Disentangling the mechanisms underlying infant fixation durations in scene perception: A computational account

The goal of this article is to investigate the unexplored mechanisms underlying the development of saccadic control in infancy by determining the generalizability and potential limitations of extending the CRISP theoretical framework and computational model of fixation durations (FDs) in adult scene‐viewing to infants. The CRISP model was used to investigate the underlying mechanisms modulating FDs in 6‐month‐olds by applying the model to empirical eye‐movement data gathered from groups of infants and adults during free‐viewing of naturalistic and semi‐naturalistic videos. Participants also performed a gap‐overlap task to measure their disengagement abilities. Results confirmed the CRISP model's applicability to infant data. Specifically, model simulations support the view that infant saccade programming is completed in two stages: an initial labile stage, followed by a non‐labile stage. Moreover, results from the empirical data and simulation studies highlighted the influence of the material viewed on the FD distributions in infants and adults, as well as the impact that the developmental state of the oculomotor system can have on saccade programming and execution at 6 months. The present work suggests that infant FDs reflect on‐line perceptual and cognitive activity in a similar way to adults, but that the individual developmental state of the oculomotor system affects this relationship at 6 months. Furthermore, computational modeling filled the gaps of psychophysical studies and allowed the effects of these two factors on FDs to be simulated in infant data providing greater insights into the development of oculomotor and attentional control than can be gained from behavioral results alone.

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title: Infant's transitions toward adult-like scanning.
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title: Individual Differences in Infant Fixation Duration Relate to Attention and Behavioral Control in Childhood
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title: Using E-Z Reader to examine the concurrent development of eye-movement control and reading skill.
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title: An analysis of the saccadic system by means of double step stimuli
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title: Dynamics of saccade target selection: Race model analysis of double step and search step saccade production in human and macaque
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title: Small Saccades to Double-Stepped Targets Moving in Two Dimensions
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title: Eye movement responses to a horizontally moving visual stimulus.
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title: Mechanisms of saccadic decision making while encoding naturalistic scenes.
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title: A dynamical model of saccade generation in reading based on spatially distributed lexical processing
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title: Toward a model of eye movement control in reading.
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title: Spatial representation and attention in toddlers with Williams syndrome and Down syndrome
abstract: The nature of the spatial representations that underlie simple visually guided actions early in life was investigated in toddlers with Williams syndrome (WS), Down syndrome (DS), and healthy chronological age- and mental age-matched controls, through the use of a "double-step" saccade paradigm. The experiment tested the hypothesis that, compared to typically developing infants and toddlers, and toddlers with DS, those with WS display a deficit in using spatial representations to guide actions. Levels of sustained attention were also measured within these groups, to establish whether differences in levels of engagement influenced performance on the double-step saccade task. The results showed that toddlers with WS were unable to combine extra-retinal information with retinal information to the same extent as the other groups, and displayed evidence of other deficits in saccade planning, suggesting a greater reliance on sub-cortical mechanisms than the other populations. Results also indicated that their exploration of the visual environment is less developed. The sustained attention task revealed shorter and fewer periods of sustained attention in toddlers with DS, but not those with WS, suggesting that WS performance on the double-step saccade task is not explained by poorer engagement. The findings are also discussed in relation to a possible attention disengagement deficit in WS toddlers. Our study highlights the importance of studying genetic disorders early in development.

title: Body-centered representations for visually-guided action emerge during early infancy
abstract: The nature of the spatial representations that underlie simple visually guided actions early in life were investigated through the application of a 'double-step' saccade paradigm to 3- and 7-month-old infants. Saccades in the older infants, like those observed in adults, were executed within body-centered spatial coordinates that take into account the effects of intervening eye movements. In contrast, younger infants tended to respond according to the targets' retinocentric locations and did not incorporate the effects of displacements caused by previous saccades. These results indicate that contrary to prevailing views, body-centered representations for action are not present from birth but emerge, probably through experience, over the first few months of life.

title: Egocentric Action in Early Infancy: Spatial Frames of Reference for Saccades
abstract: The extent to which infants combine visual (i e, retinal position) and nonvisual (eye or head position) spatial information in planning saccades relates to the issue of what spatial frame or frames of reference influence early visually guided action We explored this question by testing infants from 4 to 6 months of age on the double-step saccade paradigm, which has shown that adults combine visual and eye position information into an egocentric (head- or trunk-centered) representation of saccade target locations In contrast, our results imply that infants depend on a simple retinocentric representation at age 4 months, but by 6 months use egocentric representations more often to control saccade planning Shifts in the representation of visual space for this simple sensorimotor behavior may index maturation in cortical circuitry devoted to visual spatial processing in general

title: Do six-month-old infants perceive causality?
abstract: The idea of cause and effect is often assumed to originate in prolonged learning. However, the present findings suggest that 27-week-old infants may already perceive a cause-effect relationship. Reversal of an apparently causal event (direct launching) produced more recovery of attention following habituation than the reversal of a similar but apparently non-causal event (delayed reaction). In both cases the changes in the spatiotemporal properties of the stimuli were identical. Hence the infant's percept of direct launching may involve more than an encoding of its spatiotemporal properties. Since the same kind of stimulus gives rise to a causal illusion in adults, it may be that the additional factor at work is the perception of a causal relationship. This finding may be significant in terms of the modularity of the infant visual system and the later development of causal understanding.

