Performance of a computer system for recording eye fixations using limbus reflection

A computer system was developed to measure and record locus and duration of the eye axis of gaze using a limbus reflection technique. System hardware and operating procedures for on-line data collection and correction are described. Algorithms are presented that separate fixations from movements. Based on these algorithms, system performance was measured in terms of spatial accuracy of eye fixations and temporal accuracy of saccadic movements.     

Emotion words affect eye fixations during reading

Emotion words are generally characterized as possessing high arousal and extreme valence and have typically been investigated in paradigms in which they are presented and measured as single words. This study examined whether a word's emotional qualities influenced the time spent viewing that word in the context of normal reading. Eye movements were monitored as participants read sentences containing an emotionally positive (e.g., lucky), negative (e.g., angry), or neutral (e.g., plain) word. Target word frequency (high or low) was additionally varied to help determine the temporal locus of emotion effects, with interactive results suggesting an early lexical locus of emotion processing. In general, measures of target fixation time demonstrated significant effects of emotion and frequency as well as an interaction. The interaction arose from differential effects with negative words that were dependent on word frequency. Fixation times on emotion words (positive or negative) were consistently faster than those on neutral words with one exception-high-frequency negative words were read no faster than their neutral counterparts. These effects emerged in the earliest eye movement measures, namely, first and single fixation duration, suggesting that emotionality, as defined by arousal and valence, modulates lexical processing. Possible mechanisms involved in processing emotion words are discussed, including automatic vigilance and desensitization, both of which imply a key role for word frequency. Finally, it is important that early lexical effects of emotion processing can be established within the ecologically valid context of fluent reading.     

The influence of dimensionality on eye fixations.

Eye fixation patterns were explored for sixty adult subjects, each of whom viewed one of three stimuli, either in a three-dimensional model format or in a two-dimensional photographic format. The stimuli consisted of one symmetrical and two asymmetrical color representational drawings displayed in the form of a photograph or of a model. Total fixation times (in ms) were computed for seven portions of each stimulus: top, bottom, left, right, foreground, middle ground, and background. Results indicated that for all stimuli, subjects viewing the 3-D model spent significantly more time fixating the foreground and significantly less time fixating the background than subjects viewing the 2-D photograph. For the two asymmetrical stimuli subjects in the two groups differed significantly in their fixation patterns for the left/right variables. It was concluded that eye fixation patterns vary as a function of dimensionality.     

Spelling-sound regularity effects on eye fixations in reading

An interaction of word frequency and word regularity has typically been observed in naming and lexical decision experiments in which, in addition to an overall effect of word frequency, responses to low-frequency exception words are slower than those to low-frequency regular words, while no such difference occurs with high-frequency words. The only eye movement study to examine this effect in reading (Inhoff & Topolski, 1994) reported only transient effects of regularity. In the present experiment, we examined the frequency x regularity interaction using different stimuli than those of Inhoff and Topolski and also varied the parafoveal preview of the target word prior to fixation. When the preview was valid, the frequency x regularity interaction appeared. However, with an invalid preview, the effect of regularity disappeared. The results suggest that the activation of phonological codes is a very early component of reading.     

Fast priming during eye fixations in reading.

Near-threshold primes were "flashed" in a target location prior to the onset of a target word while Ss read. The type and duration of the prime were manipulated. In Exp. 1, identical, related, and unrelated primes were presented for 60, 45, or 30 ms from onset of an eye fixation. The prime was then replaced with the target word, which remained in place while Ss finished reading the sentence. Fixation time on the target word was measured. Exp. 2 replicated Exp. 1, with two exceptions: A random letter string replaced the identical prime condition, and prime durations of 39, 30, or 21 ms were used. In both experiments, significant priming effects (related vs. unrelated) were obtained when the prime was presented for 30 ms. Results are discussed with regard to subliminal priming effects. Applications to the study of word recognition processes are also discussed.     

Information influences the pattern of eye fixations during sentence comprehension

How does the pattern of eye fixation vary as an informative part of a word is encountered? If the processing of information lags behind the movement of the eyes, then we should expect no variation in the pattern; but if processing is immediate, then the movements of the reader's eyes should correspond to the distribution of information being inspected. An experiment is reported which examined the ways that the text ahead of the point of current fixation can be used to guide the eyes to future fixations, by monitoring fixations during a sentence comprehension task. The patterns of eye fixations upon words with uneven distributions of information (where, for example, words predictable from the sight of their first few letters but not from their last few letters are defined as containing informative beginnings) were observed, and it was found that more and longer fixations were produced when subjects looked at the informative parts of words, particularly at the informative endings of words. The results support the suggestion that eye movements are under the moment-to-moment control of cognitive mechanisms.     

Activation of phonological codes during eye fixations in reading.

