1. Parafoveal processing influences word frequency and predictability effects on eye movements during reading
Christopher J. Hand
Glasgow
Language
Processing

2. Background
The ease or difficulty associated with processing a particular word influences when the eyes move from one fixation to another
Studies of eye movement (EM) behaviour have demonstrated that both low-level oculomotor factors and high-level linguistic factors influence EMs during reading
See Rayner (1998) for a review
Word Length
Major influence on reading time
As word length increases, fixation time increases.
(Just & Carpenter, 1980; Rayner, Sereno, & Raney, 1996)

3. Background
However, after controlling for word length, two variables in particular strongly influence fixation time on a word:
Word Frequency
Contextual Predictability

4. Word frequency effects on eye movements in reading
Words can be defined as high or low frequency dependent on their frequencies of occurrence being above or below certain thresholds
Published norms, i.e., Francis and Kučera (1982)
On-line resources, i.e.,100-million word British National Corpus (BNC) (1995;

5. Word frequency effects on eye movements in reading
Many studies have demonstrated that readers look longer at low-frequency (LF) words than at high-frequency (HF) words.
Inhoff & Rayner, 1986; Just & Carpenter, 1980; Raney & Rayner, 1995; Rayner & Raney, 1996; Rayner & Duffy, 1986; Rayner et al., 1996; Rayner, Ashby, Pollatsek & Reichle, 2004; Rayner, Fischer & Pollatsek, 1998; Sereno & Rayner, 2000.
“Spillover” effects
Fixation on LF word n inflates fixation time on word n + 1 (Rayner & Duffy, 1986).
Argued that spillover reflects not an effect of frequency, but is caused by less parafoveal preview benefit when the parafoveal word is LF (Henderson & Ferreira, 1990)

6. Contextual predictability effects on eye movements in reading
Research has established that there is a substantial effect of a word being more predictable from prior context on
Reading times
Skipping Behaviour
Balota, Pollatsek & Rayner, 1985; Ehrlich & Rayner, 1981.
Contextually constrained (i.e., predictable) words are fixated for less time and skipped more often than unconstrained (i.e., unpredictable) words
Ehrlich & Rayner, 1981; Binder, Pollatsek & Rayner, 1999; Rayner et al., 2004; Rayner & Well, 1996.

7. Contextual predictability effects on eye movements in reading
Unfortunately…
There is no agreed metric of contextual constraint.
Constraint is typically measured via word-rating experiments and / or Cloze tasks:
Word Rating
To be a dentist, you must not be afraid of touching people’s teeth
Unpredictable Predictable
Cloze Probability
To be a dentist, you must not be afraid of touching people’s ______

8. Examining the effects of word frequency and predictability simultaneously
Reaction Time Studies
Stanovich & West (1979, 1983) West & Stanovich (1982)
Typically reported an interactive pattern of frequency and predictability effects
Event-Related Potential (ERP) Study
Sereno, Brewer, & O’Donnell (2003)
Evidence to suggest an interaction between frequency and context in early ERP component (~ ms post-stimulus).

9. Examining the effects of word frequency and predictability simultaneously
Although the separate effects of word frequency and contextual predictability on EMs during reading have been demonstrated many times, fewer EM studies have examined these variables simultaneously.

10. Examining the effects of word frequency and contextual predictability simultaneously
A frequency × predictability interaction on EM behaviour during reading suggests that these variables affect the same stage of processing.
Word frequency affects early lexical processing (Sereno & Rayner, 2000)
Debate as to whether context affects early, lexical processing or later, post-lexical processing.
Important for models of EM control in reading.

11. Examining the effects of word frequency and contextual predictability simultaneously
Rayner et al. (2004)
Simultaneously varied the frequency and predictability of target words to determine whether these to variables yielded additive or interactive effects on
Fixation durations on target words
Probability of skipping the target word.
Fixation Duration Data
Significant main effects of frequency and predictability across various measures
No interaction (all Fs < 1).
Probability of fixating the target word
Significant frequency × predictability interaction

12. Limitations of Rayner et al. (2004)
Aspects of the Rayner et al. (2004) study were of concern:
Number of experimental items per condition
Length of each experimental item
Style of contexts; anomalous targets vs. unpredictable targets.
Number of experimental items
Rayner et al. (2004) used 16 pairs of HF and LF target words.
The results of this is that each participant only saw 8 target words in each condition.
All experimental items in Rayner et al. (2004) were short (maximum length 72 characters, including spaces and punctuation).