title: Principles of Object Perception
abstract: Research on human infants has begun to shed light on early-developing processes for segmenting perceptual arrays Into objects. Infants appear to perceive objects by analyzing three-dimensional surface arrangements and motions. Their perception does not accord with a general tendency to maximize flgural goodness or to attend to nonaccidental geometric relations in visual arrays. Object perception does accord with principles governing the motions of material bodies: Infants divide perceptual arrays into units that move as connected wholes, that move separately from one another, that tend to maintain their size and shape over motion, and that tend to act upon each other only on contact. These findings suggest that a general representation of object unity and boundaries is interposed between representations of surfaces and representations of objects of familiar kinds. The processes that construct this representation may be related to processes of physical reasoning.

title: Developmental Changes in Visual Scanning of Dynamic Faces and Abstract Stimuli in Infants: A Longitudinal Study.
abstract: The characteristics of scanning patterns between the ages of 6 and 26 weeks were investigated through repeated assessments of 10 infants. Eye movements were recorded using a corneal-reflection system while the infants looked at 2 dynamic stimuli: the naturally moving face of their mother and an abstract stimulus. Results indicated that the way infants scanned these stimuli stabilized only after 18 weeks, which is slightly later than the ages reported in the literature on infants' scanning of static stimuli. This effect was especially prominent for the abstract stimulus. From the 14-week session on, infants adapted their scanning behavior to the stimulus characteristics. When scanning the video of their mother's face, infants directed their gaze at the mouth and eye region most often. Even at the youngest age, there was no indication of an edge effect.

title: Changes in infants' visual scanning across the 2- to 14-week age period.
abstract: The characteristics of visual scanning over the 2- to 14-week age period were examined through repeated assessments conducted on a sample of 10 infants. Scanning patterns were measured using a bright-pupil corneal reflex system, and the stimuli consisted of various sets of static, moving, or flickering geometric figures. There appear to be a number of age-related changes in the dominant mode of visual scanning. At the youngest ages the infants' scanning often proved unrelated to the locations of the stimulus contours, and in instances where a stimulus figure was in fact attended the infants typically centered their regard on a single prominent feature. In contrast, as the infants grew older they more consistently directed their saccades toward stimulus contours, became increasingly disposed to scan between different stimulus features, and directed their saccades with increased accuracy. When a stimulus was flickering, however, the infants' scanning characteristics reverted to those typically found at younger ages. The mechanisms which might account for the effects of age and of stimulus quality on visual scanning are considered.

title: The Developing Visual Brain
abstract: 1.  Paediatric vision testing 3. Models of visual development 4. Newborn vision 5. Development optics - refraction and focusing or accommodation 6. Functional onset of specific cortical modules 7. Development of integration ('binding') and segmentation processes leading to object perception 8. The interlinked approach to development of attention and action 9. Plasticity in visual development 10. Concluding remarks References Index

title: The postnatal growth of visual capacity.
abstract: BRONSON, GOnDON. The Postnatal Growth of Visual Capacity. CHILD DEVELOPMENT, 1974, 45, 873-890. Behavioral studies of early visual development are interpreted within a framework provided by data from the neurosciences. It is concluded that the visual responses elicited during the first month of life are mediated directly by components of a phylogenetically older "second visual system," and that the more sophisticated reactions that typically begin to appear during the second and third months reflect a dawning participation of the primary visual system in the processing of visual input. The process of postnatal visual development is viewed as a progressive encoding, within different components of the visual network, of increasingly more complex aspects of the information contained in the visual signal.

title: Developmental Cognitive Neuroscience
abstract: ion for integrated biological models. Starting from this premise, Mjolsness et al. (1991) have introduced a modeling framework for the study of development, centered around genes and their interactions. This framework shares features with the models described earlier, but in a combination that is not found in any of the others. It incorporates features that allow modeling of processes at the tissue level, such as in the reaction-di¤usion and mechanical models, but unlike the biochemical kinetics and phage l models; and unlike the former but similar to the latter, it also includes a description of molecular processes, such as gene expression. The modeling framework consists of two major components: 1. The first is a neural network representation of molecular-level interactions. Gene interactions, as well as other molecular signaling and regulatory events, are modeled as a particular kind of neural net, namely, recurrent nets, with connections allowed in both directions between any pair of nodes (Hopfield, 1984; Hertz et al., 1991). In this formulation, gene product concentrations correspond to node activation levels and gene interaction strengths to connection weights. 2. The second component is a Lindenmayersystemlike grammar of rules (Lindenmayer, 1968; Prusinkiewicz and Lindenmayer, 1990), L-grammar, which describe cell-cell interactions and changes in number, type, and state of cells.

title: The gap effect in newborns
abstract: In four experiments we investigated the gap effect in infants within the first 3 days of life. Reaction times (RTs) to make a saccade to a peripheral target were measured on gap trials, in which the central fixation stimulus went off 500  ms before target presentation, and on overlap trials, in which the central fixation stimulus remained on. In every experiment the fixation stimulus was a flashing light. The target stimulus was a schematic face in Experiment 1, a flashing light shown at 20° eccentricity in Experiment 2, a flashing light shown at 30° eccentricity in Experiment 3, and an upside-down schematic face in Experiment 4. In Experiments 1–3 a gap effect was found. That is, RT was faster on gap than on overlap trials. In contrast, the gap effect was absent in Experiment 4. These findings are consistent with the view that the superior colliculus plays a major role in producing the gap effect at birth.

