The comprehension of anaphoric relations may be guided not only by discourse, but also syntactic information. In the literature on online processing, however, the focus has been on audible pronouns and descriptions whose reference is resolved mainly on the former. This paper examines one relation that both lacks overt exponence, and relies almost exclusively on syntax for its resolution: adjunct control, or the dependency between the null subject of a non-finite adjunct and its antecedent in sentences such as
A speaker of (1) can use both
(1) | Mickey Mouse talked to Minnie Mouse before he ate. |
To understand this use of the name
Much work in psycholinguistics has therefore been directed at the online processing of pronouns and other anaphoric expressions, since its study promises to illuminate the mechanisms by which disparate information sources are integrated in language comprehension (
Seminal work by Arnold et al. (
However, such studies target only one specific type of anaphoric dependency, in which the cue to anaphora is an audible noun phrase, and its resolution is guided mainly by properties of the discourse—like what its topic is (
(2) | Mickey Mouse talked to Minnie Mouse before eating. |
A speaker can use (2) just like (1), to say that Mickey talked to Minnie before he, Mickey, ate. But now the process of understanding the speaker is different in two important ways. First, understanding that it was Mickey who ate depends on different sorts of information in the two cases. For (2) but not (1) the sentence itself determines the interpretation, due to its structure and meaning.
(3) | Mickey Mouse talked to Minnie Mouse before eating was forbidden. |
Determining whether these differences in understanding synonymous uses of (1) versus (2) impact the timing of reference resolution is an important step toward understanding which aspects of processing anaphora are fully general, and which are instead specific to the kind of anaphoric dependency involved—for example, whether the referential expression is audible or inaudible, and whether its resolution is guided mainly by discourse or syntax.
In contrast to pronouns, there has been relatively little work on the timing of the resolution of control structure anaphora. And the majority of what we do know comes from studies of complement control as in (4), rather than adjunct control (5).
(4) | a. | Mickeyi managed [___i to eat]. |
b. | Mickeyi promised Minnie [___i to eat]. | |
c. | Mickey persuaded Minniei [___i to eat]. |
(5) | Mickeyi talked to Minnie [before ___i eating]. |
Studies on complement control (e.g.
This paper compares the processing of audible pronouns and the implicit anaphora in adjunct control structures to examine the speed with which structural information can be used in reference resolution. In two experiments, we use visual-word eyetracking to measure the timecourse of reference resolution in sentences such as (6).
(6) | Mickeyi ran into Daisyj in front of the school… | |
a. | …[before ___i picking up a blue ball]. | |
b. | …[before hei picked up a blue ball]. |
There are several differences between anaphora involving overt pronouns and adjunct control that might cause the processing and interpretation of the null subject in adjunct control structures to proceed relatively slowly, but there are also reasons to expect it to happen quickly. In what follows, we outline the reasons for both expectations.
As was already mentioned, one might expect the processing of adjunct control to proceed slowly because control structures have no overt morpheme dedicated to reference in their subject position, in contrast to when there is an overt pronoun. Instead, the first indication that a referent is needed is given indirectly by the non-finite morphology (
(7) | a. | Mickey talked to Minnie before eating pizza at the park… |
b. | … was forbidden. |
It has been demonstrated, though, that listeners often do not wait for disambiguating information before building a preferred parse (e.g.
But even if at the non-finite verb listeners immediately assume a control dependency is present, using structural information to retrieve a referent from memory may still be more difficult than using the morphological and discourse information relevant for overt pronouns. In cue-based retrieval models of sentence processing (e.g.
Another reason anaphora resolution in adjunct control may be fast is that words like
Our results show that when adjunct control structures are highly frequent within the experiment, listeners are just as quick to resolve reference when they hear the non-finite verb in a sentence such as (6a) as they are when they hear the overt pronoun in a sentence like (6b). This suggests that the large differences between the two forms of anaphora—that one is implicit and relies mainly on structural information and the other is explicit and relies on mostly morphological and discourse information—are in at least some contexts irrelevant to the timing of anaphora resolution. When adjunct control structures are less frequent within the experiment, however, anaphora resolution in adjunct control slows in comparison to overt pronouns. We argue that this is not due to greater difficulty in using structural information, but rather to difficulty in identifying the presence of a control dependency.
In a design similar to that of Arnold et al. (
Both (6a) and (6b) involve coreference with the main clause subject. Pronouns are often biased to corefer with a prior subject rather than with an object (e.g.
Thirty participants (20 female, 9 male, 1 declined response) were recruited at the University of Maryland. Participants were all native speakers of American English, and were at least 18 years of age (mean age = 22.5). Each received $10 for their time. Three additional participants were excluded, two for low accuracy on comprehension questions (less than 80%), and one for equipment failure.
