The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Douglas P. Munoz - One of the best experts on this subject based on the ideXlab platform.
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mechanisms of saccade suppression revealed in the anti saccade task
Philosophical Transactions of the Royal Society B, 2017Co-Authors: Brian C Coe, Douglas P. MunozAbstract:The anti-saccade task has emerged as an important tool for investigating the complex nature of voluntary behaviour. In this task, participants are instructed to suppress the natural response to look at a peripheral visual stimulus and look in the opposite direction instead. Analysis of saccadic reaction times (SRT: the time from stimulus appearance to the first saccade) and the frequency of direction errors (i.e. looking toward the stimulus) provide insight into saccade suppression mechanisms in the brain. Some direction errors are reflexive responses with very short SRTs (express latency saccades), while other direction errors are driven by automated responses and have longer SRTs. These different types of errors reveal that the anti-saccade task requires different forms of suppression, and neurophysiological experiments in macaques have revealed several potential mechanisms. At the start of an anti-saccade trial, pre-emptive top-down inhibition of saccade generating neurons in the frontal eye fields and superior colliculus must be present before the stimulus appears to prevent express latency direction errors. After the stimulus appears, voluntary anti-saccade commands must compete with, and override, automated visually initiated saccade commands to prevent longer latency direction errors. The frequencies of these types of direction errors, as well as SRTs, change throughout the lifespan and reveal time courses for development, maturation, and ageing. Additionally, patients diagnosed with a variety of neurological and/or psychiatric disorders affecting the frontal lobes and/or basal ganglia produce markedly different SRT distributions and types of direction errors, which highlight specific deficits in saccade suppression and inhibitory control. The anti-saccade task therefore provides valuable insight into the neural mechanisms of saccade suppression and is a valuable tool in a clinical setting.This article is part of the themed issue 'Movement suppression: brain mechanisms for stopping and stillness'.
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deficits in saccadic eye movement control in parkinson s disease
Neuropsychologia, 2005Co-Authors: Florence Chan, Irene T Armstrong, Giovanna Pari, Richard J Riopelle, Douglas P. MunozAbstract:In contrast to their slowed limb movements, individuals with Parkinson's disease (PD) produce rapid automatic eye movements to sensory stimuli and show an impaired ability to generate voluntary eye movements in cognitive tasks. Eighteen PD patients and 18 matched control volunteers were instructed to look either toward (pro-saccade) or away from (anti-saccade) a peripheral stimulus as soon as it appeared (immediate, gap and overlap conditions) or after a variable delay; or, they made sequential saccades to remembered targets after a variable delay. We found that PD patients made more express saccades (correct saccades in the latency range of 90-140 ms) in the immediate pro-saccade task, more direction errors (automatic pro-saccades) in the immediate anti-saccade task, and were less able to inhibit saccades during the delay period in all delay tasks. PD patients also made more directional and end-point errors in the memory-guided sequential task. Their inability to plan eye movements to remembered target locations suggests that PD patients have a deficit in spatial working memory which, along with their deficit in automatic saccade suppression, is consistent with a disorder of the prefrontal-basal ganglia circuit. Impairment of this pathway may release the automatic saccade system from top-down inhibition and produce deficits in volitional saccade control. Parallel findings across various motor, cognitive and oculomotor tasks suggest a common mechanism underlying a general deficit in automatic response suppression.