Two experiments addressed the issue of whether phonological codes are activated early in a fixation during reading using the fast-priming technique (S. C. Sereno & K. Rayner, 1992). Participants read sentences and, at the beginning of the initial fixation in a target location, a priming letter string was displayed, followed by the target word. Phonological priming was assessed by the difference in the gaze duration on the target word between when the prime was a homophone and when it was a control word equated with the homophone on orthographic similarity to the target. Both experiments demonstrated homophonic priming with prime durations of about 35 ms, but only for high-frequency word primes, indicating that lexicality was guiding the speed of the extraction of phonological codes early in a fixation. Evidence was also obtained for orthographic priming, and the data suggest that orthographic and phonological priming effects interact in a mutually facilitating manner.     

Effects of verbal and spatial-imagery tasks on eye fixations while driving

The consequences of performing verbal and spatial-imagery tasks on visual search when driving were studied. Twelve participants drove 84 km on 2 highways and 2 roads. On each route, they performed 2 verbal tasks and 2 spatial-imagery tasks while their eye movements were recorded. The same results were repeated on all routes. Pupillary dilation indicated similar effort for each task. Visual functional-field size decreased horizontally and vertically, particularly for spatial-imagery tasks. Compared with ordinary driving, fixations were longer during the spatial-imagery task. With regard to driving performance, glance frequency at mirrors and speedometer decreased during the spatial-imagery task. Results are interpreted in terms of multiple attention-resource theories; implications of internal distractions on road safety are discussed in terms of possible impairment in relevant information processing.     

Masking of foveal and parafoveal vision during eye fixations in reading

A window or visual mask as moved across text in synchrony with the reader's eye movements. The size of the window or mask was varied so that either information in foveal or parafoveal vision was masked on each fixation. In another experiment, the onset of the mask was delayed for a certain amount of time following the end of the saccade. The results of the experiments point out the relative importance of foveal and parafoveal vision for reading and further indicate that most of the visual information necessary for reading can be acquired during the first 50 msec that information is available during an eye fixation.     

Implications of measurement of eye fixations for a psychophysics of form perception

It was suggested that insights into feature analysis of processes involved in form identification might be gained from an analysis of eye movements made by Ss as they identified patterns. Fixations were measured during identifications of histoforms, polygons, and Vargus 10 figures. Eye fixations were measured, and Ss rated sections of the figures in terms of their importance. Eye fixations were measured in terms of number of changes and duration of fixations. The number of changes in fixation were found to reflect only individual differences. Duration of fixation was found to vary significantly with location within figures, with fixations being longest where changes of contour occurred. There was also a tendency to look longer at the top of polygons and Vargus 10 figures and at the center of histoforms. Ratings of importance were highest for sections of figures fixated for longer duration-generally areas in which changes of contour were present.     

Temporal relationships between eye fixations and manual reactions in visual search

Observers freely searched for, and manually responded to, the presence of a target in multistimulus displays. The stimuli were presented on a cinema screen such that each display subtended a large visual angle to encourage the use of eye movements. Times taken to initially fixate the target (T1Fs) were compared to manual response times (MRTs). The results of two experiments were qualitatively similar, despite different levels of difficulty between them. MRTs were a linear function of T1Fs, but only when fixations did not occur very early after the onset of the stimulus display. When fixations were made very soon after the onset of the display, T1Fs were independent of MRTs. The findings were described within the framework of a one-way synchronization model which was modified to accommodate attention effects in visual search. Finally, the methodology provides a novel means of quantifying the contributions of eye movements to manual acknowledgements in real-world vision-guided tasks.     

Working memory and inferences: evidence from eye fixations during reading

Eye fixations during reading were monitored to examine the relationship between individual differences in working memory capacity-as assessed by the reading span task-and inferences about predictable events. Context sentences predicting likely events, or non-predicting control sentences, were presented. They were followed by continuation sentences in which a target word represented an event to be inferred (inferential word) or an unlikely event (non-predictable word). A main effect of reading span showed that high working memory capacity was related to shorter gaze durations across sentence regions. More specific findings involved an interaction between context, target, and reading span on late processing measures and regions. Thus, for high- but not for low-span readers, the predicting condition, relative to the control condition, facilitated reanalysis of the continuation sentence that represented the inference concept. This effect was revealed by a reduction in regression-path reading time in the last region of the sentence, involving less time reading that region and fewer regressions from it. These results indicate that working memory facilitates elaborative inferences during reading, but that this occurs at late text-integration processes, rather than at early lexical-access processes.     

