Excerpt from Psych 9A Lecture (UC Irvine)

The brain

Different areas of the brain are specialized for different functions. It is possible to divide the brain up into different modules which can cooperate in performing the functions of pereception, movement, thought, and speech.

One important brain module is the language module.

We shall see that there our linguistic abilities really require several modules that cooperate.

An epileptic seizure has a source. The seizure spreads from the source to other areas of the brain, thus more and more areas of the brain become involved. There are cases of intractable epilepsy so severe that radical surgery can be justifiable. The object of the surgeries is to control the spreading of seizures. One of the operations developed for epilepsy is known as the split brain operation. It was first carried out in California, by the doctor Joe Bogen.

In the human brain, the two hemispheres are joined together by fiber pathways. The major connective structure is the corpus callosum. The surgery developed by Bogan and associates, involves the severing of the corpus callosum that connects the two halves of the brain and two other pathways connecting the right and left hemispheres. With these connection severed, an epileptic seizure cannot spread to the other hemisphere and become totally generalized.  

 

In the brain, the right side of the brain controls and processes information from the left side of the body and the left side of the brain controls and processes information from the right side of the body.

 

For example, the right visual field is projected back to the left visual cortex. The left visual field projects to the right visual cortex. Thus in right handers body control on the left side of the brain seems to be dominant and in left handers it's the right side.  



     
     
     
     
     

Differences between the two hemispheres of the brain

Body control and vision processing are two of many functions which are shared by both sides of the brain.

But many functions are specialized for one side of the brain or the other. We say they are lateralized. For example, language skills seem to be primarily be handled on the left side of the brain. This tendency usually overrules handedness.

Some function differences in the two hemispheres:

Left	Right
Emotion	Emotion
Language	Melody
Rhythmn	Face Recognition
Temporal Order	Pattern Recognition
	Spatial Orientation

There are exceptions. In 95% of right-handers, the left side of the brain is dominant for language. Even in 60-70% of left-handers, the left side of brain is used for language.

Along with differences in function, there are noticeable physical differences between certain areas of the left hemisphere and their mirror image areas in the right hemisphere. For example, the left hemisphere areas devoted to language tend to be larger than their parallel regions in the right hemisphere.

There are also asymmetries favoring the right hemisphere. For instance, the right hemisphere is bigger in some ways, e.g. the primary auditory cortex is twice as big in the right hemisphere as in the left hemisphere. This might explain why the right hemisphere plays an important role in the ability to follow melody.

The frontal lobe of the right hemisphere is also wider and bigger. The frontal lobes have to do with the ability to plan and undertake purposeful activity among other functions. People with frontal lobe lesions tend to be rather apathetic and lacking in incentive, particularly when the lesions are in the right frontal lobe.

Consequences for Split-Brain Patients

Recall that the language areas are in the left hemisphere. As noted above, the left visual field projects to the right visual cortex. When an object is presented to the left visual field of a normal person and he is asked to identify the object, he can do so easily: the right hemisphere's visual-spatial representation is transmitted is sent to the left hemisphere via the corpus callosum, specifically to the language area were the process of producing a name for the object can proceed. However, in the case where the corpus callosum has been severed, the person will not be able to name the object because the information cannot be transmitted from the right hemisphere to the left hemisphere.

An number of studies have been carried out on split brain patients, particularly at the California Institute of Technology and the UC-Los Angeles. From these studies it seems clear that the right hemisphere can read a few words; it has limited vocabulary; but it cannot talk.

Experiments

The following is an illustration of a setup sometimes used in split-brain studies

A person sits at a table. There is an array of objects which the subject cannot see. The name of one object, say, key is displayed to the left visual field--thus the information will be projected to the right hemisphere. The person's task is to pick out with the left hand the object named. Under this conditions the subject can do well. However, the person cannot find the key by touch if the key is projected to the right visual field while reaching for the object with the left hand.

Another setup often used to test split-brain patients involves showing composite pictures. The following figures may be used:

These are of an eye, a bee, or a composite image made out of the other two images. The composite figure is presented to the person in such a way that the bug part is projecting to the right hemisphere and the eye part is projecting to the left hemisphere. The subject is to identify the object seen. The person invariably identifies an eye. The reason is clear, because the eye part of the image is in the right visual field, that image goes to the left hemisphere and the left hemisphere has the ability, throughout the language areas, to name objects. The right hemisphere cannot attach names to objects so that part of the image is treated as if it did not exist.