title: Individual and developmental differences in disengagement of fixation in early infancy.
abstract: The current study investigated whether individual and developmental differences in look duration are correlated with the latency for infants to disengage fixation from a visual stimulus. Ninety-four infants (52 3-month-olds, 42 4-month-olds) were tested in a procedure that measured ocular reaction time to shift fixation from a central target to a peripheral target under conditions in which the central-target either remained present ("competition" condition) or was removed from the display ("noncompetition" condition). Look duration was correlated with disengagement latency; longer-looking infants were slower than shorter-looking infants to shift fixation to the peripheral target on competition trials, but not noncompetition trials. Results were similar for 3- and 4-month-olds, although 3-month-olds showed slower latencies on all trials. Furthermore, long-looking infants were not consistently slower, but rather showed greater variability in their response latencies under conditions that required disengagement of fixation. The results support the position that developmental and individual differences in look duration are linked to the development of the neural attentional systems that control the ability to disengage, or inhibit, visual fixation.

title: Changes in Infants' Ability to Switch Visual Attention in the First Three Months of Life
abstract: The abilities of 1-month-old and 3-month-old infants to shift their gaze from a central target to a peripheral target were compared in four experiments. In experiment 1 targets matched in mean luminance to the background were presented to infants in the periphery at varying levels of contrast. The contrast thresholds for target detection were found to be significantly different for 1-month-olds compared with 3-month-olds. With targets set close to these contrast thresholds, correct refixations and the latency for shifting attention were examined in experiment 2. Two conditions were used: a peripheral target was presented against a homogeneous background (noncompetition); and in the second condition, the patterned target appeared at one of two lighter peripheral windows set against a darker background (competition). Although there was no difference between the two age groups in the latency for shifting visual attention, 1-month-olds were found to make more directional errors in the competition condition. The competition effect of two potential targets on latencies was examined in experiment 3. In the competition condition, two identical peripheral patterned targets were presented to the infants. The 3-month-olds refixated more quickly to one of the double targets in the competition condition than to a single peripheral target, whereas 1-month-olds were slowed down by a double target display. Finally, in experiment 4 the ability of the infants to process and disengage from a central stimulus and to refixate towards a similar peripheral target was examined. This type of competition disrupted both the direction of the first eye movement and the latency to shift attention in both age groups. However, the effect was significantly greater for the 1-month-olds. Taken together, the results of these experiments demonstrate the greater disruption of fixation-shift behaviour in 1-month-olds compared with 3-month-olds when competing visual stimuli are used. This developmental change is explained in terms of maturation of executive cortical orienting systems over the first months of life.

title: Sensory Visual Loss And Cognitive Deficits In The Selective Attentional System Of Normal Infants And Neurologically Impaired Children
abstract: The ability of infants to shift their gaze laterally from a central target (fixation shift) was investigated in normal one‐ and three‐month‐old infants in two visual tasks; competition (central fixating stimulus remained visible while peripheral target was presented) and non‐competition (central fixating stimulus replaced by peripheral target). The younger infants were significantly more disrupted by the competition condition, in terms of latency to refixate and direction of first eye movement. An immature attention system is proposed to explain this affect. In addition, visually evoked potentials in response to comparable stimuli were easier to elicit in older infants, suggesting that the one‐month‐olds possessed more immature sensory and perceptual visual systems, as well as poorer neural systems for controlling selective attention. Both techniques have been applied to a group of neurologically impaired children, and the results indicate that the tests may be useful in distinguishing sensory loss from attentional impairments in these patients.

title: Components of Visual Orienting in Early Infancy: Contingency Learning, Anticipatory Looking, and Disengaging
abstract: Three aspects of the development of visual orienting in infants of 2, 3, and 4 months of age are examined in this paper. These are the age of onset and sequence of development of (1) the ability to readily disengage gaze from a stimulus, (2) the ability to consistently show anticipatory eye movements, and (3) the ability to use a central cue to predict the spatial location of a target. Results indicated that only the 4--month-old group was easily able to disengage from an attractive central stimulus to orient toward a simultaneously presented target. The 4--month-old group also showed more than double the percentage of anticipatory looks than did the other age groups. Finally, only the 4--month-old group showed significant evidence of being able to acquire the contingent relationship between a central cue and the spatial location (to the right or to the left) of a target. Measures of anticipatory looking and contingency learning were not correlated. These findings are, in general terms, consistent with the predictions of matura-tional accounts of the development of visual orienting.

title: Infants’ shifts of gaze from a central to a peripheral stimulus: a longitudinal study of development between 6 and 26 weeks
abstract: This article reports the results of an intensive, longitudinal investigation of the development of infants’ ability to shift gaze from a central to a peripheral stimulus. Sixteen infants were followed at 2-week intervals from 6 to 26 weeks of age. A high degree of discontinuity was found in the development of both frequency and latency of shifts of gaze, with rapid improvement between 9 and 16 weeks, followed by more gradual improvement between 16 and 26 weeks. Individual developmental trajectories for frequency were highly similar to the group trajectory. Trajectories for latency cost differed more across infants. Inter-infant differences had not become stable for either measure at 26 weeks. The findings are consistent with explanations of the development of gaze shifting in terms of changes in the relative strength of processes which maintain the focus of attention and gaze, and processes which interrupt and shift it.