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neuronal correlates for preparatory set associated with pro saccades and anti saccades in the primate frontal eye field
The Journal of Neuroscience, 2000Co-Authors: Stefan Everling, Douglas P. MunozAbstract:Diversity in behavioral responses to sensory stimuli has been attributed to variations in preparatory set. Variability in oculomotor responses toward identical visual stimuli has been well documented, but the neuronal processes underlying this variability are poorly understood. Here, we report evidence for set-related activity for saccadic eye movements in single neurons in the frontal eye field (FEF) in monkeys trained on a task in which they either had to look toward a visual stimulus (pro-saccade) or away from the stimulus (anti-saccade) depending on a previous instruction. A portion of FEF neurons were identified as neurons projecting directly to the superior colliculus (SC) with antidromic activation techniques. Saccade-related neurons in the FEF had lower prestimulus and stimulus-related activity on anti-saccade trials compared with pro-saccade trials. The level of prestimulus activity correlated with saccadic reaction times, express saccade occurrence, and errors in the anti-saccade task. In addition, saccade-related activity in the FEF was higher for pro-saccades than for anti-saccades. These results demonstrate that the direct descending pathway from the FEF to the SC carries preparatory set-related activity for pro-saccades and anti-saccades. The results also provide insights into the neuronal basis of variations in saccadic reaction times and in the control of the prepotent response to glance to a flashed stimulus.
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role of primate superior colliculus in preparation and execution of anti saccades and pro saccades
The Journal of Neuroscience, 1999Co-Authors: Stefan Everling, Michael C Dorris, Raymond M Klein, Douglas P. MunozAbstract:We investigated how the brain switches between the preparation of a movement where a stimulus is the target of the movement, and a movement where a stimulus serves as a landmark for an instructed movement elsewhere. Monkeys were trained on a pro-/anti-saccade paradigm in which they either had to generate a pro-saccade toward a visual stimulus or an anti-saccade away from the stimulus to its mirror position, depending on the color of an initial fixation point. Neural activity was recorded in the superior colliculus (SC), a structure that is known to be involved in the generation of fast saccades, to determine whether it was also involved in the generation of anti-saccades. On anti-saccade trials, fixation during the instruction period was associated with an increased activity of collicular fixation-related neurons and a decreased activity of saccade-related neurons. Stimulus-related and saccade-related activity was reduced on anti-saccade trials. Our results demonstrate that the anti-saccade task involves (and may require) the attenuation of preparatory and stimulus-related activity in the SC to avoid unwanted pro-saccades. Because the attenuated pre-saccade activity that we found in the SC may be insufficient by itself to elicit correct anti-saccades, additional movement signals from other brain areas are presumably required.
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neuronal activity in monkey superior colliculus related to the initiation of saccadic eye movements
The Journal of Neuroscience, 1997Co-Authors: Michael C Dorris, Martin Pare, Douglas P. MunozAbstract:The introduction of a temporal gap between the disappearance of an initially fixated target and the appearance of an eccentric saccadic target results in a general reduction of saccadic reaction times (SRTs)—the gap effect—and often in the production of express saccades, the latencies of which approach the conduction time of the shortest neural pathways from the retina to the eye muscles. We investigated saccade initiation by recording neuronal activity in the superior colliculus in monkeys performing the gap paradigm. Fixation-related neurons reduced their discharge rate during the gap period, regardless of the SRT. This reduction in activity is consistent with the hypothesized release of ocular fixation that facilitates premotor processes and may contribute to the gap effect. In addition to saccade-related discharges, many saccade-related neurons displayed phasic target-related responses and/or low-frequency preparatory activity during the gap period. The level of this preparatory activity correlated with both SRT and express saccade occurrence when the saccade was made into the response field of the neuron. Evidence indicates that advanced motor preparation is required for express saccade generation, which may be subserved by specific increases in the preparatory activity of saccade-related neurons. Increased preparatory activity may allow the target-related responses to trigger short-latency express saccades directly. This study provides insights into the functional mechanism of saccade initiation and may be relevant to the generation of all voluntary motor responses.
Ming Yan - One of the best experts on this subject based on the ideXlab platform.
