Saccadic Times Research Articles

Two distinct types of remapping in primate cortical area V4

Visual neurons typically receive information from a limited portion of the retina, and such receptive fields are a key organizing principle for much of visual cortex. At the same time, there is strong evidence that receptive fields transiently shift around the time of saccades. The nature of the shift is controversial: Previous studies have found shifts consistent with a role for perceptual constancy; other studies suggest a role in the allocation of spatial attention. Here we present evidence that both the previously documented functions exist in individual neurons in primate cortical area V4. Remapping associated with perceptual constancy occurs for saccades in all directions, while attentional shifts mainly occur for neurons with receptive fields in the same hemifield as the saccade end point. The latter are relatively sluggish and can be observed even during saccade planning. Overall these results suggest a complex interplay of visual and extraretinal influences during the execution of saccades.

Commentary: Attentional tradeoffs maintain the tracking of moving objects across saccades.

Commentary: Attentional tradeoffs maintain the tracking of moving objects across saccades.

Interference during eye movement preparation shifts the timing of perisaccadic compression.

Our perception of the surrounding environment remains stable despite the fact that we frequently change the retinal position of input by rapid gaze shifts (saccades). There is a long-standing debate whether visual stability depends on an active mechanism using an efference copy of the impending saccadic motor command. Behavioral studies showing changes in perception around the time of saccades are consistent with a predictive mechanism, but previous studies of perceptual effects in humans confounded saccade programming with the resulting physical eye movement. In three experiments, we used a saccadic inhibition (SI) paradigm to delay saccadic onset while participants were performing a perisaccadic localization task. As expected, the perceived position of the probe stimulus was systematically biased (compressed) toward the saccadic goal, already during the presaccadic interval. In the SI condition, the localization error was shifted in time, in line with it following saccade intention rather than execution. The pattern was not the consequence of the probe being captured by the timing of the flashed distractor, but depended instead on the delay in saccadic onset time caused by SI. Importantly, the same configurations of perceptual probes presented with a flashed backward mask when participants maintained fixation did not lead to similar localization errors as saccade trials. This pattern of results is consistent with an active, sensorimotor explanation for perisaccadic mislocalization and, more generally, theories emphasizing the role of motor prediction in visual stability.

Suppression and reversal of motion perception around the time of the saccade.

We make fast, “saccadic” eye movements to capture finely resolved foveal snapshots of the world but these saccades cause motion artefacts. The artefacts go unnoticed, perhaps because the brain suppresses them through subcortical oculomotor signals feeding back into visual cortex. Opposing views, however, claim that passive mechanisms suffice: saccadic shearing forces might render the retina insensitive to the artefacts or post-saccadic snapshots might mask them before they enter consciousness. Crucially, only active suppression could explain perceptual changes that precede saccades but existing evidence for presaccadic misperception are ill-suited for addressing this issue: Previous studies have found misperceptions of space for objects briefly flashed before saccades, but perhaps only because observers confused the timing of flashes and saccades before they could be tested (“postdiction”), and presaccadic motion perception might have appeared to decline because motion stimuli persisted past eye movement onset. Here we addressed these concerns using briefly flashed two-frame animations (50 ms) to probe people’s motion sensitivity during and around saccades. We found that sensitivity declined before saccade onset, even when the probe appeared entirely outside the saccade, and this sensitivity decline was present for motion in every direction relative to saccade, ruling out problems with postdiction. Intriguingly, brief periods during the saccade produced negative sensitivity as if motion was reversed, arguably due to postsaccadic enhancement. These data suggest that motion perception is minimized during saccades through active suppression, complementing neurophysiological findings of colliculo-pulvinar projections that suppress the cortical middle temporal area around the time of the saccade.

Visual mislocalization during double-step saccades.

