How Reliably Do Eye Parameters Indicate Internal Versus External Attentional Focus?

Eye behavior is increasingly used as an indicator of internal versus external focus of attention both in research and application. However, available findings are partly inconsistent, which might be attributed to the different nature of the employed types of internal and external cognition tasks. The present study, therefore, investigated how consistently different eye parameters respond to internal versus external attentional focus across three task modalities: numerical, verbal, and visuo-spatial. Three eye parameters robustly differentiated between internal and external attentional focus across all tasks. Blinks, pupil diameter variance, and fixation disparity variance were consistently increased during internally directed attention. We also observed substantial attentional focus effects on other parameters (pupil diameter, fixation disparity, saccades, and microsaccades), but they were moderated by task type. Single-trial analysis of our data using machine learning techniques further confirmed our results: Classifying the focus of attention by means of eye tracking works well across participants, but generalizing across tasks proves to be challenging. Based on the effects of task type on eye parameters, we discuss what eye parameters are best suited as indicators of internal versus external attentional focus in different settings.     

Thalamic pathways for active vision

Active vision requires the integration of information coming from the retina with that generated internally within the brain, especially by saccadic eye movements. Just as visual information reaches cortex via the lateral geniculate nucleus of the thalamus, this internal information reaches the cerebral cortex through other higher-order nuclei of the thalamus. This review summarizes recent work on four of these thalamic nuclei. The first two pathways convey internal information about upcoming saccades (a corollary discharge) and probably contribute to the neuronal mechanisms that underlie stable visual perception. The second two pathways might contribute to the neuronal mechanisms underlying visual spatial attention in cortex and in the thalamus itself.     

An Investigation of Attention Allocation During Sequential Eye Movement Tasks

Allocation of visuo-spatial attention during dynamic viewing was investigated with a dual task. Primary tasks (reading, scanning, searching) all required sequential left-to-right eye movements. An additional speeded manual response was made to a visual probe that appeared early or late after the onset of a randomly determined fixation (25 or 170 msec probe delay). The probe appeared to the left, directly above, or to the right of the currently fixated character (-10, -5, 0, +5, or +10 characters probe eccentricity). Faster probe detection near the location of the forthcoming eye fixation was found in the search task, but not during reading or scanning. Fixation times increased and saccade lengths decreased as a consequence of probing in all three tasks. Fixations were, however, less prolonged when the probe appeared in the right than when it appeared in the left hemifield, and saccades were greatest when the probe appeared at +10 characters. The results extend the notion of goal-directed attention shifts to free viewing and highlight the impact of task-specific processing requirements.     

Information processing during saccadic eye movements

Saccadic eye movements are made at least 100,000 times each day. It is well known that sensitivity to visual input is suppressed during saccades; recent evidence suggests that some kinds of information processing are suppressed as well. Suppression during saccades implies that processing occurs discretely (during eye fixations only), rather than continuously (during both fixations and saccades). We examined this issue in the context of the Posner and Snyder (1975) primed letter-matching task. We found that a prime viewed in one fixation had a larger influence on targets viewed in a second fixation when a long rather than a short saccade separated the two fixations. This result demonstrates that at least some information processing occurs during saccades.     

The role of saccades in multitasking: towards an output-related view of eye movements

The present paper presents an overview of research on the role of saccades in multitasking. Multitasking is known to cause performance costs in terms of increased response times and/or error rates. However, most of the previous research on multitasking was focused on manual and vocal action demands, and the role of eye movements has been largely neglected. As a consequence, saccade execution was mainly considered with respect to its functional role in gathering new visual information (input side of information processing). However, several more recent experiments confirmed that saccades both exhibit and cause dual-task costs in the context of other actions and should thus also be regarded as a response modality (output side of information processing). Theoretical implications as well as several open issues for future research will be outlined.     