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font size modulates saccade target selection in chinese reading
The Mind Research Repository, 2014Co-Authors: Hua Shu, Wei Zhou, Ming YanAbstract:Shu, H., Zhou, W., Yan, M. & Kliegl, R. (2011). Font size modulates saccade-target selection in Chinese reading. Attention, Perception, & Psychophysics , 73 (2), 482-490. In alphabetic writing systems, saccade amplitude (a close correlate of reading speed) is independent of font size, presumably because an increase in the angular size of letters is compensated for by a decrease of visual acuity with eccentricity. We propose that this invariance may (also) be due to the presence of spaces between words, guiding the eyes across a large range of font sizes. Here we test whether saccade amplitude is also invariant against manipulations of font size during reading Chinese, a character-based writing system without spaces as explicit word boundaries for saccade-target selection. In contrast to word-spaced alphabetic writing systems, saccade amplitude decreased significantly with increased font size, leading to an increase in the number of fixations at the beginning of words and in the number of refixations. These results are consistent with a model which assumes that word beginning (rather than word center) is the default saccade target if the length of the parafoveal word is not available. Attention, Perception, & Psychophysics
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font size modulates saccade target selection in chinese reading
Attention Perception & Psychophysics, 2011Co-Authors: Hua Shu, Wei Zhou, Ming YanAbstract:In alphabetic writing systems, saccade amplitude (a close correlate of reading speed) is independent of font size, presumably because an increase in the angular size of letters is compensated for by a decrease of visual acuity with eccentricity. We propose that this invariance may (also) be due to the presence of spaces between words, guiding the eyes across a large range of font sizes. Here, we test whether saccade amplitude is also invariant against manipulations of font size during reading Chinese, a character-based writing system without spaces as explicit word boundaries for saccade-target selection. In contrast to word-spaced alphabetic writing systems, saccade amplitude decreased significantly with increased font size, leading to an increase in the number of fixations at the beginning of words and in the number of refixations. These results are consistent with a model which assumes that word beginning (rather than word center) is the default saccade target if the length of the parafoveal word is not available.
Nathan E. Schroeder - One of the best experts on this subject based on the ideXlab platform.
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Convergent evolution of Saccate body shapes in nematodes through distinct developmental mechanisms
EvoDevo, 2019Co-Authors: Sita Thapa, Michael K. Gates, Ursula Reuter-carlson, Rebecca J. Androwski, Nathan E. SchroederAbstract:Background The vast majority of nematode species have vermiform (worm-shaped) body plans throughout post-embryonic development. However, atypical body shapes have evolved multiple times. The plant-parasitic Tylenchomorpha nematode Heterodera glycines hatches as a vermiform infective juvenile. Following infection and the establishment of a feeding site, H. glycines grows disproportionately greater in width than length, developing into a Saccate adult. Body size in Caenorhabditis elegans was previously shown to correlate with post-embryonic divisions of laterally positioned stem cell-like ‘seam’ cells and endoreduplication of seam cell epidermal daughters. To test if a similar mechanism produces the unusual body shape of Saccate parasitic nematodes, we compared seam cell development and epidermal ploidy levels of H. glycines to C. elegans . To study the evolution of body shape development, we examined seam cell development of four additional Tylenchomorpha species with vermiform or Saccate body shapes. Results We confirmed the presence of seam cell homologs and their proliferation in H. glycines . This results in the adult female epidermis having approximately 1800 nuclei compared with the 139 nuclei in the primary epidermal syncytium of C. elegans . Similar to C. elegans, we found a significant correlation between H. glycines body volume and the number and ploidy level of epidermal nuclei. While we found that the seam cells also proliferate in the independently evolved Saccate nematode Meloidogyne incognita following infection, the division pattern differed substantially from that seen in H. glycines . Interestingly, the close relative of H. glycines, Rotylenchulus reniformis does not undergo extensive seam cell proliferation during its development into a Saccate form. Conclusions Our data reveal that seam cell proliferation and epidermal nuclear ploidy correlate with growth in H. glycines . Our finding of distinct seam cell division patterns in the independently evolved Saccate species M. incognita and H. glycines is suggestive of parallel evolution of Saccate forms. The lack of seam cell proliferation in R. reniformis demonstrates that seam cell proliferation and endoreduplication are not strictly required for increased body volume and atypical body shape. We speculate that R. reniformis may serve as an extant transitional model for the evolution of Saccate body shape.
