• A whole which is divided into vertical halves that
seem to be mirror images of one another. It looks
much like a walnut with the two parts joined
around the middle, except that there is little
space between the two halves in the real brain.
Each half of the brain is called a hemisphere.
There is a left hemisphere and a right
hemisphere. The hemispheres come out of the
brain stem, which connects to the spinal cord.
The hemispheres maintain connection with one
another through a bundle of fibres called the
corpus callosum. The brain, together with the
spinal cord, is referred to as the central nervous
system of the human body.
The cerebral cortex
There is a covering on each hemisphere, called the cortex, which is a
furrowed outer layer of cell matter. It is the cortex that is concerned
with higher brain functions in both humans and animals. The cerebral
cortex in humans has increased in size and complexity to become the
largest part of the brain.
Each cerebral hemisphere is divided into four parts or lobes: from
front to back there are the frontal, temporal, parietal (located above
the temporal), and the occipital. This division of the brain into lobes is
loosely based on physical features and not on actual separations.
General functions such as cognition (to some degree) occur in the
frontal lobe, hearing occurs in the temporal lobe, general
somaesthetic sensing (feeling in the arms, legs, face, etc.) in the
parietal lobe, and vision in the occipital lobe. Each hemisphere has
these lobes with these functions. As we shall see later, there are other
hemispheric-specific functions that are also located in some of these
areas. For example, the left hemisphere typically involves language.
The front part of the parietal lobe, along the fissure of Rolando, is primarily
involved in the processing of sensation, and may be connected with the speech
and auditory areas at a deeper level.
l The area in front of the fissure of Rolando is mainly involved in motor
functioning, and is thus relevant to the study of speaking and writing.
l An area in the upper back part of the temporal lobe, extending upwards into
the parietal lobe, plays a major part in the comprehension of speech. This is
l In the upper part of the temporal lobe is the main area involved in auditory
reception, known as ‘Heschl’s gyri’, after the Austrian pathologist R. L. Heschl
l The lower back part of the frontal lobe is primarily involved in the encoding
of speech. This is ‘Broca’s area
Some of the neural pathways that are considered to be involved in the
processing of spoken language:
1. Speech production. The basic structure of the utterance is thought to be
generated in Wernicke’s area and is sent to Broca’s area for encoding. The
motor programme is then passed on to the adjacent motor area, which
governs the articulatory organs.
2. Reading aloud. The written form is first received by the visual cortex,
then transmitted via the angular gyrus to Wernicke’s area, where it is
believed to be associated with the auditory representation. The utterance
structure is then sent on to Broca’s area, as in (1).
3. Speech comprehension. The signals arrive in the auditory cortex from
the ear, and are transferred to the adjacent Wernicke’s area, where they
• Left and right hemispheres control opposite sides of the
• Dysfunctions seem to be caused by the two hemispheres
vying with one another for dominance. Some even argue
that left-handers die younger (Halpern and Coren, 1991).
• Because dominance is a congenital condition, the practice of
forcing children who are naturally left-handers to use their
right hand for writing, etc., will not remedy such problems
but may serve to worsen them and create others. Many
countries still force natural left-handers to be right-handers
• About 10 per cent of the population worldwide are left-
• counter to expectations, only about 30 per cent of left-
handers have righthemisphere dominance (Klar, 1999).
• The majority of left-handers are lefthemisphere dominant
but their dominance tends to be much less marked than in
natural right-handed persons.
• The lack of strong dominance for lefthanders is believed to
be a factor contributing to speech disorders and to various
reading and writing dysfunctions, such as stuttering and
dyslexia, which includes the reversal or mirror-imaging of
letters and words when reading or writing. Lamm and
Explain the relation between the two hemispheres and
the different sounds.
• Speech sounds are differentiated from other types of sounds including music,
animal sounds, and noises.
• . The two hemispheres specialize in processing these two types of sounds
(speech and non-speech).
• right-handers, speech sounds are mainly processed in the left hemisphere
while music, noises, and animals sounds are mainly processed in the right
• The opposite will be the case for some left-handers.
• Because of the nature of the arrangement of large and small bundles of fibres,
right-handed persons with lateralization for language in the left hemisphere
will perceive speech sounds more readily through the right ear than the left.
if you are a right-hander, is: ‘Right ear
forward’. This is because
(1) speech sounds are processed in the
(2) the first big impulse of speech sound
will be transmitted to the left hemisphere
from the right ear.
• (3) the first big impulse will precede and dominate
any other big impulse.
Pierre Paul Broca
• He was a French pathologist and neurosurgeon
• who made the first great discovery regarding brain
and language. He discovered a certain area of the
cortex that is involved with the production of speech;
that part of the cortex bears his name, Broca’s area.
• The speech-production process would begin in Broca’s
area, pass on through the arcuate fasciculus to the
motor area and from there to the articulators of
speech for vocalization.
Carl Wernicke, a German neurologist (1848–1905)
According to Wernicke, on hearing a word, the sound
of a word goes from the ear to the auditory area and
then to Wernicke’s area. It is from Broca’s area that the
vocalization of speech would then be activated
(see Figure 12.1).
