The relationship between working memory (WM) and sentence comprehension (SC) has drawn many researchers’ attention. The current study examined whether healthy older adults have difficulty comprehending potentially WM-demanding garden-path sentences involving syntactic ambiguities, and whether their comprehension is predicted by their working memory capacity or inhibitory control.
Older adults (n=35, ages 60–89) and younger adults (n=36, ages 19–33) completed two self-paced reading experiments and a battery of cognitive measures (working memory and inhibition tasks). Participants read the sentences containing a Minimal Attachment (MA) ambiguity in Experiment 1 and a Late Closure (LC) ambiguity in Experiment 2.
The older adults’ garden-path effect was larger than younger adults’ in on-line measures. However, older adults exhibited higher off-line acceptability judgments for garden-path sentences than younger adults, for both LC and MA sentences. Working memory predicted off-line performance of both younger and older groups in Experiment 2 (LC).
The results showed age-related differences in the comprehension of sentences with temporary syntactic ambiguities. Successful recovery from garden paths (revealed by off-line measures) was predicted by working memory. However, the source of age-related differences in real-time processing remains unclear. These results indicate that healthy aging can affect comprehension of challenging, syntactically ambiguous material.
Understanding syntactically ambiguous sentences has been a central research topic in the psycholinguistic literature. Sentences with syntactic ambiguities are often referred to as garden-path sentences [
Frazier [ (1) a. While the man hunted the pheasant the deer ran into the woods. b. While the man hunted the deer ran into the woods.
Comprehenders strongly tend to interpret “the deer” as the object of “hunted” initially in (1b), following the Late Closure principle. However, reanalysis of this initial analysis is required when the following verb, “ran”, is processed. Encountering this verb forces comprehenders to revise their initial interpretation of “the deer” as the object of “hunted,” and instead to treat it as the subject of “ran.” Comprehenders experience processing difficulty when they must reanalyze the structure. This processing difficulty appears as increased reading or listening times for the verb “ran” in garden-path sentences like (1b) compared to non-garden-path control sentences like (1a) [
According to the second principle, Minimal Attachment [ (2) a. The editor played the tape and agreed the story was big. b. The editor played the tape agreed the story was big.
Following Minimal Attachment, comprehenders strongly prefer to treat the first five words of (2a–b) as the structurally simplest and highly frequent structure, Subject-Verb-Object. As a result, “the editor” is initially interpreted as the subject of “played the tape.” When comprehenders encounter the verb “agreed” in (2b), reanalysis for the structure is forced. They must change their interpretation to one in which “the editor” is in fact the person being played the tape, a low-frequency and more complex syntactic structure [
The relationship between working memory (WM) and sentence comprehension (SC) has been a popular topic in SC studies since it is widely assumed that understanding sentences requires verbal WM resources (e.g., [
The focus of this paper is on age-related differences in SC (specifically syntactic ambiguity) in healthy aging, and their potential relationship to WM and inhibition. Data from healthy older adults often serves as the baseline for evaluating SC impairments among persons with aphasia. Understanding the nature of differences in SC performance due to healthy aging is therefore important for measuring SC performance in aphasia, and for evaluating the contribution of WM to SC impairments in aphasia. Although there is fairly consistent evidence that elderly adults have reduced WM capacity [
There are at least two theoretical distinctions from the SC and WM literature which are relevant to examining how SC is affected by healthy aging. The first of these issues is how specialized or domain-specific WM is: is WM a single resource, with one pool of memory resources being used for SC and other cognitively-demanding tasks (the SR theory of Just and Carpenter [
A related issue regarding the relationship between WM and SC is which aspects of SC rely most strongly on potentially limited WM resources. Caplan and Waters [
As evidence of the relationship between WM and Late Closure sentences, Christianson et al. [
As evidence of the relationship between WM and Minimal Attachment sentences, Kemper and colleagues [
Another aspect of cognition that is relevant to syntactic ambiguity resolution and which also declines with age is inhibitory function. Garden-path sentences require readers to abandon their initial interpretation when they encounter later words or phrases that are inconsistent with it, as part of re-analysis. This process requires successful inhibition of the previous interpretation. Novick et al. [
Inhibitory function also declines with age, like working memory [
There are a number of studies investigating the relationship between aging, working memory, and sentence comprehension (e.g., [
However, there is a relative paucity of studies investigating the relationship between syntactic ambiguity resolution and aging specifically. Christianson et al. [
The current study examined older and younger adults’ comprehension of both Late Closure and Minimal Attachment garden-path sentences like (1–2). To date, no study has directly compared older and younger adults’ comprehension of both these types of garden-path sentences in the same study. The primary goals of the study were to determine whether older adults have more difficulty in comprehending garden-path sentences than younger adults, and to determine whether working memory or inhibitory function predicted any age-related differences. Some previous findings suggest that older adults are as successful in reanalyzing garden-path sentences as younger adults (e.g., [
A total of 71 subjects (36 younger adults and 35 older adults) participated in this study. All participants met the following selection criteria: (a) they were native American English speakers; (b) had at least 12 years of education; (c) had normal or corrected-to-normal vision; (d) passed a simplified reading screening; (e) performed within normal limits on the language recall task of the
Cognitive measures: Sentence-span [
Language processing measures: Participants read 24 Late Closure sentences like (3a–b) in Experiment 1, and 20 Minimal Attachment sentences like (4a–b) Experiment 2.