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convergent evolution of Saccate body shapes in nematodes through distinct developmental mechanisms
Evodevo, 2019Co-Authors: Sita Thapa, Michael K. Gates, Rebecca J. Androwski, Ursula Reutercarlson, Nathan E. SchroederAbstract:The vast majority of nematode species have vermiform (worm-shaped) body plans throughout post-embryonic development. However, atypical body shapes have evolved multiple times. The plant-parasitic Tylenchomorpha nematode Heterodera glycines hatches as a vermiform infective juvenile. Following infection and the establishment of a feeding site, H. glycines grows disproportionately greater in width than length, developing into a Saccate adult. Body size in Caenorhabditis elegans was previously shown to correlate with post-embryonic divisions of laterally positioned stem cell-like ‘seam’ cells and endoreduplication of seam cell epidermal daughters. To test if a similar mechanism produces the unusual body shape of Saccate parasitic nematodes, we compared seam cell development and epidermal ploidy levels of H. glycines to C. elegans. To study the evolution of body shape development, we examined seam cell development of four additional Tylenchomorpha species with vermiform or Saccate body shapes. We confirmed the presence of seam cell homologs and their proliferation in H. glycines. This results in the adult female epidermis having approximately 1800 nuclei compared with the 139 nuclei in the primary epidermal syncytium of C. elegans. Similar to C. elegans, we found a significant correlation between H. glycines body volume and the number and ploidy level of epidermal nuclei. While we found that the seam cells also proliferate in the independently evolved Saccate nematode Meloidogyne incognita following infection, the division pattern differed substantially from that seen in H. glycines. Interestingly, the close relative of H. glycines, Rotylenchulus reniformis does not undergo extensive seam cell proliferation during its development into a Saccate form. Our data reveal that seam cell proliferation and epidermal nuclear ploidy correlate with growth in H. glycines. Our finding of distinct seam cell division patterns in the independently evolved Saccate species M. incognita and H. glycines is suggestive of parallel evolution of Saccate forms. The lack of seam cell proliferation in R. reniformis demonstrates that seam cell proliferation and endoreduplication are not strictly required for increased body volume and atypical body shape. We speculate that R. reniformis may serve as an extant transitional model for the evolution of Saccate body shape.
Yasushi Kobayashi - One of the best experts on this subject based on the ideXlab platform.
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characterization of oculomotor and visual activities in the primate pedunculopontine tegmental nucleus during visually guided saccade tasks
European Journal of Neuroscience, 2009Co-Authors: Kenichi Okada, Yasushi KobayashiAbstract:The pedunculopontine tegmental nucleus (PPTN) has anatomical connections with numerous visuomotor areas including the basal ganglia, thalamus, superior colliculus and frontal eye field. Although many anatomical and physiological studies suggest a role for the PPTN in the control of conditioned behavior and associative learning, the detailed characteristics of saccade- and visual-related activities of PPTN neurons remain unclear. We recorded the activity of PPTN neurons in monkeys (Macaca fuscata ) during visually guided saccade tasks, and examined the response properties of saccade- and visual-related activities such as time course, direction selectivity and contextual modulation. Saccade-related activity occurred either during saccade execution or after saccade end. The preferred directions of the neuronal activity were biased toward the contralateral and upward sides. Half of the saccade-related neurons showed activity modulation only for task saccades and not for spontaneous saccades outside the task. Visually-responsive neurons responded with short latencies. Some responded to the appearance of the visual stimulus in a directionally selective manner, and others responded to both the appearance and disappearance of the visual stimulus in a directionally non-selective manner. Many of these neurons exhibited distinct visual responses to the appearance of two different stimuli presented under different stages of the task, whereas a population of the neurons responded equally to the disappearance of the two stimuli. Thus, many PPTN neurons exhibited context-dependent activity related to the visuomotor events, consistent with a role in controlling conditioned behavior.
