Investigating the combined effects of word frequency and contextual

predictability on eye movements during reading

Christopher J. Hand

GlasgowLanguageProcessin

g

Background

• The ease or difficulty associated with processing a word influences when the eyes move from one fixation to another.

• Two higher-level linguistic variables in particular influence eye movements (EMs) during reading– Word frequency– Contextual predictability

Effects of word frequency on EMs during reading

• Words can be defined as high or low frequency (HF or LF) depending on how often they occur in natural text.

• LF words are fixated longer than HF words– Inhoff & Rayner, 1986; Just & Carpenter, 1980; Raney &

Rayner, 1995; Rayner & Raney, 1996; Rayner & Duffy, 1986; Rayner, Sereno, & Raney, 1996; Rayner, Ashby, Pollatsek & Reichle, 2004; Rayner, Fischer & Pollatsek, 1998; Sereno & Rayner, 2000.

Effects of contextual predictability on EMs during reading

• Words that are more constrained by prior context (i.e., predictable) are read quicker than words that are less constrained (i.e., unpredictable).– Balota, Pollatsek & Rayner, 1985; Binder, Pollatsek &

Rayner, 1999; Ehrlich & Rayner, 1981; Rayner et al., 2004; Rayner & Well, 1996.

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 the early N1 ERP component (~132-192 ms post-stimulus).

Examining the effects of word frequency and contextual predictability simultaneously

• Few EM studies have examined the joint effects of frequency and predictability as their principal focus

• 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.

Examining the effects of word frequency and contextual predictability simultaneously

• Rayner et al. (2004)– Reported no interaction on target word fixation

time measures

• However, Rayner et al.’s (2004) study had perceived limitations– Few experimental items per condition– Short length of pre-target context

Present Study

• 22 experimental items per condition vs. 8 (Rayner et al., 2004)

• Maximum item length 120 characters vs. 72 (Rayner et al., 2004)

• Present Study HF-predictable“Callum was having trouble with his homework. He asked hisuncle who was a teacher to help him with the assignment.”

• Rayner et al. (2004) HF-predictable“June Cleaver always serves meat and potatoes for dinner.”

Present Study: Method

• Subjects– 64 participants– Native English speakers– No serious reading disorders, i.e., dyslexia.

• Apparatus– Dual-Purkinje eye tracker (Generation 5.5)

Results

• 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).

Target Word Fixation Time Data

• For FFD, SFD, GD and TT, 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)

Single Fixation Data• Significant 26 ms main effect of frequency

– F1 (1,63) = 104, p < 0.0001; F2 (1,43) = 148, p < 0.0001.

• 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.

Frequency × Predictability - SFD

240

250

260

270

280

290

300

Predictability

SF

D (

ms)

HF target

LF target

HF target 259 269

LF target 285 294

Pred Unpred

Discussion

• 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)

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).

Frequency × Predictability × Launch Site

• Initial re-analysis of the EM data from this experiment, contingent on parafoveal preview has yielded some interesting results…

• Significant three-way interaction between frequency, predictability and launch site– SFD – F1 (2,63) = 7.19, p < 0.01; F2 (2,43) = 7.49, p <

0.01– Similar patterns for FFD, GD and TT

Frequency × Predictability × Launch Site – Single Fixation Duration

Launch site Frequency Predictability Freq × Pred1-3 chars p<0.0001 p<0.0001 p<0.054-6 chars p<0.0001 p=0.10 p<0.01

7-9 chars p<0.01 F<1 F<1

SFD Frequency × Predictability by Launch Site

200

220

240

260

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300

320

1-3 4-6 7-9

Launch Site (chars)

SF

D (

ms)

HF-P

HF-U

LF-P

LF-U

Conclusion

• 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.

• Accurately delineating the precise time-course of the effects of contextual predictability has important consequences for models of EM control during reading and will aid to resolve contention between currently equivocal theories of language processing.

Thanks

Sébastien MielletPaddy O’Donnell Sara Sereno