Initial Pursuit Research Articles

Smooth pursuit adaptation (SPA) exhibits features useful to compensate changes in the properties of the smooth pursuit eye movement system due to usage

Smooth-pursuit adaptation (SPA) refers to the fact that pursuit gain in the early, still open-loop response phase of the pursuit eye movement can be adjusted based on experience. For instance, if the target moves initially at a constant velocity for ~100–200 ms and then steps to a higher velocity, subjects learn to up-regulate the pursuit gain associated with the initial target velocity (gain-increase SPA) in order to reduce the retinal error resulting from the velocity step. Correspondingly, a step to a lower target velocity leads to a decrease in gain (gain-decrease SPA). In this study we demonstrate that the increase in peak eye velocity during gain-increase SPA is a consequence of expanding the duration of the eye acceleration profile while the decrease in peak velocity during gain-decrease SPA results from reduced peak eye acceleration but unaltered duration. Furthermore, we show that carrying out stereotypical smooth pursuit eye movements elicited by constant velocity target ramps for several hundred trials (=test of pursuit resilience) leads to a clear drop in initial peak acceleration, a reflection of oculomotor and/or cognitive fatigue. However, this drop in acceleration gets compensated by an increase in the duration of the acceleration profile, thereby keeping initial pursuit gain constant. The compensatory expansion of the acceleration profile in the pursuit resilience experiment is reminiscent of the one leading to gain-increase SPA, suggesting that both processes tap one and the same neuronal mechanism warranting a precise acceleration-duration trade-off. Finally, we show that the ability to adjust acceleration duration during pursuit resilience depends on the integrity of the oculomotor vermis (OMV) as indicated by the complete loss of the duration adjustment following a surgical lesion of the OMV in one rhesus monkey we could study.

Illusory bending of a pursuit target

To pursue a small target moving in front of a drifting background, motion vectors from the target need to be integrated and segmented from those belonging to the background. Smooth pursuit eye movements typically integrate target and background directions initially and after some time shift towards the veridical target direction. The perceived target direction on the other hand is generally stable over time: the target is perceived to move in the same direction as long as the motion information maintains the same properties over time. If illusory target motion is observed, this tends to be shifted away from the background. Here we investigated how initial motion integration and segmentation of such stimuli are modulated by direction cues. We presented a small pursuit target moving along a straight path, in front of a background moving in a different direction. Without a direction cue, initial pursuit was biased towards the background direction before shifting towards the veridical target direction. The target’s perceived direction on the other hand was near veridical. A cue in the background direction increased initial pursuit integration but also caused perception to behave in a similar way: the target initially had an illusory motion component in the background direction and after about 200ms it was perceived to curve towards its veridical direction. This illusion shows that during the initial process of segmenting the direction of a pursuit target from irrelevant background motion, both pursuit and perception can be erroneously influenced by a direction cue and integrate the cued background motion. Both modalities corrected this initial integration error as more information about the target became available.

Total Synthesis of (±)-Rocaglamide via Oxidation-Initiated Nazarov Cyclization

This article describes the evolution of a Nazarov cyclization-based synthetic strategy targeting the anticancer, antiinflammatory, and insecticidal natural product (±)-rocaglamide. Initial pursuit of a polarized heteroaromatic Nazarov cyclization to construct the congested cyclopentane core revealed an unanticipated electronic bias in the pentadienyl cation. This reactivity was harnessed in a successful second-generation approach using an oxidation-initiated Nazarov cyclization of a heteroaryl alkoxyallene. Full details of these two approaches are given, as well as the characterization of undesired reaction pathways available to the Nazarov cyclization product. A sequence of experiments that led to an understanding of the unexpected reactivity of this key intermediate is described, which culminated in the successful total synthesis of (+)-rocaglamide.

Motion transparency: Depth ordering and smooth pursuit eye movements

When two overlapping, transparent surfaces move in different directions, there is ambiguity with respect to the depth ordering of the surfaces. Little is known about the surface features that are used to resolve this ambiguity. Here, we investigated the influence of different surface features on the perceived depth order and the direction of smooth pursuit eye movements. Surfaces containing more dots, moving opposite to an adapted direction, moving at a slower speed, or moving in the same direction as the eyes were more likely to be seen in the back. Smooth pursuit eye movements showed an initial preference for surfaces containing more dots, moving in a non-adapted direction, moving at a faster speed, and being composed of larger dots. After 300 to 500 ms, smooth pursuit eye movements adjusted to perception and followed the surface whose direction had to be indicated. The differences between perceived depth order and initial pursuit preferences and the slow adjustment of pursuit indicate that perceived depth order is not determined solely by the eye movements. The common effect of dot number and motion adaptation suggests that global motion strength can induce a bias to perceive the stronger motion in the back.