Mindless reading revisited: Eye movements during reading and scanning are different

In an extension of a study by Vitu, O’Regan, Inhoff, and Topolski (1995), we compared global and local characteristics of eye movements during (1) reading, (2) the scanning of transformed text (in which each letter was replaced with a z), and (3) visual search. Additionally, we examined eye behavior with respect to specific target words of high or low frequency. Globally, the reading condition led to shorter fixations, longer saccades, and less frequent skipping of target strings than did scanning transformed text. Locally, the manipulation of word frequency affected fixation durations on the target word during reading, but not during visual search or z-string scanning. There were also more refixations on target words in reading than in scanning. Contrary to Vitu et al.’s (1995) findings, our results show that eye movements are not guided by a global strategy and local tactics, but by immediate processing demands.     

Fixation positions after skipping saccades: A single space makes a large difference

During reading, saccadic eye movements are generated to shift words into the center of the visual field for lexical processing. Recently, Krügel and Engbert (Vision Research 50:1532?C1539, 2010) demonstrated that within-word fixation positions are largely shifted to the left after skipped words. However, explanations of the origin of this effect cannot be drawn from normal reading data alone. Here we show that the large effect of skipped words on the distribution of within-word fixation positions is primarily based on rather subtle differences in the low-level visual information acquired before saccades. Using arrangements of ??x?? letter strings, we reproduced the effect of skipped character strings in a highly controlled single-saccade task. Our results demonstrate that the effect of skipped words in reading is the signature of a general visuomotor phenomenon. Moreover, our findings extend beyond the scope of the widely accepted range-error model, which posits that within-word fixation positions in reading depend solely on the distances of target words. We expect that our results will provide critical boundary conditions for the development of visuomotor models of saccade planning during reading.     

Trans-saccadic perception

A basic question in cognition is how visual information obtained in separate glances can produce a stable, continuous percept. Previous explanations have included theories such as integration in a trans-saccadic buffer or storage in visual memory, or even that perception begins anew with each fixation. Converging evidence from primate neurophysiology, human psychophysics and neuroimaging indicate an additional explanation: the intention to make a saccadic eye movement leads to a fundamental alteration in visual processing itself before and after the saccadic eye movement. We outline five principles of 'trans-saccadic perception' that could help to explain how it is possible - despite discrete sensory input and limited memory - that conscious perception across saccades seems smooth and predictable.     

Blinks as an index of cognitive activity during reading

Horizontal and vertical EOG recordings of eye movements were analyzed to determine the spatial and temporal distribution of blinks and the patterns of eye movements (saccades and fixation pauses) exhibited by six subjects during the reading of stories presented in two formats (on paper and on a VDT). The frequency and placement of blinks was not affected by the presentation condition. Blinks were determined to be non-randomly distributed during reading. Significantly more blinks (36%) occurred in conjunction with saccades than the proportion of time consumed by saccades (12%) would predict. Significantly more blinks (36%) occurred in the vicinity of line change saccades, which accounts for 15% of reading time, and with fixation pauses associated with regressions (42%), which accounts for 26% of reading time, than with fixation pauses during normal reading (22%), which accounts for 60% of reading time. The results of the study suggest that blink behavior during reading is under perceptual and cognitive control.     

Neurophysiology and neuroanatomy of reflexive and volitional saccades: evidence from studies of humans

This review provides a summary of the contributions made by human functional neuroimaging studies to the understanding of neural correlates of saccadic control. The generation of simple visually guided saccades (redirections of gaze to a visual stimulus or pro-saccades) and more complex volitional saccades require similar basic neural circuitry with additional neural regions supporting requisite higher level processes. The saccadic system has been studied extensively in non-human (e.g., single-unit recordings) and human (e.g., lesions and neuroimaging) primates. Considerable knowledge of this system’s functional neuroanatomy makes it useful for investigating models of cognitive control. The network involved in pro-saccade generation (by definition largely exogenously-driven) includes subcortical (striatum, thalamus, superior colliculus, and cerebellar vermis) and cortical (primary visual, extrastriate, and parietal cortices, and frontal and supplementary eye fields) structures. Activation in these regions is also observed during endogenously-driven voluntary saccades (e.g., anti-saccades, ocular motor delayed response or memory saccades, predictive tracking tasks and anticipatory saccades, and saccade sequencing), all of which require complex cognitive processes like inhibition and working memory. These additional requirements are supported by changes in neural activity in basic saccade circuitry and by recruitment of additional neural regions (such as prefrontal and anterior cingulate cortices). Activity in visual cortex is modulated as a function of task demands and may predict the type of saccade to be generated, perhaps via top-down control mechanisms. Neuroimaging studies suggest two foci of activation within FEF - medial and lateral - which may correspond to volitional and reflexive demands, respectively. Future research on saccade control could usefully (i) delineate important anatomical subdivisions that underlie functional differences, (ii) evaluate functional connectivity of anatomical regions supporting saccade generation using methods such as ICA and structural equation modeling, (iii) investigate how context affects behavior and brain activity, and (iv) use multi-modal neuroimaging to maximize spatial and temporal resolution.     

