Trans-saccadic processing of visual and motor planning during sequential eye movements (original) (raw)
Related papers
Human Movement Science, 2004
The present experiment examined the one-target advantage (OTA) with regard to saccadic eye movements. The OTA, previously found with manual pointing responses, refers to the finding that movements are executed faster when the limb is allowed to stop on the target compared to the situation where it has to proceed and hit a second target. Using an adapted limb movement OTA task, saccades of 5°and 15°were made to (a) a single target (one-target), (b) one target and immediately to another target without a change in direction (two-target-extension), and (c) one target and immediately back to the start location (two-target-reversal). Unlike manual movements, the movement times for the initial saccade in the two-target-extension condition were not prolonged compared to either of the other two conditions. Moreover, this pattern of results was found for both the shorter and longer amplitude saccades. The results indicate that the OTA does not occur in the oculomotor system and therefore is not a general motor control phenomenon.
Brain Research, 2008
Previous studies have shown that a saccade is coded in a specific reference frame according to its goal: to aim for a new object or to explore an object which has already been fixated. In a two saccade sequence, the second saccade aiming for a new object is programmed in a retinocentric reference frame in which the spatial location of the second object is stored in spatial memory before the first saccade and updated after its execution. The second saccade exploring the same object is coded in an oculocentric reference frame in which object size is directly transformed into a fixed motor vector, encoded in motor memory before the first saccade and simply applied after its execution. The integration of parafoveal visual information appears to be crucial in the selection of the appropriate reference frame. The two experiments presented here investigate how and when the saccadic system integrates visual information to plan a sequence of saccades. In separate blocks, subjects were asked to execute a sequence of prosaccades directed toward a single object or two short objects, or to execute a sequence of antisaccades in the opposite direction of the stimuli. The latency of the initial saccade was modulated by using the Gap-200, Gap-0 and Overlap-600 ms paradigms. The results show that the time available for segmenting the visual stimulation into discrete objects and application of a specific reference frame according to this segmentation is critical for saccadic planning.
Information processing during saccadic eye movements
Acta Psychologica, 1995
Saccadic eye movements are made at least 100,000 times each day. It is wel1 known that sensitivity to visual input is suppressed during saccades; recent evidente 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. Tel.: + 1 217 333-7746.
Efficient saccade planning requires time and clear choices
Vision Research, 2015
We use eye movements constantly to gather information. Saccades are efficient when they maximize the information required for the task, however there is controversy regarding the efficiency of eye movement planning. For example, saccades are efficient when searching for a single target (Nature, 434 (2005) 387-91), but are inefficient when searching for an unknown number of targets in noise, particularly under time pressure (Vision Research 74 (2012), 61-71). In this study, we used a multiple-target search paradigm and explored whether altering the noise level or increasing saccadic latency improved efficiency. Experiments used stimuli with two levels of discriminability such that saccades to the less discriminable stimuli provided more information. When these two noise levels corresponded to low and moderate visibility, most observers did not preferentially select informative locations, but looked at uncertain and probable target locations equally often. We then examined whether eye movements could be made more efficient by increasing the discriminability of the two stimulus levels and by delaying the first saccade so that there was more time for decision processes to influence the saccade choices. Some observers did indeed increase the proportion of their saccades to informative locations under these conditions. Others, however, made as many saccades as they could during the limited time and were unselective about the saccade goal. A clear trend that emerges across all experiments is that conditions with a greater proportion of efficient saccades are associated with a longer latency to initiate saccades, suggesting that the choice of informative locations requires deliberate planning.
Scientific Reports
Diverse psychophysical and neurophysiological results show that oculomotor networks are continuously active, such that plans for making the next eye movement are always ongoing. So, when new visual information arrives unexpectedly, how are those plans affected? At what point can the new information start guiding an eye movement, and how? Here, based on modeling and simulation results, we make two observations that are relevant to these questions. First, we note that many experiments, including those investigating the phenomenon known as "saccadic inhibition", are consistent with the idea that sudden-onset stimuli briefly interrupt the gradual rise in neural activity associated with the preparation of an impending saccade. And second, we show that this stimulus-driven interruption is functionally adaptive, but only if perception is fast. In that case, putting on hold an ongoing saccade plan toward location A allows the oculomotor system to initiate a concurrent, alternative plan toward location B (where a stimulus just appeared), deliberate (briefly) on the priority of each target, and determine which plan should continue. Based on physiological data, we estimate that the advantage of this strategy, relative to one in which any plan once initiated must be completed, is of several tens of milliseconds per saccade. A fundamental function of oculomotor circuits is to determine where the eyes should look next and produce the appropriate eye movement. Neurally, each saccade is the culmination of a motor planning process whereby the firing rates of movement-related neurons rise gradually, monotonically, until the ramping activity of the population reaches a particular threshold level, at which point the plan becomes an uncancelable command and the saccade is triggered 1-6. A timing conflict is likely to arise because this rise-to-threshold process unfolds over a sizable period of time, but new, potentially critical visual information may arrive at any moment. Furthermore, due to two prominent features of oculomotor circuits, this conflict must be extremely common. On one hand, at least four lines of evidence indicate that saccades are programmed continuously, which is to say that there is always a subset of movement-related neurons (encoding a particular movement vector) that is steadily increasing its activity toward threshold. First, both humans and monkeys generate saccades at similar rates under a wide variety of viewing conditions 7-9 , even in the dark 10,11. Second, during free viewing, activity recorded in the frontal eye field (FEF) shows variations in firing rate, from one saccade to the next, occurring around a relatively high mean compared to that seen after prolonged fixation 9,12,13 , as if the movement-related activity never fell far below threshold. Third, motor plans are not contingent on the completion of a target selection process 5,14-17 and may proceed in parallel 5,6,9,16,18-20. And fourth, motor plans are strongly driven by current task contingencies and behavioral goals 21,22 ; that is, by internal, already acquired information, and not necessarily by the visual stimuli currently in view. On the other hand, saccades are rapidly and preferentially drawn to physically salient or highly relevant visual stimuli 8,23-30 , such as a traffic light turning red, or a mouse suddenly scurrying across the kitchen floor. The draw of such stimuli is often described as "attentional capture" (refs 31,32) or, when particularly potent, "oculomotor capture" (refs 25,26). Stimuli that capture attention engage dedicated neural mechanisms that are highly sensitive
