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.     

The limits of visual resolution in natural scene viewing

We examined the limits of visual resolution in natural scene viewing, using a gaze-contingent multiresolutional display having a gaze-centred area-of-interest and decreasing resolution with eccentricity. Twelve participants viewed high-resolution scenes in which gaze-contingent multiresolutional versions occasionally appeared for single fixations. Both detection of image degradation (five filtering levels plus a no-area-of-interest control) in the gaze-contingent multiresolutional display, and eye fixation durations, were well predicted by a model of eccentricity-dependent contrast sensitivity. The results also illuminate the time course of detecting image filtering. Detection did not occur for fixations below 100 ms, and reached asymptote for fixations above 200 ms. Detectable filtering lengthened fixation durations by 160 ms, and interference from an imminent manual response occurred by 400-450 ms, often lengthening the next fixation. We provide an estimate of the limits of visual resolution in natural scene viewing useful for theories of scene perception, and help bridge the literature on spatial vision and eye movement control.     

An eye movement analysis system (EMAS) for the identification of cognitive processes on figural tasks

EMAS is a software system (written in VAX-11 FORTRAN) for the analysis of eye movement data recorded during the performance of figural tasks. Its main functions are: (1) Calibration of raw coordinates of eye movements to determine their actual position on the stimulus display. Different kinds of measurement distortion may be corrected. (2) Identification of eye fixations and the determination of their locations and durations. (3) Analysis of fixation sequences. The frequency of transitions of fixations among specified sectors of the stimulus display is computed. A sequential list is made of the successive fixations in which the fixated sector and the fixation duration are graphically indicated. (4) Plotting of raw or calibrated eye movement data and fixation points. The sequence of fixations in specified display sectors can also be plotted in real time. Applications of the programs to the Embedded Figures Test and the Hidden Figures Test are illustrated.     

Human faces capture attention and attract first saccades without longer fixation

Human faces attract attention, evidenced by reaction time (RT) advantages over non-face stimuli in visual search tasks. In the current study, participants’ eye movements were tracked during a search task to test how the attentional capture of faces is related to looking behaviour. On each trial, participants were cued with a category name (automobiles, birds, chairs, dogs, faces, bodies, or plants). An array of images, one exemplar from each category, was then presented until participants indicated whether the target matched the cue. Results showed that faces as targets resulted in faster search times and were more likely to capture first fixations. Fixations on faces were also shorter compared to other categories. Faces captured attention, attracting first fixations, and participants appeared to be more fluent at processing faces, resulting in shorter fixations. Reaction time advantages for faces could be due to both attention capture and ultra-rapid processing.     

Eye movement control during reading: Evidence for direct control

In three experiments, subjects read text as their eye movements were monitored and display changes in the text were made contingent upon the eye movements. In one experiment, a window of text moved in synchrony with the eyes. In one condition, the size of the window was constant from fixation to fixation, while in the other condition the size of the window varied from fixation to fixation. In the other experiments, a visual mask was presented at the end of each saccade which delayed the onset of the text, and the length of the delay was varied. The pattern of eye movements was influenced by both the size of the window and the delay of the onset of the text, even when the window size or text delay was varying from fixation to fixation. However, there was also evidence that saccade length was affected by the size of the window on the prior fixation and that certain decisions to move the eye are programmed either before the fixation begins or are programmed during the fixation but without regard to the text fixated on. The results thus provide support for a mixed control model of eye movements in reading, in which decisions about when and where to move the eyes are based on information from the current fixation, the prior fixations, and possibly, other sources as well.     

