control group, stuttering increased with DAF
- for the stutter group, stuttering decreased with DAF
Define schizophrenia
A serious mental illness which results in delusional thought patterns, hallucinations and inappropriate affect
What are some of the biological characteristics of schizophrenics?
- increased ventricular volume
- decrease cortical thickness
- altered patterns of structural asymmetry
Explain Crowe’s theory of LH dominance & schizophrenia
Crowe suggests that when a person lacks the typical pattern of LH dominance, they can develop schizophrenia
What did Dragovic and Hammond (2005) find in relation to handedness and schizophrenia?
All three types of atypical hand preference are over-represented in schizophrenic individuals
Was there a link found between schizotypy and aytpical hand preference?
No difference between dextrals and sinistrals, but mixed handedness was associated with schizotypy
What is the logic behind left handers being more likely to be artists/musicians/architects?
sinistrality leads to increased right hemisphere function, and since the RH deals with spatial processing, this leads to an increase in spatial ability
