The method was designed to investigate the role of inhibition of return (IOR) in regressive eye movements during reading. The focus is on differentiating between regressions triggered as a result of comprehension difficulty versus those triggered from oculomotor error, including the role of IOR in the two types of regressions.
Regressive eye movements are eye movements that move backwards through the text and comprise approximately 10-25% of eye movements during reading. As such, understanding the causes and mechanisms of regressions plays an important role in understanding eye movement behavior. Inhibition of return (IOR) is an oculomotor effect that results in increased latency to return attention to a previously attended target versus a target that was not previously attended. Thus, IOR may affect regressions. This paper describes how to design materials to distinguish between regressions caused by comprehension-related and oculomotor processes; the latter is subject to IOR. The method allows researchers to identify IOR and control the causes of regressions. While the method requires tightly controlled materials and large numbers of participants and materials, it allows researchers to distinguish and control the types of regressions that occur in their reading studies.
The method described in this paper was designed to investigate the role of inhibition of return (IOR) in regressive eye movements during reading, focusing on regressions triggered as a result of comprehension difficulty versus those triggered as a result of oculomotor error. Specifically, we investigated whether regressions launched as a result of comprehension difficulty and those launched as a result of oculomotor error are subject to IOR effects.
Regressive eye movements, or regressions, are eye movements that move backwards through the text. Depending on reader and text characteristics, 10-25% of eye movements move backwards1. This has led researchers to investigate whether IOR effects affect regressive eye movements during natural reading. IOR is an oculomotor effect that results in increased latency to return attention to a target that had been previously attended compared to a target that had not been previously attended2. While much of the work done to establish IOR effects has involved non-reading visual attention tasks3, the effect has been extended to reading4,5.
The work examining regressions and IOR in reading has focused on whether an oculomotor effect such as IOR can influence eye movement control in reading. One study5 found evidence of IOR in a reading task. They found that readers spent approximately 30 ms longer on the fixation preceding a regression. This was interpreted as the IOR "cost" – the delay before returning to a previously fixated position. This was supported in regular reading and mindless reading conditions6.
Despite evidence that IOR can be found in regular reading situations, it is clear that regressive eye movements do not all have the same underlying cause. Regressions resulting from comprehension difficulty have been well documented7,8,9,10. Despite the evidence that eye movements during reading are generally guided by cognitive and linguistic factors1, it is also assumed that sometimes regressions occur in response to low-level oculomotor factors, such as target overshoot1. It is assumed that on some trials, readers mis-program a saccade and land beyond their intended target word (an overshoot). In this case, a short, corrective regressive saccade may occur so that the unintentionally skipped word can be fixated. Given that two underlying mechanisms – linguistic and oculomotor – have been posited for regressive eye movements, it is not clear whether IOR occurs for both. The current method allows for the measurement of IOR effects when regressive eye movements have been launched as a result of comprehension difficulties and as a result of oculomotor overshoot. Thus, the method allows researchers to distinguish the underlying mechanisms of regressive eye movements, allowing for the evaluation of IOR effects.
The current method takes advantage of the two identified mechanisms triggering regressive eye movements. By designing the materials so that re-reading is likely to be triggered by comprehension difficulty or overshoot, researchers are able to examine the circumstances under which IOR might occur in reading. To encourage re-reading as a result of oculomotor error, we embedded short target words that show high skipping rates of about 50% (adapted from previous research11). Skipped words are often followed by a corrective regressive saccade when the skipping is a result of oculomotor error11. The other set of materials was comprised of sentences that contained semantically ambiguous homographic homophones (e.g., grade: school/incline). The sentences were adapted from an ambiguity study12 and contained information as to the intended meaning of the homophone that followed the word. Thus, this would increase the chances that readers would re-read for comprehension. The context was consistent with the less-likely meaning of the homophone, making it likely that readers would have to re-read after having initially selected the more frequent, dominant meaning on their first encounter with the target word. The combination of eye-movement monitoring and materials designed to increase regressions makes this method unique in allowing for the examination of regressive eye movements with differing underlying causes.
Understanding the mechanisms underlying regressive saccades and the role that oculomotor factors such as IOR play in them is important to models of eye movement control as well as for understanding the relationship between oculomotor and cognitive control of eye movements. For example, a recent version of the E-Z Reader model of eye movement control employs a 30 ms cost for all regressive eye movements13. However, our methodology demonstrated that such a cost only applies to regressions resulting from oculomotor error.
Eye movement measures allow researchers to track the moment-to-moment cognitive processing during reading1. Recently, models of eye movement control have begun to try to explain the mechanisms underlying regressive eye movements. Since regressions are often launched in relation to comprehension difficulties, any researcher interested in understanding the comprehension processes during reading should attempt to differentiate regressions resulting from oculomotor error versus comprehension processes. This methodology indicates that a cost for regressions is a result only of oculomotor error, serving as a launching point for differentiating between types of regressions. The combination of eye movement measures (regressions, fixation times before regressions) and carefully controlled materials allow for this differentiation.