The relevance of the first two eye fixations for recognition memory processes

ABSTRACT

Stimuli can be recognised based on information from only one or two eye fixations. With only one fixation, item recognition is typically above chance level and performance generally saturates by the second fixation. Thus, the first two eye fixations play an important role for recognition memory performance. However, little is known about the involved processes. Therefore, two experiments were conducted to investigate hypotheses regarding the role of the first two eye fixations for specific recognition memory processes, that is, familiarity and recollection. In addition, we looked in detail at the unique contributions of (a) longer input duration and (b) additional information provided by a second fixation for familiarity- and recollection-based recognition, using a gaze-contingent stimulus presentation technique. The experiments showed that recollection- but not familiarity-based recognition increased with two compared to only one fixation, and that the second fixation boosted recollection both due to longer availability of the input and additional stimulus information gathered.     

Measuring the effect of multiple eye fixations on memory for visual attributes

Because of limited peripheral vision, many visual tasks depend on multiple eye fixations. Good performance in such tasks demonstrates that some memory must survive from one fixation to the next. One factor that must influence performance is the degree to which multiple eye fixations interfere with the critical memories. In the present study, the amount of interference was measured by comparing visual discriminations based on multiple fixations to visual discriminations based on a single fixation. The procedure resembled partial report, but used a discrimination measure. In the prototype study, two lines were presented, followed by a single line and a cue. The cue pointed toward one of the positions of the first two lines. Observers were required to judge if the single line in the second display was longer or shorter than the cued line of the first display. These judgments were used to estimate a length threshold. The critical manipulation was to instruct observers either to maintain fixation between the lines of the first display or to fixate each line in sequence. The results showed an advantage for multiple fixations despite the intervening eye movements. In fact, thresholds for the multiple-fixation condition were nearly as good as those in a control condition where the lines were foveally viewed without eye movements. Thus, eye movements had little or no interfering effect in this task. Additional studies generalized the procedure and the stimuli. In conclusion, information about a variety of size and shape attributes was remembered with essentially no interference across eye fixations.     

Parafoveal processing of words and saccade computation during eye fixations in reading

Studied parafoveal word processing during eye fixations in reading to answer two questions: (a) Is the processing of parafoveally available words limited to the identification of beginning letters? (b) Does the parafoveal processing of words affect the following interword saccade? Reading afforded either no parafoveal preview, preview of beginning trigrams, preview of ending trigrams, or preview of the whole parafoveal word. Previews were controlled by replacing original letters either with X's or dissimilar letters. Preview benefits were larger for the whole word previews than for beginning or ending trigram previews. X-masks yielded preview benefits from intact beginning and ending trigrams but dissimilar letter masks yielded benefits from beginning trigrams only. Saccades were larger for whole word previews than for no previews. These results support Logogen-type models of word recognition and a model of saccade computation that posits a time-locked functional relation between the acquisition of parafoveal word information and the positioning of each fixation.     

Mislocated fixations can account for parafoveal-on-foveal effects in eye movements during reading

Contrasting predictions of serial and parallel views on the processing of foveal and parafoveal information during reading were tested. A high-frequency adjective (young) was followed by either a high-frequency word_n (child) or a low-frequency word_n (tenor), which in turn was followed by either a correct (performing) or an orthographic illegal word_{n + 1} (pxvforming) as a parafoveal preview. A limited parafoveal-on-foveal effect was observed: There were inflated fixation times on word_n when the preview of word_{n + 1} was orthographically illegal. However, this parafoveal-on-foveal effect was (a) independent of the frequency of word_n, (b) restricted to those instances when the eyes were very close to word_{n + 1}, and (c) associated with relatively long prior saccades. These observations are all compatible with a mislocated fixation account in which parafoveal-on-foveal effects result from saccadic undershoots of word_{n + 1} and with a serial model of eye movement control during reading.     

Measuring the effect of multiple eye fixations on memory for visual attributes.

Because of limited peripheral vision, many visual tasks depend on multiple eye fixations. Good performance in such tasks demonstrates that some memory must survive from one fixation to the next. One factor that must influence performance is the degree to which multiple eye fixations interfere with the critical memories. In the present study, the amount of interference was measured by comparing visual discriminations based on multiple fixations to visual discriminations based on a single fixation. The procedure resembled partial report, but used a discrimination measure. In the prototype study, two lines were presented, followed by a single line and a cue. The cue pointed toward one of the positions of the first two lines. Observers were required to judge if the single line in the second display was longer or shorter than the cued line of the first display. These judgments were used to estimate a length threshold. The critical manipulation was to instruct observers either to maintain fixation between the lines of the first display or to fixate each line in sequence. The results showed an advantage for multiple fixations despite the intervening eye movements. In fact, thresholds for the multiple-fixation condition were nearly as good as those in a control condition where the lines were foveally viewed without eye movements. Thus, eye movements had little or no interfering effect in this task. Additional studies generalized the procedure and the stimuli. In conclusion, information about a variety of size and shape attributes was remembered with essentially no interference across eye fixations.