Failed States and the Rule of Law

The last decade has seen an emerging consensus that the rule of law is critical in both domestic and international affairs. ‘Failed’ states generate important issues for both the rule of law and, importantly, for their intersection or interaction. A ‘failed’ state almost inevitably involves a breakdown of the domestic rule of law. When international intervention occurs, it raises concerns over substantive issues. Among these is the application of international law and international norms, including among other, the conventions and treaties, the responsibility to protect and protection of civilians. Where international missions seek to assist the people of ‘failed’ states in rebuilding their nations, establishing the rule of law is often the primary or initial pursuit. Any such international assistance/intervention is more effective if it is clearly subject to the rule of law and provides an exemplar/demonstration of how power should be exercised.

The Human Illnesses: Neuropsychiatric Disorders and the Nature of the Human Brainby WilliamsonPeter C., M.D., and AllmanJohn M., Ph.D. New York, Oxford University Press, 2011, 256 pp., $75.00.

The Human Illnesses: Neuropsychiatric Disorders and the Nature of the Human Brainby WilliamsonPeter C., M.D., and AllmanJohn M., Ph.D. New York, Oxford University Press, 2011, 256 pp., $75.00.

Role of MSTd Extraretinal Signals in Smooth Pursuit Adaptation

The smooth pursuit (SP) system is able to adapt to challenges associated with development or system drift to maintain pursuit accuracy. Short-term adaptation of SP can be produced experimentally using a step-ramp tracking paradigm with 2 steps of velocity (double-step paradigm). Previous studies have demonstrated that the macaque cerebellum plays an essential role in SP adaptation. However, it remains uncertain whether neuronal activity in afferent structures to the cerebellum shows changes associated with SP adaptation. Therefore, we focused on the dorsal-medial part of medial superior temporal cortex (MSTd), which is part of the cortico-ponto-cerebellar pathway thought to provide extraretinal signals needed for maintaining SP. We found that 54% of the SP-related neurons showed significant changes in the first 100 ms of response correlated with adaptive changes of initial pursuit. Our results indicate that some cortical neurons in MSTd could be inside the circuit involved in SP adaptation. Furthermore, our sample of MSTd neurons started their discharge on average 103 ms after SP onset. Therefore, we suggest that extraretinal signals carried in MSTd might be due to efference copy of pursuit eye velocity signals, which reflect plastic changes in the downstream motor output pathways (e.g., the cerebellum).

Residential Design Idea - As a Case of Xinyang Greentown Estate in Mudanjiang

This paper takes the planning scheme of Xinyang Greentown Estate in Mudanjing as an example and studies the modern theory of human settlements. Meanwhile, we start the plan with general plotting, designing and planning, and architectural design. We also focus on creating humanized living environment, the harmony between commercial and residential buildings, and the separation of noise and silence. Then we use Air-pak to simulate the wind environment after the completion of it, and it fills the blanks of wind environment research of estate planning. Under the guiding principle of “people oriented”, the target of estate planning is to establish the mechanism which makes different functions of the estate run-in synchronism. In order to build a civilized, comfortable and healthy estate, it is necessary to follow the guidance of sustainable development strategy to meet people's increasing material and spiritual needs. Along with China’s economy development and the improvement of people’s living standard, people’s environmental awareness is becoming stronger and stronger, and the requirements of living environment is becoming higher and higher. After meeting with the basic material needs, people will begin to pursue a higher level of spiritual needs. Which embodied in residence is that the initial pursuit of shelter gradually transforms into the pursuit of a higher level of ownership, respect and value realization. Today high-quality living environment is the noble pursuit of modern living, and estate planning is directly related to the quality of living environment. This paper takes the planning scheme of Xinyang Greentown Estate in Mudanjing as an example and conducts some initial research on the improvement of the quality of living environment in various aspects.