Participants listened to auditory descriptions of illustrated scenes, and were asked to indicate whether the description matched the scene. The scenes involved two main participants selected out of a set of four well-known characters: Mickey and Minnie Mouse, and Donald and Daisy Duck. The auditory stimuli were composed of two sentences: an initial sentence to focus attention on one of the two characters, and a second sentence describing the content of the picture. The second sentence began with a main clause predicate, with the two characters as arguments (the subject and the object/indirect object). This was followed by a prepositional phrase describing the third element of the image in order to draw attention away from the two characters immediately before the critical region. The description concluded with a temporal adjunct headed by
Sample stimuli.
Condition | Preamble |
---|---|
Focussubj | Look there’s Minnie! She was talking to Mickey in front of a huge tree after |
Focusobj | Look there’s Mickey! Minnie was talking to him in front of a huge tree after |
PRO | |
pronsubj | |
pronobj |
In a 2 × 3 design, stimuli varied with respect to which character was the attentional focus of the first sentence of the preamble (the subject or the object of the main clause), and with respect to the referential expression used as the subject of the temporal adjunct. Because the preference for pronouns to co-refer with the subject of a preceding clause can be reduced if attention is placed on another character at the beginning of the discourse (
Auditory stimuli were recorded in a sound-attenuated room by a male speaker of American English. Each stimulus set was recorded in parts, with each part in a carrier phrase, as in (8). After normalizing for intensity, the two recordings were spliced together at the point indicated by the vertical bar. This was done in order to minimize potentially confounding differences in the acoustics of the stimuli before the critical word. The splice point immediately preceded the non-finite verb in the PRO conditions, and the pronoun otherwise, so that there would be no coarticulatory clues about the content of the upcoming critical word. After splicing, the stimuli were filtered to remove noise. All recording and processing of the auditory stimuli was done in Praat (
(8) | a. | Look there’s Mickey! Minnie was talking to him in front of a huge tree after | Tom left. |
b. | Tom left after | putting on a nice new bow, and they seem to be having a good time. |
Visual stimuli consisted of scenes containing two characters located in the bottom right and bottom left corners of the picture, equally distant from the center and of roughly equal size. The stimuli were counterbalanced with respect to which two characters were seen together and which character appeared on the left or right side of the screen. The pictures also contained a third prominent, inanimate element that was placed at the top center. A sample image is given in Figure
Sample visual stimulus and regions of interest.
Thirty sets of stimuli were distributed across six lists using a Latin square design. Each participant saw 30 critical trials—5 from each condition. For all of the critical items, the auditory description matched the scene depicted. Twenty fillers were also included in each list, for a total of 50 items. The fillers were similar in form to the critical items, and contained an equal number of PRO, pronsubj, and pronobj sentences. The only difference was that the filler stimuli contained discrepancies between the picture and the auditory description of it; the location of the discrepancy varied across filler items to include all parts of the auditory description (in both the preamble and the adjunct), and could involve any of the mentioned objects or characters; for a small number of fillers, detection of the discrepancy depended on successful reference resolution in the adjunct.
Eye movements were recorded using an EyeLink 1000 tower-mounted eyetracker (S.R. Research, Mississauga, Ontario, Canada), interfaced with a PC, with a sampling rate of 1000 Hz. Visual stimuli were displayed on a 23-in. LCD monitor, approximately 104 cm away from where participants were seated. Viewing was binocular, but only the right eye was recorded. Auditory stimuli were presented at a comfortable volume using speakers situated next to the monitor.
The experiment was implemented using the Experiment Builder software (S.R. Research,
Each participant was presented with the items from one of the six lists. The order of experimental and filler items within that list was randomized for each participant.
Eye movements were analyzed using the
To determine whether participants looked to the target character after the onset of the critical word, we compared looks to the target or competitor in the critical window for each condition. The proportion of looks to each character at each time point is plotted in Figure
Experiment 1: Proportion of looks to the character corresponding to the target (orange) or competitor (blue) for the PRO (left), pronsubj (middle), and pronobj (right) conditions when either the subject character (top) or object character (bottom) was given focus.
Although traditional analyses comparing the total proportion of looks or time spent looking at the target or competitor (e.g.
Experiment 1: Proportion of trials where participants switched from their initial fixation region across conditions, either toward the target (dotted line) or away from it (solid line).
If participants have successfully resolved reference, then they should be quicker to switch
Experiment 1: Average time of first switch of looking region during critical window. Error bars represent standard error of the mean.
Experiment 1: Main results.
Factor | ||
---|---|---|
Switch type | 92.73 | |
Cue | 1.87 | 0.15 |
Focus | 12.15 | |
Switch type × Cue | 3.94 | |
Switch type × Focus | 2.34 | 0.13 |
Switch type × Cue × Focus | 0.99 | 0.41 |
The main effect of switch type was due to faster switches toward the target than away from it (estimated difference = 342 ms, SE = 25.8). The main effect of focus was the result of faster switches generally when focus was on the subject compared to when it was on the object (estimated difference = 87.2 ms, SE = 25.2), but since focus did not interact with whether switches were toward or away from the target, this effect is taken to be orthogonal to reference resolution and will not be discussed further.