Because there is no way to communicate between the right and the left hemispheres, the split-brain operations provide scientists with valuable information about the lateralizations of the human brain. In particular, the left hemisphere's dominance for language and the right hemisphere's dominance for visual spatial tasks.

Brain injuries

Non-linguistic impairments

Agnosia (Typical Brain Area: superior right parietal lobe)

a-	gnosia
not/without	knowing

Diagnosis		This behavior is characteristic of a person with visual agnosia. Visual agnosia is characterized by: Inability to identify names or describe visually projected objects. Inabilty to select an object from an array. At best, can draw or copy major features of an object. The main features of the pictures drawn by agnosics are not coordinated. Usually have no trouble repeating sentences.
Action vs. talking about actions		Agnosia involves the inability to do certain kinds of perceptual organization. These limitations have several interesting properties, for instance, if the patient Jones is asked to go out to his car and drive home, Mr. Jones will know exactly what to do and he will drive home. Thus, it is not a disorganization of sensory knowledge when it comes to action; it is a disorganization of sensory knowledge in a more abstract sense and for more abstract uses. From this predicament, scientists can deduce, what they might never have guessed, that there is a dissociation between sensory knowledge for action and sensory knowledge of such things as drawing a picture of Abraham Lincoln and knowing where to place his eyebrows. Agnosics cannot select an object from an array. Associative agnosis can draw or describe major features of an object. Apperceptive agnosics cannot copy a drawing or even match visual stimuli.

Other types of agnosia

Aphasia: Language Impairments

This triangular area is where language is located in the brain.

A stroke causing damage in this domain will cause a person to have a language deficit. The deficit will be restricted to the ability to use language. The person's cognitive functioning will otherwise be in tact, i.e. the person will be able take care of his or her house, balance a checkbook, recognize faces, etc.

The two main language areas are Broca's area, which is located in the frontal lobe, and Wernicke's area, which is located in the temporal lobe.

Broca's Aphasia

Damage to Broca's area results in Broca's aphasia. The characteristics of Broca's aphasia are most pronounced in production. Therefore Broca's aphasia is often called the expressive aphasia (which is a somewhat misleading term). The language patterns of Broca's aphasic are quite striking.

1. They tend to pause between words in their sentences. These are lengthy pauses of up to five seconds between words in utterances. Thus it can be difficult to follow their speech.

2.Their sentences exhibit a disorder called agrammatism. Agrammatism is the tendency to omit function words as well as endings such as -ed in indicating past tense. Function words are words which tie sentences together: the, of, is, by, a, etc.

There is a test used with patients which demonstrates their comprehension deficits. If given the sentence:

The patient will say Bill is the chaser and Mary is the chasee (or the one who is being chased). However, there is a problem when Broca's aphasiacs are given the sentence:

This is a passive sentence indicating Mary as the chaser. In order to know that Mary is the one who is doing the chasing, an understanding of the passive structure is required. This means, there is a need for interpreting the was and knowing the by signals the agent, or the doer of the chasing. Thus, Bill was chased by Mary is a sentence where there is only one correct interpretation, i.e. Mary chased Bill, and that requires function words interpretation.

One method of testing comprehension is to present the patients with pictures and have them point to the one which best represents the sentence. For instance, given the sentence "The dog bit the postman," the following four pictures symbolize four different scenarios from which the patients may choose.
 

The patient is asked to point to the picture which best represents the sentence, "The dog bit the postman." Invariably the patient will point to the correct picture, picture A. However, if the patient is presented with the unusual sentence, "The dog was bitten by the postman," the patient will again point to picture A, the picture representing the postman being bitten by the dog. Apparently the patient cannot exploit the information contained in the words and endings in order to arrive at the correct interpretation.

The patient utilizes knowledge of the real world to draw inferences about what would be the most plausible interpretation of dog, bite, and postman. With respect to most real world situations, the most likely scenario is that of the dog biting the postman.

