Discourse Comprehension
- The Problem
- Narratives
- A Computational Analysis of Narrative Comprehension
- A Top-Down Approach
- A Bottom-Up Approach
- Inferences
- Discourse Comprehension and the Brain
The Problem
- (1) Danny wanted to have the red bike (2) that he saw in the window of the neighborhood
bike shop. (3) Danny knew that first he had to have $50 (4) to buy the bike. (5) He asked
his parents if they would give him the money. (6) His parents denied his request. (7) They
suggested that Danny earn the money himself (8) by getting a job. (9) Danny was mad at his
parents (10) for not giving him the money, (11) but he was determined to get the $50
somehow. (12) He knew that he would have to find a job, (13) so he called the newspaper
(14) and asked for a paper route. (15) He started delivering papers in his neighborhood
the next week (16) and earned $10 a week. (17) With this job, (18) Danny had $50 within a
few weeks. (19) He took his hard-earned money to the shop, (20) bought the bike, (21) and
happily rode home.
The Problem
- A typical text describes many states and events.
- Those states and events are richly interconnected.
- Given the architecture of the HIP system, how do we discover all of the connections?
Two events must be in STM simultaneously for us to perceive the connection between
them.
STM can only hold one sentence plus a little more.
Retrieval from LTM is too slow for a reader to search his or her representation of the
entire discourse after each sentence.
Narratives
- Narratives Include:
A Protagonist
A Complication that Leads to a Goal
A Series of Problem Solving Episodes
An Outcome
- Narratives are the most thoroughly researched genre of discourse.
- The coherence of a narrative is provided primarily by causal and enabling relations.
- Other types of discourse include logical, rhetorical, set-theoretic, spatial, and other
types of relations.
A Computational Analysis of Narrative Comprehension
- What information is available?
A sequence of states and events.
- What is the goal of the computation?
A richly interconnected network of states and events.
- What strategy is used to achieve the goal with the available information?
Schema theory offers a top-down strategy.
Van Dijk & Kintsch (1983) offer a bottom-up strategy.
A Top-Down Approach
- The War of the Ghosts
- Schemata (Bartlett, 1932)
- Story Grammars
- Scripts
- Problems with Schemata
The War of the Ghosts
- One night two young men from Egulac went down to the river to hunt for seals, and while
they were there it became foggy and calm. Then they heard war-cries, and they thought:
"Maybe this is a war-party". They escaped to the shore, and hid behind a log.
Now canoes came up, and they heard the noise of paddles, and saw one canoe coming up to
them. There were five men in the canoe, and they said: "What do you think? We wish to
take you along. We are going up the river to make war on the people." One of the
young men said: "I have no arrows." "Arrows are in the canoe", they
said. "I will not go along. I might be killed. My relatives do not know where I have
gone. But you", he said, turning to the other, "may go with them." So one
of the young men went, but the other returned home. And the warriors went up the river to
a town on the other side of Kalama. The people came down to the water, and they began to
fight, and many were killed. But presently the young man heard one of the warriors say:
"Quick,let us go home: that indian has been hit". Now he thought: "Oh, they
are ghosts." He did not feel sick, but they said he had been shot. So the canoes went
back to Egulac, and the and young man went ashore to his house, and made a fire. And he
told everybody and said: "Behold I accompanied the ghosts, and we sent to fight. Many
of our fellows were killed, and many of those who attacked us were killed. They said I was
hit, and I did not feel sick". He told it all, and then he became quiet. When the sun
rose he fell down. Something black came out of his mouth. His face became contorted. The
people jumped up and cried. He was dead.
Schemata (Bartlett, 1932)
- Bartlett studied memory for the Native American folktale "The War of the
Ghosts".
- He observed:
Sharpening: Some details are remembered extremely well.
Rationalizing: Some details are altered in the direction of cultural expectations.
Omissions: Some information is recalled very poorly.
- Bartlett argued that each of us develops culturally specific expectations about the
parts of a story and the relationships among those parts.
- These expectations form a knowledge structure called a schema.
- Schemata explain sharpening, rationalizing and omissions.
Story Grammars
- The Dog Story
- Mandler & Johnson’s (1977) Story Grammar
- An Analysis of the Dog Story
- The Comprehension Process
- Experiments on Story Grammars
The Dog Story
- (1) It happened that a dog got a piece of meat (2) and was carrying it home in his
mouth. (3) Now on his way home he had to cross a plank lying across a stream. (4) As he
crossed he looked down (5) and saw his own shadow reflected in the water beneath. (6)
Thinking it was another dog with another piece of meat, (7) he made up his mind to have it
also. (8) So he made a snap at the shadow, (9) but as he opened his mouth the piece of
meat fell out, (19) dropped into the water, (11) and was never seen again.
