The roles of vision and eye movements in the control of activities of daily living

The aim of this study was to determine the pattern of fixations during the performance of a well-learned task in a natural setting (making tea), and to classify the types of monitoring action that the eyes perform. We used a head-mounted eye-movement video camera, which provided a continuous view of the scene ahead, with a dot indicating foveal direction with an accuracy of about 1 deg. A second video camera recorded the subject's activities from across the room. The videos were linked and analysed frame by frame. Foveal direction was always close to the object being manipulated, and very few fixations were irrelevant to the task. The first object-related fixation typically led the first indication of manipulation by 0.56 s, and vision moved to the next object about 0.61 s before manipulation of the previous object was complete. Each object-related act that did not involve a waiting period lasted an average of 3.3 s and involved about 7 fixations. Roughly a third of all fixations on objects could be definitely identified with one of four monitoring functions: locating objects used later in the process, directing the hand or object in the hand to a new location, guiding the approach of one object to another (e.g. kettle and lid), and checking the state of some variable (e.g. water level). We conclude that although the actions of tea-making are 'automated' and proceed with little conscious involvement, the eyes closely monitor every step of the process. This type of unconscious attention must be a common phenomenon in everyday life.     

Concurrent schedule control of human visual target fixations

Operant conditioning techniques were applied to the study of how target fixations are controlled by the probability of signal occurrence. In a standard vigilance setting, gaze at three illuminable volt meters was monitored by a Mackworth television eye camera with automatic recording capability. Gaze at a given meter produced illumination of the meter, and signals (deflections of the needle on the meter) were scheduled as intermittent consequences of this response. Target fixations were thus placed under the control of concurrent variable-ratio, differential-reinforcement-of-low-rate, and fixed-interval schedules in normal adult volunteers.     

Eye movements as a function of response contingencies measured by blackout technique

A program may have a low error rate but, at the same time, require little of the student and teach him little. A measure to supplement error rate in evaluating a program has recently been developed. This measure, called the blackout ratio, is the percentage of material that may be deleted without increasing the error rate. In high blackout-ratio programs, obtaining a correct answer is contingent upon only a small portion of the item. The present study determined if such low response-contingent material is read less thoroughly than programmed material that is heavily response-contingent. Eye movements were compared for two versions of the same program that differed only in the choice of the omitted words. The alteration of the required responses resulted in a version with a higher blackout ratio than the original version, which had a low blackout ratio. Eighteen undergraduates received half their material from the high and half their material from the low blackout-ratio version. The order was counterbalanced. Location and duration of all eye fixations in each item were recorded by a Mackworth Eye Marker Camera. On high blackout-ratio material, subjects used fewer fixations, shorter fixation time, and shorter scanning time. High blackout-ratio material failed to evoke the students' attention.     

The span of the effective stimulus during a fixation in reading

A computer-based eye-movement controlled, display system was developed for the study of perceptual processes in reading. A study was conducted to identify the region from which skilled readers pick up various types of visual information during a fixation while reading. This study involved making display changes, based on eye position, in the text pattern as the subject was in the act of reading from it, and then examining the effects these changes produced on eye behavior. The results indicated that the subjects acquired word-length pattern information at least 12 to 15 character positions to the right of the fixation point, and that this information primarily influenced saccade lengths. Specific letter- and word-shape information were acquired no further than 10 character positions to the right of the fixation point.     

Data acquisition system for precision eye-fixation studies

A system has been developed to sense and record eye point-of-gaze for on-line computer processing, using a Mackworth camera in conjunction with a closed-circuit television system. System optics and electronics are described, together with computer software for system calibration and automatic artifact removal.     

Perception of object-context relations: eye-movement analyses in infants and adults

Twenty-eight 4-month-olds' and twenty-two 20-year-olds' attention to object-context relations was investigated using a common eye-movement paradigm. Infants and adults scanned both objects and contexts. Infants showed equivalent preferences for animals and vehicles and for congruent and incongruent object-context relations overall, more fixations of objects in congruent object-context relations, more fixations of contexts in incongruent object-context relations, more fixations of objects than contexts in vehicle scenes, and more fixation shifts in incongruent than congruent vehicle scenes. Adults showed more fixations of congruent than incongruent scenes, vehicles than animals, and objects than contexts; equal fixations of animals and their contexts but more fixations of vehicles than their contexts; and more shifts of fixation when inspecting animals in context than vehicles in context. These findings for location, number, and order of eye movements indicate that object-context relations play a dynamic role in the development and allocation of attention.     

