Being left handed

As a left handed person and psychology graduate, this is a post I’ve wanted to write for a while because there’s actually a lot I don’t know about how being left handed affects the brain. Me and my dad are both left handed, but at opposite ends of the spectrum – he writes with his left hand (but that’s about it) whereas for me, even picking up something with my right hand feels weird and requires conscious effort. So if being left handed is genetic, why this difference?

Another reason I wanted to find out more information is that I actually quite like being left handed, despite the obvious irritation of everything from scissors to tin openers to computer keyboards being biased to the right-hander (and don’t even get me started on trying to write in anything other than biro). And there might even be some benefits to being a leftie, with theories that it’s linked to creativity, sports, or being good at playing an instrument. Here’s what we know:

About 10% of the population are left handed, although as you can see from the comparison between me and my dad, the degree of left handedness can vary. Men are also more likely to be left handed than women (e.g. Papadatou-Pastou et al, 2008). Scientists still aren’t sure of the exact cause of being left handed, although they are sure there is some genetic component – studies have shown that you are more likely to be left handed if one of your parents is (e.g. McManus & Brydon, 1991b).

Handedness has also been thought to relate closely to language functions in the brain. As you may remember if you read this post, in most people, language functions are lateralised to the left hemisphere (see below). As each hemisphere controls the opposite side of the body, there is thought to be a relationship between hand dominance and language, with right- handers having right side preference due to language functions located in the dominant left hemisphere.

lateralization-langauge-areas

However, in left-handers this relationship is not so clean cut – only about 30% are thought to have their language dominance in their right hemisphere. I actually participated in an fMRI experiment at uni which tested my handedness and language location in the brain, which found that even though I’m left handed, my language functions are normally lateralised in the left hemisphere. So opposite language lateralisation in the brain can’t be the only reason people are left handed, the process is way more complex, and still not something science fully understands.

Several studies have identified a link between being left handed and creativity. For example, Newland (1981) asked almost 100 right handed, and 100 left handed people to complete a test on creative thinking. The results showed that left handed participants scored more highly on all 4 sub-tests, suggesting they have greater creativity. Another study by Coren (1995) found that left-handers have better divergent thinking skills than right-handers – in other words, they are better at exploratory thinking to find solutions and create ideas. Being better at divergent thinking could explain why left handed people are more creative, and thought to be better at logic.

There is a lot of anecdotal evidence which suggests left-handers are smarter, or better at politics e.g. Mensa reported that 20% of its members are left handed (which is double what you’d expect, at 10% of the population). However, unfortunately, I can’t seem to find any actual experiments comparing IQ that back this up! Studies have shown however that professional orchestras have a higher proportion of left-handers, and that during school, a high proportion of children who excel at maths are left-handed.

Annoyingly, there don’t seem to be answers to all my questions about left handedness, and there is still a way to go to establish the genetic basis and to understand how the brain is organised in left handed individuals. Regardless, I hope you found this post interesting and let me know in the comments if there’s anything else you’d like me to feature on this blog.

 

 

 

 

The McGurk Effect

Here’s the first post in a new section of my blog called ‘Brainteasers’.

This section will be made up of short posts with videos which will show you things you can amaze your friends and family with. They will also fit in with the other sections of my blog, and will show the practical applications of some of the theories I’ve discussed. I hope you will find these demonstrations as fun as I do 🙂

So first up – the McGurk Effect!

Unsurprisingly, this was first identified by someone called McGurk in 1976. It shows the interaction between vision and hearing, and illustrates that what we see overrides what we hear.

When we see a speaker mouth the phoneme ‘ga’ while the sound ‘fa’ is played into our ears, we perceive the sound as ‘ga’. In other words, we believe what our eyes are suggesting is being spoken rather than our ears. This shows the importance of vision in language perception.

Try it for yourselves:

I hope you enjoyed this post – check back soon for more brainteasers and thank you for reading 🙂

Dyslexia

Dyslexia is a disorder which affects a person’s ability to read fluently, despite normal intelligence and comprehension. In order for a person to read, they must be able to decode the words and understand them – both of these processes are needed.

It can also affect a person’s writing – letters are likely to be written backwards and words can be spelt wrongly. Words are often written as they sound, and individuals have a poor phonological awareness. It is thought that English speakers show more severe effects of dyslexia due to the difficulty of the language- it had several irregular verbs and spellings, and therefore takes longer to learn than other European languages such as Italian.

Here are examples of the word ‘teapot’ written by different individuals with dyslexia.