Mandler & Johnson’s (1977) Story Grammar
- FABLE --> STORY AND MORAL
- STORY --> SETTING AND EVENT STRUCTURE
- SETTING --> {STATE* (AND EVENT*) \ EVENT*}
- STATE* --> STATE ((AND STATE)n)
- EVENT* --> EVENT (({AND \ THEN \ CAUSE} EVENT)n) ((AND STATE)n)
- EVENT STRUCTURE --> EPISODE ((THEN EPISODE)n)
- EPISODE --> BEGINNING CAUSE DEVELOPMENT CAUSE ENDING
- BEGINNING --> {EVENT* \ EPISODE}
- DEVELOPMENT --> {SIMPLE REACTION CAUSE ACTION \ COMPLEX REACTION CAUSE GOAL PATH}
- SIMPLE REACTION --> INTERNAL EVENT ((CAUSE INTERNAL EVENT)n)
- ACTION --> EVENT
- COMPLEX REACTION --> SIMPLE REACTION CAUSE GOAL
- GOAL --> INTERNAL STATE
- GOAL PATH --> {ATTEMPT CAUSE OUTCOME \ GOAL PATH (CAUSE GOAL PATH)n)
- ATTEMPT --> EVENT*
- OUTCOME --> {EVENT* \ EPISODE}
- ENDING --> {EVENT* (AND EMPHASIS) \ EMPHASIS \ EPISODE}
- EMPHASIS --> STATE
An Analysis of the Dog Story
The Comprehension Process
- The story grammar is a set of rewrite rules.
- It is also a set of expectations about the parts of a story and the relationships among
those parts.
- Comprehension is a process of matching clauses in the story with terminal nodes in the
story grammar.
- Comprehension is a top-down process guided by the story grammar.
- Story grammars reduce the load on STM.
- The story grammar provides the appropriate connections between states and events in the
story.
Experiments on Story Grammars
Levels Effects
High level states and events are recalled better than low level states and events
(Thorndyke, 1977).
They are also more likely to be included in a summary (Rumelhart, 1977).
Effects of State/Event Type on Free Recall
Settings = Beginnings > Outcomes = Attempts > Endings = Reactions (Mandler &
Johnson, 1977)
Scripts
- What is a script?
- The Restaurant Script
- Script-Based Understanding
- Experiments on Scripts
What is a script?
- A script is a schema for simple stereotyped events like riding a bus, going to the
dentist, or getting ready in the morning.
- Each script includes information about the elements of the activity and the
relationships among those elements.
- The elements include props, roles, entry conditions, results, states and events.
- The states and events are organized into scenes.
- The relationships among script elements are primarily temporal, enabling and causal.
- Scripts include slots that need to be filled.
- Some slots have default values.
The Restaurant Script
- Name: Restaurant
- Roles: Customer, Owner, Waiter, Cook, Cashier
- Props: Menu, Food, Bill, Money, Tip
- Entry Conditions: Customer Hungry, Customer has Money
- Results: Customer has Less Money, Owner has More Money, Customer is Not Hungry
- Scene1_Entering: Customer Enters Restaurant, Customer Looks for Table, Customer Decides
Where to Sit, Customer Goes to Table, Customer Sits Down
- Scene2_Ordering: Customer Picks Up Menu, Customer Looks at Menu, Customer Decides on
Food, Customer Signals Waitress, Waitress Comes to Table, Customer Orders Food, Waitress
Goes to Cook, Waitress Gives Food Order to Cook, Cook Prepares Food
- Scene3_Eating: Cook Gives Food to Waitress, Waitress Brings Food to Customer, Customer
Eats Food
- Scene4_Exiting: Waitress Writes Bill, Waitress Goes Over to Customer, Waitress Gives
Bill to Customer, Customer Gives Tip to Waitress, Customer Goes to Cashier, Customer Gives
Money to Cashier, Customer Leaves Restaurant
Script-Based Understanding
- Texts describing script-based situations are understood by
recognizing the appropriate script
then inserting information from the text into the script’s slots.
- Script-based understanding is mostly top-down.
- Scripts reduce the load on STM.
- Script encode the relationships among events.
- The script’s default values allow us to make inferences.