Table
Experiment 1: Pairwise follow-up comparisons.
Comparison | Estimate | SE | |||
---|---|---|---|---|---|
Switch toward target – away from target by Cue | |||||
PRO | –235 | 42.4 | –5.55 | ||
Pronsubj | –393 | 45.6 | –8.63 | ||
Pronobj | –396 | 45.1 | –8.78 | ||
PRO – Pronsubj by switch type | |||||
Toward target | 32.16 | 32.8 | 0.98 | 0.59 | |
Away from target | –125.91 | 52.0 | –2.42 | 1.36 | |
PRO – Pronobj by switch type | |||||
Toward target | 27.67 | 32.9 | 0.84 | 0.68 | |
Away from target | –133.13 | 51.7 | –2.58 | 1.43 | |
Pronsubject – Pronobj by switch type | |||||
Toward target | –4.48 | 32.0 | –0.14 | 0.99 | |
Away from target | –7.22 | 55.1 | –0.13 | 0.99 |
Regardless of cue, switch times were faster toward the target than away from it; there was no difference between cues in switch times toward the target, but looks away from the target appear to have happened earlier in the PRO condition than for the pronoun conditions. However, although the differences pass a significance threshold of
Experiment 1 investigated the process of reference resolution for the null (PRO) subject of non-finite temporal adjuncts in comparison to overt pronouns. For PRO in the adjuncts used here, reference is determined based on structural features of the sentence. For overt pronouns, on the other hand, reference resolution is influenced by discourse factors, guided by the morphological features of the pronoun; structural features are only important insofar as they affect information structure.
Our results indicate that upon encountering a non-finite verb in a temporal adjunct, listeners are just as quick to look toward PRO’s referent as they do an overt pronoun’s. Participants may have looked away from the target sooner when interpreting PRO than they did with pronouns, but the evidence only weakly supports such a difference. If we infer that consistent looks to the correct character indicate successful reference resolution, then these results suggest that the interpretation of PRO in adjunct control is just as fast as the interpretation of a pronoun, at least in some instances.
The interpretation of PRO in our items required participants to recognize and interpret the non-finite verb, realize that it required a subject, and find a referent for that subject based on their knowledge of the adjunct control dependency. Where present, this dependency requires the use of structural information about the adjunct and its host sentence; PRO’s referent is tied to that of the closest structurally-accessible antecedent (
This fast interpretation of the null subject is also somewhat surprising considering how different a cue to reference resolution a non-finite verb is in comparison to an overt pronoun in terms of semantics and morphology. On top of those differences, the duration of the non-finite verb in the PRO condition was twice as long as the duration of the overt pronouns in the other conditions, with an average of 314 ms vs. 153 ms, meaning that even if participants were able to use either structural or morphological information just as quickly to search for a referent, the bottom-up cue to anaphora simply was not heard as quickly in the PRO condition as in the pronoun conditions, especially considering that the part of the verb that indicates a control dependency, the
There are at least two additional factors beyond the bottom-up input of the non-finite verb that could have contributed to early resolution of PRO. First, participants may have been predicting upcoming reference to the main clause subject, making it easier to resolve control dependencies satisfying such predictions. Second, in addition to or instead of predicting upcoming reference to the subject character, participants may have been making structural predictions such that they assumed a control dependency would be needed. Either of these types of prediction could in turn have two different sources: individual item contexts, or the high frequency of coreference with the subject and of control structures within the experiment. If participants were actively predicting a control structure or reference to the subject character, either based on individual items or on frequency-based expectations, then the speed of looks to the correct character in the PRO condition would not necessarily reflect the speed of bottom-up interpretation of PRO. Instead, interpretation of PRO upon encountering a non-finite verb in an adjunct clause may actually take longer than resolution of an overt pronoun, but the difference may not have been seen if participants began that process early in the PRO condition based on prediction.
The effect on reference resolution of prediction about who is likely to be mentioned next is well known (e.g.
In addition to item-based predictions, it may have been the case that the experimental context had a large enough proportion of either control structures or of initial reference to the subject character in the adjunct that participants began making relevant structural or referential predictions within the experiment. Two-thirds of our items required participants to look at the subject at the critical word, since that was the case for both the PRO and the pronsubj conditions. However, if a subject bias were strongly contributing to the speed of interpretation of the null subject, then we would expect the PRO and pronsubj conditions to both be faster than the pronobj condition. This was not the case; participants were just as fast to look at the correct character in both pronoun conditions. In the pronobj condition, this could not have been due to a subject preference. However, it could have been the case that participants were using different strategies for pronouns than for PRO. Even if a preference to look at the subject character did not influence looks in the pronoun conditions (perhaps because of the unambiguous gender information), that does not rule out the possibility that participants relied on such a preference in the PRO condition without actually resolving reference. And although control structures were found in only a third of the items participants saw, this is still more frequent than these structures are seen in real life.