13. Limitations of Rayner et al. (2004) cont.
Content of experimental materials
A final concern over the materials used by Rayner et al. (2004) concerns the anecdotal or “conventional” nature of their experimental materials.
HF-P | LF-U
“June Cleaver always serves meat and potatoes | carrots for dinner.”
LF-P | HF-U
“Bugs Bunny eats lots of carrots | potatoes to stay healthy.”

14. Present Study Number of Items 88 experimental items
Half of items contained HF targets, the other half contained LF target.
In addition, half of the targets were presented in a predictable context, the other half in an unpredictable context.
Thus, participants see 22 experimental items per experimental condition vs. 8 per condition in Rayner et al. (2004).

15. Present Study Length of materials
Materials were a maximum of 120 characters, including spaces and punctuation vs. 72 characters in Rayner et al. (2004).
Materials were presented over two lines of visual display, max. line length 60 characters
Target words were always in the middle of the second line of display
It is argued that using longer materials allows for a stronger development of context with which to constrain target words.

16. Present Study Example materials HF-P | LF-U
Guests were arriving and Jen’s flat was a sty. She picked up
her clothes from the floor | couch and quickly cleaned the bathroom.
LF-P | HF-U
Clare had been on her feet all day. Armed with a pizza and
a video, she laid down on the couch | floor for a relaxing evening.

17. Present Study - Materials
HF-P HF-U LF-P LF-U
Mean BNC freq
Predictability (1-7)
Cloze probability
Mean Word Length
No. of syllables
Target words were never line or sentence final
Target words were never immediately preceded or followed by a punctuation mark.

18. Present Study Subjects Method 64 participants
Normal or corrected-to-normal vision
Native English speakers
No serious reading disorders, i.e., dyslexia.
Method
Dual-Purkinje eye tracker (Generation 5.5)
Materials displayed over two lines of visual display (maximum line length 60 character spaces)
4.14 characters subtended 1º of visual angle.

19. Results
3.6% of total experimental trials were rejected due to track losses or excessive blinking
A 2 (frequency; high, low) × 2 (context; predictable, unpredictable) ANOVA was performed both by participants (F1) and items (F2)
A range of standard EM measures were examined
First fixation duration (FFD), single fixation duration (SFD), gaze duration (GD), total time (TT), probability of fixating the target, and spillover fixation duration.

20. Forward Fixation Data
For FFD, SFD and GD, highly significant main effects of word frequency and predictability were found by both participants and items
However, no evidence of an interaction was found on these measures (all Fs < 1)
SFD
Significant 26 ms main effect of frequency
F1 (1,63) = 104, p < ; F2 (1,43) = 148, p <
Significant 10 ms main effect of predictability
F1 (1,63) = 13.8, p < 0.001; F2 (1,43) = 12.1, p < 0.01.
No evidence of interaction
Both Fs < 1.

21. Single Fixation Data

22. Total Time Similar to forward fixation duration measures TT
Highly significant main effects of word frequency and predictability were found by both participants and items
no evidence of an interaction was found on these measures (all Fs < 1) TT
Significant 45 ms main effect of frequency
F1 (1, 63) = 71.0, p < .0001; F2 (1, 43) = 51.7, p <.0001
Significant 39 ms main effect of predictability
F1 (1, 63) = 56.0, p < .0001; F2 (1, 43) = 37.1 , p < .0001
Frequency × Interaction was marginally significant by participants [F1 (1, 63) = 2.86, p = 0.096], but non-significant by items [F2 (1, 43) < 1].