Neural activity in the frontal pursuit area does not underlie pursuit target selection

The frontal pursuit area (FPA) contains neurons that are directionally selective for pursuit eye-movements. We found that FPA neurons discriminate target from distracter too late to account for pursuit directional selection. Rather, the timing of neuronal discrimination is linked to pursuit onset, suggesting a role in motor execution. We also found buildup of activity of FPA neurons prior to pursuit onset that correlated with eye acceleration. These results show that the FPA is unlikely to be involved in selection of initial pursuit direction, but could be involved in motor preparation by increasing pursuit gain prior to pursuit onset.

The effect of a temporary absence of target velocity information on visual tracking

Experiments with the Rashbass ‘step-ramp’ paradigm have revealed that the initial catchup saccade that occurs near pursuit onset uses target velocity as well as position information in its programming. Information about both position and motion also influences smooth pursuit. To investigate the timing of velocity sampling near the initiation of saccades and smooth pursuit, we analyzed the eye movements made in nine ‘step-ramp’ conditions, produced by combining –2, 0 and +2 deg steps with –8, 0 and +8 deg/s ramps. Each trial had either no temporal gap or a 50-ms gap during which the laser target was extinguished, beginning 25, 50, 75 or 100 ms after the step. Six subjects repeated each of the resulting 45 conditions 25 times. With no temporal gap, saccades were larger in the step-ramp-away’ than the ‘step-only’ condition, confirming that saccade programming incorporates ramp velocity information. A temporal gap had no effect on the accuracy of saccades on ‘step-only’ trials, but often caused undershoots in ‘step-ramp’ trials. A 50-ms gap within the first 100 ms also increased the latency of the initial saccade. Although initial pursuit velocity was unaffected by a temporal gap, a gap that started at 25 ms reliably delayed pursuit onset for ramp motion of the target toward the fovea. Later gaps had a minimal effect on initial pursuit latency. The similar timing of the temporal gaps in target motion information that affect the initiation of saccades and pursuit provides further behavioral evidence that the two types of eye movements share pre-motor neural mechanisms.

Role of Primate Cerebellar Hemisphere in Voluntary Eye Movement Control Revealed by Lesion Effects

The anatomical connection between the frontal eye field and the cerebellar hemispheric lobule VII (H-VII) suggests a potential role of the hemisphere in voluntary eye movement control. To reveal the involvement of the hemisphere in smooth pursuit and saccade control, we made a unilateral lesion around H-VII and examined its effects in three Macaca fuscata that were trained to pursue visually a small target. To the step (3 degrees)-ramp (5-20 degrees/s) target motion, the monkeys usually showed an initial pursuit eye movement at a latency of 80-140 ms and a small catch-up saccade at 140-220 ms that was followed by a postsaccadic pursuit eye movement that roughly matched the ramp target velocity. After unilateral cerebellar hemispheric lesioning, the initial pursuit eye movements were impaired, and the velocities of the postsaccadic pursuit eye movements decreased. The onsets of 5 degrees visually guided saccades to the stationary target were delayed, and their amplitudes showed a tendency of increased trial-to-trial variability but never became hypo- or hypermetric. Similar tendencies were observed in the onsets and amplitudes of catch-up saccades. The adaptation of open-loop smooth pursuit velocity, tested by a step increase in target velocity for a brief period, was impaired. These lesion effects were recognized in all directions, particularly in the ipsiversive direction. A recovery was observed at 4 wk postlesion for some of these lesion effects. These results suggest that the cerebellar hemispheric region around lobule VII is involved in the control of smooth pursuit and saccadic eye movements.

Competition between color and luminance for target selection in smooth pursuit and saccadic eye movements

Visual processing of color and luminance for smooth pursuit and saccadic eye movements was investigated using a target selection paradigm. In two experiments, stimuli were varied along the dimensions color and luminance, and selection of the more salient target was compared in pursuit and saccades. Initial pursuit was biased in the direction of the luminance component whereas saccades showed a relative preference for color. An early pursuit response toward luminance was often reversed to color by a later saccade. Observers' perceptual judgments of stimulus salience, obtained in two control experiments, were clearly biased toward luminance. This choice bias in perceptual data implies that the initial short-latency pursuit response agrees with perceptual judgments. In contrast, saccades, which have a longer latency than pursuit, do not seem to follow the perceptual judgment of salience but instead show a stronger relative preference for color. These substantial differences in target selection imply that target selection processes for pursuit and saccadic eye movements use distinctly different weights for color and luminance stimuli.