In order to test whether looks in PRO items were influenced by high predictability of reference to the subject character or of control structures, or by a learned strategy within the experiment, we fit a linear mixed effects regression on the PRO items measuring the influence on first switch times of switch type, focus, order within the experiment, cloze probability of reference to the subject character, and cloze probability of PRO (i.e. of a control structure), as well as interactions between these factors that included switch type, with random intercepts for participants. Order within the experiment and the two cloze measures were coded as a scaled, centered, continuous variables over items, based on when each item was seen by each participant and on responses to corresponding items in the offline cloze task. Significant results of this model are given in Table
Experiment 1, PRO analysis: Significant results.
Factor | ||
---|---|---|
Switch type | 24.45 | |
Focus | 5.80 | |
Switch × Clozesubj. ref. | 3.06 | 0.08 |
Besides the main effects of switch type and focus (which were also seen in the main analysis above), these results do not indicate that switch times were affected by experiment order or by cloze probability of a control structure. The only possible new effect revealed is a marginal interaction between switch type and cloze probability of reference to the subject character, illustrated in Figure
Experiment 1, PRO items: Residualized time of first switch of looking region during critical window based on cloze probability of reference to the subject character and switch type. Each point represents a single observation. Regression lines represent the estimated effect of cloze of subject reference. Shading indicates the standard error of the estimated slope.
If the interpretation of PRO were affected by the likelihood of referring to the subject character in the adjunct, then a similar effect would be expected to be evident in the pronsubj items, since the target character is the same for both conditions. As a comparison to the PRO items, we performed the same analysis as above for the pronsubj condition, testing the effects of order, cloze of reference to the subject character, and cloze of a control structure on switch times toward or away from the target character. Significant effects in this regression are given in Table
Experiment 1, pronsubj analysis: Significant results.
Factor | ||
---|---|---|
Switch type | 60.24 | |
Switch × Clozesubj. ref. | 12.20 | |
Switch × Focus × Clozesubj. ref. | 5.84 | |
Switch × Order × Clozesubj. ref. × ClozePRO | 4.51 |
Follow-ups to the interactions between switch type and cloze of subject reference, and between those factors and focus indicate that higher cloze of reference to the subject character led to longer fixations on the target when focus was on the subject (
Experiment 1, pronsubj items: Residualized time of first switch of looking region during critical window based on focus, cloze probability of reference to the subject character, and switch type. Each point represents a single observation. Regression lines represent the estimated effect of cloze of subject reference. Shading indicates the standard error of the estimated slope.
The interpretation of PRO in this experiment was surprisingly fast. If rather than just relying on bottom-up information to identify and resolve the necessary dependency, participants were predicting an upcoming control structure or reference to the subject character, then this fast interpretation could be explained. However, the results of the exploratory analysis show little effect of such prediction. There was no effect of item-wise predictability of a control structure in the PRO condition, suggesting that participants’ looks were not being driven by structural predictions. There was also no effect of order within the experiment, suggesting that participants did not develop strategies over the course of the experiment to aid in their resolution of PRO. Higher predictability of reference to the subject character did lead to numerically longer looks at the target in the PRO condition, but this effect was small and statistically non-significant.
In contrast to PRO, reference resolution in the pronsubj condition was strongly affected by prediction. When focus was on the subject character, participants were much more likely to look longer at the target the more predictable reference to it was. This suggests that interpretation of an overt pronoun in this experiment was highly sensitive to participants’ referential predictions, at least when initial focus was placed on that character. This strong effect, in contrast to the lack of an effect in the PRO condition, further suggests that the fast interpretation of PRO was not due to referential predictions. When focus was on the object character, higher predictability of subject reference was associated with faster looks toward the target in the pronsubj condition. This again suggests an effect of referential prediction, but since participants were also numerically faster to look away from the target, this may have just been a trend toward faster switches overall. We take this result to mean that focusing on the object made participants less likely to rely on strong predictions about reference to the subject character. The fact that they were still more likely to look toward the target than away from it meant that they were successfully using the morphological information on the pronoun to resolve reference, regardless of predictions made.