title: Infants' fast saccades in the gap paradigm and development of visual attention☆
abstract: The saccadic reaction times (SRTs) in the overlap, no-overlap, and gap conditions of 2.5- to 12-month-old infants and adults were measured. In the overlap condition, the SRTs of younger infants were over 600 ms longer than those of older infants, whereas the SRTs in the gap condition of the younger infants were 300–350 ms, much faster than reported hitherto, and were shortened only by about 100 ms. The results indicate that the oculo-motor system and attention process for disengagement in the gap condition mature earlier than the attention process for disengagement in the overlap condition.

title: Orienting in normal and pathological development
abstract: The term plasticity is often confined to changes due to learning. We believe, however, that the rapid lability of human behavior as different mental contents receive attention represents an important form of plasticity. Recent research in temperament and cognitive neuroscience provides an account of the development of a specific neural system involved in attentional self-regulation. In this paper, we concentrate on a network involved in orienting. We describe what is currently known about this network and its development during the first years of life. This network interacts with other attentional networks that come to control orienting to remembered events as well as those currently present. Orienting reflects processes that are both deeply biological and also open to cultural influences through learning. Attention is influenced by the current emotional state and is also important in achieving control over the emotional state. We present evidence on how learning influences eye position between 4 and 18 months of life and indicate influences of orienting on important aspects of infant behavior. Like any biological system, problems can arise in these mechanisms. We speculate on how individual differences in distress proneness and orienting may relate to the development of psychopathology.

title: Disengaging visual attention in the infant and adult
abstract: The latency to make an eye movement towards a phase-reversing peripheral target was measured in 1.5-, 3-, and 6-month-old infants and adults using four interleaved conditions. In the short-gap condition, the central fixating stimulus (schematic face) disappeared 240 ms prior to the onset of the peripheral target. In the long-gap condition, the interval between the offset of the central stimulus and the target was 720 ms. In the no-overlap condition, the appearance of the peripheral target coincided with the offset of the central stimulus, and in the overlap condition, the central stimulus remained present for 2,120 ms following the onset of the peripheral target. In general, latencies decreased with age, though there was very little difference between the 3-and 6-month-olds. Gap conditions produced the fastest saccadic latencies compared to the no-overlap and overlap conditions in all groups. In line with previous studies, the overlap condition produced the slowest responses, even for adults who had been instructed to make an eye movement as quickly as possible. However, a manual response measure in the adult group using the same paradigm did not produce longer latencies for the overlap condition, suggesting that the effect may be specific to mechanisms controlling saccades and not motor responses per se. The short latencies for gap conditions and the longer saccadic latencies in the overlap condition are taken as evidence to support a cortical disengagement hypothesis of orienting eye movements.

title: The E-Z Reader model of eye-movement control in reading: Comparisons to other models
abstract: The E-Z Reader model (Reichle et al. 1998; 1999) provides a theoretical framework for understanding how word identification, visual processing, attention, and oculomotor control jointly determine when and where the eyes move during reading. In this article, we first review what is known about eye movements during reading. Then we provide an updated version of the model (E-Z Reader 7) and describe how it accounts for basic findings about eye movement control in reading. We then review several alternative models of eye movement control in reading, discussing both their core assumptions and their theoretical scope. On the basis of this discussion, we conclude that E-Z Reader provides the most comprehensive account of eye movement control during reading. Finally, we provide a brief overview of what is known about the neural systems that support the various components of reading, and suggest how the cognitive constructs of our model might map onto this neural architecture.

title: SWIFT: a dynamical model of saccade generation during reading.
abstract: Mathematical models have become an important tool for understanding the control of eye movements during reading. Main goals of the development of the SWIFT model (R. Engbert, A. Longtin, & R. Kliegl, 2002) were to investigate the possibility of spatially distributed processing and to implement a general mechanism for all types of eye movements observed in reading experiments. The authors present an advanced version of SWIFT that integrates properties of the oculomotor system and effects of word recognition to explain many of the experimental phenomena faced in reading research. They propose new procedures for the estimation of model parameters and for the test of the model's performance. They also present a mathematical analysis of the dynamics of the SWIFT model. Finally, within this framework, they present an analysis of the transition from parallel to serial processing.

title: ICAT: a computational model for the adaptive control of fixation durations
abstract: Eye movements depend on cognitive processes related to visual information processing. Much has been learned about the spatial selection of fixation locations, while the principles governing the temporal control (fixation durations) are less clear. Here, we review current theories for the control of fixation durations in tasks like visual search, scanning, scene perception, and reading and propose a new model for the control of fixation durations. We distinguish two local principles from one global principle of control. First, an autonomous saccade timer initiates saccades after random time intervals (local-I). Second, foveal inhibition permits immediate prolongation of fixation durations by ongoing processing (local-II). Third, saccade timing is adaptive, so that the mean timer value depends on task requirements and fixation history (Global). We demonstrate by numerical simulations that our model qualitatively reproduces patterns of mean fixation durations and fixation duration distributions observed in typical experiments. When combined with assumptions of saccade target selection and oculomotor control, the model accounts for both temporal and spatial aspects of eye movement control in two versions of a visual search task. We conclude that the model provides a promising framework for the control of fixation durations in saccadic tasks.

title: The Psychophysics Toolbox.
abstract: The Psychophysics Toolbox is a software package that supports visual psychophysics. Its routines provide an interface between a high-level interpreted language (MATLAB on the Macintosh) and the video display hardware. A set of example programs is included with the Toolbox distribution.