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contribution of pedunculopontine tegmental nucleus neurons to performance of visually guided saccade tasks in monkeys
Journal of Neurophysiology, 2002Co-Authors: Yasushi Kobayashi, Yuka Inoue, Masaru Yamamoto, Tadashi Isa, Hiroshi AizawaAbstract:The cholinergic pedunculopontine tegmental nucleus (PPTN) is one of the major ascending arousal systems in the brain stem and is linked to motor, limbic, and sensory systems. Based on previous studies, we hypothesized that PPTN would be related to the integrative control of movement, reinforcement, and performance of tasks in behaving animals. To investigate how PPTN contributes to the behavioral control, we analyzed the activity of PPTN neurons during visually guided saccade tasks in three monkeys in relation to saccade preparation, execution, reward, and performance of the task. During visually guided saccades, we observed saccade-related burst (26/70) and pause neurons (19/70), indicating that a subset of PPTN neurons are related to both saccade execution and fixation. Burst neurons exhibited greater selectivity for saccade direction than pause neurons. The preferred directions for both burst and pause neurons were not aligned with either horizontal or vertical axes, nor biased strongly in either the ipsilateral or the contralateral direction. The spatial representation of the saccade-related activity of PPTN neurons is different from other brain stem saccade systems and may therefore relay saccade-related activity from different areas. Increasing discharges were observed around reward onset in a subset of neurons (22/70). These neurons responded to the freely delivered rewards within ∼140 ms. However, during the saccade task, the latencies of the responses around reward onset ranged between 100 ms before and 200 ms after the reward onset. These results suggest that the activity observed after appropriate saccade during the task may include response associated with reward. We found that the reaction time to the appearance of the fixation point (FP) was longer when the animal tended to fail in the ensuring task. This reaction time to FP appearance (RTFP) served as an index of motivation. The RTFP could be predicted by the neuronal activity of a subset of PPTN neurons (13/70) that varied their activity levels with task performance, discharging at a higher rate in successful versus error trials. A combination of responses related to saccade execution, reward delivery, and task performance was observed in PPTN neurons. We conclude from the multimodality of responses in PPTN neurons that PPTN may serve as an integrative interface between the various signals required for performing purposive behaviors.
Heiner Deubel - One of the best experts on this subject based on the ideXlab platform.
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visual attention and eye movement control during oculomotor competition
Journal of Vision, 2020Co-Authors: Luca Wollenberg, Nina M Hanning, Heiner DeubelAbstract:Saccadic eye movements are typically preceded by selective shifts of visual attention. Recent evidence, however, suggests that oculomotor selection can occur in the absence of attentional selection when saccades erroneously land in between nearby competing objects (saccade averaging). This study combined a saccade task with a visual discrimination task to investigate saccade target selection during episodes of competition between a saccade target and a nearby distractor. We manipulated the spatial predictability of target and distractor locations and asked participants to execute saccades upon variably delayed go-signals. This allowed us to systematically investigate the capacity to exert top-down eye movement control (as reflected in saccade endpoints) based on the spatiotemporal dynamics of visual attention during movement preparation (measured as visual sensitivity). Our data demonstrate that the predictability of target and distractor locations, despite not affecting the deployment of visual attention prior to movement preparation, largely improved the accuracy of short-latency saccades. Under spatial uncertainty, a short go-signal delay likewise enhanced saccade accuracy substantially, which was associated with a more selective deployment of attentional resources to the saccade target. Moreover, we observed a systematic relationship between the deployment of visual attention and saccade accuracy, with visual discrimination performance being significantly enhanced at the saccade target relative to the distractor only before the execution of saccades accurately landing at the saccade target. Our results provide novel insights linking top-down eye movement control to the operation of selective visual attention during movement preparation.
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the spread of presaccadic attention depends on the spatial configuration of the visual scene
Scientific Reports, 2019Co-Authors: Martin Szinte, Michael Puntiroli, Heiner DeubelAbstract:When preparing a saccade, attentional resources are focused at the saccade target and its immediate vicinity. Here we show that this does not hold true when saccades are prepared toward a recently extinguished target. We obtained detailed maps of orientation sensitivity when participants prepared a saccade toward a target that either remained on the screen or disappeared before the eyes moved. We found that attention was mainly focused on the immediate surround of the visible target and spread to more peripheral locations as a function of the distance from the cue and the delay between the target's disappearance and the saccade. Interestingly, this spread was not accompanied with a spread of the saccade endpoint. These results suggest that presaccadic attention and saccade programming are two distinct processes that can be dissociated as a function of their interaction with the spatial configuration of the visual scene.