Saccadic and smooth pursuit eye movements: Computational modeling of a common inhibitory mechanism in brainstem

The oculomotor system coordinates different types of eye movements in order to orient the visual axis, including saccade and smooth pursuit,. It was traditionally thought that the premotor pathways for these different eye movements are largely separate. In particular, a group of midline cells in the pons called omnipause neurons were considered to be part of only the saccadic system. Recent experimental findings have shown activity modulation of these brainstem premotor neurons during both kinds of eye movements. In this study, we propose a new computational model of the brainstem circuitry underlying the generation of saccades and smooth pursuit eye movements. Similar models have been developed earlier, but mainly looking at pure saccades. Here, we integrated recent neurophysiological findings on omnipause neuron activity during smooth pursuit. Our computational model can mimic some new experimental findings as the similarity of “eye velocity profile” with “omnipause neuron pattern of activity” in pursuit movement. We showed that pursuit neuron activity is augmented during catch-up saccades; this increment depends on the initial pursuit velocity in catch-up saccade onset. We conclude that saccadic and pursuit components of catch-up saccades are added to each other nonlinearly.

Velocity scaling of cue-induced smooth pursuit acceleration obeys constraints of natural motion

Information about the future trajectory of a visual target is contained not only in the history of target motion but also in static visual cues, e.g., the street provides information about the car's future trajectory. For most natural moving targets, this information imposes strong constraints on the relation between velocity and acceleration which can be exploited by predictive smooth pursuit mechanisms. We questioned how cue-induced predictive changes in pursuit direction depend on target speed and how cue- and target-induced pursuit interact. Subjects pursued a target entering a +/-90 degrees curve and moving on either a homogeneous background or on a low contrast static band indicating the future trajectory. The cue induced a predictive change of pursuit direction, which occurred before curve onset of the target. The predictive velocity component orthogonal to the initial pursuit direction started later and became faster with increasing target velocity. The predictive eye acceleration increased quadratically with target velocity and was independent of the initial target direction. After curve onset, cue- and target-induced pursuit velocity components were not linearly superimposed. The quadratic increase of eye acceleration with target velocity is consistent with the natural velocity scaling implied by the two-thirds power law, which is a characteristic of biological controlled movements. Comparison with linear pursuit models reveals that the ratio between eye acceleration and actual or expected retinal slip cannot be considered a constant gain factor. To obey a natural velocity scaling, this acceleration gain must linearly increase with target or pursuit velocity. We suggest that gain control mechanisms, which affect target-induced changes of pursuit velocity, act similarly on predictive changes of pursuit induced by static visual cues.

Preparatory Gain Modulation of Visuomotor Transmission for Smooth Pursuit Eye Movements in Monkeys

It has been reported that the visuomotor processing underlying the initiation of smooth pursuit eye movement is modulated in relation to the recent experience of eye movements: the initial pursuit eye velocity is larger after experiencing repeated pursuits than saccades. To assess which parameters of the previously executed pursuits play an essential role in modulating the gain of visuomotor transmission, we recorded the ocular responses of monkeys to a brief perturbing motion of the tracking target injected before the start of the eye movements. First, we compared the perturbation responses among the blocks in which the duration of executing pursuit was varied. We found that the response amplitude increased with the increase of the pursuit duration and it reached a plateau level at 100-200 ms of the duration. Second, a comparison of the perturbation responses in the blocks in which target velocity was different showed a gradual increase of the response as a function of the required pursuit velocity. Third, when the animals repeatedly performed pursuits, the response amplitude gradually increased with increasing interval between the appearance of the target and the onset of perturbation. On the other hand, such an increase was not observed when the animals repeatedly performed saccades. These results suggest that before initiating eye movements, the pursuit system modulates the gain of visuomotor transmission so as to be closely related to the properties of the repeatedly experienced eye movements and this gain modulation is triggered by the target's appearance.