Visual perception and corollary discharge

Perception depends not only on sensory input but also on the state of the brain receiving that input. A classic example is perception of a stable visual world in spite of the saccadic eye movements that shift the images on the retina. A long-standing hypothesis is that the brain compensates for the disruption of visual input by using advance knowledge of the impending saccade, an internally generated corollary discharge. One possible neuronal mechanism for this compensation has been previously identified in parietal and frontal cortex of monkeys, but the origin of the necessary corollary discharge remained unknown. Here, we consider recent experiments that identified a pathway for a corollary discharge for saccades that extends from the superior colliculus in the midbrain to the frontal eye fields in the cerebral cortex with a relay in the medial dorsal nucleus of the thalamus. We first review the nature of the evidence used to identify a corollary discharge signal in the complexity of the primate brain and show its use for guiding a rapid sequence of eye movements. We then consider two experiments that show this same corollary signal may provide the input to the frontal cortex neurons that alters their activity with saccades in ways that could compensate for the displacements in the visual input produced by saccadic eye movements. The first experiment shows that the corollary discharge signal is spatially and temporally appropriate to produce the alterations in the frontal-cortex neurons. The second shows that this signal is necessary for this alteration because inactivation of the corollary reduces the compensation by frontal-cortex neurons. The identification of this relatively simple circuit specifies the organization of a corollary discharge in the primate brain for the first time and provides a specific example upon which consideration of the roles of corollary activity in other systems and for other functions can be evaluated.     

Taking a new look at looking at nothing

A crucial question in cognitive science is how linguistic and visual information are integrated. Previous research has shown that eye movements to objects in the visual environment are locked to linguistic input. More surprisingly, listeners fixate on now-empty regions that had previously been occupied by relevant objects. This 'looking at nothing' phenomenon has been linked to the claim that the visual system constructs sparse representations of the external world and relies on saccades and fixations to extract information in a just-in-time manner. Our model provides a different explanation: based on recent work in visual cognition and memory, it assumes that the visual system creates and stores detailed internal memory representations, and that looking at nothing facilitates retrieval of those representations.     

Influence of attentional capture on oculomotor control

Previous research has shown that when searching for a color singleton, top-down control cannot prevent attentional capture by an abrupt visual onset. The present research addressed whether a task-irrelevant abrupt onset would affect eye movement behavior when searching for a color singleton. Results show that in many instances the eye moved in the direction of the task-irrelevant abrupt onset. There was evidence that top-down control could neither entirely prevent attentional capture by visual onsets nor prevent the eye from starting to move in the direction of the onset. Results suggest parallel programming of 2 saccades: 1 voluntary goal-directed eye movement toward the color singleton target and 1 stimulus-driven eye movement reflexively elicited by the abrupt onset. A neurophysiologically plausible model that can account for the current findings is discussed.     