This experiment demonstrates that these patients do have a deficit in comprehension which parallels their deficit in speech production: just as they omit many of the functional elements when they are speaking, so too when they have to rely on the functional element to correctly interpret a sentence.

Question: What would happen if we give the sentence: "The postman bit the dog". Which picture would the Broca's patient point to?

Answer: I don't know. My guess: They point to the right picture.

Another example to support this: Japanese. A "case" language. Two ways of saying "Taro hit Hanako".

(1)	Taro-	ga	Hanako-	ni	nagutta
	Taro-	SUBJECT	Hanako-	OBJECT	hit
(2)	Hanako-	ni	Taro-	ga	nagutta
	Hanako-	OBJECT	Taro-	SUBJECT	hit


Taro hit Hanako.

bit
be bitten by

It's not just little function words that cause problems. It's syntactically complicated constructions:

1. The apple that the boy is eating is red.
2. The cow that the monkey is scaring is yellow.

Consider the second sentence and a variation:

1. The cow that the monkey is scaring is yellow.
2. The monkey that the cow is scaring is yellow.

Now consider:

1. The apple that the boy is eating is red.
2. The boy that the apple is eating is red.

But the relationships aren't so easily guessed in the cow-monkey sentence. A cow might just as easily scare a monkey as a monkey might scare a cow. Neither one is more likely to be yellow. And with this kind of sentence to get the meaning right you have to pay attention to the syntax

Note: In the sentence "The apple the boy ate was red" the italicized part is called a relative clause. It helps describe or pick out the particular boy we're talking about.

This shows two things: First there are certain kinds of reasoning Broca's patients are good at, because they understand the boy-apple sentence. Second, they have trouble with complex syntactic constructions when there's no extra information to help. [Caramazza and Zurif (1976)]

The deficit is not limited to speaking and comprehension. In all true aphasiacs, all aspects of language are equally impaired. For instance, in writing, these people will leave out the function word in their written language. In experiments where a patient is asked to read a list such as:

                    ant
                    tree
                    of
                    dog
                    be
                    house
                    bee

Summary of Problems for Broca's Patients

• Problems with Function words
• Problems with complex syntactic constructions
• Problems involve both comprehension and production
• Problems with writing and reading
• They tend to be aware that something is wrong with them.

Wernicke's Aphasia

Lesions in Wernicke's area lead to what is called Wernicke's aphasia.

Wernicke's aphasiacs make what is known as semantic paraphasias i.e. word substitutions which can be labeled as semantic errors. For instance, they may say arm when they mean leg.

It is an important indicator of Wernicke's that these substitutions often involve mistaking one word for a semantically related word, such as arm for leg, and not just one word for a completely unrelated word, such as wax for tongue. Furthermore, these patients create novel word structures. For instance, the word ending -er is used to form the word sickser for a doctor. The conjunction is from the word sick and the ending -er. This word, if it existed, might mean something like one who engages in some activity related to sickness. This is an example of a novel word based being used in a semantically motivated way. Wernicke's patients will also use completely made up words that no sense can be made of, such as "bangahanga bangahanga bangahanchepie."

Wernicke's patients suffer from Anomia, where anomia means "no names".

Anomic patients, cannot reliably find and use nouns in conversation nor can they name objects (although often they substitute a semantically related word for the appropriate word).

Doctor	[Showing, a pen] Can you tell me what this is?
Patient	Geez, you know . . . isn't that funny, oh I know, it's one of those things, . . .it's. . . it's funny, you know . . . I know that it is . . . you know . . .it's hummmm . . . it's one of those things.
Doctor	[Produces a comb] How about this?
Patient	Ooohhh. . . . isn't that funny . . . I'm getting old . . . it's so terrible, ohhh . . . you know . . . I just . . it's that funny, oh geez . . you know . . . I know, it's that thing you use to comb your hair with.
Doctor	I'm going to read a sentence. I want you to repeat it: "The big lanky first baseman ambled out to the bull pen."
Patient	"The big long lacquered lanky first second range man ambled up out to the bull player pen."

Note that the patient uses the word comb as a verb: ". . . the thing you use to comb your hair with." Yet she could not associate the noun "comb" with the object. The deficit appears to be related to naming, specifically to the use of nouns rather than verbs.

