Pickering & Barry (1991) #
@cite{pickering-barry-1991}
Sentence Processing without Empty Categories. Language and Cognitive Processes, 6(3), 229–259.
Core Thesis #
Processing of unbounded dependencies does not involve empty categories (traces). Fillers associate directly with their subcategorizing verbs — filler-verb association — without intermediary gap sites. Processing difficulty is determined by the nesting pattern of filler-verb associations:
- Nested (abba): must hold first filler while processing inner pairs → hard
- Disjoint (aabb): each pair completed before the next begins → easy
This single distinction correctly predicts processing difficulty across four sentence types (Table 2), where the trace-based account (requiring separate filler-gap and gap-verb association patterns) makes incorrect predictions for multiple pied-piping constructions.
Connection to CCG #
The gap-free account is made possible by CCG's forward composition (the B combinator), which allows partial constituents like S/NP for "John saw" without positing a gap after "saw." In the derivation of "Sue wonders whom John saw" (ex 84):
- John : NP type-raises to S/(S\NP) via T
- saw : (S\NP)/NP
- T(John) >B saw yields S/NP — a sentence missing an object
- whom : Q/(S/NP) combines with S/NP to form Q
No empty category is needed because composition creates the filler-verb
association directly. This is the subject_verb_composition theorem in
CCG.Combinators.
Sections #
- §1: Association patterns and the two competing analyses
- §2: The four sentence types with empirical difficulty
- §3: Table 2 — the gap-free classification and its processing predictions
- §4: Contrast with the trace-based analysis (Table 1)
- §5: Bridges to ProcessingProfile, CrossSerial, and CCG
Nesting pattern of associations in a sentence.
Two concurrent associations can be nested (abba: the second pair is enclosed within the first) or disjoint (aabb: each pair completed before the next begins).
This is the central formal object of @cite{pickering-barry-1991}.
- nested : NestingPattern
- disjoint : NestingPattern
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Under the gap-free account, there is only one type of association: filler-verb. Under the trace account, there are two: filler-gap and gap-verb.
The trace account must classify both patterns independently, while the gap-free account needs only one.
- gapFree : AnalysisType
- traceBased : AnalysisType
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Number of independent association types required by each analysis.
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The gap-free analysis is simpler: fewer association types to track.
The four sentence types classified in Tables 1 and 2 (p. 242, 246).
Each involves multiple extractions and exhibits characteristic processing difficulty that discriminates between the two analyses.
- engMultiSubjRel : SentenceType
"I saw the farmer who owned the dog which chased the cat." (ex 44) Subject extracted from each relative clause.
- engMultiObjRel : SentenceType
"The cat which the dog which the farmer owned chased fled." (ex 45) Object extracted from each relative clause (center-embedded).
- gerMultiSubjRel : SentenceType
"Der Bauer der das Mädchen das den Jungen küßte schlug ging." (ex 48) German: subject extracted, verb-final order creates nesting.
- engMultiPiedPiping : SentenceType
"John found the saucer on which Mary put the cup into which I poured the tea." (ex 42) Pied-piped PPs, successive relatives.
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Empirical processing difficulty for each sentence type.
Subject relatives and pied-piping are easy to extend with further relative clauses (exx 51, 54–55); object relatives and German subject relatives become rapidly incomprehensible (exx 52–53).
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Filler-verb association pattern under the gap-free analysis (Table 2).
This is the ONLY association type needed. The annotation scheme from p. 245:
- Subject relative (ex 56): [who]₁ [owned]₁ ... [which]₂ [chased]₂ → disjoint (1122)
- Object relative (ex 57): [which]₁ ... [which]₂ [owned]₂ [chased]₁ → nested (1221)
- German subj rel (ex 58): [der]₁ [das]₂ [küßte]₂ [schlug]₁ → nested (1221)
- Pied-piping (ex 59): [on which]₁ [put]₁ [into which]₂ [poured]₂ → disjoint (1122)
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Is the construction nested in Chomsky's (1965) sense?
Under the gap-free analysis (no empty categories), the definition simplifies: a construction is nested iff its filler-verb associations are nested. This collapse is the central result.
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- Phenomena.FillerGap.Studies.PickeringBarry1991.isNestedConstruction Phenomena.FillerGap.Studies.PickeringBarry1991.SentenceType.engMultiSubjRel = false
- Phenomena.FillerGap.Studies.PickeringBarry1991.isNestedConstruction Phenomena.FillerGap.Studies.PickeringBarry1991.SentenceType.engMultiObjRel = true
- Phenomena.FillerGap.Studies.PickeringBarry1991.isNestedConstruction Phenomena.FillerGap.Studies.PickeringBarry1991.SentenceType.gerMultiSubjRel = true
- Phenomena.FillerGap.Studies.PickeringBarry1991.isNestedConstruction Phenomena.FillerGap.Studies.PickeringBarry1991.SentenceType.engMultiPiedPiping = false
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Table 2 correspondence (p. 246): under the gap-free analysis, the filler-verb pattern directly determines construction nestedness.
Table 1 (trace-based) has three independent columns (filler-gap pattern, gap-verb pattern, construction type) with no systematic relationship. Table 2 collapses to two identical columns.
Gap-free processing prediction: nested filler-verb associations are hard, disjoint are easy.
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The gap-free analysis correctly predicts all four observations.
Filler-gap pattern under the trace-based analysis (Table 1).
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Gap-verb pattern under the trace-based analysis (Table 1).
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Trace-based prediction: a construction is hard if EITHER filler-gap or gap-verb associations are nested.
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The trace-based analysis incorrectly predicts pied-piping is hard. It has nested filler-gap AND nested gap-verb (Table 1), yet the construction is easy to process and easily extensible (exx 54–55).
The gap-free analysis correctly predicts pied-piping is easy — the critical case where it outperforms the trace-based account.
Table 1 has no systematic relationship between its three columns. The filler-gap pattern, gap-verb pattern, and construction type are all independent. German subject relatives are nested constructions with disjoint filler-gap associations — the columns disagree.
Bridge to ProcessingProfile #
Map nesting pattern to ProcessingProfile.
Nested associations require holding unfinished fillers in working memory while forming inner associations — higher locality (longer dependency span) and referential load (more intervening material to track).
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Nested associations are Pareto-harder than disjoint.
Processing ordering predictions verified via Pareto dominance.
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Bridge to CrossSerial dependencies #
German verb-final order produces nested filler-verb associations,
consistent with the nested dependency pattern in German verb clusters
(CrossSerial.german_3np_3v). Both German constructions — subject
relatives and verb clusters — exhibit nesting because the verb that
closes each dependency comes in reverse order.
@cite{bach-brown-marslen-wilson-1986} confirms the processing prediction: German nested constructions are hard, like their Dutch cross-serial counterparts (though for different structural reasons).
Bridge to CCG combinators #
The gap-free account requires a grammar that can establish filler-verb associations without positing gap positions. CCG achieves this via forward composition (B) and type-raising (T):
subject_verb_composition in CCG.Combinators proves:
B (T subj) verb obj = verb obj subj
This is exactly derivation (84) in the paper: "John saw" becomes
a constituent S/NP via rule (80a) (type-raising + composition), and
"whom" : Q/(S/NP) combines with S/NP to form Q — no trace needed. The variable-free semantics
(ccgVariableFree in CCG.Combinators) guarantees that all semantic
operations use combinators rather than bound variables, which is the
formal counterpart of "no empty categories."