One algorithm to rule them all? An evaluation and discussion of ten eye movement event-detection algorithms

Almost all eye-movement researchers use algorithms to parse raw data and detect distinct types of eye movement events, such as fixations, saccades, and pursuit, and then base their results on these. Surprisingly, these algorithms are rarely evaluated. We evaluated the classifications of ten eye-movement event detection algorithms, on data from an SMI HiSpeed 1250 system, and compared them to manual ratings of two human experts. The evaluation focused on fixations, saccades, and post-saccadic oscillations. The evaluation used both event duration parameters, and sample-by-sample comparisons to rank the algorithms. The resulting event durations varied substantially as a function of what algorithm was used. This evaluation differed from previous evaluations by considering a relatively large set of algorithms, multiple events, and data from both static and dynamic stimuli. The main conclusion is that current detectors of only fixations and saccades work reasonably well for static stimuli, but barely better than chance for dynamic stimuli. Differing results across evaluation methods make it difficult to select one winner for fixation detection. For saccade detection, however, the algorithm by Larsson, Nyström and Stridh (IEEE Transaction on Biomedical Engineering, 60(9):2484–2493,2013) outperforms all algorithms in data from both static and dynamic stimuli. The data also show how improperly selected algorithms applied to dynamic data misestimate fixation and saccade properties.     

Assessing cue usage in performance contexts: A comparison between eye-movement and concurrent verbal report methods

The relationship between eye fixations and concurrent verbal reports as measures of selective attention was examined in two different performance contexts. Experienced and less experienced soccer players were presented with filmed action sequences. In Experiment 1, subjects reacted to 11-versus-11 soccer simulations; in Experiment 2, 3-versus-3 situations were presented. Each study involved two experimental conditions: (1) visual fixations were recorded using an eye-movement system and (2) subjects continuously verbalized the location of their visual attention. In 11-versus-11 situations, there were no differences in performance across the two conditions, indicating that verbalization had no effect on performance. Also, there were no differences between the two methods in identifying important information sources. In 3-versus-3 situations, concurrent verbalization resulted in reactivity. Moreover, there were differences between the two methods in identifying important display areas. Findings showed that the relationship between visual fixation and selective attention is dependent on the nature of the stimulus presented. When peripheral vision is employed to extract task-specific information, verbal reports provide a more veritable measure of selective attention; eye fixations may yield a more accurate measure when the task requires information to be extracted foveally. Findings are discussed with regard to the differences between “looking” and “seeing” as a methodological issue.     

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.     

Automatizing of visual attention

Perceptual automatizing was argued to occur as a consequence of repeated experience with a stimulus. Automatizing was hypothesized to entail a stereotyping in sampling of sensory information together with an attendant decrease in the rate of sampling of that information. An experiment was performed in which human Ss observed stimulus pictures for several trials, during which records were made of their visual fixations. It was found that fixation rate habituated and that this habituation was accompanied by a reduction in the uncertainty (entropy) of the spatial distributions of fixations. These results were interpreted as evidence for automatizing of visual fixation processes. Analysis of eye-movement distances suggested a possible mechanism for the reported loss of vividness of a stimulus which is perceived habitually.     

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.     

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 effect of the first glimpse at a scene on eye movements during search

Previewing scenes briefly makes finding target objects more efficient when viewing is through a gaze-contingent window (windowed viewing). In contrast, showing a preview of a randomly arranged search display does not benefit search efficiency when viewing during search is of the full display. Here, we tested whether a scene preview is beneficial when the scene is fully visible during search. Scene previews, when presented, were 250 ms in duration. During search, the scene was either fully visible or windowed. A preview always provided an advantage, in terms of decreasing the time to initially fixate and respond to targets and in terms of the total number of fixations. In windowed visibility, a preview reduced the distance of fixations from the target position until at least the fourth fixation. In full visibility, previewing reduced the distance of the second fixation but not of later fixations. The gist information derived from the initial glimpse of a scene allowed for placement of the first one or two fixations at information-rich locations, but when nonfoveal information was available, subsequent eye movements were only guided by online information.     