Visual objects presented briefly at the time of saccade onset appear compressed toward the saccade target. Compression strength depends on the presentation of a visual saccade target signal and is strongly reduced during the second saccade of a double-step saccade sequence (Zimmermann et al., 2014b). Here, I tested whether perisaccadic compression is linked to saccade planning by contrasting two double-step paradigms. In the same-direction double-step paradigm, subjects were required to perform two rightward 10° saccades successively. At various times around execution of the saccade sequence a probe dot was briefly flashed. Subjects had to localize the position of the probe dot after they had completed both saccades. I found compression of visual space only at the time of the first but not at the time of the second saccade. In the reverse-direction paradigm, subjects performed first a rightward 10° saccade followed by a leftward 10° saccade back to initial fixation. In this paradigm compression was found in similar magnitude during both saccades. Analysis of the saccade parameters did not reveal indications of saccade sequence preplanning in this paradigm. I therefore conclude that saccade planning, rather than saccade execution factors, is involved in perisaccadic compression.

Intense Physical Exercise Reduces Overt Attentional Capture.

The abrupt onset of a visual stimulus typically results in overt attentional capture, which can be quantified by saccadic eye movements. Here, we tested whether attentional capture following onset of task-irrelevant visual stimuli (new object) is reduced after a bout of intense physical exercise. A group of participants performed a visual search task in two different activity conditions: rest, without any prior effort, and effort, immediately after an acute bout of intense exercise. The results showed that participants exhibited (1) slower reaction time of the first saccade toward the target when a new object was simultaneously presented in the visual field, but only in the rest activity condition, and (2) more saccades to the new object in the rest activity condition than in the effort activity condition. We suggest that immediately after an acute bout of effort, participants improved their ability to inhibit irrelevant (distracting) stimuli.

Spatial compression: Dissociable effects at the time of saccades and blinks.

Various studies have identified systematic errors, such as spatial compression, when observers report the locations of objects displayed around the time of saccades. Localization errors also occur when holding spatial representations in visual working memory. Such errors, however, have not been examined in the context of eye blinks. In this study, we examined the effects of blinks and saccades when observers reproduced the locations of a set of briefly presented, randomly placed discs. Performance was compared with a fixation-only condition in which observers simply held these representations in working memory for the same duration; this allowed us to elucidate the relationship between the perceptual phenomena related to blinks, saccades, and visual working memory. Our results indicate that the same amount of spatial compression is experienced prior to a blink as is experienced in the control fixation-only condition, suggesting that blinks do not increase compression above that occurring from holding a spatial representation in visual memory. Saccades, however, tend to increase these compression effects and produce translational shifts both toward and away from saccade targets (depending on the time of the saccade onset in relation to the stimulus offset). A higher numerosity recall capacity was also observed when stimuli were presented prior to a blink in comparison with the other conditions. These findings reflect key differences underlying blinks and saccades in terms of spatial compression and translational shifts. Such results suggest that separate mechanisms maintain perceptual stability across these visual events.

Decoding the timing and target locations of saccadic eye movements from neuronal activity in macaque oculomotor areas

Objective. The control of movement timing has been a significant challenge for brain–machine interfaces (BMIs). As a first step toward developing a timing-based BMI, we aimed to decode movement timing and target locations in a visually guided saccadic eye movement task using the activity of neurons in the primate frontal eye field (FEF) and supplementary eye field (SEF). Approach. For this purpose, we developed a template-matching method that could recruit a variety of neurons in these areas. Main results. As a result, we were able to achieve a favorable estimation of saccade onset: for example, data from 20 randomly sampled FEF neurons or 40 SEF neurons achieved a median estimation error of ∼10 ms with an interquartile range less than 50 ms (± ∼25 ms). In the best case, seven simultaneously recorded SEF neurons using a multi-electrode array achieved a comparable accuracy (10 ± 30 ms). The method was significantly better than a heuristic method that used only a group of movement cells with sharp discharges at the onset of saccades. The estimation of target location was less accurate but still favorable, especially when we estimated target location at a timing of 200 ms after the onset of saccade: the method was able to discriminate 16 targets with an accuracy of 90%, which differed not only in their directions (eight directions) but also in amplitude (10/20°) when we used data from 61 randomly sampled FEF neurons. Significance. The results show that the timing, amplitude and direction of saccades can be decoded from neuronal activity in the FEF and SEF and further suggest that timing-based BMIs can be developed by decoding timing information using the template-matching method.

