Fixation disparity during reading: Fusion, not suppression

In this paper I present a brief review of some recent studies my colleagues and I have carried out to investigate binocular coordination during reading. These studies demonstrate that the eyes are often not perfectly aligned during reading, with fixation disparities of approximately one character on average. Both crossed and uncrossed disparities are common and vergence movements during fixations serve to reduce, but not eliminate disparity. Fixation disparity results in different retinal inputs from each eye, yet a single non diplopic visual representation of the text is perceived when we read. A further experiment, with dichoptically presented target words in normally presented sentence frames, showed that a mechanism of fusion rather than suppression operates at an early stage during visual processing. Saccade metrics appear to be computed according to a unified visual representation based on input from both eyes. based on input from both eyes

Eye Movements and Fixation-Related Potentials in Reading: A Review

The present review is addressed to researchers in the field of reading and psycholinguistics who are both familiar with and new to co-registration research of eye movements (EMs) and fixation related-potentials (FRPs) in reading. At the outset, we consider a conundrum relating to timing discrepancies between EM and event related potential (ERP) effects. We then consider the extent to which the co-registration approach might allow us to overcome this and thereby discriminate between formal theoretical and computational accounts of reading. We then describe three phases of co-registration research before evaluating the existing body of such research in reading. The current, ongoing phase of co-registration research is presented in comprehensive tables which provide a detailed summary of the existing findings. The thorough appraisal of the published studies allows us to engage with issues such as the reliability of FRP components as correlates of cognitive processing in reading and the advantages of analysing both data streams (i.e., EMs and FRPs) simultaneously relative to each alone, as well as the current, and limited, understanding of the relationship between EM and FRP measures. Finally, we consider future directions and in particular the potential of analytical methods involving deconvolution and the potential of measurement of brain oscillatory activity

Is orthographic information from multiple parafoveal words processed in parallel: an eye- tracking study

In the current study we investigated whether orthographic information available from one upcoming parafoveal word influences the processing of another parafoveal word. Across two experiments we used the boundary paradigm (Rayner, 1975) to present participants with an identity preview of the two words after the boundary (e.g. hot pan), a preview in which two letters were transposed between these words (e.g. hop tan), or a preview in which the same two letters were substituted (e.g. hob fan). We hypothesized that if these two words were processed in parallel in the parafovea then we may observe significant preview benefits for the condition in which the letters were transposed between words relative to the condition in which the letters were substituted. However, no such effect was observed, with participants fixating the words for the same amount of time in both conditions. This was the case both when the transposition was made between the final and first letter of the two words (e.g. hop tan as a preview of hot pan; Experiment 1) and when the transposition maintained within word letter position (e.g. pit hop as a preview of hit pop; Experiment 2). The implications of these findings are considered in relation to serial and parallel lexical processing during reading.<br/

Reading sentences of uniform word length: evidence for the adaptation of the preferred saccade length during reading

In the current study we investigated the effect of removing word length variability within sentences on spatial aspects of eye movements during reading. Participants read sentences that were uniform in terms of word length, with each sentence consisting entirely of three, four, or five letter words, or a combination of these word lengths. Several interesting findings emerged. Adaptation of the preferred saccade length occurred for sentences with different uniform word length; participants would be more accurate at making short saccades while reading uniform sentences of three letter words, while they would be more accurate at making long saccades while reading uniform sentences of five letter words. Furthermore, word skipping was affected such that three and four letter words were more likely, and five letter words less likely, to be directly fixated in uniform compared to non-uniform sentences. It is argued that saccadic targeting during reading is highly adaptable and flexible towards the characteristics of the text currently being read, as opposed to the idea implemented in most current models of eye movement control during reading that readers develop a preference for making saccades of a certain length across a lifetime of experience with a given language<br/

Investigating eye movement acquisition and analysis technologies as a causal factor in differential prevalence of crossed and uncrossed fixation disparity during reading and dot scanning

Previous studies examining binocular coordination during reading have reported conflicting results in terms of the nature of disparity (e.g. Kliegl, Nuthmann, &amp; Engbert (Journal of Experimental Psychology General 135:12-35, 2006); Liversedge, White, Findlay, &amp; Rayner (Vision Research 46:2363-2374, 2006). One potential cause of this inconsistency is differences in acquisition devices and associated analysis technologies. We tested this by directly comparing binocular eye movement recordings made using SR Research EyeLink 1000 and the Fourward Technologies Inc. DPI binocular eye-tracking systems. Participants read sentences or scanned horizontal rows of dot strings; for each participant, half the data were recorded with the EyeLink, and the other half with the DPIs. The viewing conditions in both testing laboratories were set to be very similar. Monocular calibrations were used. The majority of fixations recorded using either system were aligned, although data from the EyeLink system showed greater disparity magnitudes. Critically, for unaligned fixations, the data from both systems showed a majority of uncrossed fixations. These results suggest that variability in previous reports of binocular fixation alignment is attributable to the specific viewing conditions associated with a particular experiment (variables such as luminance and viewing distance), rather than acquisition and analysis software and hardware.<br/