Expertise in pictorial perception: eye-movement patterns and visual memory in artists and laymen

In two sessions with free scanning and memory instructions, eye-movement patterns from nine artists were compared with those of nine artistically untrained participants viewing 16 pictures representing a selection of categories from ordinary scenes to abstraction: 12 pictures were made to accommodate an object-oriented viewing mode (selection of recognisable objects), and a pictorial viewing mode (selection of more structural features), and 4 were abstract. The artistically untrained participants showed preference for viewing human features and objects, while the artists spent more scanning time on structural/abstract features. A group by session interaction showed a change of viewing strategy in the artists, who viewed more objects and human features in the memory task session. A verbal test of recall memory showed no overall difference in the number of pictures remembered, but the number of correctly remembered pictorial features was significantly higher for artists than for the artistically untrained viewers, irrespective of picture type. No differences in fixation frequencies/durations were found between groups across sessions, but a significant task-dependent-group by session interaction of fixation frequency/duration showed that the artistically untrained participants demonstrated repetition effects in fewer, longer fixations with repeated viewing, while the opposite pattern obtained for the artists.     

Reading strategy modulates parafoveal-on-foveal effects in sentence reading

Task demands and individual differences have been linked reliably to word skipping during reading. Such differences in fixation probability may imply a selection effect for multivariate analyses of eye-movement corpora if selection effects correlate with word properties of skipped words. For example, with fewer fixations on short and highly frequent words the power to detect parafoveal-on-foveal effects is reduced. We demonstrate that increasing the fixation probability on function words with a manipulation of the expected difficulty and frequency of questions reduces an age difference in skipping probability (i.e., old adults become comparable to young adults) and helps to uncover significant parafoveal-on-foveal effects in this group of old adults. We discuss implications for the comparison of results of eye-movement research based on multivariate analysis of corpus data with those from display-contingent manipulations of target words.     

The revealing glance: Eye gaze behavior to concealed information

We explored the usefulness of eye fixation durations as a dependent measure in a concealed knowledge test, drawing on Ryan, Hannula, and Cohen (2007), who found eye fixations on a familiar face to be longer than fixations on an unknown face. However, in their study, participants always had to select the known face out of three faces; thus, recognition and response intention could not be differentiated. In the experimental phase of our experiment, participants saw six faces per trial and had to select one of them. We had three conditions: In the first, one of the six faces was a known face, and the participants had to conceal that knowledge and select another face (concealed display); in another, one of the six faces was a known face, and the participants had to select that face (revealed display); or finally, all six faces were unknown, and participants had to select any of the six faces (neutral display). Using fixation durations as the dependent measure, we found a pure and early recognition effect; that is, fixations on the concealed faces (known but not selected) were longer than fixations on the nonselected unknown target faces in the neutral display. In addition, we found a response intention effect; that is, fixation durations on the selected known faces were longer than those on concealed faces (known but not selected).     

Central Fixations are Inadequately Controlled by Instructions Alone: Implications for Studying Cerebral Asymmetry

A fundamental concern when using visual presentations to study cerebral asymmetry is to ensure that stimuli are presented with the same degree of retinal eccentricity from a central fixation point in either visual field. However, a widely used procedure intended to control fixation location merely instructs participants to fixate appropriately without any other means of ensuring that central fixations actually occur. We assessed the validity of assuming that instructions alone ensure central fixation by using the traditional R VF advantage for words and either (a) only instructions to fixate centrally, or (b) an eye-tracking device that ensured central fixation on every trial. Experiments 1 and 2 found that when only instructions were given, the vast majority of fixations were not central, and more occurred to the right of centre than to the left. Moreover, the prevalence of non-central fixations was otherwise disguised by the finding that both fixation procedures produced similar R VF advantages in overt performance. The impact of typical non-central fixations on performance was revealed by systematically manipulating fixation location in Experiment 3, where deviations in fixation of only 0.25 from centre had a reliable impact on visual field effects. Implications of these findings for studies of cerebral asymmetry are discussed.     

Differences in eye-movement patterns between anorexic and control observers when judging body size and attractiveness

Attentional biases may influence the eye-movements made when judging bodies and so alter the visual information sampled when making a judgment. This may lead to an overestimation of body size. We measured the eye-movements made by 16 anorexic observers and 16 age-matched controls when judging body size and attractiveness. We combined behavioural data with a novel eye-movement analysis technique that allowed us to apply spatial statistical techniques to make fine spatial discriminations in the pattern of eye-movements between our observer groups. Our behavioural results show that anorexic observers overestimate body size relative to controls and find bodies with lower body mass indexes more attractive. For both judgments, the controls' fixations centre on the stomach, but the anorexic observers show a much wider fixation pattern extending to encompass additional features such as the prominence of the hip and collar bones. This additional visual information may serve to alter their behavioural judgments towards an overestimation of body size and shift their ideal body size towards a significantly lower value.     

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.