A self-organizing model of perisaccadic visual receptive field dynamics in primate visual and oculomotor system.

We propose and examine a model for how perisaccadic visual receptive field dynamics, observed in a range of primate brain areas such as LIP, FEF, SC, V3, V3A, V2, and V1, may develop through a biologically plausible process of unsupervised visually guided learning. These dynamics are associated with remapping, which is the phenomenon where receptive fields anticipate the consequences of saccadic eye movements. We find that a neural network model using a local associative synaptic learning rule, when exposed to visual scenes in conjunction with saccades, can account for a range of associated phenomena. In particular, our model demonstrates predictive and pre-saccadic remapping, responsiveness shifts around the time of saccades, and remapping from multiple directions.

초등과학부진학생의 기초과학탐구능력 향상을 위한 중재프로그램 개발 -안구운동을 중심으로-

이 연구는 초등과학부진학생들의 기초과학탐구능력을 향상하기 위해 중재프로그램을 개발하고 안구추적기를 활용해 중재프로그램의 효과를 검증하는데 있다. 연구 참여자는 초등과학부진학생 35명이었다. 안구운동추적기는 SMI사의 iView XTM RED로 고정형이고 샘플링 속도는 120 Hz이었다. 실험을 설계하고 분석하기 위해 Experiment 3.4와 BeGaze 3.4 프로그램을 사용하였다. 연구결과는 다음과 같다. 첫째 기초탐구 교수전략, 교사 학생 행동, 교수-학습지도안, 학습 활동지를 포함하여 중재프로그램을 개발하였다. 둘째, 중재프로그램 적용결과 기초과학탐구능력이 향상되었고 전체 문제해결시간이 통계적으로 유의미하게 줄어들었다. 셋째, 기초과학탐구 문제영역과 핵심단어에 대한 평균응시시간이 통계적으로 유의미하게 감소하였다. 넷째, 기초과학탐구문제해결과정에서 동공 크기(pupil diameter)가 통계적으로 유의미하게 확장되었다. 다섯째, 기초과학탐구문제해결과정에서 평균도약시간(average saccade time)은 통계적으로 유의미하게 증가하였다. 여섯째, 문제 단서영역에 대한 평균응시도입시간(average fixation entry time)은 통계적으로 유의미하게 빨라졌고, 평균응시시간은 통계적으로 유의미하게 줄어들었다. The purpose of this study is to develop an intervention program for improvement of elementary science-poor students' Basic Science Process Skill (BSPS) and to validate the intervention program's effectiveness using eye-tracker. The participants of this study were 35 elementary science-poor students. This study's method was the analysis of real-time eye movements during basic science process skill problem solving. SMI's 120 Hz iView XTM RED was used to collect EMD (eye movement data). Experiment 3.4 and BeGaze 3.4 programs were used to design experiment and to analyze EMD. The results of this study are as follows. First, we developed an intervention program including BSPS instructional strategy, behavior of teachers & student according instructional strategy stage, teachinglearning plan and learning note. Second, science poor students' BSPS ability has improved statistically significantly through the application of intervention program and BSPS problem-solving time decreased statistically significantly. Third, AFT (average fixation time) of BSPS Question and keyword area decreased statistically significantly. Fourth, APD (average pupil diameter) of BSPS problem-solving process expanded statistically significantly. Fifth, AST (average saccade time) of BSPS problem-solving process increased statistically significantly. Sixth, AFET (average fixation entry time) of BSPS problem-clue area was accelerated statistically significantly, AFT of BSPS problem-clue area reduced statistically significantly.