Saccade kinematics modulate perisaccadic perception
Around the time of execution of an eye movement, participants systematically misperceive the spatial location of briefly flashed visual stimuli. This phenomenon, known as perisaccadic mislocalization, is thought to involve an active process that takes into account the motor plan (efference copy) of the upcoming saccade. While it has been proposed that the motor system anticipates and informs the visual system about the upcoming eye movements, at present the type and detail of information carried by this motor signal remains unclear. Some authors have argued that the efference copy conveys only coarse information about the direction of the eye movement, while a second theoretical view proposes that it provides specific details about the direction, amplitude, and velocity of the saccade to come. To test between these alternatives, we investigated the influence of saccade parameters on a perisaccadic unmasking task in which performance in discriminating the identity of a target (face or house) followed by a trailing mask is dramatically improved around the time of saccade onset. We found that the amplitude and peak velocity of the upcoming saccade modulated target perception, even for stimuli presented well before saccadic onset. We developed a predictive model for the generation of the efference copy that incorporates both saccade amplitude and saccade velocity planning prior to saccade execution. Overall, these results suggest that the efference copy stores specific information about the parameters of upcoming eye movement and that these parameters influence perception even prior to saccade onset.
Evidence for a role of corrective eye movements during gaze fixation in saccade planning
European Journal of Neuroscience, 2014
In a three-dimensional (3D) world most saccades are made towards visual targets that are located at different distances. We previously demonstrated that gaze shifts within 3D space consist of two stages: a target saccade followed by a corrective saccade during gaze fixation that directs the eyes to the physical target location. We proposed that, by accurately positioning the eyes on the visual object, the visual system maintains an orderly representation of the visual world. In this study we used a double saccade experiment to assess the function of corrective saccades in humans. We found that, when a corrective eye movement occurred during fixation on the first target point, the direction of the second saccade towards the next target point was accurate. When a corrective saccade was absent, a directional error of the second target saccade was observed. This finding, which cannot be explained by current models of eye movement control, supports the idea of a two-step model in saccade programming. We suggest that the motor system sends a corollary discharge when programming a corrective saccade for maintaining an orderly representation of the visual world. In conclusion, our results indicate that corrective saccades have a role in programming target saccades within 3D space.
Planning of saccadic eye movements
Psychological research, 2003
Most theories of the programming of saccadic eye movements (SEM) agree that direction and amplitude are the two basic dimensions that are under control when an intended movement is planned. But they disagree over whether these two basic parameters are specified separately or in conjunction. We measured saccadic reaction time (SRT) in a situation where information about amplitude and direction of the required movement became available at different moments in time. The delivery of information about either direction or amplitude prior to another reduced duration of SRT demonstrated that direction and amplitude were specified separately rather than in conjunction or in a fixed serial order. All changes in SRT were quantitatively explained by a simple growth-process (accumulator) model according to which a movement starts when two separate neural activities, embodying the direction and amplitude programming, have both reached a constant threshold level of activity. Although, in isolation...
Optimal and Suboptimal Use of Postsaccadic Vision in Sequences of Saccades
The Journal of Neuroscience, 2011
Saccades are imprecise, due to sensory and motor noise. To avoid an accumulation of errors during sequences of saccades, a prediction derived from the efference copy can be combined with the reafferent visual feedback to adjust the following eye movement. By varying the information quantity of the visual feedback, we investigated how the reliability of the visual information affects the postsaccadic update in humans. Two elements of the visual scene were manipulated, the saccade target or the background, presented either together or in isolation. We determined the weight of the postsaccadic visual information by measuring the effect of intrasaccadic visual shifts on the following saccade. We confirmed that the weight of visual information evolves with information quantity as predicted for a statistically optimal system. In particular, we found that the visual background alone can guide the postsaccadic update, and that information from target and background are optimally combined. Moreover, these visual weights are adjusted dynamically and on a trial-to-trial basis to the level of visual noise determined by target eccentricity and reaction time. In contrast, we uncovered a dissociation between the visual signals used to update the next planned saccade (main saccade) and those used to generate an involuntary corrective saccade. The latter was exclusively based on visual information about the target, and discarded all information about the background: a suboptimal use of visual evidence.
Role of Supplementary Eye Field in Saccade Initiation: Executive, Not Direct, Control
Journal of Neurophysiology, 2010
Isoda, Masaki and Jun Tanji. Cellular activity in the supplementary eye field during sequential performance of multiple saccades. J Neurophysiol 88: 3541-3545, 2002; 10.1152/jn.00299.2002. To investigate how single neurons in the supplementary eye field (SEF) participate in sequential performance of multiple saccades, we analyzed presaccadic activity while monkeys were performing three saccades in six different orders from memory. The saccades in each sequence were separated by a fixation period and initiated from the same fixation point with intervening return saccades. We found that the majority of the presaccadic activity of the SEF neurons differed significantly depending on the numerical position of saccades in each sequence (rank order). This rank-order selectivity was found in parallel with the selectivity for the sequence of three saccades. Our data suggest a role for SEF neurons in the coding of temporally ordered saccadic eye movements.