Showing posts with label Reinhard Blutner. Show all posts
Showing posts with label Reinhard Blutner. Show all posts

Wednesday, April 18, 2012

Blutner: "Some Aspects of Optimality in Natural Language" (2000)

This paper by Reinhard Blutner is the one that introduced the idea of "bidirectional" optimality theory. Bidirectional optimality theory is bidirectional because it doesn't just optimize an input parse or an output expression, but does both at the same time. The whole speech situation thus defines a little game, and Blutner defines an equilibrium concept for such speaking/hearing games.

The Phenomenon in Focus

The observation that drives Blutner's idea is that non-standard forms tend to designate non-standard referents. So the straightforward formulation I killed him designates a stereotypical killing-event, while I caused him to die designates an atypical one (p. 9).

This can be explained economically if we assume that being ambiguous is more "costly" than being brief. Then the pairing (s, t')—i.e., unmarked sentence with marked meaning—is suboptimal because it makes the unmarked sentence ambiguous. It also makes sense information-theoretically, because you want to reserve the short sentences for the frequently occurring referents.

Blutner's Idea

It seems that Blutner wants to arrive at this conclusion, too, but from a different angle. Imagine that we still only have two signals and two interpretations, and we put them into a table like this:


tt'
s–m, –m –m, +m
s'+m, –m +m, +m

Here, being marked is taken to be bad, so we can imagine that people try to choose cells with as many occurrences of "–m" as possible. This means that the top left cell is the best one, corresponding to a pairing of unmarked form with unmarked meaning.

We accordingly take the whole first row and first column out of the game, since they have now been coupled with something. We are then left with a reduced subgame:


tt'
s–m, –m –m, +m
s'+m, –m +m, +m

In this subgame, both players have but a single option, so this obviously becomes optimal. We thus couple the marked form with the marked meaning, and we're done.

The same little game could of course be played with more signals and more meanings. We would then couple forms to meanings in increasing order of  markedness, until one of the sets had been exhausted. We could also play it with a single meaning and two forms, as his fury/furiosity example points out.

A More Formal Version of The Idea


In an attempt to capture the dynamics of this process, Blutner suggests the following definition (p. 11), here in a slightly reformulated version:
(s,t) is super-optimal if s is a candidate reading of t, and if
Q: There is no other pair (s',t) that satisfies I as well as u(s',t) ≥ u(s,t).
I: There is no other pair (s,t') that satisfies Q as well as u(s,t') ≥ u(s,t).
A different way of putting this is to translate it into an update procedure:

Let a table of numbers be given.

Randomly write crosses in some cells and nothing in others. This is your start configuration.

Then repeat the following loop:

    For each cell c:

        Find the set of competitors; these are the cells that
        are in the same row or the same column as c and are
        marked with a cross in the current configuration.

        If the number in c is larger than the number in all
        of these competing cells, give it a cross in the
        following configuration.

    If the last configuration is equal to the next, halt.

I realize this is not as romantic as a circular definition, but it is easier to apply. For instance, let's imagine we're starting with the following table:
 
897
321
564

If we start with a completely empty start configuration (no crosses in any cells), then we can apply the procedure 6 times before we arrive at the following configuration of crosses:


×


×
×


At this point, we have indeed reached a fixed point: No crossed cell can out-compete another crossed cell. Note that this is achieved by having the characteristic one-to-one mapping between forms and meanings.

Thursday, April 12, 2012

Hendriks, de Hoop, and de Swart in Journal of Logic, Language, and Information (2012)

In their brief introduction to a special issue on game theory and bidirectional game theory, Petra Hendriks, Helen de Hoop, and Henriëtte de Swart discuss the parallels between the two frameworks and their limits.

Handy References

The text contains the following references on bidirectional optimality theory:
In addition, they cite the following paper as pointing out "the connection between bidirectional Optimality Theory and Game Theory" (p. 2):

A Theoretical Point

Besides the general introduction of the field and the players, the three authors point to a possible theoretical shortcoming of both bidirectional optimality theory and game theory.

The problem they point out is that "these frameworks generally predict a one-to-one pairing of forms and meanings," which is not empirically true (p. 2). They illustrate this with the Dutch question Wie heeft Frank vermoord?, which is ambiguous between Who did Frank kill? and Who killed Frank?

More specifically, they note that while it is true that "marked forms go with marked meanings," the reverse is not: "unmarked forms can often be used to express unmarked as well as marked meanings" (p. 3). This claim is supported by a reference to a paper in Lingua, but I don't know exactly what the example they have in mind is.

A Note On That Point

Just on the face of it, there doesn't seem to be anything wrong, from the standpoint of microeconomics, with the many-to-many relation, but it does require a slightly more sophisticated model of the "cost" of an utterance. Consider for instance:
  • He is dead (+m) = "He is dead" (+m)
  • He is gone (–m) = "He is dead" (+m)
  • He is dead (+m) = *"He is gone" (–m)
  • He is gone (–m) = "He is gone" (–m)
I haven't done the math here, but this might be explained by pragmatic effects under the right assumptions: If all messages are equally cheap, then we should indeed expect a one-to-one correspondence to emerge; however, since one of the meanings is taboo, it will tend to increase the cost of whatever message gravitates towards it. This might sustain the incentive to use analogical references instead of direct (unambiguous) references.