A surprising result in the pronsubj analyses was that the cloze probability of a control structure played a role, interacting with predictability of subject reference and experiment order. The interaction indicated that early on in the experiment, participants were faster to look toward the target when both subject reference and a control structure were predictable. Why would prediction of a control structure affect interpretation of overt pronouns, but not the interpretation of PRO? Perhaps the speed-up in looks toward the target was due to multiple different factors all indicating reference to the subject character, including item-based prediction of subject reference, prediction of a control structure (which also generally entails reference to the subject character), the easily-accessible morphological information from the pronoun, in addition to the high proportion of items with subject reference in the adjunct. Perhaps for PRO, structural information from the control dependency was not as easy to access, and so early looks toward the target were not affected, despite possible structural or referential predictions. As to why this effect was only seen early in the experiment in the pronsubj items, participants may have stopped using item-based structural predictions, if they learned due to the high proportion of items with a control dependency within the experiment that item-based structural predictions were unnecessary.
From these results, it appears that the resolution of PRO based on structural information provided by the control dependency was as fast or nearly as fast as the resolution of an overt pronoun. But if looks in the pronsubj condition were influenced by referential and/or structural predictions, why weren’t the PRO items? If we are correct that looks toward the target were not influenced by predictability in the PRO condition because structural information was more difficult to access, then why weren’t switch times toward the target slower for PRO versus overt pronouns? And why were looks away from the target not affected by referential predictions for PRO the way they were for overt pronouns? One possibility is that the high proportion of items with control structures in Experiment 1 led participants to expect control structures generally, independent of individual item contexts. We attempted to test this by including experiment order in our exploratory linear regression and found no effect in the PRO condition. However, a linear order effect would only be seen if the strategy participants adopted affected looks linearly over time. It is possible that participants were affected by the within-experiment frequency of PRO so quickly that it did not show up as a linear effect, but rather as an effect over the whole experiment. We test this possibility in Experiment 2.
Experiment 2 included all the items from Experiment 1, in addition to extra fillers designed to reduce the overall proportion of control structures and the within-experiment bias to refer to the subject character. Although these changes do not affect the predictability of reference to a single character or of control structures for any individual item, since the same critical items were used in both experiments, they do change the overall biases within the experiment, which in turn may affect participants’ interpretive strategies.
Thirty participants (19 female, 11 male) were recruited at the University of Maryland. Participants were all native speakers of English, and were at least 18 years of age (mean age = 21). Twenty-nine of the participants were compensated with course credit, and one with $5. Two additional participants were excluded for high trackloss (>33%).
All stimuli from Experiment 1 were included. In addition to the 20 fillers from Experiment 1, 40 new filler items were added. These consisted of 10 items similar to the original fillers, but all with a pronoun coreferring with the main clause object as the subject of the temporal adjunct, in order to reduce the overall proportion of items with subject reference in the adjunct. The remaining 30 new fillers had a subject in the adjunct referring to something or someone other than the two main characters (e.g.
Stimuli were presented in nine blocks of 10 items each. The procedure followed that of Experiment 1 in all other respects.
Twenty-seven trials were excluded for high trackloss (greater than 25%), resulting in a loss of 3% of the data. The mean trackloss per trial in the remaining data was 3.5%.
Looks to the target or competitor beginning at the onset of the critical word in each condition are plotted in Figure
Experiment 2: Proportion of looks to the character corresponding to the target (orange) or competitor (blue) for the PRO (left), pronsubj (middle), and pronobj (right) conditions when either the subject character (top) or object character (bottom) was given focus.
Experiment 2: Proportion of trials where participants switched from their initial fixation region across conditions, either toward the target (dotted line) or away from it (solid line).
Mean switch times by condition based on whether that switch was toward or away from the target are given in Figure
Experiment 2: Average time of first switch of looking region during critical window. Error bars represent standard error of the mean.
Experiment 2: Main results.
Factor | ||
---|---|---|
Switch type | 50.93 | |
Cue | 0.91 | 0.40 |
Focus | 0.90 | 0.34 |
Switch type × Cue | 4.47 | |
Switch type × Focus | 2.34 | 0.13 |
Switch type × Cue × Focus | 0.42 | 0.79 |
Experiment 2: Pairwise follow-up comparisons.
Comparison | Estimate | SE | |||
---|---|---|---|---|---|
Switch toward target – away from target by Cue | |||||
PRO | –119 | 44.4 | –2.69 | 2.29 | |
Pronsubj | –364 | 43.6 | –8.35 | ||
Pronobj | –214 | 44.6 | –4.79 | ||
PRO – Pronsubj by switch type | |||||
Toward target | 81.8 | 33.4 | 2.45 | ||
Away from target | –162.6 | 51.3 | –3.17 | ||
PRO – Pronobj by switch type | |||||
Toward target | 31.5 | 32.8 | 0.96 | 0.60 | |
Away from target | –63.0 | 52.7 | –1.20 | 0.46 | |
Pronsubject – Pronobj by switch type | |||||
Toward target | –50.3 | 33.2 | –1.52 | 0.28 | 0.50 |
Away from target | 99.6 | 52.0 | 1.92 | 0.13 | 0.45 |
As with Experiment 1, two other linear mixed-effects models tested whether looks in the PRO and pronsubj conditions were affected by the cloze probability of reference to the subject character or of a control structure, or by trial order within the experiment. Including random effects in the pronsubj model led to non-convergence due to singular fit; therefore, for this analysis only, a general linear regression without random effects was used. Significant results are given in Table
Experiment 2, PRO analysis: Significant results.