Eye movements blink the attentional blink

When presented with a sequence of visual stimuli in rapid succession, participants often fail to detect a second salient target, a phenomenon referred as the attentional blink (AB; Raymond, Shapiro, & Arnell, 1992; Shapiro, Raymond, & Arnell, 1997). On the basis of a vast corpus of experiments, several cognitive theories suggest that the blink results from a discrete structuring of attention, sampling information from temporal episodes during which several items can access encoding process (Wyble, Bowman, & Nieuwenstein, 2009; Wyble, Potter, Bowman, & Nieuwenstein, 2011). The objective of this work is to explore the AB when multiple items are presented at the fovea during ocular movements. The authors reasoned that each fixation may cohesively form an episode and hence expected that the blink may vanish within a single fixation. In turn, they expected saccades to accentuate episodic borders and hence shorten the regime of interference when 2 targets are presented fovealy in successive fixations. Evidence is provided in favor of this hypothesis, showing that the blink vanishes when both targets are presented in the core of a single fixation (far from the saccadic boundaries) and that it recovers more rapidly in successive fixations. These studies support current views that episodes should have an effect on the AB and provide evidence that eye movements play an important role in the formation of episodes.     

场景情境和目标模板在视觉搜索中的交互作用

以真实场景图像中的物体搜索为实验任务, 操纵场景情境和目标模板, 采用眼动技术将搜索过程分为起始阶段、扫描阶段和确认阶段, 考察场景情境和目标模板对视觉搜索过程的影响机制。结果发现, 场景情境和目标模板的作用方式及时间点不同, 二者交互影响搜索的正确率和反应时, 仅场景情境影响起始阶段的时间, 随后二者交互影响扫描阶段和确认阶段的时间及主要眼动指标。作者由此提出了场景情境和目标模板在视觉搜索中的交互作用模型。     

A rapid effect of stimulus quality on the durations of individual fixations during reading

We developed a variant of the single fixation replacement paradigm (Yang & McConkie, 2001, 2004) in order to examine the effect of stimulus quality on fixation duration during reading. Subjects' eye movements were monitored while they read passages of text for comprehension. During critical fixations, equal changes to the luminance of the background produced either an increase (Up-Contrast) or a decrease (Down-Contrast) of the contrast of the text. The durations of critical fixations were found to be lengthened in the Down-Contrast but not the Up-Contrast condition. Ex-Gaussian modelling of the distributions of fixation durations showed that the reduction in stimulus quality lengthened the majority of fixations, and a survival analysis estimated the onset of this effect to be approximately 141 ms following fixation onset. Because the stimulus quality of the text during critical fixations could not be predicted or parafoveally previewed prior to foveation, the present effect can be attributed to an immediate effect of stimulus quality on fixation duration.     

Recognition memory strength is predicted by pupillary responses at encoding while fixation patterns distinguish recollection from familiarity

Thirty-five healthy participants incidentally encoded a set of man-made and natural object pictures, while their pupil response and eye movements were recorded. At retrieval, studied and new stimuli were rated as novel, familiar (strong, moderate, or weak), or recollected. We found that both pupil response and fixation patterns at encoding predict later recognition memory strength. The extent of pupillary response accompanying incidental encoding was found to be predictive of subsequent memory. In addition, the number of fixations was also predictive of later recognition memory strength, suggesting that the accumulation of greater visual detail, even for single objects, is critical for the creation of a strong memory. Moreover, fixation patterns at encoding distinguished between recollection and familiarity at retrieval, with more dispersed fixations predicting familiarity and more clustered fixations predicting recollection. These data reveal close links between the autonomic control of pupil responses and eye movement patterns on the one hand and memory encoding on the other. Moreover, the data illustrate quantitative as well as qualitative differences in the incidental visual processing of stimuli, which are differentially predictive of the strength and the kind of memory experienced at recognition.     

