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Semantic Knowledge in Patient HM

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Semantic Knowledge in Patient HM

HM is a famous case study that significantly advanced our understanding of memory. This case study revealed that:

  • Specific brain regions are responsible for memory and learning processing.

    • The hippocampus is an important part of the brain responsible for memory.

  • Different brain regions are responsible for the retrieval of memories and the formation of new memories.

  • Different parts of the brain are responsible for short-term memory, long-term memory, and other types of memory, such as procedural memory.

The patient HM suffered from severe epileptic seizures. To relieve them, he underwent surgery in 1953 to remove both (bilateral) medial temporal lobes, including the hippocampi. It was not known that the hippocampus was needed for memory formation. HM Seizures decreased significantly, but his long-term memory was no longer present. After surgery, he could no longer form new memories, but his short-term memory remained intact.

What did Schmolck et al. (2002) research?

Previous research on the patient HM has shown that different brain parts are responsible for different types of memories. Schmolk et al. (2002) investigated which area of the brain is responsible for long-term semantic memory. The research goal was to learn more about semantic knowledge in patient HM and other patients with bilateral medial and lateral temporal lobe damage.

Semantic long-term memories are long-term memories that do not stem from personal experiences. They are facts and knowledge acquired throughout life.

An example of semantic memory is knowledge of facts about the world, such as the order of the colours of the rainbow, the capitals of countries, etc.

Aim

Schmolck et al. (2002) wanted to investigate the relationship between damage to the lateral temporal cortex and performance on semantic tests. They also wanted to find out if there were any peculiarities in the test performance of HM compared to other patients.

Design

The design of the study included the following variables and samples:

Variables

  • Independent variables: the location of lesions (brain regions damaged usually due to injury or disease) found in the brain.
  • Dependent variables: scores on 13 tests of semantic memory.

This study was a natural experiment. The naturally occurring IV was the patients’ brain lesions.

Sample

  • Six patients participated in the study: two patients with hippocampal damage, three with large lesions of the medial temporal lobe and different lesions of the lateral temporal cortex (MTL+), and the patient HM, who had mainly medial temporal lobe damage. The researchers used brain scans (MRI and CT) to determine which areas of the brain were damaged.
  • Eight controls.

Procedure

Participants were presented with nine tests on three to five occasions. Seven tests were from the Semantic Test Battery (Hodges et al., 1992a). In addition, the researchers developed two tests of their own. The tests were all based on line drawings of 24 animals and 24 objects and their names. The animals and objects could be classified into eight categories, e.g., land animals and aquatic creatures.

The researchers gave the participants nine tests:

  1. Pointing to a picture (cue-name): Researchers told the participants the names of all the animals/objects and asked them to point out the correct picture from a choice of eight pictures in the same category (e.g., eight water creature pictures).
  2. Pointing to a picture (cue-description): the researchers told participants the names of all the animals/objects. They asked them to point to the correct picture from a selection of eight pictures in the same category (e.g., eight pictures of aquatic animals).
  3. Naming (cue-picture): the researchers showed participants pictures of all the animals/objects and asked them to name the animals.
  4. Naming (cue-description): researchers verbally described all animals/objects to participants and asked them to name the animals.
  5. Semantic features: participants had to answer eight yes/no questions about all the animals/objects, e.g., ‘Is a toaster round?’.
  6. Category fluency: participants had to name as many examples from the eight categories (e.g., animals, birds, household objects, musical instruments) as they could.
  7. Category sorting: this test consisted of two parts. First, participants had to categorise all the pictures as ‘living’ or ‘man-made’. Then they had to sort the 24 animals and 24 objects into eight categories.
  8. Naming definitions: the researchers gave participants the names of the 24 least common items and asked them to define the items as if they were explaining them to someone who had never seen the items. One minute was allotted for each definition.
  9. Definitions to picture: the researchers showed participants pictures of the 24 least common items and asked them to define them. One minute was allotted for each definition.

Four additional tests were performed. Researchers have previously used these tests to examine semantic knowledge in patients with semantic dementia or Alzheimer’s disease.The four additional tests were:

  1. Object/non-object discrimination task: participants saw 30 line drawings of real objects and 30 line drawings of non-objects (composed of parts of real objects). They had to say whether the object shown was real or not.
  2. Colouring object task: Participants had to colour 28 line drawings of objects. The colours had to be appropriate (e.g., grass should be coloured green).
  3. Pyramids and palm trees test: researchers showed participants 52 cards. Each card contained a target picture and two test pictures. Participants had to match which test picture matched the target picture.

    For example, one card contained the target picture of a saddle with two test pictures of a horse and a goat. The participant had to select whether the horse or the goat matched the saddle. The word version of this test consisted of words on cards instead of pictures.

  4. Nouns and verbs test: the researchers showed participants two sentences and asked them to fill in the blank in the second sentence.
    For example, ‘The hoof is hard. In fact, most ___ are hard.’ They had to find 64 irregular and 64 regular past tense forms and 16 regular and 16 irregular plurals.