Factor | ||
---|---|---|
Switch type | 4.34 | |
Switch × Focus × Clozesubj. ref. × ClozePRO | 3.30 |
Experiment 2, pronsubj analysis: Significant results.
Factor | ||
---|---|---|
Switch type | 71.07 | |
Switch × Order × Clozesubj. ref. | 3.10 |
In PRO items, there was a significant four-way interaction between switch type, focus, and the two cloze measures. This interaction was driven by the object focus condition, in which the effect of cloze probability of subject reference on switch times away from the target was significant when the cloze of PRO was high (
Experiment 2, PRO, focusobj items: Residualized time of first switch of looking region during critical window, based on cloze probability of reference to the subject character, cloze probability of PRO, and switch type. Each point represents a single observation, with darker points indicating higher cloze of PRO. Regression lines represent the estimated effect of cloze of subject reference across three values of the cloze of PRO: the mean (dashed line), and one standard deviation above (solid line) or below (dotted line) the mean. Shading indicates the standard error of the estimated slope.
In pronsubj items, there was a significant three-way interaction between switch type, order, and cloze probability of subject reference. Follow-up analysis revealed that there was a significant effect of order on switches away from the target when cloze of subject reference was high (
Experiment 2, pronsubj items: Residualized time of first switch of looking region during critical window based on trial order, cloze probability of reference to the subject character, and switch type. Each point represents a single observation, with darker points indicating higher cloze of subject reference. Regression lines represent the estimated effect of order across three values of the cloze of subject reference: the mean (dashed line), and one standard deviation above (solid line) or below (dotted line) the mean. Shading indicates the standard error of the estimated slope.
In Experiment 1, PRO appeared to be interpreted just as fast as overt pronouns. We hypothesized that this was in part due to the high proportion of control structures and/or of items that contain elements in the adjunct clause that make reference to the character named by the main-clause subject; participants may have adjusted quickly to these within-experiment frequencies and begun to predict PRO and resolve its reference earlier than would normally be possible. If that were the case, then we would expect reference resolution to be slower in Experiment 2, in which the within-experiment frequency of both control structures and subject reference was reduced. This prediction was confirmed. In Experiment 2, participants were both slower to look toward the target and faster to look away from it in the PRO condition than in the pronsubj condition. Switch times in the pronobj condition were between the other two, with no significant difference between the pronobj condition and either of the others. The fact that reference resolution in the pronobj condition may have been somewhat more difficult than in the pronsubj condition could be due a lingering subject preference for the pronouns. Importantly, despite this possible preference, the PRO condition, which also included reference to the subject character, was still more difficult than the pronsubj condition.
This result strongly suggests that in Experiment 1, the interpretation of PRO was indeed influenced by the high within-experiment frequency of a control structure. In Experiment 2, participants could no longer depend on the high frequency of control structures to predict the presence of PRO, and instead had to rely more on bottom-up input. The fact that reference resolution slowed in comparison to overt pronouns could be due to more difficulty either in using structural information as opposed to morphological/gender information to resolve reference, or simply in recognizing that a referential dependency was necessary, since the bottom-up cue to anaphora was longer in duration for the PRO versus pronoun conditions.
Additionally, although the difference in switch times toward or away from the target in the PRO condition still reached significance, the Bayes factor analysis indicates only weak evidence for that difference, as compared to both pronoun conditions, in which there is extreme evidence for faster looks toward the target than away from it. The exploratory analyses of the PRO items indicate that the small difference that was present was due to both structural and referential predictions. When focus was on the object, participants looked longer at the target only if reference to the subject character was predicted
Turning to the exploratory analyses of the pronsubj items, in Experiment 1, looks away from the target were affected by the cloze probability of reference to the subject character when the focus was on that character. Experiment 2 saw a similar effect, in that participants looked longer at the target the more predictable reference to the subject was, but only later on in the experiment. This may be due to the lower proportion of items in Experiment 2 with reference to the subject character. Participants could not use within-experiment frequency expectations, but did rely more on referential predictions as the experiment went on.
The pronsubj condition of Experiment 1 also saw an effect of the cloze probability of a control structure in an interaction with other measures. We hypothesized that participants were faster to look toward the target when multiple factors all led to a prediction of subject reference, including the high proportion of items in the experiment with subject reference. When in Experiment 2 this proportion decreased, the effect of item-wise prediction of a control structure disappeared. If it had any effect, it was too small to detect without all the other factors involved.
