Executive control of gaze by the frontal lobes

Executive control requires controlling the initiation of movements, judging the consequences of actions, and adjusting performance accordingly. We have investigated the role of different areas in the frontal lobe in executive control expressed by macaque monkeys performing a saccade stop signal task. Certain neurons in the frontal eye field respond to visual stimuli, and others control the production of saccadic eye movements. Neurons in the supplementary eye field do not control directly the initiation of saccades but, instead, signal the production of errors, the anticipation and delivery of reinforcement, and the presence of response conflict. Neurons in the anterior cingulate cortex signal the production of errors and the anticipation and delivery of reinforcement, but not the presence of response conflict. Intracranial local field potentials in the anterior cingulate cortex of monkeys indicate that these medial frontal signals can contribute to event-related potentials related to performance monitoring. Electrical stimulation of the supplementary eye field improves performance in the task by elevating saccade latency. An interactive race model shows how interacting units produce behavior that can be described as the outcome of a race between independent processes and how conflict between gaze-holding and gaze-shifting neurons can be used to adjust performance.     

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.     

自主控制眼跳：实验范式、神经机制和应用

自主控制眼跳是眼跳类型之一。自主控制眼跳实验范式为研究各种脑损伤,神经疾病和精神失调提供了一种新的研究手段,为研究眼跳的神经机制以及反应抑制、空间工作记忆等高级认知功能提供了重要的方法。文章介绍了自主控制眼跳的两种实验范式：反向眼跳和记忆导向眼跳,阐述了自主控制眼跳的神经机制及其实验范式的应用,指出自主控制眼跳实验范式为评定精神分裂症等脑功能失调病人的神经功能状态提供了重要的信息,为研究各种脑功能失调和精神疾病提供了重要的研究方法。今后的研究趋势是眼跳研究与神经成像技术和临床观察相结合     

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.     

Interdependence of Saccadic and Fixational Fluctuations

Recent research suggests that the different components of eye movements (fixations, saccades) are not strictly separate but are interdependent processes. This argument rests on observations that gaze-step sizes yield unimodal distributions and exhibit power-law scaling, indicative of interdependent processes coordinated across timescales. The studies that produced these findings, however, employed complex tasks (visual search, scene perception). Thus, the question is whether the observed interdependence is a fundamental property of eye movements or emerges in the interplay between cognitive processes and complex visual stimuli. In this study, we used a simple eye movement task where participants moved their eyes in a prescribed sequence at several different paces. We outlined diverging predictions for this task for independence versus interdependence of fixational and saccadic fluctuations and tested these predictions by assessing the spectral properties of eye movements. We found no clear peak in the power spectrum attributable exclusively to saccadic fluctuations. Furthermore, changing the pace of the eye movement sequence yielded a global shift in scaling relations evident in the power spectrum, not just a localized shift for saccadic fluctuations. These results support the conclusion that fixations and saccades are interdependent processes.     

Is target movement as well as target displacement a stimulus for saccadic eye movements?

The effects of visual movement on saccadic eye movement have been examined. In a classic apparent-movement demonstration with two successively exposed line-segment targets the quality of the movement is dependent on the relative orientation of the line segments. If saccadic eye movements are elicited between the targets in this situation, the configuration leading to optimal apparent movement also leads to the shortest-latency saccades. When a single line segment is succeeded by two line segments flanking it on opposite sides, and if one of these has the same orientation as the initial one and the other a different orientation, then apparent motion is seen between the two lines with the same orientation. However, the direction of saccades elicited in this configuration is not influenced by the relative orientations of the line segments. The two results together suggest that the effect of visual movement on saccadic eye movement is nonspecific.     

Strategic control over saccadic eye movements: studies of the fixation offset effect

We studied the strategic (presumably cortical) control of ocular fixation in experiments that measured the fixation offset effect (FOE) while manipulating readiness to make reflexive or voluntary eye movements. The visual grasp reflex, which generates reflexive saccades to peripheral visual signals, reflects an opponent process in the superior colliculus (SC) between fixation cells at the rostral pole, whose activity helps maintain ocular position and increases when a stimulus is present at fixation, and movement cells, which generate saccades and are inhibited by rostral fixation neurons. Voluntary eye movements are controlled by movement and fixation cells in the frontal eye field (FEF). The FOE--a decrease in saccade latency when the fixation stimulus is extinguished--has been shown to reflect activity in the collicular eye movement circuitry and also to have an activity correlate in the FEF. Our manipulation of preparatory set to make reflexive or voluntary eye movements showed that when reflexive saccades were frequent and voluntary saccades were infrequent, the FOE was attenuated only for reflexive saccades. When voluntary saccades were frequent and reflexive saccades were infrequent, the FOE was attenuated only for voluntary saccades. We conclude that cortical processes related to task strategy are able to decrease fixation neuron activity even in the presence of a fixation stimulus, resulting in a smaller FOE. The dissociation in the effects of a fixation stimulus on reflexive and voluntary saccade latencies under the same strategic set suggests that the FOEs for these two types of eye movements may reflect a change in cellular activity in different neural structures, perhaps in the SC for reflexive saccades and in the FEF for voluntary saccades.     