title: The span of the effective stimulus during a fixation in reading
abstract: 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.

title: Training Attentional Control in Infancy
abstract: Several recent studies have reported that cognitive training in adults does not lead to generalized performance improvements [1, 2], whereas many studies with younger participants (children 4 years and older) have reported distal transfer [3, 4]. This is consistent with convergent evidence [5–8] for greater neural and behavioral plasticity earlier in development. We used gaze-contingent paradigms to train 11-month-old infants on a battery of attentional control tasks. Relative to an active control group, and following only a relatively short training period, posttraining assessments revealed improvements in cognitive control and sustained attention, reduced saccadic reaction times, and reduced latencies to disengage visual attention. Trend changes were also observed in spontaneous looking behavior during free play, but no change was found in working memory. The amount of training correlated with the degree of improvement on some measures. These findings are to our knowledge the first demonstration of distal transfer following attentional control training in infancy. Given the longitudinal relationships identified between early attentional control and learning in academic settings [9, 10], and the causal role that impaired control of attention may play in disrupting learning in several disorders [11–14], the current results open a number of avenues for future work.

title: It's in your eyes--using gaze-contingent stimuli to create truly interactive paradigms for social cognitive and affective neuroscience.
abstract: The field of social neuroscience has made remarkable progress in elucidating the neural mechanisms of social cognition. More recently, the need for new experimental approaches has been highlighted that allow studying social encounters in a truly interactive manner by establishing 'online' reciprocity in social interaction. In this article, we present a newly developed adaptation of a method which uses eyetracking data obtained from participants in real time to control visual stimulation during functional magnetic resonance imaging, thus, providing an innovative tool to generate gaze-contingent stimuli in spite of the constraints of this experimental setting. We review results of two paradigms employing this technique and demonstrate how gaze data can be used to animate a virtual character whose behavior becomes 'responsive' to being looked at allowing the participant to engage in 'online' interaction with this virtual other in real-time. Possible applications of this setup are discussed highlighting the potential of this development as a new 'tool of the trade' in social cognitive and affective neuroscience.

title: Consequences of eye color, positioning, and head movement for eye-tracking data quality in infant research
abstract: Eye tracking has become a valuable tool for investigating infant looking behavior over the last decades. However, where eye-tracking methodology and achieving high data quality have received a much attention for adult participants, it is unclear how these results generalize to infant research. This is particularly important as infants behave different from adults in front of the eye tracker. In this study, we investigated whether eye physiology, positioning, and infant behavior affect measures of eye-tracking data quality: accuracy, precision, and data loss. We report that accuracy and precision are lower, and more data loss occurs for infants with bluish eye color compared to infants with brownish eye color. Moreover, accuracy was lower for infants positioned in a high chair or in the parents' lap compared to infants positioned in a baby seat. Finally, precision decreased and data loss increased as a function of time. We highlight the importance of data quality when comparing multiple groups, as differences in data quality can affect eye-tracking measures. In addition, we investigate how two different measures to quantify infant movement influence eye-tracker data quality. These findings might help researchers with data collection and help manufacturers develop better eye-tracking systems for infants.

title: GraFIX: A semiautomatic approach for parsing low- and high-quality eye-tracking data
abstract: Fixation durations (FD) have been used widely as a measurement of information processing and attention. However, issues like data quality can seriously influence the accuracy of the fixation detection methods and, thus, affect the validity of our results (Holmqvist, Nyström, & Mulvey, 2012). This is crucial when studying special populations such as infants, where common issues with testing (e.g., high degree of movement, unreliable eye detection, low spatial precision) result in highly variable data quality and render existing FD detection approaches highly time consuming (hand-coding) or imprecise (automatic detection). To address this problem, we present GraFIX, a novel semiautomatic method consisting of a two-step process in which eye-tracking data is initially parsed by using velocity-based algorithms whose input parameters are adapted by the user and then manipulated using the graphical interface, allowing accurate and rapid adjustments of the algorithms’ outcome. The present algorithms (1) smooth the raw data, (2) interpolate missing data points, and (3) apply a number of criteria to automatically evaluate and remove artifactual fixations. The input parameters (e.g., velocity threshold, interpolation latency) can be easily manually adapted to fit each participant. Furthermore, the present application includes visualization tools that facilitate the manual coding of fixations. We assessed this method by performing an intercoder reliability analysis in two groups of infants presenting low- and high-quality data and compared it with previous methods. Results revealed that our two-step approach with adaptable FD detection criteria gives rise to more reliable and stable measures in low- and high-quality data.

title: Parsing eye-tracking data of variable quality to provide accurate fixation duration estimates in infants and adults
abstract: Researchers studying infants’ spontaneous allocation of attention have traditionally relied on hand-coding infants’ direction of gaze from videos; these techniques have low temporal and spatial resolution and are labor intensive. Eye-tracking technology potentially allows for much more precise measurement of how attention is allocated at the subsecond scale, but a number of technical and methodological issues have given rise to caution about the quality and reliability of high temporal resolution data obtained from infants. We present analyses suggesting that when standard dispersal-based fixation detection algorithms are used to parse eye-tracking data obtained from infants, the results appear to be heavily influenced by interindividual variations in data quality. We discuss the causes of these artifacts, including fragmentary fixations arising from flickery or unreliable contact with the eyetracker and variable degrees of imprecision in reported position of gaze. We also present new algorithms designed to cope with these problems by including a number of new post hoc verification checks to identify and eliminate fixations that may be artifactual. We assess the results of our algorithms by testing their reliability using a variety of methods and on several data sets. We contend that, with appropriate data analysis methods, fixation duration can be a reliable and stable measure in infants. We conclude by discussing ways in which studying fixation durations during unconstrained orienting may offer insights into the relationship between attention and learning in naturalistic settings.