The experiments reported here provide evidence for the rapid interpretation of PRO in temporal adjuncts, modulated by the predictability of reference to PRO’s antecedent as well as by how likely a structure containing PRO was to occur. Our results show that participants can use the structural information inherent in the control dependency to resolve PRO just as quickly as they can use gender information to resolve an overt pronoun, but only when a structure containing PRO is predicted. The strongest effect of such prediction in these experiments was due to the high within-experiment frequency of such structures seen in Experiment 1. A a weaker effect was also seen with a lower within-experiment frequency of PRO in Experiment 2 based on predictions arising from individual item contexts. When neither factor led to prediction of PRO, its interpretation slowed significantly.
There are two main tasks a listener faces in interpreting referential expressions: recognition and resolution. Listeners must recognize that a speaker is attempting to refer to someone, and they must also use the information available—from the discourse context, structural and morphological features of the speaker’s utterance, etc.—to decide who that someone is, i.e. to resolve reference. The slowdown in the interpretation of PRO seen in Experiment 2, especially for items where PRO or reference to the character corresponding to the main clause subject was not predicted, could in principle be due to difficulties in either of these tasks.
First, the interpretation of PRO may be slowed due to difficulties in using structural information versus morphological/discourse information in reference resolution. However, a large body of literature has argued that structural constraints can apply at the earliest stages of processing for reflexives such as
The other possible explanation for the slow interpretation of PRO when it is not predicted is that it simply took listeners longer to recognize that reference resolution was necessary. This seems likely for a number of reasons. First, the bottom-up cue that a referential dependency is needed in the PRO sentences, namely the nonfinite verb, had a longer duration than
There are many different kinds of referential expressions and types of anaphora. Each may rely on syntactic, discourse, and conceptual sources of information in different ways. The interpretation of PRO in adjunct control structures is heavily dependent on structural features of the sentence, while pronouns, although restricted by their “
One additional note on the use of structural information as a cue to retrieval is necessary. Although Parker & Phillips (
Kush, Lidz & Phillips (
(9) | a. | Kathi didn’t think |
b. | Kathi didn’t think |
Kush, Lidz & Phillips argue that the pronoun triggers retrieval of an antecedent based in part on the cue ACCESSIBLE, which is only present on the memory chunk for
(10) | Kathi didn’t think |
Although this allows the structural information relevant to bound variable anaphora to be encoded in a content-addressable way, this approach cannot be directly applied to the resolution of PRO. The reason is that the antecedent to PRO need not be a quantificational phrase. Because of this, there is no reason that only c-commanding antecedents would remain accessible.
(11) | Mickeyi talked to Minniej before PROi/*j putting on a hat. |
If, however, a similar feature to Kush, Lidz & Phillips’s ACCESSIBLE were to represent syntactic accessibility for any NP, then the structural information relevant to adjunct control could be encoded. In (11), the chunk for
Regardless of whether the slowdown is due to difficulty in recognizing the referential dependency, as we have argued, or in its resolution, the results of these experiments make clear that when an adjunct control dependency is highly frequent, its resolution is just as easy as the resolution of overt pronouns.
This experiment also has implications for the role of prediction in the processing of anaphora. Effects of prediction in reference resolution have been well documented. For example, Kehler et al. (
(12) | a. | Jane hit Mary because she had stolen a tennis racket. |
b. | Jane angered Mary because she had stolen a tennis racket. |
(13) | Jane hit Mary because she reacts violently to criticism. |
The present experiments give evidence that not only conceptual predictions, but also predictions about the upcoming structure of a sentence may affect anaphora resolution. How quickly a listener can resolve the reference of the null subject of an adjunct control structure is impacted by how strongly that control structure was predicted. This is in line with the arguments of Kehler (
There were two sources for effects of prediction in the present experiments. In Experiment 1, participants seem to have been affected by the high frequency of control structures within the experiment, which may have led them to predict PRO more often then they otherwise would have. This is in line with a large body of research demonstrating that statistical learning within an experiment can increase reaction times and lead participants to make new predictions (see, e.g.
One remaining question is the extent to which these kinds of structural predictions influence reference resolution in real-world language use. The frequency effect seen in Experiment 1 is unlikely to be seen in every-day situations outside the lab, simply because adjunct control structures are generally less frequent than what was present in the experiment. In Experiment 2, individual item contexts appeared to favor prediction of control structures. But was that due to properties unique to these items or to the simple image and discourse context? Or are control structures predicted in similar sentences more generally? Although these experiments do not answer this question, it is clear that listeners
These experiments also add to a large body of literature demonstrating incremental parsing and interpretation in sentence processing (e.g.