23. Total Time Data

24. Probability of Fixation Data
Significant main effect of word frequency
F1 (1, 63) = 5.63, p < 0.05 ; F2 (1, 43) = 4.89, p < 0.05
Non-significant main effect of predictability
Both Fs < 1
Significant frequency × predictability interaction
F1 (1, 63) = 11.3, p < 0.01; F2 (1, 43) = 6.45, p < 0.05
Nature of the interaction was such that HF-P targets were more likely to be skipped than the other three conditions

25. Spillover Data Non-significant main effect of frequency Both Fs < 1
Main effect of predictability was marginally significant by participants [F1 (1,63) = 3.71, p = 0.059], but was non-significant by items [F2 (1,43) = 1.98, p > 0.15]
Frequency × predictability interaction was significant by subjects [F1 (1, 63) = 7.25, p < 0.01], and was marginally significant by items [F2 (1, 43) = 3.81, p = 0.06]
Nature of interaction was such that spillover fixation duration was shortest after HF-P targets than the other three conditions

26. Summary of Results…so far
Additive effects of word frequency and predictability on target word fixation duration measures
BUT
Interactive effects on the probability of fixating the target word
Interactive effects on spillover fixation duration

27. So…?
An interaction between frequency and predictability effects may be an elusive effect, that does not manifest itself in the EM record.
However, research has demonstrated that the ability to extract information from words viewed parafoveally is influenced by the frequency and predictability of that parafoveal word
Inhoff & Rayner (1986)
Balota et al. (1985)

28. Parafoveal Preview
Readers obtain more parafoveal preview benefit from HF parafoveal words than LF parafoveal words.
Fixation times on parafoveal word n + 1 were significantly lower for HF words previously viewed parafoveally (Inhoff & Rayner, 1986)
Readers obtain more parafoveal preview benefit when words viewed parafoveally are contextually predictable
Balota et al., 1985.

29. Parafoveal processing
It may be the case that parafoveal preview operates in conjunction with the effects of frequency and predictability.
Parafoveal preview typically manipulated by gaze-contingent display change paradigms
Parafoveal preview benefit can also be indexed dependent on the distance of the fixation prior to fixating the target word and the beginning of the target word (launch site).

30. Frequency × Predictability × Launch Site
Data from original EM analyses was conditionalised post-hoc on the launch site to the target.
Word identification span typically does not exceed 7-9 characters
(McConkie & Zola, 1987)
Three ‘groups’ of launch site
1-3 characters
4-6 characters
7-9 characters

31. Frequency × Predictability × Launch Site
Present Study - 64 Ss × 88 Itms = 5632 data points
Rayner et al. (2004) - 54 Ss × 36 Itms = 1944 data points
After skips / rejected trials, 4489 data points in initial analyses
Data Points Percentage data from
initial analyses
1-3 chars %
4-6 chars % = 76.5%
7-9 chars %
10-12 chars %
13+ chars %

32. Frequency × Predictability × Launch Site - Results
A 3 (launch site; 1-3 chars, 4-6 chars) × 2 (frequency; high, low) × 2 (context; predictable, unpredictable) ANOVA was performed both by participants (F1) and items (F2)
A range of standard EM measures were examined
FFD, SFD, GD, TT, probability of fixating the target, and spillover fixation duration.

33. Frequency × Predictability × Launch Site – Forward Fixation Data
For FFD, SFD, and GD, highly significant main effects of frequency, predictability, and launch site were observed by both participants and items (all ps < )
Non-significant frequency × predictability interactions (all Fs < 1)
Significant three-way interactions between frequency, predictability, and launch site (all ps < 0.05)

34. Frequency × Predictability × Launch Site – Single Fixation Duration
Significant main effect of frequency
F1 (1,63) = 77.6, p < ; F2 (1,43) = 107, p <
Significant main effect of predictability
F1 (1,63) = 19.1, p < ; F2 (1,43) = 13.7, p <
Significant main effect of launch site
F1 (2,63) = 50.0, p < ; F2 (2,43) = 32.2, p <
Non-significant frequency × predictability interaction
Both Fs < 1
Significant three-way interaction between frequency, predictability and launch site
F1 (2,63) = 7.19, p < 0.01; F2 (2,43) = 7.49, p < 0.01

35. Launch site Frequency Predictability Freq × Pred
1-3 chars p< p< p<0.05
4-6 chars p< p=0.10 p<0.01
7-9 chars p<0.01 F<1 F<1