Detection of residual cognitive function through non-spontaneous eye movement in a patient with advanced frontotemporal dementia.

As dementia progresses, cognitive functions decline in patients, and caregivers and other support staff gradually lose the means to communicate with them. However, some caregivers believe that patients can still recognize their surroundings even when they show akinesis with mutism. In this study, we observed eye movements (preferential-looking paradigm) to detect the presence of residual cognitive functions in a patient with severe frontotemporal dementia (FTD). The subject was a 76-year-old female. At the time of observation, she had lost all spontaneous activities. Magnetic resonance imaging (MRI) imaging showed dense atrophy of the bilateral frontotemporal lobe, but the parieto-occipital lobe was preserved. A preferential-looking paradigm was used in the experiment, whereby two different faces (learned and non-learned) were simultaneously presented to the patient on a TV monitor. As a result, we found no significant differences in looking time between the two faces. However, when the saccade timing to the presented faces was examined, a much longer latency was observed for the right than the left side of the target faces. Even though the patient had lost capacity for spontaneous activity due to severe FTD, we were able to observe partial residual cognitive ability using the eye-movement paradigm.

Study on Novice Drivers' Fixation Features under Different Car-Following Risk Levels

Through early interviews 22 common traffic scenes were found and leveled by questionnaires. Six scenes of low-risk, medium risk and high risk were selected and implemented in the simulation software using the software of Creator, Vega, C++, etc. Simulation experiments were conducted to analyze the novice drivers fixation features under different levels of risk based on the designed real car simulation platform. The results showed that both novice and experienced drivers saccade times are more than 3 times greater than the fixation times, suggesting that drivers visual search are found mainly in saccadic movement other than watch movement. In potentially dangerous environment, experience drivers always reduce fixation time and increase saccade time to make early warnings of danger that may arise, while novice drivers saccade time and fixation time are relatively stable. Novice drivers concern more about the dashboard regardless of the level of risk in any scenarios comparatively. In the three levels of risk conditions, novice drivers watching areas are more concentrate, namely, their fixation area mostly focus on some certain areas while ignoring other areas, such as rearview mirror and traffic signals.

Moving your head reduces perisaccadic compression.

Flashes presented around the time of a saccade appear to be closer to the saccade endpoint than they really are. The resulting compression of perceived positions has been found to increase with the amplitude of the saccade. In most studies on perisaccadic compression the head is static, so the eye-in-head movement is equal to the change in gaze. What if moving the head causes part of the change in gaze? Does decreasing the eye-in-head rotation by moving the head decrease the compression of perceived positions? To find out, we asked participants to shift their gaze between two positions, either without moving their head or with the head contributing to the change in gaze. Around the time of the saccades we flashed bars that participants had to localize. When the head contributed to the change in gaze, the duration of the saccade was shorter and compression was reduced. We interpret this reduction in compression as being caused by a reduction in uncertainty about gaze position at the time of the flash. We conclude that moving one's head can reduce the systematic mislocalization of flashes presented around the time of saccades.

Saccadic timing is determined by both accumulated evidence and the passage of time

Saccadic timing is determined by both accumulated evidence and the passage of time

Acute hypoxic hypoxia and isocapnic hypoxia effects on oculometric features.