Eye movement indices of mental workload

Four investigations were carried out to assess the feasibility of using eye movement measures as indices of mental workload. In the first experiment, saccadic extent was measured during free viewing while subjects performed low, moderate and high complexity, auditory tone counting as the workload tasks. The range of saccadic extent decreased significantly as tone counting complexity (workload) was increased. In the second experiment the range of spontaneous saccades was measured under three levels of counting complexity with a visual task that did not require fixation or tracking. The results indicated that the extent of saccadic eye movements was significantly restricted as counting complexity increased. In the third experiment, the effects of practice were examined and decreased saccadic range under high tone counting complexity was observed even when significant increases in performance occurred with practice. Finally, in experiment 4, the first experiment was repeated with additional optokinetic stimulation and the saccadic range was again observed to decrease with tone counting complexity. The results indicated that the extent of spontaneous and elicited eye movements was significantly restricted as counting complexity increased. We conclude that this measure may provide a valuable index of mental workload.     

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。     

Perception of self-motion from visual flow

Accurate and efficient control of self-motion is an important requirement for our daily behavior. Visual feedback about self-motion is provided by optic flow. Optic flow can be used to estimate the direction of self-motion (‘heading’) rapidly and efficiently. Analysis of oculomotor behavior reveals that eye movements usually accompany self-motion. Such eye movements introduce additional retinal image motion so that the flow pattern on the retina usually consists of a combination of self-movement and eye movement components. The question of whether this ‘retinal flow’ alone allows the brain to estimate heading, or whether an additional ‘extraretinal’ eye movement signal is needed, has been controversial. This article reviews recent studies that suggest that heading can be estimated visually but extraretinal signals are used to disambiguate problematic situations. The dorsal stream of primate cortex contains motion processing areas that are selective for optic flow and self-motion. Models that link the properties of neurons in these areas to the properties of heading perception suggest possible underlying mechanisms of the visual perception of self-motion.     

Saccades to targets in three-dimensional space: dependence of saccadic latency on target location.

The latency of saccadic movements to targets appearing at various positions in three-dimensional visual space was measured in four experiments. The first experiment confirmed that latencies of saccades to visual targets are greater in the lower visual field and showed that the increase is not influenced by the vertical starting position of the eye in the orbit, nor by a time gap between the fixation offset and the target onset. A hypothesis that this visual field difference was caused by a link between downward saccades and convergence movements was tested by recording saccade latencies when the targets were in a different depth plane from that of the original fixation. We did not find any direct support for the vergence involvement hypothesis, although the lower/upper visual field effect was shown to decrease consistently in monocular viewing. It was also shown that saccades to targets positioned in a different depth plane have longer latencies. In a final experiment, the visual field effect was shown to depend on the egocentric rather than the gravitational vertical.     

Saccades to targets in three-dimensional space: Dependence of saccadic latency on target location

The latency of saccadic movements to targets appearing at various positions in three-dimensional visual space was measured in four experiments. The first experiment confirmed that latencies of saccades to visual targets are greater in the lower visual field and showed that the increase is not influenced by the vertical starting position of the eye in the orbit, nor by a time gap between the fixation offset and the target onset. A hypothesis that this visual field difference was caused by a link between downward saccades and convergence movements was tested by recording saccade latencies when the targets were in a different depth plane from that of the original fixation. We did not find any direct support for the vergence involvement hypothesis, although the lower/upper visual field effect was shown to decrease consistently in monocular viewing. It was also shown that saccades to targets positioned in a different depth plane have longer latencies. In a final experiment, the visual field effect was shown to depend on the egocentric rather than the gravitational vertical.     

Search performance without eye movements

Visual search performance (with sets chosen to elicit both serial and parallel search patterns) under two conditions that precluded saccades was compared to the typical situation in which visual inspection of the array is possible. In one condition, the display duration was so brief that any saccades that were executed would be too late to bring the targeted portion of the array into the fovea. In the other, the display remained present until the subject's response, but eye position was monitored and trials with shifts in fixation were excluded from analysis. The latter condition produced search latencies that were nearly identical to those with free inspection. Brief exposure, in contrast, did not produce the pattern typical of serial search, presumably because of strategies induced to deal with the rapid decay of the visual array. It is concluded that saccadic eye movements play little role in the patterns of performance used to infer serial and parallel search, and that brief exposure is not a satisfactory technique for exploring the role of saccadic eye movements in visual search.     

Attention and saccadic eye movements

Four threshold detection experiments addressed three issues concerning the relationship between movements of spatial attention and saccadic eye movements: (a) the time course of attention shifts wit saccades, (b) the response of the two systems to changes in stimulus parameters, and (c) the relationship of attention to saccadic suppression. These issues bear on the more general question of the degree of independence between the saccadic and attentional movement systems. The results of these experiments support the contention that the mechanisms that shift attention are separate from those that control saccadic eye movements. Relevant events in the visual field periphery, however, will trigger both a saccade and attention shift. The attentional response to such events does not appear to be under subjects' control. The implication of these results for theories of saccadic suppression is discussed.     