Patients with Wernicke's aphasia also suffer from comprehension problems, i.e. they have trouble understanding what is being said to them.

As previously mentioned, Broca's aphasiacs have some awareness of their deficits. However, people with Wernicke's aphasia are what is known as anosagnosic: they are unaware of the nature of their illness. Consequently they will attribute their language problems to a learning disorder or some other irrelevant and/or nonexistent cause.

In summary, the problems associated with Wernicke's aphasia are:

• Production problems:
  1. Word structure errors: sickser for doctor
  2. Completely made-up words (these are called neologisms)
  3. Words that are halfway right: "bife" for "knife"
  4. Words that are associated with what they're trying to say: "knife" for "fork".
• Comprehension problems
• Anosagnosia (Unawareness of condition).
• Repetition is faulty, often with irrelevant things thrown in.
• Anomia: Can't name objects and often have trouble finding nouns in conversation
• Usually has a worse prognosis than Broca's

Summary and Diagnosis of disorders

Let's summarize the main points of the previous discussion by In this lecture a number of disorders have been outlined. This leaves the question of how to diagnose a patient's disorder and how to distinguish between patients with different disorders. The following is an example of three tests which can be used to distinguish between agnosia and aphasia.

In both cases most patients have problems naming objects. It is possible to design separate tests where the responses from a person suffering from visual agnosia will be different from an aphasic.

1. Naming: In this test, the patient is presented with, say, a set of keys and the patient is asked to name the object.
   • Visual Agnosia: It is known that visual agnostics have trouble naming objects: their answers are unreliable; even in the case they produce some answer it is often inappropriate.
   • Aphasia: an aphasic will respond in two ways depending on the location of their lesion.
     • Broca's: A patient suffering from Broca's aphasia will likely provide the correct name though they may have trouble producing the name of the object
     • Wernicke's: a Wernicke's aphasiac may respond with a semantically related word, i.e. a word which as a meaningful relations to the word in question, such as, say, a lock, or a door, etc., or a neologism.
2. Name selection: The second test is similar to the first test in that the patient is shown an object, say a set of keys, but rather than attempting to name the object, the person conducting the test will recite a list of names of objects. The patients task is to indicate when the correct name is said.
   • Visual Agnosia: Visual agnostics, on the other hand, typically will not be able to select the correct name. In particular, the visual agnosic will make a random selection. Since such patients are selecting at random they are as likely to chose the word key as they are to chose the word toothbrush. Thus, given any list of words visual agnosics will select one word, and it may or may not be the correct word.
   • Aphasia: Aphasiacs are, in general, rather good at name selection: Broca's aphasiacs are quite good, and Wernicke's aphasiacs are fairly good.
3. Object selection: In the third test objects are arranged in front of the patient. The patient is then asked to select the object the tester asks for, e.g. "Point to the keys" or "Point to the toothbrush."
   • Visual Agnosia: random responses
   • Aphasia: Good at this task

In sum: 

                   Visual Agnosic            Aphasic

1. Naming         No name or                Correct name 
                                            (Broca's aphasia)

                  inappropriate name        Semantically related word 
                                            or neologism
                                            (Wernicke's aphasia)

2. Name 
   Selection      Random                    Good (Broca's aphasia)
                                            Good (Wernicke's aphasia)

3. Object         Random                    Very good (Broca's aphasia)
   selection                                Good (Wernicke's aphasia)

Summary of differences between Wernicke's and Broca's patients.

1. Picture test
   • Pictures distinguishing between active and passive sentences. Wernicke's patients do no worse on active than on passive sentences, though they may have trouble comprehending both. Suppose the sentence is the hamster bit the postman. A Wernicke's patient might point to a picture with a postman and a dog, indicating that he has not correctly processed the content word hamster. Broca's patients will do poorly with the passives, but they should point to pictures indicating they have understood all the nouns, pictures with both hamsters and postman in this case.
   • Pictures distinguishing interpretations of sentences with complex syntax (such as relative clauses). Broca's patients will do poorly if the sentences describe relationships that can't be easily guessed. Wernicke's patients may also do poorly since they have general comprehension problems.
2. Word list reading Wernicke's patients will do equally well at reading all words; Broca's patients will have special trouble with function words (prepositions, conjunctions, articles).