(14) | a. | Mickey talked to Minnie before eating pizza at the park… |
b. | … was forbidden. |
The fact that participants assume a control structure when a continuation such as (14b) is possible is perhaps not surprising, however, since such continuations are likely less frequent. In addition, assuming a control structure rather than a structure where the non-finite verb is part of a gerundival subject may be preferred due to general processing strategies such as Minimal Attachment (
Additionally, however, a non-finite verb in a temporal adjunct could also be part of a non-obligatory control structure, in which the null subject may refer to an antecedent that is not syntactically represented, as in (15), although this is far less common (
(15) | The pizza tasted better [after drinking root beer]. |
Although non-obligatory control in temporal adjuncts is used infrequently compared to obligatory control structures, where PRO is syntactically bound, and although all of the examples in our experiment did require control by the main clause subject, it is still possible that participants in principle would wait to interpret the null subject until it was clearly necessary. But this was not the case; participants quickly looked to the character corresponding to the main clause subject upon hearing the non-finite verb, evidently establishing the anaphoric control dependency at the earliest possible indication that it might be necessary.
The results of these experiments have several other relevant implications. First, they call into question a previous claim that the interpretation of PRO in adjuncts involves a “most-recent filler strategy.” Based on the results of an eyetracking-while-reading study, Betancort, Carreiras & Acuña-Fariña (
Second, previous research on the processing of PRO (e.g.
Throughout this paper, we have remained neutral with respect to the theoretical representation of what we have been calling “PRO” and the control dependency, and theories differ with respect to how PRO is resolved. In some theories, obligatory control in adjuncts is nothing more than predication (
Finally, an additional area for future research would be to compare the processing of obligatory control structures such as those examined in this paper with the processing of non-obligatory control adjuncts. Participants were quick to assume that an anaphoric dependency was needed in these experiments. If participants automatically attempt to retrieve an antecedent to PRO upon encountering the non-finite verb, then in sentences like (15), where the intended referent of PRO is not in the sentence, participants may experience processing difficulty due to retrieval failure. Such a difficulty has been given as one possible explanation for why obligatory control is so much more prevalent than non-obligatory control in adjuncts (
This paper used visual-world eyetracking to investigate the processing of the null subject in adjunct control. It has shown that when adjunct control structures are predicted, the reference of the null subject can be resolved just as quickly as that of overt pronouns. Studying different forms of reference can shed light on how different sources of information are implemented during sentence processing, and this study contributes to this agenda by providing evidence that structural information can be immediately utilized in reference resolution, especially when aided by prediction of structures where such information is crucial.
This is only true when “Obligatory Control” is involved. See Landau (
This is not to say, necessarily, that that missing subject is present syntactically. A major question in the study of adjunct control concerns exactly what the adjunct control dependency is. For simplicity, we will assume the presence of a null subject, and use the “PRO” label for clarity. However, our results and conclusions are not dependent on a PRO analysis of the null subject of control structures, or on the presence of a syntactically-represented subject. For a discussion on the debate over the representation of PRO, see Hornstein (
A reviewer suggests the fact that the verb provides the theta role of the null subject may counteract this potential slowdown, since it provides conceptual information about the antecedent, and the plausibility of potential arguments has been shown to affect resolution of other, similar dependencies such as in filler-gap constructions (
A reviewer notes that fully interpreting the sentence still requires someone to do the eating, even if it is an arbitrary “anyone”. Even if that were to be true, though, this is crucially different from the anaphora we are describing, because it does not involve coreference with a previous expression.
In the Corpus of Contemporary American English (COCA) (
As discussed in §1, a non-finite verb in general is ambiguous in that it can be followed by continuations that do not require a control dependency, but such continuations were absent in these experiments.
A reviewer notes that since these fillers also included PRO or pronouns, they could in principle be analyzed with the critical items. The main reason they were not included was that in roughly half of the fillers, the discrepancy between the auditory stimulus and the visual scene occurred before the adjunct; for those items, participants could correctly answer that the scene and description did not match without having to resolve reference in the adjunct.
See Footnote 5.
A reviewer notes that the same is true for other instances of bound variable anaphora that do not involve quantificational antecedents, but that still require c-command (e.g. sloppy readings in ellipsis).
Whether obligatory control would be preferred under Minimal Attachment depends on which control theory is adopted. In the Two-tiered Theory of Control (
See also Jeffrey, Han & Pappas (
A reviewer notes that if the adjunct control dependency is processed similarly to predication or to filler-gap dependencies, then it may be fruitful to examine Gibson’s (
This research involved human subjects, and was approved by the University of Maryland IRB (approval 00972). All subjects gave written consent prior to participating.
Thank you to the audience at CLS 54 for helpful feedback, and to Jan Edwards and Marissa Barlaz for comments at various stages of this research.
This material is based upon work supported in part by the National Science Foundation under Grants No.1449815 and No.1749407.
The authors have no competing interests to declare.
JJG and MM designed the experiments with feedback from AW and EL. JJG and MM collected the data. JJG analyzed the data and wrote the paper. All four authors participated in editing and revising the manuscript.