Schlotterbeck & Wang (2023): An incremental RSA model for adjective ordering preferences #
This file formalizes the paper's fully incremental Rational Speech Act model (Table 1) and the
qualitative predictions it draws from it for the order of two prenominal adjectives. The
incremental literal listener (l0) interprets a word sequence from the noun outward, each word
against the support of the distribution the later words left, so a context-dependent meaning such
as the k%-semantics of a dimension adjective (kPercent) can resolve differently in the two
orders. The incremental sequence speaker produces the words left to right, scoring each prefix by
its utility for the referent and each word by a language model (seqSpeaker); the global speaker
scores whole sequences, and the incremental utterance speaker is a softmax over the sequence
speaker with an utterance prior.
The paper's theoretical result is the listener-level sanity check: at a context-independent
semantics the incremental listener is the one-shot literal listener at the product meaning,
because Bayesian updates compose, so it cannot distinguish word orders (l0_perm), and the
global speaker is then indifferent between them. The speaker-level prediction, the effect of
discriminatory strength, comes from the language model that produces either adjective first and
then the other: with an order-blind listener the sequence speaker's preference between the two
orders is its preference between their first words, and at a uniform prior and Boolean meanings
the more informative first word is the one true of fewer referents
(seqSpeaker_real_lt_of_card_lt). The k%-semantics witnesses that the listener does distinguish
orders once meanings depend on the comparison class (l0_big_blue_ne).
Implementation notes #
- Meanings are graded and bounded by one; the comparison class is a finset of referents, and
the support of a distribution is the finset of referents it gives positive mass. Sequences are
surface-order lists with the noun-adjacent word last, and the speakers over sequences of a
fixed length are weight kernels on
Fin n → U. - The paper leaves the cost function unspecified; here the cost factor
exp (−β c)depends on the sequence length alone, which covers per-word costs and cost zero, and the rationalityβis free rather than pinned to the paper's one. - With the noise floor
ε > 0of the paper's color semantics no color word empties the support, so in the paper's simulations every later word is interpreted against the whole display; the order-sensitivity witness uses a sharp color meaning. The perceptual blur of the size distribution manipulation is not modeled.
References #
Meanings and the language model #
A Boolean semantics, as graded meanings.
Equations
- SchlotterbeckWang2023.sharp ext u C = (↑(ext u C)).indicator 1
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The sequentially intersective update of a Boolean semantics builds the extension of a sequence from the noun outward.
Equations
- SchlotterbeckWang2023.extSeq ext [] = Finset.univ
- SchlotterbeckWang2023.extSeq ext (u :: us) = SchlotterbeckWang2023.extSeq ext us ∩ ext u (SchlotterbeckWang2023.extSeq ext us)
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The paper's language model puts either adjective first, with equal probability, then the other.
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- SchlotterbeckWang2023.alternation a b [] x✝ = if x✝ = a ∨ x✝ = b then 2⁻¹ else 0
- SchlotterbeckWang2023.alternation a b [u'] x✝ = if u' = a ∧ x✝ = b ∨ u' = b ∧ x✝ = a then 1 else 0
- SchlotterbeckWang2023.alternation a b x✝¹ x✝ = 0
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The support of a distribution over referents, the comparison class the next word is interpreted against.
Equations
- SchlotterbeckWang2023.supp ν = {r : R | ν {r} ≠ 0}
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The incremental listener (rows 1–2) #
The incremental literal listener of rows (1)–(2) reads a word sequence in surface order, the noun-adjacent word last. That word is interpreted first, against the prior's support, and each earlier word against the support of the distribution the later words left.
Equations
- One or more equations did not get rendered due to their size.
- SchlotterbeckWang2023.l0 μ sem [] = μ
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Utilities and sequence weights (rows 4–5 and 7) #
The utility of row (7) scores the sequence us for the referent r at rationality β,
with cost n the cost factor exp (−β c) of an n-word sequence.
Equations
- SchlotterbeckWang2023.utility μ sem β cost us r = (SchlotterbeckWang2023.l0 μ sem us) {r} ^ β * cost us.length
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Unrolling rows (4)–(5), the weight of producing us word by word scores each prefix by its
utility and each word by the language model's probability given the words before it.
Equations
- SchlotterbeckWang2023.seqWeight μ sem β cost pLang r us = ∏ i : Fin us.length, SchlotterbeckWang2023.utility μ sem β cost (List.take (↑i + 1) us) r * pLang (List.take (↑i) us) us[i]
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Two adjectives #
Under the paper's language model the sequence speaker's order preference compares the utilities accumulated along the two production paths.
With an order-blind listener, the sequence speaker's preference between the two orders is its preference between their first words, the discriminatory strength of the first word.
At a positive rationality the first-word utility comparison is the listener comparison.
Order-blind listeners #
At a context-independent semantics the incremental listener is the one-shot literal listener at the product meaning, since Bayesian updates compose.
A context-independent semantics cannot distinguish word orders, the paper's sanity check.
At a uniform prior and a Boolean semantics the incremental listener is uniform on the sequentially intersected extension.
At a uniform prior and Boolean meanings, of two words true of the referent the one true of fewer referents is the more informative first word.
The speaker kernels (rows 3–6) #
The incremental sequence speaker of rows (4)–(5) chooses among sequences of length n.
Equations
- SchlotterbeckWang2023.seqSpeaker μ sem β cost pLang n = ProbabilityTheory.Kernel.ofWeights fun (r : R) (v : Fin n → U) => SchlotterbeckWang2023.seqWeight μ sem β cost pLang r (List.ofFn v)
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The global speaker of row (3) chooses among sequences of length n with utterance
prior P.
Equations
- SchlotterbeckWang2023.globalSpeaker μ sem β cost P = ProbabilityTheory.Kernel.ofWeights fun (r : R) (v : Fin n → U) => SchlotterbeckWang2023.utility μ sem β cost (List.ofFn v) r * P v
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The incremental utterance speaker of row (6) is a softmax at rationality α over the
sequence speaker with utterance prior P.
Equations
- One or more equations did not get rendered due to their size.
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An order preference of the sequence speaker is a weight comparison; normalization cancels.
A global speaker (row (3)) cannot prefer an order the listener cannot distinguish.
The order preference of the utterance speaker (row (6)) is the sequence speaker's, weighed against the utterance prior.
At a uniform prior, sharp context-independent meanings and the paper's language model, the sequence speaker prefers first the adjective true of fewer referents, the relevance effect.
The k%-semantics (3a) distinguishes the orders #
Under the k%-semantics (3a) of a dimension adjective against the comparison class C, an
object is big when its size exceeds the maximum of C less k% of the range of C.
Equations
- SchlotterbeckWang2023.kPercent k size C = {x : R | ∃ (hC : C.Nonempty), 100 * C.sup' hC size < 100 * size x + k * (C.sup' hC size - C.inf' hC size)}
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Equations
- SchlotterbeckWang2023.instDecidableEqSticker x✝ y✝ = if h : x✝.ctorIdx = y✝.ctorIdx then isTrue ⋯ else isFalse ⋯
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- One or more equations did not get rendered due to their size.
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A sticker's size.
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The two adjectives of the paper's stimuli.
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Equations
- SchlotterbeckWang2023.instDecidableEqAdj x✝ y✝ = if h : x✝.ctorIdx = y✝.ctorIdx then isTrue ⋯ else isFalse ⋯
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- One or more equations did not get rendered due to their size.
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big by the 50%-semantics of the paper's simulations, and blue sharply.
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Big blue and blue big resolve differently, since big interpreted against the blue stickers admits the second-largest one, which it excludes against the whole display.