Common Ground

1
Common Ground

• Linguistic referents are established w/in a
  domain of interpretation, which includes
  context
• One component of context Common Ground
• Mutual knowledge, beliefs, assumptions among
  participants in conversation
• Comes from community co-membership, physical
  co-presence, linguistic co-presence,

2
Conversation Common Ground

• Clark (1996)
• Language Joint action by people cooperating to
  achieve particular goals
• Optimal communication requires keeping track of
  whats in Common Ground and using that in both
  producing and understanding language
• As usual, whats at issue is timing
• How quickly do/can language users make use of
  knowledge about Common Ground when speaking
  listening?

3
Keysar Colleagues (1996, 2000)

• In several studies, find that listeners
  immediate interpretations are egocentric
• i.e., Dont take into account which knowledge
  they share with speaker vs which knowledge only
  they have
• Monitor eye movements to visual display
  containing referents for items mentioned in
  speech
• Speaker (confederate) gives listener spoken
  instructions to move objects in display
• Some objects visible to both (Common Ground)
• Some objects visible only to listener (Privileged
  Ground)
• Listeners just as likely to look at Privileged
  objects as at Common objects, if they match
  instructions best

4
Problem with Keysars Studies

• Very best physical match for instruction object
  in Privileged Ground
• Put the bottom block below the apple.
• When bottom-most block in listeners display is
  visible only to listener
• Listeners just as likely to look at the
  bottom-most block in their display as to look at
  the block that they know is bottom-most in the
  speakers display
• Better to make the object in Common Ground just
  as good a match for the instructions as the
  object in Privileged Ground is

5
Another Potential Problem

• Common Ground is typically accumulated and
  adjusted incrementally over the course of
  conversation
• In Keysars studies, listeners simply instructed
  about what was visible to whom
• Better to use an explicit grounding process with
  common ground established on the basis of
  linguistic co-presence

6
Hanna et al. (2003) Experiment 1

• Participants
• 12 Listeners (L) Confederate Speaker (S) pairs
• Listener told that Speaker was lab assistant but
  naïve about purpose of study (false)
• Apparatus Head-mounted eyetracker
• Eye camera tracks pupil using infrared light
• Scene camera shows line of sight, so head can
  move still know where eyes are looking
• Spatial resolution 1 degree
• Temporal resolution 33.33 msec
• Sampling rate 30 frames/sec

7
Experiment 1 Procedure

• Materials (more on next slide)
• Boxes containing 3 x 3 grid of locations
• For each trial, 7 objects each for S L
• 5 are to be placed in the grid by L according to
  Ss instructions
• S and L dont see each others grids or objects
• Instructions
• On each trial, get envelope with 7 objects
  printed instructions
• Ss instructions show layout of objects for trial
  script of instructions to give Listener
• Ls instructions include which of the objects is
  secret
• ( Privileged Ground) where to put it in
  grid
• L knows S doesnt know what shape is secret or
  where it is (true)

8
Visual Display Stimuli

• Target Red triangle
• Competitor Other triangle
• - Same or diff color from Target
• S Secret Shape, seen by Listener only
• Competitor or some other shape
• When Competitor Secret, its in Privileged
  Ground
• - Will they look at it as much as they do to a
  Competitor thats in Common Ground???

Critical ( last) instruction from Speaker
9

• Same color competitor in Common Ground
• - L has to ask for clarification in this cond
• Same color competitor in Privileged Ground
• Fewer looks to Competitor in Privileged Ground by
  400 msec after onset of Adj
• - Very similar to diff color conds

10
Hanna et al. (2002) Expt 2

• Possible criticism of Expt 1 ( other expts w/
  similar design)
• By design, Confederate Speaker doesnt know about
  Privileged Ground objects so never mentions
  them
• Maybe Listeners move their eyes to objects that
  are more likely to be mentioned by Speaker
• Rather than taking Speakers perspective into
  account while interpreting referring expressions?
• Solution Give Speaker Listener different
  information about the state of some objects

11
Stimulus Displays Descriptions

• Listener given 2 pairs of objects of same type
• 2 jars, 2 martini glasses,
• Objects described aloud by Exptr, left to right
• Sometimes objects described inaccurately
• 2 empty jars, when there is only 1 empty jar
  2 empty martini glasses
• Listener told will be mistakes sometimes but not
  to talk with Speaker to correct them
• Told theres another condition in Expt where
  Listeners get to make corrections

12
Instructions Displays

• Display properties disambiguate instruction Early
  or Late
• Pick up the empty martini glass
• Late 1 empty version of both types
  of objects
• Early 1 empty version of 1 type of object 2
  empty versions of other type of object
• Disambiguates early because definite the empty
  can have a unique ref only if only 1 of objects
  of a type is empty

13
Definite vs Indefinite Displays Instructions
Pick up the empty martini glass.
vs Pick up one of the empty martini glasses.
Late
Late
Mismatch Speaker told this But Listener
sees this
Early
Early
14
Design Logic

• Listeners told to remember how objects were
  described to Speaker to do what they think the
  Speaker intends them to do
• In Mismatch conditions, which type of object is
  the referent is disambiguated Early
• But its a different object type for Speaker
  Listener
• Instruction Pick up the empty martini glass
• Speaker believes Only 1 empty martini glass 2
  empty jars
• Listener sees 2 empty martini glasses only 1
  empty jar
• Questions
• Will Listener look at glass she knows Speaker
  thinks empty?
• If yes, how soon, compared to Early Late Match
  conditions?

15
Results
Late
Early
Mismatch
16
Conclusions

• Listeners look at target faster when instructions
  pick out a unique referent earlier
• the empty when only 1 pair of objects has only
  1 empty version
• Listeners can quickly take Speakers perspective
  into account
• Look at target faster in Mismatch than in Late
  conditions
• From Speakers perspective, instruction picks out
  a unique referent early
• From Listeners perspective, picks out other
  object type
• But not as fast as in Early conditions
• So theres some effort in taking Speakers
  perspective
• No evidence here for an initial egocentric stage