title: Computing Inter-Rater Reliability for Observational Data: An Overview and Tutorial.
abstract: Many research designs require the assessment of inter-rater reliability (IRR) to demonstrate consistency among observational ratings provided by multiple coders. However, many studies use incorrect statistical procedures, fail to fully report the information necessary to interpret their results, or do not address how IRR affects the power of their subsequent analyses for hypothesis testing. This paper provides an overview of methodological issues related to the assessment of IRR with a focus on study design, selection of appropriate statistics, and the computation, interpretation, and reporting of some commonly-used IRR statistics. Computational examples include SPSS and R syntax for computing Cohen's kappa and intra-class correlations to assess IRR.

title: Eye tracking: a comprehensive guide to methods and measures
abstract: Holmqvist, K., Nystrom, N., Andersson, R., Dewhurst, R., Jarodzka, H., & Van de Weijer,  (2011). Eye tracking: a comprehensive guide to methods and measures, Oxford, UK:

title: Age-related change and stability of individual differences in infant saccade reaction time
abstract: Several facets of continuity in infant information processing were studied longitudinally using the visual expectation paradigm in a sample of 24 infants. At both 4 and 6 months of age, infants viewed an identical left-right alternating sequence of pictures while their eye movements were recorded. Human observers coded the videotape records to document saccadic reaction times (RT), rates of anticipatory fixation shifts to future pictures, and off-task behaviors. Measures of RT were reliable within each assessment and showed strong stability of individual differences across sessions. Measures of anticipation and off-task behaviors revealed few age differences, some within-session reliability, but no stability across sessions. Results provide strong evidence for continuity in some component of infant information processing during the early months of life.

title: A longitudinal study of visual expectation and reaction time in the first year of life.
abstract: Developmental change and stability of visual expectation and reaction times (RT) were examined at 5, 7, and 12 months in a longitudinal sample of term and preterm infants (birthweight <1,750 g). Using the traditional 200-ms cut-point to separate anticipatory from reactive saccades, RTs (and their standard deviations) declined markedly over age, whereas anticipations increased. Those infants who had faster RTs were more likely to anticipate upcoming events and were more attentive (fewer trials off-task and less response variability). Crossage stability was modest for most measures from 5 to 7 and 7 to 12 months, but rarely significant from 5 to 12 months. When the cut-point was lowered to 150 ms (to accommodate recent concerns that the higher cut-point may misclassify some true RTs as anticipations), the age-related increase in anticipations disappeared. Thus, although the results indicate marked increases in processing speed with age, evidence for increasing anticipations is equivocal. Findings were similar for preterm and term infants.

title: Express saccades and visual attention
abstract: One of the most intriguing and controversial observations in oculomotor research in recent years is the phenomenon of express saccades in monkeys and man. These are saccades with such short reaction times (100 msec in man, 70 msec in monkeys) that some experts on eye movements still regard them as artifacts or as anticipatory reactions that do not need any further explanation. On the other hand, some research groups consider them not only authentic but also a valuable means of investigating the mechanisms of saccade generation, the coordination of vision and eye movements, and the mechanisms of visual attention. This target article puts together pieces of experimental evidence in oculomotor and related research – with special emphasis on the express saccade – to enhance our present understanding of the coordination of vision, visual attention, and the eye movements subserving visual perception and cognition. We hypothesize that an optomotor reflex is responsible for the occurrence of express saccades, one that is controlled by higher brain functions involved in disengaged visual attention and decision making. We propose a neural network as the basis for more elaborate mathematical models or computer simulations of the optomotor system in primates.

title: The Past, Present, and Future of Computational Models of Cognitive Development.
abstract: Does modeling matter? We address this question by providing a broad survey of the computational models of cognitive development that have been proposed and studied over the last three decades. We begin by noting the advantages and limitations of computational models. We then describe four key dimensions across which models of development can be organized and classified. With this taxonomy in hand, we focus on how the modeling enterprise has evolved over time. In particular, we separate the timeline into three overlapping historical waves and highlight how each wave of models has not only been shaped by developmental theory and behavioral research, but in return also provided valuable insights and innovations to the study of cognitive development.

title: A computational model of the emergence of gaze following
abstract: We present a computational model of the emergence of gaze following in infant caregiver interactions. Using the model we explore the plausibility of the hypothesis that gaze following is a skill that infants acquire because they learn that monitoring their caregiver’s direction of gaze allows them to predict where interesting objects or events in their environment are. In particular, we demonstrate that a speciflc basic set of mechanisms is su‐cient for gaze following to emerge and we show how plausible alterations of model parameters motivated by flndings on developmental disorders lead to impairments in the learning of gaze following.