(3) a. While | the man | hunted | the pheasant | the deer | ran | into | the woods. b. While | the man | hunted | the deer | ran | into | the woods. (4) a. The editor | played | the tape | and | agreed | the story | was big. b. The editor | played | the tape | agreed | the story | was big. The ‘|’ indicates presentation regions for the self-paced reading task. The Late Closure items were adapted from the stimuli in Christianson et al. [
Cognitive measures: Sentence-span, forward- and backward-digit span tasks were presented using the E-Prime 1.0 software program [
Language processing stimuli: Participants read in a self-paced segment-by-segment reading task without cumulative display. Participants were presented with a row of dashes as a preview and pressed the space bar to reveal each segment of the sentence. After reading each sentence, participants responded to a speeded grammaticality judgment task prompt of “Acceptable?” and responded by pressing one of two buttons marked “YES” or “NO”. The percentage (%) of YES responses was computed in order to get the “acceptability rate” for analysis.
Cognitive measures: Based on an exploratory factor analysis [
Language processing measures: For data analysis of on-line performance, reading times for the disambiguating region of each sentence requiring reanalysis were collected and analyzed. The disambiguating region is underlined in (3–4) above. The reading times for the following two regions immediately after the disambiguating region were also measured. Longer reading times in the garden-path condition (3b, 4b) compared to the non-garden path condition is evidence of elevated processing related to reanalysis. For data analysis of off-line performance, the acceptability rate (percentages YES responses) for the garden-path condition (3b, 4b) was computed for each sentence. A higher acceptability rate for the garden-path condition means more successful reanalysis for the garden-path sentence [
The older age group performed significantly worse on the WM1 and WM2 composite scores and on the Flankers task than the younger group (Mann-Whitney U, WM1: z=−6.21,
Older adults were significantly slower than younger adults in the garden-path condition (3b) at the disambiguating verb (Mann-Whitney U: z=−4.669,
Older adults were significantly slower than younger adults in the garden-path condition (4b) at disambiguating verb (Mann Whitney U: z=−4.014,
In summary, older and younger adults exhibited garden-path effects for both Late Closure and Minimal Attachment garden-path sentences, and the size of the garden-path effect was significantly larger for older adults. This finding is consistent with previous findings suggesting that older adults experienced more difficulty in reanalyzing Late Closure [
As shown in
As shown in
In summary, both age groups judged garden-path conditions acceptable less often than non-garden path conditions. This is in line with previous findings showing that garden-path sentences are judged unacceptable more often than non-garden-path sentences, because comprehenders have failed to successful reanalyze their structure [
Bootstrapping regression analyses [
Interestingly, there was no prediction of the garden-path difference for Late Closure (LC) sentences (Experiment 1) or Minimal Attachment (MA) sentences (Experiment 2) by any of the cognitive factors, individually or in combination, for either group. This finding suggests that the source of the differences in on-line processing (on-line garden-path effect) is not working memory or inhibition, and implies that some other factors might be related to these on-line differences.
