Avoiding the Garden Path: Eye Movements in Context

1. Avoiding the Garden Path: Eye Movements in Context Gerry T. M. Altmann, Alan Garnham & Yvette Dennis Journal of Memory and Language 31, 685-712

2. Garden path theory vs. Incremental interactive theory • Garden Path theory: (Clifton & Ferreira 1989) • Initial processing: purely syntactic, context and other info affect reanalysis • Principles: Minimal attachment, Late Closure • Ambiguity resolution: favor the simpler structure • Incremental Interactive theory: (Altmann & Steedman 1988) • Initial processing: contexts influence the first pass analysis • Principles: referential hypothesis, principle of parsimony • Ambiguity resolution: whether a referent can be found in the felicitous context

3. Incremental interactive theory (Altmann & Steedman 1988) • Referential Hypothesis (The principle of referential support): An NP analysis which is referentially supported will be favored over one that is not The psychologist told the woman that he was having trouble with to visit him again. (relative-supporting context) A psychologist was counseling two women. He was worried about one of them but not about the other. • Principle of parsimony: A reading which carries fewer unsupported presuppositions will be favored over one that carries more Did you see the man who just walked past the window?

4. Garden path theory vs. Incremental interactive theory 1) The fireman told the woman that he had risked his life forto install a smoke detector. 2) The fireman told the woman that he had risked his life formany people in similar fires. • GP: (1) is always garden-pathed • Interactive: garden path could be reduced with referential context

5. Methodology Issues • Eye movement measures: • First pass reading times per character in a region • Total pass reading times per character in a region • The number of regressions out of a region • However… • Effects in second pass reading is not necessarily a first pass parsing effect. • Initial analysis process: first pass reading • Need appropriate measures to make comparisons across different experimental conditions

6. Goals of this study • Previous studies: no unambiguous control, no good referential contexts, lack of eye movement data to support the context effect • To test the referential hypothesis • Use eye movements to demonstrate the context effect • Provide an analysis that could reflect the initial process (regression contingent analysis)

7. Predictions of Context effect: S1) The fireman told the woman that he had risked his life forto install a smoke detector. (ambiguous relative) S2) The fireman told the woman that he had risked his life formany people in similar fires. (ambiguous complement) S3) The fireman asked the woman that he had risked his life for to install a smoke detector. (unambiguous control)

8. Experiment 1: method • Subject: 42 paid subjects • Apparatus: infrared limbus eye-tracking system, sampled every 5 ms • Material: 36 experimental + 34 filler passages, followed by comprehension questions, sentence by sentence presentation, 3 targets x 2 contexts, block design for context conditions (null & referential)

9. Limbus tracking • The limbus is the boundary between the white sclera and the dark iris of the eye. Due to the fact that the sclera is (normally) white and the iris is darker, this boundary can easily be optically detected and tracked. This technique is based on the position and shape of the limbus relative to the head, so either the head must be held quite still or the apparatus must be fixed to the user's head. • Due to the more or less occasional covering of the top and bottom of the limbus by the eyelids, "it is probably fair to regard limbus tracking as suitable for precise horizontal tracking only" (Scott & Findlay 1993). (From:http://www.diku.dk/~panic/eyegaze/node9.html)

10. Experiment 1: material

11. Experiment 1: possible material problems • Supporting context for complement clause? • Structural priming? • Only one verb ‘told’ is used for ambiguous stimuli, 4 verbs for unambiguous • Not clear about the null context or what’s the felicitous context for unambiguous sentences

12. Predictions of Exp 1

13. Experiment 1: Results (first pass reading time) That he had risked life for A smoke detector To install

14. Experiment 1: Discussion • Garden path effect in the null context • Unambiguous control has longer reading time in the ambiguous region  because use of a relative clause presupposes things, whereas complement clauses do not. Longer reading times in RC signals the violation of presuppositions. Context eliminates this processing complexity. • Evidence for subcategorization: if ignored, both null and referential context should have longer reading time in the ambiguous region. But no differences found in the referential context.

15. Experiment 1: Discussion • Context has different effects on different regions of the ambiguous relative. • Disambiguating region: slower reading times in the null context  no garden path in the felicitous context • Ambiguous region: slower reading times in the null context  complement is read more slowly in the null context, because under the felicitous context, complement clause repeats info contained in the context or it is easier to integrate new info.

16. Experiment 1: Results (first pass regression)

17. Experiment 1: Discussion • Regression data: • More likely to have regression out of the disambiguating region for the ambiguous relative than the unambiguous control. • The first pass reading time: garden path has been eliminated by the provision of referential context, the regression data: still some increased processing complexity for relatives. • Still garden pathed even with context, but it’s easier to recover (first pass reading time may not be a good garden path indicator) • If regression data indicates garden path in the referential context, then need explanations for why majority of cases (66%) do not have first pass regression out of the disambiguating region? • The discrepancy between the reading time and regression data suggests the regression data reflect a minority cases where people still garden pathed. The effect is overshadowed in the overall reading time.

18. Experiment 1: regression contingent analysis (absence of a regression)

19. Experiment 1: regression contingent analysis (prior to a regression)

20. Experiment 1: Discussion • Regression contingent analysis: • Referential context only eliminates a minority of garden paths. Garden path still occurs in the felicitous context. • Subjects are not concentrate enough, failed to build the correct representations, lose track of information… • Subjects may give one of the referents more prominence than the other

21. Experiment 2 • Whether people is biased to attend the referential contexts • All the procedure is the same as exp1, except the comprehension questions.

22. Experiment 2: Results (first pass reading for exp1 &2)

23. Experiment 2: Results (first pass reading)

24. Experiment 1&2: first pass reading comparison

25. Experiment 2: Results

26. Experiment 2: discussion • In exp 2, a residual difference in the disambiguating region between RC and unambiguous control was found. • Is this contributed by minority cases?

27. Experiment 2: Results (first pass without regression)

28. Experiment 2: Results (prior to regression)

29. Experiment 1&2: prior to regression comparison

30. Conclusion • Contexts help to avoid garden path in most of the cases. • Residual differences in reading times between the relative and the other two targets were due entirely to minority cases