Neurophysiology and neuroanatomy of reflexive and volitional saccades: Evidence from studies of humans

This review provides a summary of the contributions made by human functional neuroimaging studies to the understanding of neural correlates of saccadic control. The generation of simple visually guided saccades (redirections of gaze to a visual stimulus or pro-saccades) and more complex volitional saccades require similar basic neural circuitry with additional neural regions supporting requisite higher level processes. The saccadic system has been studied extensively in non-human (e.g., single-unit recordings) and human (e.g., lesions and neuroimaging) primates. Considerable knowledge of this system’s functional neuroanatomy makes it useful for investigating models of cognitive control. The network involved in pro-saccade generation (by definition largely exogenously-driven) includes subcortical (striatum, thalamus, superior colliculus, and cerebellar vermis) and cortical (primary visual, extrastriate, and parietal cortices, and frontal and supplementary eye fields) structures. Activation in these regions is also observed during endogenously-driven voluntary saccades (e.g., anti-saccades, ocular motor delayed response or memory saccades, predictive tracking tasks and anticipatory saccades, and saccade sequencing), all of which require complex cognitive processes like inhibition and working memory. These additional requirements are supported by changes in neural activity in basic saccade circuitry and by recruitment of additional neural regions (such as prefrontal and anterior cingulate cortices). Activity in visual cortex is modulated as a function of task demands and may predict the type of saccade to be generated, perhaps via top-down control mechanisms. Neuroimaging studies suggest two foci of activation within FEF - medial and lateral - which may correspond to volitional and reflexive demands, respectively. Future research on saccade control could usefully (i) delineate important anatomical subdivisions that underlie functional differences, (ii) evaluate functional connectivity of anatomical regions supporting saccade generation using methods such as ICA and structural equation modeling, (iii) investigate how context affects behavior and brain activity, and (iv) use multi-modal neuroimaging to maximize spatial and temporal resolution.     

Expedited suppression signal in ocular go/no-go decision

When scrutinizing the visual world, complex and unexpected stimuli often lead to prolonged eye fixations to enhance cognitive processing, likely by temporarily suppressing a planned saccade. The present study examined whether the suppression signal is tightly linked to a specific planned saccade and if it conforms to the viewer's intention. A novel Go/No-go task was devised where participants made consecutive saccades to fixate a stimulus appearing across the screen horizontal meridian in 4° steps. At times, the features of the stimulus (colour and/or shape) were altered when it reappeared at a new location. Participants had to suppress the saccade that would otherwise leave the stimulus if its features matched instructed criteria. Saccade suppression was determined by the reduced probability for saccades towards and away from a target stimulus. Results show both correct suppression to saccades leaving the target and erroneous suppression to saccades towards it. The erroneous suppression was initially observed for any change in features but later lifted. The suppression shortened the length of saccades leaving a target but not those towards it. The initial suppression during previewing the target appears to be based on expedited but incomplete evaluation of visual stimulus, and is not linked to any specific saccade. These properties might reflect the stage of ocular decision based on which the suppression signal is generated. They also account for the phenomenon of “peripheral-to-foveal” effect on eye movements in reading.     

The cognitive impact of epileptiform EEG-discharges; relationship with type of cognitive task.

In this study we analyzed the effect of differing task dimensions (high vs. low information demand; short vs. long testing duration) on the occurrence of epileptiform EEG-discharges and the cognitive impact of such discharges. We performed this study only in patients with focal discharges as this appears to be the most complicated group to assess any relationship between epileptiform EEG-discharges and cognitive impairment. Seventeen patients with focal discharges in the EEG and an established diagnosis of localization-related (partial) epilepsy were included. The following tasks were used: Low information demand: auditory and visual RT; high information demand: BCRT and CVST. Short testing duration: Arithmetic and Reading; long testing duration: Vocabulary and Block Design. The percentage of patients with epileptiform EEG-discharge and EEG-related cognitive impact were compared using Chi-square testing. The occurrence of epileptiform EEG-discharges was not associated with one of the experimental conditions introduced in our study, that is, high/low information demand or short/long testing period. Also the difference between computerized reaction-time measurement and more traditional 'paper and pencil tasks' such as reading was not statistically significant. The only statistical significant difference was the more frequent occurrence of epileptiform EEG-discharges during tasks that used the visual input mode. In addition, we could identify one test that appeared to be particularly sensitive to direct cognitive effects of epileptiform EEG-discharges. Only for the CVST, the computerized visual searching task, the relationship with epilepsy-related cognitive impact is statistically significant. This test is the most mentally demanding test of the tests presented in our study and measures speed of visual information processing, using complex stimulus patterns and has a long testing duration. Our results do not confirm that any of the investigated task dimensions (high vs. low information demand; short vs. long testing duration) have a dominant effect on the occurrence of epileptiform EEG-discharges and the cognitive impact of such discharges. The effect found for the CVST suggest that three factors combined are necessary to assess the impact of epileptiform EEG-discharges on cognition: visual input mode, longer testing duration and high information processing demand.     