Bootstrapping regression analyses [
In summary, the results from the regression analysis showed no predictions of on-line performance by any of the cognitive factors, for either group. However, the off-line results showed several predictions of LC performance. All predictions of acceptability judgments were by factors related to working memory, both for younger (WM2) and older groups (WM1 and WM2) (see
The primary goals of the current study were to investigate whether older adults exhibit difficulty in recovering from syntactic garden paths, and to investigate whether this difficulty is predicted by cognitive factors, working memory and inhibition. A secondary goal was to examine whether any age-related differences in garden-path sentence comprehension appeared in off-line measures, on-line measures, or both.
The primary results for this study are summarized in
With respect to the primary goals of the study, two different pictures emerge. First, there were significant aging effects (differences in size of garden-path effect between the two age groups) in on-line measures for Experiment 1 and Experiment 2. This is consistent with previous findings suggesting that older adults may have particular difficulty with reanalysis, going back and re-structuring words and phrases once they have discovered their initial interpretation is incorrect (e.g., [
Second, even though there are aging effects in this study, they do not appear to be mediated by working memory [
With respect to the secondary goal of the study, two pictures again emerge. First, there were clear aging effects in the online measures for Experiment 1 and Experiment 2. As noted above, this is not consistent with previous results suggesting that on-line processing is immune to aging ([
One other finding from the off-line results which merits discussion is the performance of older adults in Experiment 1, with Late Closure sentences. Acceptability rates were higher for non-garden-path than garden-path sentences for both age groups in Experiment 2 (Minimal Attachment), but only for young adults in Experiment 1 (Late Closure). Older adults did not show significant differences between garden-path and non-garden-path sentences in Experiment 1. The exact source of this difference is unclear, but it is worth noting that the acceptability rate for the non-garden path sentence in Experiment 1 (“While the man hunted the pheasant the deer ran into the woods”) was unusually low compared to the typical acceptability rate of 80% for non-garden-path sentences in previous studies [
The current study examined how healthy older and younger adults comprehend challenging garden-path sentences, which involve syntactic ambiguities. Such sentences have been extensively studied in the psycholinguistic literature but have received little attention in the communicative impairment literature, despite evidence that neurogenically impaired adults may have difficulty understanding sentences requiring reanalysis [
This research was supported by an SHRS Research Development Fund award to Hyunsoo Yoo, by a University of Pittsburgh Central Research Development Fund grant to Michael Walsh Dickey, and by grant number UL1TR000005 to the Clinical and Translational Science Institute of the University of Pittsburgh. This research is the result of work supported with resources and the use of facilities at the VA Pittsburgh Healthcare System. The authors are grateful to audiences at the 2011 CUNY Conference on Human Sentence Processing and the 41st Clinical Aphasiology Conference for helpful discussion, and to Will Hula for assistance with factor analysis. The authors are particularly grateful to the residents of the Benedictine Center of Pittsburgh, PA, who participated in this study.
Reading time for
Reading time for
Acceptability rate (% Yes responses) for LC sentences (Experiment 1).
Acceptability rate (% Yes responses) for MA sentences (Experiment 2).
Predictions from bootstrap regression analyses.
Descriptive information and screening test results for participants
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Younger adults | 36 | 23 | 2.83 | 15.5 | 0.71 | 29.5 | 0.5 | 19.5 | 0.5 | 98 | 6 |
Older adults | 35 | 70 | 5.66 | 15.5 | 4.95 | 29.5 | 0.5 | 17 | 3 | 100 | 0 |
Working memory (WM) & inhibition tasks results
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Younger adults | 55.08 | 4.5 | 65.39 | 6.5 | 56.64 | 0.97 | 58.37 | 2 | 20.89 | 3 | 57.13 | 23.67 |
Older adults | 38.61 | 9.5 | 57 | 0 | 42.94 | 19.54 | 42.67 | 7 | 15.11 | 2 | 70.78 | 22.17 |
Patterns of results from on-line and off-line measurements
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LC | Younger | Yes | Yes | Younger | Yes | No |
Older | Yes | Older | No | |||
MA | Younger | Yes | Yes | Younger | Yes | No |
Older | Yes | Older | Yes |
Patterns of predictions in regression analyses
LC | Younger | No | Younger | Yes (by WM2) |
Older | No | Older | Yes (by WM1 & WM2) | |
MA | Younger | No | Younger | No |
Older | No | Older | No |