Predicting 2D Target Velocity Cannot Help 2D Motion Integration for Smooth Pursuit Initiation

Smooth pursuit eye movements reflect the temporal dynamics of bidimensional (2D) visual motion integration. When tracking a single, tilted line, initial pursuit direction is biased toward unidimensional (1D) edge motion signals, which are orthogonal to the line orientation. Over 200 ms, tracking direction is slowly corrected to finally match the 2D object motion during steady-state pursuit. We now show that repetition of line orientation and/or motion direction does not eliminate the transient tracking direction error nor change the time course of pursuit correction. Nonetheless, multiple successive presentations of a single orientation/direction condition elicit robust anticipatory pursuit eye movements that always go in the 2D object motion direction not the 1D edge motion direction. These results demonstrate that predictive signals about target motion cannot be used for an efficient integration of ambiguous velocity signals at pursuit initiation.

Anticipatory Gain Modulation in Preparation for Smooth Pursuit Eye Movements

We studied the effect of the probability of required tracking on the gain of visuomotor transmission for pursuit initiation in monkeys. We recorded the ocular responses to a brief movement (perturbation) of a target located at an eccentric position from the central fixation spot. As soon as the central fixation spot went off, the animal was required to make a saccade to the target if it remained stationary or to track if it moved. The probability of an upcoming ramp motion of the target (horizontal, 20 degrees /sec), requiring pursuit, was varied (target motion probability [TMP] = 0, 0.25, 0.5, 0.75, and 1, which was fixed in a block). We found that the magnitude of the response to the perturbation increased gradually as the TMP increased. The initial pursuit response and the perturbation response showed very similar dependence on the TMP, suggesting that the response to the perturbation could be used as an index of the gain of visuomotor transmission for pursuit initiation. We also found that the changes in the ocular responses after the TMP was changed from one probability to another occurred rapidly (decay constant of only a few trials). These results suggest that the gain of visuomotor transmission in preparing for pursuit is rapidly modulated in accordance with the anticipated future need for pursuit.

Prediction in the timing of pursuit eye movement initiation revealed by cross-axis vestibular–pursuit training in monkeys

The smooth-pursuit system interacts with the vestibular system to maintain the image of a moving target on the fovea. Efficient tracking performance requires information about the velocity and the initiation of target motion. Previous studies in monkeys have shown that training with orthogonal pursuit and whole body rotation results in adapted eye movement direction during chair rotation. In addition, the latency of the pursuit shortens and initial eye velocity increases in a task-dependent manner. To examine whether these adapted eye movements are predictive pursuit, we studied whether our monkeys could predict the timing of smooth eye movement initiation during chair rotation. Two young Japanese monkeys were rotated horizontally in a trapezoidal waveform (20 degrees/s, +/-10 degrees) with random inter-trial intervals. A laser spot was moved vertically with the same trajectory at a constant delay ranging from 100 to 700 ms after the onset of the chair motion. The monkeys were required to pursue the spot. After this training, the latencies of pursuit eye movements following the onset of chair motion were examined in the presence of the target motion. The target was also briefly (for 500-700 ms) extinguished at 80 ms after the onset of chair rotation. Pursuit eye movements after training were initiated before the onset of target motion and the latencies were proportional to the delays used for training. The latencies and response magnitudes of pursuit with or without target blanking were similar. The auditory-pursuit training did not induce an initial pursuit response similar to that induced by vestibular-pursuit training. These results indicate that smooth eye movements during the chair rotation after the vestibular-pursuit training included a predictive pursuit component. The monkeys' estimate of the delays revealed by the latencies of pursuit was shorter by 22-36% than the actual delays.

Shared Response Preparation for Pursuit and Saccadic Eye Movements

Tracking a single target in the visual world requires coordination between pursuit and saccadic eye movements. The constraints imposed on pursuit and saccade decisions by visual processing and response preparation are difficult to compare because latency differences between the two movements provide different amounts of visual sampling time. The present study compares pursuit and saccade decisions when visual processing was directly manipulated. Human observers were asked to select between two stationary stimuli presented simultaneously at two different locations based on which had the higher contrast. The stimuli were presented for a brief, variable interval and then occluded by masks. Because the masks moved horizontally and were offset vertically, subjects were obliged to make both pursuit and saccadic eye movements to track the mask covering the target stimulus. For each of the exposure durations, we constructed oculometric curves for pursuit and saccades. We found that both systems had similar oculometric thresholds and response biases. The initial pursuit decisions differed from the subsequent saccade decisions on 1-13% of the trials but were the same more often than predicted by independent mechanisms. Moreover, pursuit reversed direction on discordant trials, so that the pursuit decision always matched that of the saccade by the time the saccade was started. These results support the view that, in addition to overlap in early visual areas and the final motor pathways, the pursuit and saccadic systems share processing at the level of response preparation. This shared processing may help ensure the coordination of pursuit and saccadic eye movements in selecting a single target.