Recognition memory strength is predicted by pupillary responses at encoding while fixation patterns distinguish recollection from familiarity

Thirty-five healthy participants incidentally encoded a set of man-made and natural object pictures, while their pupil response and eye movements were recorded. At retrieval, studied and new stimuli were rated as novel, familiar (strong, moderate, or weak), or recollected. We found that both pupil response and fixation patterns at encoding predict later recognition memory strength. The extent of pupillary response accompanying incidental encoding was found to be predictive of subsequent memory. In addition, the number of fixations was also predictive of later recognition memory strength, suggesting that the accumulation of greater visual detail, even for single objects, is critical for the creation of a strong memory. Moreover, fixation patterns at encoding distinguished between recollection and familiarity at retrieval, with more dispersed fixations predicting familiarity and more clustered fixations predicting recollection. These data reveal close links between the autonomic control of pupil responses and eye movement patterns on the one hand and memory encoding on the other. Moreover, the data illustrate quantitative as well as qualitative differences in the incidental visual processing of stimuli, which are differentially predictive of the strength and the kind of memory experienced at recognition.     

Dyslexic and normal readers' eye movements

Dyslexic and normal readers' eye movements were compared while tracking a moving fixation point and in reading. Contrary to previous reports, the dyslexic and normal readers did not differ in their number of saccades, percentage of regressions, or stability of fixations in the tracking task. Thus, defective oculomotor control was not associated with or a causal factor in dyslexia, and the dyslexics' abnormal eye movements in reading must be related to differences in higher cognitive processes. However, individual differences in oculmotor efficiency, independent of reading ability, were found within both the dyslexic and normal groups, and these differences were correlated in reading and tracking tasks.     

Eye movements in drawing simple lines

As part of an investigation into real-world drawing, eye movements and eye-hand interactions have been recorded for twenty subjects of varying drawing experience drawing simple straight and curved lines and a square. Two modes of eye-hand behaviour were observed. In the first, named 'close pursuit', fixations closely followed the pencil with a sequence of small saccades. In the second, named 'target locking', a stable fixation was made on the end-point of the line throughout the entire drawing action. Depending on subject and type of line, close pursuit, target locking, or a combination of these modes was used regardless of previous drawing experience. The results are discussed in terms of the role of the eye in the control of the movement trajectory of the hand.     

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.     

Rapid eye-fixation training without eyetracking

Maintenance of stable central eye fixation is crucial for a variety of behavioral, electrophysiological, and neuroimaging experiments. Naive observers in these experiments are not typically accustomed to fixating, either requiring the use of cumbersome and costly eyetracking or producing confounds in results. We devised a flicker display that produced an easily detectable visual phenomenon whenever the eyes moved. A few minutes of training using this display dramatically improved the accuracy of eye fixation while observers performed a demanding spatial attention cuing task. The same amount of training using control displays did not produce significant fixation improvements, and some observers consistently made eye movements to the peripheral attention cue, contaminating the cuing effect. Our results indicate that (1) eye fixation can be rapidly improved in naive observers by providing real-time feedback about eye movements, and (2) our simple flicker technique provides an easy and effective method for providing this feedback. S. Suzuki, satoru@northwestern.edu     

Evidence against visual integration across saccadic eye movements

One of the classic problems in perception concerns how we perceive a stable, continuous visual world even though we view it via a temporally discontinuous series of eye movements. Previous investigators have suggested that our perception of a stable visual environment is due to anintegrative visual buffer, a special memory store capable of fusing the visual contents of successive fixations according to their environmental coordinates. In this paper, three experiments are reported that attempted to demonstrate the existence of an integrative visual buffer. The experimental procedure required subjects to mentally fuse two halves of a dot matrix presented in the same spatial region of a display, but separated by an eye movement so that each half was viewed only during one fixation. Thus, subjects had to integrate packets of visual information that had the same environmental coordinates, but different retinal coordinates. No evidence was found in any experiment for the fusion of visual information from successive fixations in memory, leaving the status of the integrative visual buffer in serious doubt.     