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Attentional selection determines saccade endpoint.
2018Co-Authors: Luca Wollenberg, Heiner Deubel, Martin SzinteAbstract:Two nearby saccade targets (gray dots) are flashed in the periphery from the fixation target and projected onto the retina, triggering a cascade of bottom-up (upward arrows) and top-down (downward arrows) processes throughout the visual processing hierarchy. Colors of the neurons and arrows indicate the level of activation. Each retinal projection connects to a specific neuron (in fact, a population of neurons) in retinotopic feature maps (V1–V4, MT). Feature map neurons, in turn, are linked to priority maps (FEF, LIP, SC). Priority map activity is later integrated by the saccade generator (brainstem) driving the extra-oculomotor muscles. Note that the priority maps and the saccade generator are distinct components within the processing hierarchy. The data panels show the predicted sensitivity at the saccade targets (ST1 and ST2) and in between them (BTW), and curved black arrows show the predicted saccade path. (A) Before attentional selection, ST1 and ST2 neuronal columns are highly activated by bottom-up connections driven by the saccade target onset. (B) Following a decay in the activity of both ST1 and ST2 neuronal columns, a completed attentional selection leads to a high activation of either ST1 or ST2 neurons in the priority maps (in this example, ST1 is selected), propagating via top-down connections to the feature maps. This leads to a presaccadic enhancement of sensitivity at the selected target and subsequently to an accurate saccade towards it (in this example, towards ST1). (C, D) Uncompleted attentional selection leads to an equal and moderate presaccadic sensitivity enhancement at the saccade targets, but not in between. Subsequently, the bimodal collicular activity distribution merges into a unimodal distribution around the intermediate collicular site (panel C) or remains bimodal and is later integrated by the saccade generator (panel D). In either case, an averaging saccade is executed towards the intermediate location (BTW). BTW, position in between the saccade targets; DT, discrimination target; FEF, Frontal Eye Field; LIP, Lateral Intraparietal Cortex; MT, Middle Temporal Visual Area; SC, Superior Colliculus; ST1, saccade target 1; ST2, saccade target 2; V, Visual Area.
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predictive remapping of attention across eye movements
Nature Neuroscience, 2011Co-Authors: Heiner Deubel, Martin Rolfs, Donatas Jonikaitis, Patrick CavanaghAbstract:Just before a rapid eye movement (saccade), attentional performance improves for the targeted position where the saccade will land. This behavioral study finds that attentional performance also improves at the subsequent locations that the target of the saccade will move to, suggesting that attentional remapping occurs at least two steps ahead.
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saccade target selection and object recognition evidence for a common attentional mechanism
Vision Research, 1996Co-Authors: Heiner Deubel, Werner X SchneiderAbstract:The spatial interaction of visual attention and saccadic eye movements was investigated in a dual-task paradigm that required a target-directed saccade in combination with a letter discrimination task. Subjects had to saccade to locations within horizontal letter strings left and right of a central fixation cross. The performance in discriminating between the symbols "E" and "E", presented tachistoscopically before the saccade within the surrounding distractors was taken as a measure of visual attention. The data show that visual discrimination is best when discrimination stimulus and saccade target refer to the same object; discrimination at neighboring items is close to chance level. Also, it is not possible, in spite of prior knowledge of discrimination target position, to direct attention to the discrimination target while saccading to a spatially close saccade target. The data strongly argue for an obligatory and selective coupling of saccade programming and visual attention to one common target object. The results favor a model in which a single attentional mechanism selects objects for perceptual processing and recognition, and also provides the information necessary for motor action.