Dyslexic words.jpg
http://en.wikipedia.org/wiki/Dyslexia#Signs_and_symptoms

There is a genetic basis for dyslexia: males are more likely to be dyslexic than females. The genes associated with this disorder have been identified on chromosomes 6,15 and 18. Neuroimaging studies have shown that there are also differences in the brain between dyslexics and normal controls: areas connecting language and visual areas show less activity in dyslexics. There is also evidence that there are structural abnormalities in Broca’s and Wernicke’s areas (shown in the diagram below).

http://athome.readinghorizons.com/research/dyslexia-information.aspx

Individuals with dyslexia can be helped to improve either reading and writing skills by using techniques which increase their awareness of the relationship between letters and sounds.  Certain fonts (see picture below) are thought to help dyslexics read more smoothly, as they emphasis the difference between letters. Different coloured backgrounds are also used. It is thought that extra help when the brain is still developing makes training more effective.

Dyslexie sample font.tiff
http://en.wikipedia.org/wiki/Dyslexie#Research

That’s all for now – make sure to request any topics you’d like me to write about 🙂

How do infants learn language?

If you think about it, it’s pretty impressive that, given the complexity of language, infants learn to speak their first word by the time they are about a year old, and are able to talk in sentences by the age of 2. It takes us years to become fluent in a second language as adults, but infants manage to do this within just a few years. So how do they manage it?

You’ve probably noticed the strange way adults speak to babies. Kind of cooing and repetitive, this type of talking is known as infant-directed speech, or mothereseThis talking actually has a purpose – it is higher in pitch than normal speech, and has more exaggerated intonation contours. It also has longer pauses between words and is made of shorter sentences. These characteristics make it easier for infants to recognise, and so helps them to learn the properties of language.

There are other characteristics of language which are thought to help babies learn words. One example of this is phonemic categories: for example ‘b’ and ‘p’ are phonemes that are very similar, but can be recognised by infants as young as 1 months old. This was shown by Eimas et al (1971) who got infants to suck on a dummy to hear sounds, and found they sucked more to the ‘new’ phoneme they hadn’t been played before.

It has been shown by Werker and Tees (1984) that young infants are able to discriminate between phonemic contrasts that older children and adults are not. This graph shows the decline in ability as they get older:

http://web.uvic.ca/~lalonde/psyc335/notes/lecture04.html

This suggests that infants become less able to discriminate between phonemic contrasts that they don’t need to know in their native language, and so helps them focus on this language.

Identifying single words in a sentence is more difficult than it would seem, as silences don’t always come between words. Infants are thought to learn word boundaries by categorical perception – the probability that one syllable will follow another. For example, Saffran et al (1996) showed that in the phrase ‘pretty baby’, there is a higher probability that ‘ty’ will follow ‘pret’ than ‘ba’ would follow ‘ty’. They suggested that babies use this method to work out the gaps between words.

Not surprisingly, infants learn words faster if they are exposed to more language. Hart and Risley (1995) found that in the USA, a familys’ social economic status affects the amount of language they are exposed to: high SES families = 487 utterances per hour, while for low SES families, it is 178 utterances per hour. This shows the importance of environment in language learning.

Hope you found this post interesting, check back soon for more 🙂

Language and the Brain

I’m going to talk about language in my next few posts, so here’s an overview of the language areas in our brain. As you will see, there’s a lot that goes on in a very short space of time for us to be able to understand speech and reply appropriately, but I’ll try and make it as simple as possible.

Here is a diagram of the brain showing the main areas involved in language processing. As you can see from the diagram, it is the left hemisphere which is specialised for language (the frontal lobe is on the left):

http://2012books.lardbucket.org/books/beginning-psychology/s13-03-communicating-with-others-the-.html

The auditory cortex is the part of the brain that processes speech, and enables us to make sense of it. The motor area then controls the vocal tract, throat, tongue and mouth so we can talk. Broca’s area, shown in purple on the diagram, is the inferior frontal gyrus, which is important for language production. Broca (1861) studied a patient who was unable to produce speech other than the word ‘tan’ and swear words, but could understand questions. This patient had a huge lesion in his inferior frontal cortex, so Broca concluded that this area is important for speech. He studied several patients with lesions in this area, and found that only those who had lesions in the left hemisphere had impaired speech, which shows that the left hemisphere is important for language. Patients with Broca’s Aphasia are able to produce single words but not full sentences.

Wernicke’s area is the posterior part of the superior temporal gyrus, and is important for speech understanding. Wernicke (1874) was the first to describe patients who had lost the ability to comprehend speech despite normal hearing, and could not produce meaningful speech despite normal articulation and grammar. Patients with Wernicke’s Aphasia have fluent speech but it is lacking any content or meaning.

This next diagram shows how Broca’s and Wernicke’s areas are thought to interact to produce speech, based on the Wernicke-Lichtheim Model:

http://www.frontiersin.org/Journal/10.3389/fpsyg.2013.00416/full

The arcute fasiculus is the white matter that connects the two areas. If it is cut, then Conduction Aphasia occurs – this is when speech sounds and movements are unaffected, as well as normal comprehension, but repetition of speech is impaired.

Check back soon for my next post on how infants develop language abilities!