Evaluation algorithm for eye movement patterns during a problem solving task]

Cognitive processes are accompanied by eye movements, which are interrupted by fixations of an almost infinite number of points in the visual field. To investigate these processes, a systematic analysis of those movements is required to structure the long sequences of fixations. This task is possible if there are interrelationships between the ongoing thought processes and the fixations. Such interrelationships may manifest themselves through certain patterns of eye movements. It often happens that subsets of visual points are being looked at repeatedly. This is because a cognitive connection among the subset's elements is being discovered or created by such repetition. The method presented here attempts to achieve automatic recognition of fixation point patterns. Its usefulness is demonstrated using data from an experiment where eye movements were recorded while subjects were solving Raven Test items. The method may be characterized as a variant of time series analysis for nominal data. It is suitable for non-numerical data in general.     

Scrutinization, Spatial Attention, and the Spatial Programming of Saccadic Eye Movements

Results are presented from an experiment in which subjects' eye movements were recorded while they carried out two visual tasks with similar material. One task was chosen to require close visual scrutiny; the second was less visually demanding. The oculomotor behaviour in the two tasks differed in three ways. (1) When scrutinizing, there was a reduction in the area of visual space over which stimulation influences saccadic eye movements. (2) When moving their eyes to targets requiring scrutiny, subjects were more likely to make a corrective saccade. (3) The duration of fixations on targets requiring scrutiny was increased. The results are discussed in relation to current theories of visual attention and the control of saccadic eye movements.     

Covert visual attention and extrafoveal information use during object identification

Three experiments are reported that examined the relationship between covert visual attention and a viewer's ability to use extrafoveal visual information during object identification. Subjects looked at arrays of four objects while their eye movements were recorded. Their task was to identify the objects in the array for an immediate probe memory test. During viewing, the number and location of objects visible during given fixations were manipulated. In Experiments 1 and 2, we found that multiple extrafoveal previews of an object did not afford any more benefit than a single extrafoveal preview, as assessed by means of time of fixation on the objects. In Experiment 3, we found evidence for a model in which extrafoveal information acquired during a fixation derives primarily from the location toward which the eyes will move next. The results are discussed in terms of their implications for the relationship between covert visual attention and extrafoveal information use, and a sequential attention model is proposed.     

Expertise in basketball modifies perceptual discrimination abilities,underlying cognitive processes,and visual behaviours

In this paper, the links between cognitive constraints, visual behaviours, and perceptual judgements are examined. Two experiments investigated the perceptual processes employed during same-different judgement tasks. In Experiment 1, experts' eye movements (i.e., number of fixations and fixation duration) were consistent across discrepant source and target conditions where the number of displaced elements was manipulated. In contrast, novices decreased the number of fixations employed as the number of elements displaced increased. The findings are consistent with the view that both experts and novices process information in a manner (relational or attributional) that constrains the type of visual search used (low or high sensitive to attributional change). In Experiment 2, manipulation of target presentation confirmed that recognition was viewpoint dependent for both expert and novice players. The degradation in performance was accompanied by a change in the visual search behaviours employed by experts, which confirmed thr strength of the search–cognition–performance links     

The distribution of fixation durations during reading: effects of stimulus quality

Participants' eye movements were recorded as they read single sentences presented normally, presented entirely in faint text, or presented normally except for a single faint word. Fixations were longer when the entire sentence was faint than when the sentence was presented normally. In addition, fixations were much longer on a single faint word embedded in normal text, compared to when the entire sentence was faint. The primary aim of the study was to examine the influence of stimulus quality on the distribution of fixation durations. Ex-Gaussian fitting revealed that stimulus quality affected the mean of the Normal component, but in contrast to results from single-word tasks (Plourde & Besner, 1997), stimulus quality did not affect the exponential component, regardless of whether one or all words were faint. The results also contrast with the finding (Staub, White, Drieghe, Hollway, & Rayner, 2010) that the word frequency effect on fixation durations is an effect on both of the critical distributional parameters. These findings are argued to have implications for the interpretation of the role of stimulus quality in word recognition, and for models of eye movement control in reading.