The study used a repeated-measures design to measure the cognitive test scores.

Most test scores were calculated as the percentage of participants who were correct. For tests eight and nine, which required descriptions, the researchers used a 0–4 scoring method. To assess the reliability of the scoring method, the researchers brought in 14 raters to see if they could identify which tasks were described in test number eight.

Findings

Schmolck et al. (2002) found that:

  • The hippocampus patients performed similarly to the control group.
  • The three MTL+ patients were mildly to moderately impaired on almost all tests.
  • HM performed better than the MTL+ group, but not other patients damaged only in the hippocampus.
  • There was a correlation between test performance and the extent of damage to the lateral temporal cortex.

Conclusions

The results suggest impairments in semantic knowledge are related to damage to the lateral temporal cortex. This finding suggests different parts of the brain are responsible for semantic and episodic long-term memory.

Evaluation of Schmolck et al. (2002)

Let us now evaluate the strengths and weaknesses of the Schmolck et al. (2002) study.

Strengths

The strengths of the research are:

  • High reliability.

    • The researchers used 14 raters to score the transcribed data. Reliability can be assumed if the raters have similar scores.

    • The procedure of the study is standardised and therefore easy to repeat.

  • Application: semantic memory in psychology and theories of semantic theory.

    • The research can show how the damage of specific brain regions leads to the impairment of semantic knowledge.

  • The study used a matched-pairs design, so it is more certain that the differences in performance are due to the brain lesions and not to other variables such as age.

Weaknesses

The weaknesses of the research are:

  • Generalisability – the research used a small sample, so it is difficult to generalise the results. Therefore, we can argue that the results lack external validity.

  • Potential ethical issues since the patients have brain damage, there is a question of whether they can give proper informed consent.

  • Low ecological validity as researchers did the study in a lab setting, it could have influenced the participant’s behaviour, causing validity issues.

Semantic Knowledge in Patient HM - Key takeaways

  • Schmolk et al. (2002) investigated which brain area is responsible for semantic long-term memory.
  • They conducted the study in eight healthy control subjects and six patients who had damage to the hippocampus, medial temporal lobe, and lateral temporal cortex.
  • The study tested semantic knowledge using the Semantic Test Battery and four other tests to assess dementia.
  • The MTL+ group was mildly to moderately impaired on almost all tests.
  • HM performed better than the MTL+ group but not better than other patients who had been damaged only in the hippocampus.

Frequently Asked Questions about Semantic Knowledge in Patient HM

When a person has damage in the temporal lobe, they may have impairments with long-term semantic memory.

Damage to the lateral temporal cortex can affect semantic memory.

Episodic memory is generated in the medial temporal lobe.

Patients with bilateral medial temporal lobe lesions may have difficulties remembering episodic memories. 

People who have medial temporal lobe damage may have memory impairment issues. These issues include difficulties remembering episodic memories.

Final Semantic Knowledge in Patient HM Quiz

Question

What does bilateral mean?

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Answer

Front side of the brain.

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Question

What type of memories was Schmolck et al. (2002) investigating?

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Answer

Hippocampus memories.

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Question

Which of the following variables Schmolck et al. (2002) investigated is the dependent variable?

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Answer

Scores on the semantic LTM tests Schmolck et al. created.

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Question

Which of the following variables Schmolck et al. (2002) investigated is the independent variable? 

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Answer

Scores on the semantic LTM tests Schmolck et al. created.

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Question

What is a lesion? 

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Answer

Lesions are brain regions damaged usually due to injury or disease.

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Question

What is semantic memory?

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Answer

Semantic memories are long-term memories that do not stem from personal experiences, i.e., facts and knowledge we acquire.

Show question

Question

Which of the following does not describe the procedure used in Schmolck et al. (2002)?

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Answer

Natural experiment.

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Question

Why did Schmolck et al. (2002) use MRIs?

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Answer

MRI scans were used to ensure that the damaged brain regions were only related to the ones the researchers were interested in. 

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Question

What are the strengths of the study?

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Answer

The strengths of the study are:

  • High reliability.
  • High internal validity.
  • It has practical applications, such as helping us understand more about semantic theories.

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Question

What are the weaknesses of the study?

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Answer

The weaknesses of the study are:

  • Low generalisability.
  • Potentially could have breached ethical issues.
  • Low ecological validity.

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Question

Which statements do not match how patient HM performed?

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Answer

Worse than the MTL+ group.

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Question

What was the correlation found between mistakes made in tests and brain damage?

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Answer

A positive correlation was found between mistakes made and the amount of brain damage the participants had.

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Question

What type of tests did Schmolck et al. (2002) use?

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Answer

Self-constructed.

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Question

How did patients with damage near the hippocampus do in the semantic knowledge tests? 

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Answer

Patients with damage near the hippocampus normally performed on the semantic knowledge tests.

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Question

What did Schmolck et al. conclude?

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Answer

The findings indicate impairments in semantic knowledge are related to damage to the lateral temporal cortex. This finding implies different brain parts are responsible for semantic and episodic long-term memory.

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