Visual performance impairment after hypoxia is well recognized in military and civilian aviation. The aims of this study were: 1) to assess oculometric features such as blink metrics, pupillary dynamics, fixations, and saccades as cognitive indicators of early signs of hypoxia; and 2) to analyze the impact of different hypoxic conditions ["hypoxic hypoxia" (HH) and "isocapnic hypoxia" (IH)] on specified oculometrics during mental workloads. Oculometric data were collected on 25 subjects under 3 conditions: normoxia, HH (8% O2 + balance N2), and IH (7% O2 + 5% CO2 + balance N2). The mental workload task consisted of reading aloud linear arrays of numbers after exposure to gas mixtures. Blink rates were significantly increased under hypoxic conditions (by +100.7% in HH and by +92.8% in IH compared to normoxia). A faster recovery of blink rate was observed in transitioning from IH (23.6% vs. 76.3%) to normoxia. The percentage change in pupil size fluctuation was increased under HH more than under IH (29% vs. 4.4%). Under HH average fixation time and target area size were significantly higher than under IH. Total saccadic times under hypoxic conditions were significantly increased compared with normoxia. These results suggest that oculometric changes are indicators of hypoxia, which can be monitored using compact, portable, noninvasive eye-tracking devices in a cockpit analogous environment to detect hypoxia-induced physiological changes in aircrew. Comparative results between HH and IH support the potential role of carbon dioxide in augmenting cerebral perfusion and hence improved tissue oxygen delivery.

Visual Stability During Saccades is Achieved through Transient Changes in Perceptual Space and Time

To interact rapidly and effectively with our environment, our brain needs access to a dynamic neural representation – or map – of the spatial layout of the external world. One of the major challenges to constructing such a map is the frequent rapid movements of the eyes, which displace the images on our retinae, up to three times per second. Much neurophysiological research shows that just before saccades, the receptive fields of neurons in many visual areas are subject to large shifts, in the direction of the saccade (Duhamel, Colby, & Goldberg, 1992). While the neural mechanisms of this dynamic process are now well understood (Sommer & Wurtz, 2006), it is less clear how a shift in the direction of the saccade benefits perception.We suggest that the purpose of the shifts in receptive fields is to prepare for the effects of saccades before they commence, and that the real work of stabilizing occurs when they relax back into their standard position during the actual saccade (Burr & Morrone, 2011, 2012; Cicchini, Binda, Burr, & Morrone, 2012). It is this relaxation that compensates for the saccadic displacement. The relaxation process is best described as a shift in both space and in time, and this can be well described by spatiotemporal receptive field that is slanted in space-time (see Figure 9 from Cicchini, Binda, Burr, & Morrone, 2012).We have accumulated a wealth of psychophysical evidence supporting the notion of the spatiotemporal shift. Perhaps the strongest evidence is the temporal lag that occurs during saccades, a clear signature of a spatiotemporal transformation. During saccades, visual flashes are perceived to be delayed by 100ms compared with normal viewing (Binda, Cicchini, Burr, & Morrone, 2009), and it is this delay that creates the spatiotemporal tuning (as do motion perception mechanisms, on a different timescale; Burr, Ross, & Morrone, 1986). There is also strong temporal compression, so stimuli 100ms long are perceived as 50ms (Morrone, Ross, & Burr, 2005); we have developed a simple model that explains how the temporal compression results from a spatiotemporal shift (Cicchini & Morrone, 2012). Recently, neurophysiological studies find similar delays and compression in neurones of cortical area FEF (Joiner, Cavanaugh, & Wurtz, 2013). Finally, we have explicitly measured the spatiotemporal interaction field of stimuli flashed around the time of the saccade, and report a field like that shown in Figure 9 of Cicchini, Binda, Burr, and Morrone (2012).All up these studies show clear evidence for a spatiotemporal mechanism that creates transient spatiotopy at the time of saccades, allowing perceptual systems to momentarily bridge the transition between one fixation and another. This process cannot be understood as only a spatial transform, as it is inherently spatiotemporal, resulting in strong and measureable delays and compression of time.