title: The Neural Basis for Visual Selective Attention in Young Infants: A Computational Account
abstract: Recent work by Amso and Johnson (Developmental Psychology, 42(6), 1236—1245, 2006) implicates the role of visual selective attention in the development of perceptual completion during early infancy. In the current article, we extend this finding by simulating the performance of 3-month-old infants on a visual search task, using a multi-channel, image-filtering model of early visual processing. Model parameters were systematically varied to simulate developmental change in three neural components of visual selective attention: degree of oculomotor noise, growth of horizontal connections in visual cortex, and duration of recurrent processing in parietal cortex. While two of the three components—horizontal connections and recurrent parietal processing—are each able to account for the visual search performance of 3-month-olds, recurrent parietal processing also suggests a coherent pattern of developmental change in visual selective attention during early infancy. We conclude by highlighting plausible neural mechanisms for modulating recurrent parietal activity, including the development of feedback from prefrontal cortex.

title: Models of habituation in infancy
abstract: Research on infant cognition using habituation methods has sparked considerable controversy in recent years. At the core of the debates is the issue of whether infants have early (and possibly innate) conceptual understandings. This article reviews a range of computational models of habituation that might provide insights into such discussions. The models are assessed against key behavioral and neural features of habituation: temporal unfolding, exponential decrease, familiarity-to-novelty shift, habituation to repeated testing, discriminability of habitual items, selective inhibition and cortical-subcortical interactions. The review suggests that current models fail to offer comprehensive explanations of the behavioral phenomena.

title: Computational perspectives on cognitive development.
abstract: This article reviews the efforts to develop process models of infants' and children's cognition. Computational process models provide a tool for elucidating the causal mechanisms involved in learning and development. The history of computational modeling in developmental psychology broadly follows the same trends that have run throughout cognitive science-including rule-based models, neural network (connectionist) models, ACT-R models, ART models, decision tree models, reinforcement learning models, and hybrid models among others.

title: Human anticipatory eye movements may reflect rhythmic central nervous activity
abstract: To investigate the possibility that rhythmic activity originating in the central nervous system may modulate human eye movements, anticipatory eye movements were generated by tracking an intermittently obscured sinusoidally moving target. Eight subjects tracked intermittently obscured sinusoids of three different frequencies and of two different amplitudes. Eye movements were recorded by an infra-red reflection technique. The eye velocity records were analysed in the frequency domain by power spectral estimates. During periods where the target was obscured, eye movements consisted of a staggered series of anticipatory saccades with intervening smooth anticipatory eye movements or relatively stationary periods. In sections where the intervening smooth components of anticipatory tracking were of high velocity (above 15 deg/s), a superimposed smooth tremulous oscillation at around 10 Hz was sometimes present. Coherence analysis showed that this 10 Hz range oscillation of smooth anticipatory movement was not derived from head tremor and that the same oscillation was present in both eyes. This oscillation was not generally observed during smooth tracking of pseudorandom waveforms. Investigation of anticipatory eye movements has revealed a 10-Hz range oscillation or "tremor" superimposed upon smooth movements that might in other circumstances be inhibited by direct visual feedback. This smooth eye movement oscillation is thought to originate from the central nervous system and may reflect a widespread frequency modulation of motor commands.

title: Intrinsic temporal patterning in the spontaneous movement of awake neonates.
abstract: The temporal organization of spontaneous movement in healthy, awake neonates was studied on the second or third day after birth. Movement was recorded using time lapse photography and quantified as a function of time. Fourier analysis was then used to partition the total variance of each neonate's time-based data into independent components in the frequency domain. Tests on the resulting cumulative variance distributions indicated that the fluctuations in movement over time were not random. Smoothed spectral density functions were then computed to isolate the dominant rhythms. Spectral peaks occurred in the region between .24 and 1.86 cycles per min, indicating the presence of rhythms in general motility with an average frequency (across babies) of .69 cycles per min. These findings are evidence of intrinsic temporal organization at frequencies very different from previously documented rhythms in newborn behavior and physiology.

title: Differential Frontal Cortex Activation Before Anticipatory and Reactive Saccades in Infants
abstract: Neural correlates of anticipatory and reactive saccades were studied in 4-month-old infants by recording high-density event-related potentials. Infants were presented with a fixed sequence of stimulus presentation to which they rapidly showed anticipatory saccades, as well as continuing with some reactive (stimulus-driven) saccades. As in a previous study, no clear evidence was found for adultlike, saccade-related potentials, although some presaccadic differences between reactive and anticipatory saccades were observed. Infants also showed different stimulus offset-related effects preceding the 2 types of trials with a right-frontal positivity when an anticipatory look follows, but only left-frontal positivity when a reactive saccade follows.

title: Mindless reading revisited: An analysis based on the SWIFT model of eye-movement control
abstract: In this article, we revisit the mindless reading paradigm from the perspective of computational modeling. In the standard version of the paradigm, participants read sentences in both their normal version as well as the transformed (or mindless) version where each letter is replaced with a z. z-String scanning shares the oculomotor requirements with reading but none of the higher-level lexical and semantic processes. Here we use the z-string scanning task to validate the SWIFT model of saccade generation [Engbert, R., Nuthmann, A., Richter, E., & Kliegl, R. (2005).  A dynamical model of saccade generation during reading.  as an example for an advanced theory of eye-movement control in reading. We test the central assumption of spatially distributed processing across an attentional gradient proposed by the SWIFT model. Key experimental results like prolonged average fixation durations in z-string scanning compared to normal reading and the existence of a string-length effect on fixation durations and probabilities were reproduced by the model, which lends support to the model's assumptions on visual processing. Moreover, simulation results for patterns of regressive saccades in z-string scanning confirm SWIFT's concept of activation field dynamics for the selection of saccade targets.