Processing of co-reference in autism spectrum disorder

Accuracy for reading comprehension and inferencing tasks has previously been reported as reduced for individuals with autism spectrum disorder (ASD), relative to typically developing (TD) controls. In this study, we used an eye movements and reading paradigm to examine whether this difference in performance accuracy is underpinned by differences in the inferential work required to compute a co-referential link. Participants read two sentences that contained a category noun (e.g., bird) that was preceded by and co-referred to an exemplar that was either typical (e.g., pigeon) or atypical (e.g., penguin). Both TD and ASD participants showed an effect of typicality for gaze durations upon the category noun, with longer times being observed when the exemplar was atypical, in comparison to typical. No group differences or interactions were detected for target processing, and verbal language proficiency was found to predict general reading and inferential skill. The only difference between groups was that individuals with ASD engaged in more re-reading than TD participants. These data suggest that readers with ASD do not differ in the efficiency with which they compute anaphoric links on-line during reading

Parafoveal preview effects in reading unspaced text

In English reading, eye guidance relies heavily on the spaces between words for demarcating word boundaries. In an eye tracking experiment, we examined the impact of removing spaces on parafoveal processing. Using the gaze-contingent boundary paradigm (Rayner, 1975), a high or low frequency pre-boundary word was followed by a post-boundary preview presented either normally (i.e. identical to the post- boundary word), or with letters replaced creating an orthographically illegal preview. The spaces between words were either retained or removed. Results replicate previous findings of increased reading times during unspaced reading (Rayner, Fischer &amp; Pollatsek, 1998) and indicate rather limited evidence for more distributed processing: Observations of processing of the previous word (spill-over effects) or processing of the next word (parafoveal-on-foveal effects) influencing fixation durations on the currently fixated word were limited. Spill-over effects were only observed in the unspaced layout when the post-boundary preview was correct, presumably because the orthographically illegal, incorrect preview was visually salient enough to allow for relatively easy word segmentation and therefore more focused processing of the pre- boundary word. As such, results points towards a system that prefers narrowly focused processing of a single word, at least when means for easy word segmentation are available

Does text contrast mediate binocular advantages in reading?

Humans typically make use of both of their eyes in reading and efficient processes of binocular vision provide a stable, single percept of the text. Binocular reading also comes with an advantage: reading speed is high and word frequency effects (i.e., faster lexical processing of words that are more often encountered in a language) emerge during fixations, which is not the case for monocular reading (Jainta, Blythe, &amp; Liversedge, 2014). A potential contributor to this benefit is the reduced contrast in monocular reading: reduced text contrasts in binocular reading are known to slow down reading and word identification (Reingold &amp; Rayner, 2006). To investigate whether contrast reduction mediates the binocular advantage, we first replicated increased reading time and nullified frequency effects for monocular reading (Experiment 1). Next, we reduced the contrast for binocular but whole sentences to 70% (Weber-contrast); this reading condition resembled monocular reading, but found no effect on reading speed and word identification (Experiment 2). A reasonable conclusion, therefore, was that a reduction in contrast is not the (primary) factor that mediates less efficient lexical processing under monocular reading. In a third experiment (Experiment 3) we reduced the sentence contrast to 40% and the pattern of results showed that, globally, reading was slowed down but clear word frequency effects were present in the data. Thus, word identification processes during reading (i.e., the word frequency effect) were qualitatively different in monocular reading compared with effects observed when text was read with substantially reduced contrast

The influence of a word’s number of letters, spatial extent, and initial bigram characteristics on eye movement control during reading: Evidence from Arabic.

We conducted two eye movement experiments in which we used the typographical and linguistic properties of Arabic to disentangle the influences of words’ number of letters and spatial extent on measures of fixation duration and saccade targeting (Experiment 1), and to investigate the influence of initial bigram characteristics on saccade targeting during reading (Experiment 2). In the first experiment, through the use of a proportional font, which is more natural-looking in Arabic compared to monospaced fonts, we manipulated the number of letters (5 versus 7) and the spatial extent (wide versus narrow) of words embedded in frame sentences. The results obtained replicate and expand upon previous findings in other alphabetic languages that the number of letters influences fixation durations, whereas saccade targeting (as indicated by measures of fixation count and probability of skipping and re-fixation) is more influenced by the word’s spatial extent. In the second experiment we compared saccade targeting measures (saccade amplitude and initial fixation location) in 6- and 7- letter words beginning with initial bigrams that were of extremely high frequency (?? the), relatively high frequency (?? to/for the), or beginning with the letters of the word stem. Our results showed negligible modulation of saccade targeting by initial bigram characteristics. The results also highlighted the importance of selecting the appropriate measures of initial fixation location (spatial versus character-based measures) during reading text rendered using proportional fonts