The effect of blinks and saccadic eye movements on visual reaction times

Vision is suppressed during blinks and saccadic eye movements. We hypothesized that visual reaction times (RTs) in a vigilance test would be significantly increased when a blink or a saccade happened to coincide with the stimulus onset. Thirty healthy volunteers each performed a visual RT test for 15 min while their eye and eyelid movements were monitored by a system of infrared reflectance oculography. RTs increased significantly, many by more than 200 msec, when a blink occurred between 75 msec before and up to 150 msec after the stimulus onset. A similar result was observed with saccades that started 75 to 150 msec after the stimulus. Vision or attention was evidently inhibited before each blink and for longer than the saccades lasted. We suggest that visual suppression is involved in this process, which could explain some of the normal variability in RTs over periods of seconds that has not been adequately explained before.     

Neurophysiology and neuroanatomy of reflexive and voluntary saccades in non-human primates

A multitude of cognitive functions can easily be tested by a number of relatively simple saccadic eye movement tasks. This approach has been employed extensively with patient populations to investigate the functional deficits associated with psychiatric disorders. Neurophysiological studies in non-human primates performing the same tasks have begun to provide us with insights into the neural mechanisms underlying many cognitive functions. Here, we review studies that have investigated single neuron activity in the superior colliculus (see glossary), frontal eye field, supplementary eye field, dorsolateral prefrontal cortex, anterior cingulate (see glossary) cortex and lateral intraparietal area associated with the performance of visually guided saccades, anti-saccades and memory-guided saccades in awake behaving monkeys.     

Fixation disengagement and eye-movement latency

We examined eye-movement latencies to a target that appeared during visual fixation of a stationary stimulus, a moving stimulus, or an extrafoveal stimulus. The stimulus at fixation was turned off either before target onset (gap condition) or after target onset (overlap condition). Consistent with previous research, saccadic latencies were shorter in gap conditions than they were in overlap conditions (the gap effect). In Experiment 1, a gap effect was observed for vergence eye movements. In Experiment 2, a gap effect was observed for saccades directed at a target that appeared during visual pursuit of a moving stimulus. In Experiment 3, a gap effect was observed for saccades directed at a target that appeared during extrafoveal fixation. The present results extend reports of the gap effect for saccadic shifts during visual fixation to (a) vergence shifts during visual fixation, (b) saccadic shifts during smooth visual pursuit, and (c) saccadic shifts during extrafoveal fixation. The present findings are discussed with respect to the incompatible goals of fixation-locking and fixation-shifting oculomotor responses.     

Neurophysiology and neuroanatomy of reflexive and voluntary saccades in non-human primates

A multitude of cognitive functions can easily be tested by a number of relatively simple saccadic eye movement tasks. This approach has been employed extensively with patient populations to investigate the functional deficits associated with psychiatric disorders. Neurophysiological studies in non-human primates performing the same tasks have begun to provide us with insights into the neural mechanisms underlying many cognitive functions. Here, we review studies that have investigated single neuron activity in the superior colliculus (see glossary), frontal eye field, supplementary eye field, dorsolateral prefrontal cortex, anterior cingulate (see glossary) cortex and lateral intraparietal area associated with the performance of visually guided saccades, anti-saccades and memory-guided saccades in awake behaving monkeys.     

Memory representations guide targeting eye movements in a natural task

The change blindness phenomenon suggests that visual representations retained across saccades are very limited. In this paper we sought to specify the kind of information that is in fact retained. We investigated targeting performance for saccadic eye movements, since one need for visual representations across eye and body positions may be to guide coordinated movements. We examined saccades in the context of an ongoing sensory motor task in order to make stronger generalizations about natural visual functioning and deployment of attention. Human subjects copied random patterns of coloured blocks on a computer display. Their eye movement pattern was consistent from block to block, including a precise saccade to a previously-placed, neighbouring block during each additional block placement. This natural, consistent eye movement allowed the previously-placed, neighbouring block to serve as an implicit target without instructions to the subject. On random trials, we removed the target object from the display during a preceding saccade, so that observers were required to make the targeting saccade without a currently visible target. Targeting performance was excellent, and appeared to be influenced by spatial information that was not visible during the preceding fixation. Subjects were generally unaware of the disappearance and reappearance of the target. We conclude that spatial information about visual targets is retained across eye movements and used to guide subsequent movements.     

Where does attention go when you blink?

Many studies have shown that covert visual attention precedes saccadic eye movements to locations in space. The present research investigated whether the allocation of attention is similarly affected by eye blinks. Subjects completed a partial-report task under blink and no-blink conditions. Experiment 1 showed that blinking facilitated report of the bottom row of the stimulus array: Accuracy for the bottom row increased and mislocation errors decreased under blink, as compared with no-blink, conditions, indicating that blinking influenced the allocation of visual attention. Experiment 2 showed that this was true even when subjects were biased to attend elsewhere. These results indicate that attention moves downward before a blink in an involuntary fashion. The eyes also move downward during blinks, so attention may precede blink-induced eye movements just as it precedes saccades and other types of eye movements.