title: Characteristics of saccades in human infants
abstract: Infants (14-151 days) and adults were shown two-dimensional geometric forms or stimuli from a set of highly textured patterns. Their eye movements were recorded by an infrared corneal reflection eye movement recorder as they freely scanned the stimuli. For both infants and adults, linear relationships were found between the peak velocities of fast eye movements and their amplitudes (main sequences). Infants viewing texture stimuli had main sequences with slopes comparable to those of adults. Infants viewing simple geometric forms made slower saccades. They also showed more eye movement oscillations which analyses showed were probably back-to-back saccades. Both the slower saccades and saccadic oscillations were attributed to factors related to the attentional value of the stimuli.

title: Neural correlates of saccade planning in infants: a high-density ERP study.
abstract: Neural correlates of saccade planning in 6-month-old infants were investigated by high-density event-related potentials. Subjects made saccades to a target stimulus following a time gap from fixation stimulus offset (gap trials) or with the fixation stimulus still present (overlap trials). Like adults, infants were slower to make a saccade to the target when the fixation stimulus was still present. Strikingly, infants did not show clear evidence of the pre-saccadic components observed in adults which are thought to reflect cortical saccade planning processes. They did, however, show a left frontal positivity, which we suggest reflects cortical disinhibition of the colliculus initiated by fixation stimulus offset, and clear post-saccadic lambda waves. These results indicate that the frontal cortex already plays a role in action control by 6 months of age, while other aspects of cortical action planning may not yet be present in certain task situations.

title: Vehicles, Experiments in Synthetic Psychology
abstract: These imaginative thought experiments are the inventions of one of the world's eminent brain researchers. They are "vehicles," a series of hypothetical, self-operating machines that exhibit increasingly intricate if not always successful or civilized "behavior." Each of the vehicles in the series incorporates the essential features of all the earlier models and along the way they come to embody aggression, love, logic, manifestations of foresight, concept formation, creative thinking, personality, and free will. In a section of extensive biological notes, Braitenberg locates many elements of his fantasy in current brain research.

title: Atypical Disengagement from Faces and Its Modulation by the Control of Eye Fixation in Children with Autism Spectrum Disorder
abstract: By using the gap overlap task, we investigated disengagement from faces and objects in children (9–17 years old) with and without autism spectrum disorder (ASD) and its neurophysiological correlates. In typically developing (TD) children, faces elicited larger gap effect, an index of attentional engagement, and larger saccade-related event-related potentials (ERPs), compared to objects. In children with ASD, by contrast, neither gap effect nor ERPs differ between faces and objects. Follow-up experiments demonstrated that instructed fixation on the eyes induces larger gap effect for faces in children with ASD, whereas instructed fixation on the mouth can disrupt larger gap effect in TD children. These results suggest a critical role of eye fixation on attentional engagement to faces in both groups.

title: Eye movements during scene viewing: Evidence for mixed control of fixation durations
abstract: Recent behavioral and computational research on eye movement control during scene viewing has focused on where the eyes move. However, fixations also differ in their durations, and when the eyes move may be another important indicator of perceptual and cognitive activity. Here we used a scene onset delay paradigm to investigate the degree to which individual fixation durations are under direct moment-to-moment control of the viewer’s current visual scene. During saccades just prior to critical fixations, the scene was removed from view so that when the eyes landed, no scene was present. Following a manipulated delay period, the scene was restored to view. We found that one population of fixations was under the direct control of the current scene, increasing in duration as delay increased. A second population of fixations was relatively constant across delay. The pattern of data did not change whether delay duration was random or blocked, suggesting that the effects were not under the strategic control of the viewer. The results support a mixed control model in which the durations of some fixations proceed regardless of scene presence, whereas others are under the direct moment-to-moment control of ongoing scene analysis.

title: How are eye fixation durations controlled during scene viewing? Further evidence from a scene onset delay paradigm
abstract: Recent research on eye movements during scene viewing has focused on where the eyes fixate. But eye fixations also differ in their durations. Here we investigated whether fixation durations in scene viewing are under the direct and immediate control of the current visual input. In two scene memorization and one visual search experiments, the scene was removed from view during critical fixations for a predetermined delay, and then restored following the delay. Experiment 1 compared filled (pattern mask) and unfilled (grey field) delays. Experiment 2 compared random to blocked delays. Experiment 3 extended the results to a visual search task. The results demonstrate that fixation durations in scene viewing comprise two fixation populations. One population remains relatively constant across delay, and the second population increases with scene onset delay. The results are consistent with a mixed eye movement control model that incorporates an autonomous control mechanism with process monitoring. The results suggest that a complete gaze control model will have to account for both fixation location and fixation duration.

title: Saccadic localization of visual targets by the very young human infant
abstract: The direction, latency, and form of the 1- and 2-month-old human infant’s saccadic eye movements toward peripheral targets were investigated. Infants of both ages reliably executed a directionally appropriate first saccade toward a peripheral target introduced as far as 30 deg from the line of sight along the horizontal and both diagonal axes, but only to 10 deg along the vertical axis. The presence of a second target in the central visual field reduced the probability of peripheral target localization. A significant inverse relation was found between target distance from the line of sight and probability of initiating a directionally appropriate saccade. Electro-oculography revealed that latency to first saccade, although highly variable, was less than 500 msec on a significant proportion of trials. Unlike the adult, the first saccade to target was grossly hypometric and was followed by one or more saccades of approximately equal amplitude to the first.