The effects of flicker on eye movement control

Groups of typists with extensive experience of screen-based editing and groups of students with no such experience carried out a reading task under three conditions of illumination (50-Hz flicker, 100-Hz flicker, and steady illumination). Subjects read a sentence, which was followed by the presentation of a single stimulus word on the same line to the right-hand side of the display. The task was to decide whether or not the stimulus was present in the sentence. Subjects were free to re-inspect the sentence when making the decision. Eye movements were measured as subjects completed the task. In comparison with students, typists adopted a more cautious reading style, making more right-to-left saccades, shorter saccades, and more corrective eye movements. Flicker affected the performance of both groups of subjects in the first pass, leading to shorter saccades. In the second pass, its effect for students was to shorten the extent of large saccades made to check the presence of the stimulus word. In the group of typists, flicker led to an increase in the variability of saccade extent and a doubling in the number of small corrective saccades. The results are consistent with the view that flicker has two distinct effects on reading, both of which are potentially disruptive. The first relates to an increase in the number of prematurely triggered saccades, which are, as a result, less accurate. The second is an increase in the number of saccades perturbed in flight, which land short of their intended target. These two mechanisms may have different consequences for readers, depending on their reading style.     

刺激的视觉显著性和奖赏价值对眼跳的影响

本研究旨在探索刺激的视觉显著性和奖赏价值分别在协同和竞争的条件下对眼跳过程的影响。实验材料为成对的Gabor图案,要求被试选择具有更高奖赏价值的图案,并记录下其眼动过程。实验分为协同条件和竞争条件。结果发现,在不同实验条件下,奖赏价值对眼跳命中率和潜伏期均存在显著效应;视觉显著性的效应则在不同实验条件下出现了分离。刺激驱动过程和目标驱动过程对眼动行为的影响可能是互相区别的两种不同模式。     

Action–effect associations revealed by eye movements

We move our eyes not only to get information, but also to supply information to our fellows. The latter eye movements can be considered as goal-directed actions to elicit changes in our counterparts. In two eye-tracking experiments, participants looked at neutral faces that changed facial expression 100 ms after the gaze fell upon them. We show that participants anticipate a change in facial expression and direct their first saccade more often to the mouth region of a neutral face about to change into a happy one and to the eyebrows region of a neutral face about to change into an angry expression. Moreover, saccades in response to facial expressions are initiated more quickly to the position where the expression was previously triggered. Saccade–effect associations are easily acquired and are used to guide the eyes if participants freely select where to look next (Experiment 1), but not if saccades are triggered by external stimuli (Experiment 2).     

Establishing object correspondence across eye movements: Flexible use of spatiotemporal and surface feature information

Visual input is frequently disrupted by eye movements, blinks, and occlusion. The visual system must be able to establish correspondence between objects visible before and after a disruption. Current theories hold that correspondence is established solely on the basis of spatiotemporal information, with no contribution from surface features. In five experiments, we tested the relative contributions of spatiotemporal and surface feature information in establishing object correspondence across saccades. Participants generated a saccade to one of two objects, and the objects were shifted during the saccade so that the eyes landed between them, requiring a corrective saccade to fixate the target. To correct gaze to the appropriate object, correspondence must be established between the remembered saccade target and the target visible after the saccade. Target position and surface feature consistency were manipulated. Contrary to existing theories, surface features and spatiotemporal information both contributed to object correspondence, and the relative weighting of the two sources of information was governed by the demands of the task. These data argue against a special role for spatiotemporal information in object correspondence, indicating instead that the visual system can flexibly use multiple sources of relevant information.