The Institutional Review Boards of Kent State University and Stetson University have approved all methods described here.
1. Eligible Participants
NOTE: The purpose of this research is to understand reading processes in skilled adult readers. Thus, certain eligibility requirements must be met. Such controls ensure that results are directly applicable to a population of skilled adult readers with typical cognitive processes.
2. Experimental Stimuli
NOTE: Stimuli construction involves the selection of individual target words as well as the creation of sentence contexts in which those target words are embedded.
3. Comprehension Check
4. Eye Tracking Procedure
5. Quantitative Analysis of Data
The results of our previous work using this paradigm14 resulted in a 17% regression rate in the oculomotor error condition and a 29% regression rate in the comprehension difficulty condition14. In the oculomotor error condition, 32% of the regressions were to previously fixated words and 68% of regressions were to previously skipped words. The reverse pattern occurred in the comprehension difficulty condition. Of the 29% of regressions, 61% were to previously fixated words whereas 39% were to previously skipped words (See Table 1).
The important variable of interest in these experiments is reading time on wordn+1, or the word from which the regression was launched. An IOR effect would be indicated by longer reading times on wordn+1 prior to the regression when the target wordn was previously fixated compared to when it was skipped. Figure 1 indicated that participants spent significantly more time on wordn+1 prior to a regression to wordn when it was previously fixated (mean = 296 ms, standard error (SE) = 17 ms) than when it was skipped (mean= 253 ms, SE = 14 ms), consistent with an IOR effect. However, no IOR effect was observed in the comprehension difficulty condition. In this condition, reading times on wordn+1 were no different when a regression was made to wordn when it was previously fixated (mean = 296 ms,SE = 10 ms) than when it was previously skipped (mean = 291 ms, SE = 8 ms).
Figure 1: Reading times on wordn+1 prior to making a regression to wordn. This figure represents the reading times on wordn+1 from which the regression was launched. The regression was either made to a word that was previously fixated or previously skipped. Regression to the previously fixated words are expected to be longer if there is an IOR effect, demonstrating the latency to move the eyes back to a previously fixated target. Values are mean ± SE (error bars). Please click here to view a larger version of this figure.
Oculomotor Error | Comprehension Difficulty | ||
17% Regression Rate | 29% Regression Rate | ||
Previously Fixated | Previously Skipped | Previously Fixated | Previously Skipped |
32% | 68% | 61% | 39% |
Table 1: Probability of making a regression to a previously skipped or fixated target word. This table breaks down the probability of making each type of regression. The overall regression rates for the two types are presented on the top lines. The bottom line represents the percentage of times that the eyes returned to a previously fixated or previously skipped word.
The current research provides a method for distinguishing between two different types of regressive eye movements during reading – those that are based on comprehension difficulty and those that are based on oculomotor error. The data provide evidence that a low-level attentional process, IOR, may depend on the type of regression. It was found that IOR only occurs for oculomotor-based regressions, but not for comprehension based regressions14. Thus, it is important to distinguish between different types of regressive eye movements when drawing conclusions about cognitive processing during reading.
While this protocol uses a commonly accepted and straightforward eye-tracking methodology, the critical steps are in creating the stimuli. It is important to control as many aspects of the stimuli as possible so that the researcher can accurately discriminate the two different types of regressive eye movements. It appears as though using biased ambiguous homophones that lead the reader to select the contextually incorrect meaning of the word results in comprehension-based regressive eye movements. In contrast, using short, low frequency, content words results in oculomotor corrective regressive eye movements. One modification that can be made to this design is using better control of the word from which the regression is launched. For example, in the comprehension-based regression stimuli, we were unable to control the length or frequency of the word from which the regression was launched in the original study14. In the analyses, we included the length and frequency of that word as covariates; however, it would be best to control the words as tightly as possible so that any variability can be attributed to IOR and not to other linguistic processing.
Given the design of the experiment, researchers are only able to analyze a small subset of the data. In the original experiment, only 15% of trials involved a regression that was made to the target word for oculomotor error and only 24% of trials involved a regression that was made to the target word for comprehension difficulty14. All other trials were discarded from analyses, as they were not relevant to the research question. Thus, a limitation of this design is that it requires large sample sizes of participants and a large number of items in the experiment. A typical sample size used in reading studies may not provide enough power to detect differences when they exist.
Future research could replicate and expand on these findings by investigating whether low skill and high skill readers vary in the degree to which they make different types of regressions. It is already known that beginning readers make more regressive eye movements than more skilled readers17, and that low-skill readers make more regressive eye movements than high skill readers18. However, it is not yet known whether there are differences between low skill and high skill readers on the IOR latency and whether they differ on the likelihood of making the two types of regressions. It is reasonable to expect that low skill readers would be more likely to make comprehension-based regressions than high skill readers would. However, there may be no differences in their probability of making oculomotor-based regressions as these rely less on the linguistic processing skills that distinguish high skill and low skill readers.
The authors have nothing to disclose.
The authors have no acknowledgments.
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