Experiments on Scripts
- Reordering in Free Recall (Bower, Black & Turner, 1979)
- Intrusions in Free Recall (Bower, Black & Turner, 1979)
- The Script-Pointer-Plus-Tag Hypothesis (Graesser, Gordon & Sawyer, 1979)
People are very good at discriminating between unexpected events that occurred in a
story and those that did not.
They are very poor at discriminating between expected events that occurred and those
that did not.
This suggests that memory consists of a script-pointer plus tag.
Problems with Schemata
- Where do they come from?
- How do we know which script to use?
- Are people as rigid as schemata (especially scripts) suggest?
- Are all situations stereotypical?
A Bottom-Up Approach
- The Van Dijk & Kintsch (1983) Model
- VDK Applied to Narratives
- The Current State Strategy
- Evidence for the Current State Strategy
- The Need for Reinstatement Searches
- The Minimalist-Constructivist Debate
The Van Dijk & Kintsch (1983) Model
- Processing Cycles
- The Given-New Strategy
- The STM Buffer
After each sentence is processed, the "most important" state or event is held
in STM for reprocessing.
When the state or event in STM is related to the given information in the following
sentence, processing proceeds smoothly.
- Reinstatement Searches
- Selection Strategies
What does "most important" mean?
VDK Applied to Narratives
- The Goals of Narrative Comprehension
Each state and event is understood by finding its causes and consequences.
The narrative as a whole is understood by finding a causal path that links its opening
to its final outcome.
- An appropriate selection strategy should maximize our ability to achieve these goals
while minimizing the need for reinstatement searches.
The Current State Strategy
Evidence for the Current State Strategy
- Free Recall (Fletcher & Bloom, 1988)
Time in STM: (1 - (1 - p)k)
Links Possible versus Links Allowed
- Reading Time (Bloom, et al., 1990)
Reading times are slower for sentences that include a coherence break.
This is taken as evidence for reinstatement searches.
- Probe RT (Fletcher, Hummel & Marsolek, 1990)
Instructions
- Read each sentence as it appears.
- When a probe word appears (in capital letters and surrounded on each side by asterisks)
say YES or NO as quickly as possible.
- Say YES if the word occurred earlier in the story.
- Otherwise, say NO.
Probe RT (Fletcher, Hummel & Marsolek, 1990)
- Materials
Critical Sentence: "As she was mixing the batter, her sister came home and told
Kate that the oven was broken."
Antecedent: "Her sister had tried to use the oven earlier and discovered that it
would not heat up."
Consequence: "Since she had the cake batter all ready she thought that she would
use the neighbors’ oven."
- Participants verify that they have seen "told" in the story more quickly and
more accurately in the Antecedent version of the story.
The Need for Reinstatement Searches
The Minimalist-Constructivist Debate
- Coherence Breaks
Reading Time
Priming
- Motivational Links
- The Minimalist Position
Readers are lazy!
- The Constructivist Position
Readers are active problem solvers!
- Middle Ground?
Inferences
- Discourse Comprehension = Inference Making
- Types of Inferences
Connecting, Elaborations and Associations
Backward, Forward and Orthogonal
- The Construction-Integration Model (Kintsch, 1988)
The Construction Process
Integration
Discourse Comprehension and the Brain
- Right Hemisphere Syndrome
- A Divided Visual Field Study of Inference Making (Beeman, et al., 1994)
The left hemisphere shows greater associative priming, but the right hemisphere shows
greater summation priming.
FOOT + CRY + GLASS --> CUT
- The Electrophysiology of Inference Making
An Ambiguous Text (Bransford & Johnson, 1972)
- The procedure is really quite simple. First you arrange things into different groups
depending on their makeup. Of course, one pile may be sufficient depending on how much
there is to do. If you have to go somewhere else due to lack of facilities that is the
next step, otherwise you are pretty well set. It is important not to overdo any particular
endeavor. That is, it is better to do too few things at once than too many. In the short
run this may not seem important, but complications from doing too many can easily arise. A
mistake can be expensive as well. The manipulation of the appropriate mechanisms should be
self-explanatory, and we need not dwell on it here. At first the whole procedure will seem
complicated. Soon, however, it will become just another facet of life. It is difficult to
foresee any end to the necessity for this task in the immediate future, but then one can
never tell.
The Electrophysiology of Inference Making
- The Bransford & Johnson text is easier to recall if you know in advance that it is
about doing laundry.
- Without the title, it is difficult to infer the appropriate connections between the
events described by the text.
- St. George, Mannes & Hoffman (1994) found that words in this discourse produce a
stronger N400 when the title is not available.
The End!
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