36. Frequency × Predictability × Launch Site – Total Time
Significant main effect of frequency
F1 (1,63) = 36.4, p < ; F2 (1,43) = 30.0, p <
Significant main effect of predictability
F1 (1,63) = 55.3, p < ; F2 (1,43) = 32.2, p <
Significant main effect of launch site
F1 (2,63) = 25.0, p < ; F2 (2,43) = 29.1, p <
Frequency × predictability interaction was marginally significant by participants; non-significant by items
F1 (1,63) = 3.06, p = 0.09; F2 < 1
Non-significant three-way interaction between frequency, predictability and launch site by participants; trend by items
F1 (2,63) = 1.82, p > 0.15; F2 (2,43) = 2.07, p = 0.13

37. Launch site Frequency Predictability Freq × Pred
1-3 chars p< p< p<0.05
4-6 chars p< p<0.001 F<1
7-9 chars p<0.05 p<0.001 F<1

38. Frequency × Predictability × Launch Site – Spillover
Non-significant main effect of frequency
Both Fs < 1.
Non-significant main effect of predictability
Main effect of launch site significant by participants; marginally significant by items
F1 (2,63) = 7.87, p < 0.001; F2 (2,43) = 2.56, p = 0.08.
Frequency × predictability interaction significant by participants; marginally significant by items
F1 (1,63) = 5.17, p < 0.05; F2 (1,43) = 3.61, p = 0.06.
Non-significant three-way interaction between frequency, predictability, and launch site
F1 < 1; F2 (2,63) = 1.81, p > 0.15

39. Frequency × Predictability × Launch Site – Probability of Fixation
Non-significant main effect of frequency
F1 (1,63) = 1.71, p > 0.15; F2 (1,43) = 1.32, p > 0.25.
Non-significant main effect of predictability
F1 (1,63) = 1.46, p > 0.20; F2 (1,43) = 1.30, p > 0.25.
Significant main effect of launch site
F1 (2,63) = 18.1, p < ; F2 (2,43) = 14.8, p <
Significant frequency × predictability interaction
F1 (1,63) = 20.4, p < ; F2 (1,43) = 7.63, p < 0.01.
Significant three-way interaction between frequency, predictability, and launch site by participants; trend by items
F1 (2,63) = 7.76, p < 0.001; F2 (2,43) = 2.04, p = 0.14

40. Discussion
Initial analyses found no interaction between the effects of frequency and predictability on target word reading time measures (all Fs < 1)
Interactive effects found on spillover fixation duration and probability of fixating the target word

41. Discussion
Conditionalised analyses on the basis of parafoveal preview – as indexed by launch distance to target word – revealed a significant three-way interaction between the effects of preview, frequency and predictability
Re-analyses revealed that when parafoveal preview is accounted for, word frequency and contextual predictability interact on
Forward fixation times (i.e., FFD, SFD, GD)
Spillover fixation duration
Probability of fixating target words.

42. Discussion
For LF words, predictability effects only occur at a close launch site (1-3 chars)
For HF words, predictability effects occur at further launch sites (1-3 chars & 4-6 chars)
The finding of an interactive pattern of effects when parafoveal preview is accounted for provides clear evidence of predictability effects at an early, lexical stage of processing.

43. The nature of contextual constraint
Recent research has suggested that readers are able to utilise low-level statistical probability information, i.e., the statistical likelihood of word n occurring given word n – 1 (McDonald & Shillcock, 2003)
Future research into context effects should perhaps eschew subjective tasks such as Cloze probability / word-rating tasks in favour of a more computational approach to context construction
Latent semantic analyses of large text corpora such as the 100-million word BNC.

44. Conclusion
By employing temporally-precise recording techniques, such as EMs and ERPs (Sereno & Rayner, 2003) in conjunction with carefully controlled stimulus materials, it is possible to delineate a precise time-course of contextual predictability effects.
Accurately resolving this matter has important consequences for models of EM control during reading and will aide resolve contention between equivocal theories of language processing.

45. Thanks (shameless theft of Dr. Fraser Smith’s (2006) idea)
Paddy O’Donnell
Sara Sereno
Sébastien Miellet