When a word is read, according to Wernicke, the information goes
from the eyes to the visual area of the cortex in the occipital lobe,
from there to the angular gyrus, then to Wernicke’s area and then
to Broca’s area, which causes the auditory form of the word to be
activated. Wernicke had the mistaken belief that all written words
had somehow to be speech activated (said aloud).
Although most language processes occur in Broca’s area, Wernicke’s area, and the
angular gyrus, some language functioning occurs elsewhere in the left
hemisphere, as well, and some even occurs in the right hemisphere.
The ability to understand the meaning of intonation, such as the rising tone of a
question, the ability to interpret emotional intentions, such as anger or sarcasm,
from inflections in the voice, and the ability to appreciate social meanings from
something such as whispering, may very well be located outside of what have
been traditionally regarded as the main language areas of the brain.
• There is increasing evidence that the right hemisphere
is critical for understanding discourse (Hough, 1990;
Kaplan et al., 1990; Beeman, 1993, 1998; Brownell and
Martino, 1998; Stemmer and Joanette, 1998; Paradis,
• Thus, patients with right-hemisphere damage have
impairments concerning narrative script, interpretation,
integration of information or conceptualization of the
unit as a whole, construction of new conceptual
models, and inferences about another person’s beliefs
and intentions (Stemmer and Joannett, 1998).
What happens with the damage of the right
• The right hemisphere has an ability to use ‘knowledge of the world’,
involved in scripting, where a number of sentences are related to a topic.
• Patients who have damage in their right hemisphere show structuring
problems in story recall (Moya et al., 1986), and their speech is disrupted,
particularly at the level of discourse, jumping from one topic to another
incoherently (Brownell and Martino, 1998).
can take over
• damage to language areas in the left
hemisphere of young children is compensated
for, with the right hemisphere taking over the
reacquisition of language.
• Albert and Obler (1978), Karanth and
Rangmani (1988), and Wuillemin et al.
(1994) report greater involvement of the
right hemisphere in bilinguals than in
monolinguals. Albert and Obler (1978)
argue that ‘the right hemisphere plays a
major role in the learning of a second
language, even in adulthood’ (p. 243)
Right-handed deaf signers, like hearing persons,
exhibit aphasia when critical left-hemisphere areas
are damaged (Poizner et al., 1989)
Approximately one dozen case studies provide
sufﬁcient detail to implicate left-hemisphere
structures in sign-language disturbances.
language disorders, known as aphasias, are presumed
to have as their cause some form of damage to some
speciﬁc site in the hemisphere where language is
located. Such damage causes characteristic problems
in speech, as well as in reading and writing.
One particular condition, now called Broca’s aphasia, is characterized by meaningful but
shortened speech and also occurs in writing. In the condition, grammatical inﬂections are often
lacking, such as the third-person present tense ‘-s’ (‘Mary want candy’ for ‘Mary wants candy’),
and the auxiliary ‘be’ (‘Joe coming’ for ‘Joe is coming’), as are articles, prepositions, and other so-
called function words. In a way, the speech is similar to that of children at the telegraphic stage of
Although the most noted feature of Broca’s aphasia is the fragmentary nature of speech
production, it has recently been discovered that speech
comprehension is also affected. In one experiment with a patient with Broca’s aphasia, when
presented with the spoken sentence, ‘The apple that the boy is eating is red’, the patient was able
to understand the sentence,particularly with regard to who was doing the eating (the boy).
However, whenpresented with the sentence, ‘The girl that the boy is looking at is tall’, the
samepatient could not ﬁgure out who was doing the looking (the boy).
This condition is characterized by speech that often resembles
what is called nonsense speech or double-talk. It sounds right and
is grammatical but it is meaningless. It can seem so normal that the
listener thinks that he or she has somehow misheard what was
said, as is often the case in ordinary conversation. A patient with
Wernicke’s aphasia may say, ‘Before I was in the one here, I was
over in the other one. My sister had the department in the other
one’, ‘My wires don’t hire right’, or ‘I’m supposed to take
everything from the top so that we do four ﬂashes of four volumes
before we get down low’.
Patients with Wernicke’s aphasia commonly provide substitute words for the
proper ones on the basis of similar sounds, associations, or other features.
The word ‘chair’, for example, elicited the following in some patients: ‘shair’
(similar sound), ‘table’ (association), ‘throne’ (related meaning), ‘wheelbase’
(?) and ‘You sit on it. It’s a . . .’ (word loss). As with Broca’s aphasia,
Wernicke’s aphasia can also cause a severe loss of speech understanding,
although the hearing of non-verbal sounds and music may be unimpaired
Reading and writing aphasias: dyslexias
One type of aphasia that involves disorders in reading and writing is called
dyslexia. There are many sorts of dyslexia, one category of which is due to
damage to the brain, after reading and writing have been acquired. With
children, however, dyslexias may be observed while they are in the process of
acquiring reading and writing skills. Problems of hemisphericdominance or
defects in visual perception, for example, may play some role in causing
difﬁculties in reading and writing. Some children may only be able to write
backwards (deer as reed) or upside down, or in reading they may confuse letters
(b with d, p with q, u with n, m with w) and engage in other anomalies.