The Role of Temporal Integration Windows in Visual Perception

The brain receives a constant, analogue flow of stimulation from each of the senses. One of the main goals of perceptual systems is to segregate this steady influx into meaningful spatio-temporal units such as objects and events. Perception of objects, motion or events requires information to be integrated over a period of time. Such temporal integration windows (TIW) are thought to operate across multiple timescales (Gibbon et al., 1997; Poeppel, 1999). For example, studies of perceived duration and of simultaneity have consistently found a time limit of around 40ms as the minimum integration window. In other words, only when a stimulus is presented for more than 40ms does it seem to have a duration longer than a single instant, and two stimuli presented less than 40ms apart from each other seem to be simultaneous. Longer TIWs of around 100-150ms have been found in various paradigms such as backward masking (for review, see Enns & Di Lollo, 2000). In terms of subjective perception, stimuli presented in sequence within such a time period are integrated into a single percept. In addition, a number of other studies have reported TIWs of around 200-300ms for tasks such as apparent motion, the attentional blink, and inhibition of return (Posner & Cohen, 1984; Raymond, Shapiro, & Arnell, 1992). Beyond this time period, two stimuli tend not to interact at all with each other perceptually. Thus, our subjective perceptual experience of two or more stimuli depends critically on the temporal spacing between them according to multiple TIWs. Finally, it has been suggested that relatively long temporal windows of 2-3 s can be found across different sensory modalities and tasks, corresponding to our subjective impression of “now” (Poeppel, 1999).Previous studies of TIWs raise the question of how these different TIWs interact with each other in creating our subjective experience of a spatiotemporally stable and continuous world. In a series of studies, we have examined how temporal integration is influenced by the fact that people typically make several saccadic eye movements per second. These ballistic eye movements are the main strategy for looking around scenes in everyday life, yet saccades introduce a dramatic discontinuity in visual stimulation and laboratory studies have demonstrated systematic alterations in both spatial and temporal perception around the time of saccades (Morrone et al., 2005; Yarrow et al., 2001). Here, we present new results showing that for the relatively short TIWs of around 100ms, saccades seem to reset the TIWs. Apparent motion, in contrast, is relatively unaffected by saccades, suggesting that the medium-level TIWs of around 200-300ms continue to operate across eye movements (Fracasso et al., 2010; Melcher & Fracasso, 2012). Likewise, we have found that temporal windows of around 2 s can be found under free-viewing conditions when people watch movies, with little or no interference by saccades on this long TIW. Overall, these findings suggest that relatively long TIWs underlie our subjective experience of a spatiotemporally continuous and stable visual world.

ICAT: a computational model for the adaptive control of fixation durations

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.

Counterproductive effect of saccadic suppression during attention shifts.

During saccadic eye movements, the processing of visual information is transiently interrupted by a mechanism known as “saccadic suppression” [1] that is thought to ensure perceptual stability [2]. If, as proposed in the premotor theory of attention [3], covert shifts of attention rely on sub-threshold recruitment of oculomotor circuits, then saccadic suppression should also occur during covert shifts. In order to test this prediction, we designed two experiments in which participants had to orient towards a cued letter, with or without saccades. We analyzed the time course of letter identification score in an “attention” task performed without saccades, using the saccadic latencies measured in the “saccade” task as a marker of covert saccadic preparation. Visual conditions were identical in all tasks. In the “attention” task, we found a drop in perceptual performance around the predicted onset time of saccades that were never performed. Importantly, this decrease in letter identification score cannot be explained by any known mechanism aligned on cue onset such as inhibition of return, masking, or microsaccades. These results show that attentional allocation triggers the same suppression mechanisms as during saccades, which is relevant during eye movements but detrimental in the context of covert orienting.

The Influence of Gaze Control on Visual Perception: Eye Movements and Visual Stability.

Primates make several saccadic eye movements each second, and yet the retinal motion these movements generate goes unnoticed. Saccadic suppression is a profound loss of visual sensitivity occurring around the time of eye movements, and it is thought to contribute to visual stability by blunting the perception of self-generated motion. Neurophysiological studies have produced evidence that neurons throughout the visual system, including both the dorsal and ventral streams of extrastriate visual cortex, show a reduction in visual responses or sensitivity around the time of saccades. However, the source of this suppression remains unknown. We review evidence that oculomotor regions such as the superior colliculus and frontal eye field may play a role, as well as anatomical data that place constraints on possible mechanisms of suppression.