Treatment of Recurrent Depression

Back to table of contents Previous article Next article Book Forum: Treatment of DepressionFull AccessTreatment of Recurrent DepressionPETER P. ROY-BYRNE, M.D., PETER P. ROY-BYRNESearch for more papers by this author, M.D., Seattle, Wash.Published Online:1 Jul 2002https://doi.org/10.1176/appi.ajp.159.7.1255AboutSectionsView EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail This slender volume is one of five titles for 2001 in volume 20 of the American Psychiatric Press Review of Psychiatry, all of which are designed to “inform clinicians of the latest findings” and thereby counter the growing epidemic of misinformation about mental health issues, fueled by television, Web, magazine, and newspaper accounts that usually fail to capture the balanced, evidence-based approach clinicians desire. The focus of this volume is recurrent depression, a disabling problem that is for the most part inadequately treated, despite numerous advances in the field over the last decade.Four central chapters focus largely on treatment themes and are bracketed by initial and final chapters that have a more public health perspective, highlighting, respectively, key factors that contribute to the overwhelming “burden” of recurrent depression and key steps that need to be taken to shift our current approach and adopt a more preventive and “proactive” paradigm of treatment. The core chapters, written by top experts in the field, cover gender-specific issues, including pregnancy, postpartum, and menopause; review evidence about the relative long-term and preventive efficacy of medication and psychotherapies; focus on the special population of patients with bipolar disorder; and review novel brain stimulation treatments that could improve future treatment options.The book is not meant to be an exhaustive treatment of every aspect of this subject but seems to have selected particular areas likely to be of interest to clinicians. The chapter on depression in women contains two very useful tables that compile information on the teratogenicity of relevant psychotropics and a timely, evidence-based discussion about the relative value of estrogen treatment for postmenopausal depression (it is probably effective for some but should not supplant initial pursuit of better-studied modalities). Similarly, the chapter “Chronic and Recurrent Depression” tells a story, rather than offering an exhaustive review, with a focus on key studies over the past two decades that established the value-added effect of psychotherapy, but suggests this may be true only if it is administered with sufficient frequency and intensity. The chapter on bipolar illness focuses on interepisode management, providing advice about frequency of visits, family involvement, the destabilizing effects of inadequate sleep and light exposure, and the importance of the therapeutic relationship, especially for the prevention of the manic phase. Finally, the chapter on “minimally invasive brain stimulation” modalities largely focuses on repetitive transcranial magnetic stimulation and vagal nerve stimulation, providing a cautious, sober assessment of the limited knowledge in this area. The authors’ caution about the need to limit enthusiasm for vagal nerve stimulation until it is tested in controlled studies is particularly timely in the light of recent news that the first controlled trial for this treatment was negative, casting some doubt on the open trials reported in this chapter, although the length of this trial may have been too short to measure delayed effects.For all its strengths, the book has some limitations. The chapters have different organizations, varying approaches to the “evidence-based” theme (e.g., citation of uncontrolled, anecdotal evidence), and several ways to focus on treatment (some focus exclusively on treatment, others focus on epidemiology, clinical features, and risk factors as well). Although this diversity allows the interested clinician to read chapters separately, without having to appreciate the book as a whole, it does detract from the book’s attempt to present an integrated view of the treatment of recurrent depression. To some extent, the excellent initial and concluding chapters by the editor, which seem to echo a number of themes and concepts covered in the other chapters, serve this purpose and can be read by themselves to accomplish this task.Edited by John F. Greden, M.D. Washington, D.C., American Psychiatric Press, 2001, 208 pp., $31.95 (paper). FiguresReferencesCited byDetailsCited ByNone Volume 159Issue 7 July 2002Pages 1255-1256 Metrics History Published online 1 July 2002 Published in print 1 July 2002