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Vision Research Feb 1998Fixation disparities (FD) were measured as a function of forced vergence using binocular scleral search coils and simultaneously with nonius lines. The slope of the...
Fixation disparities (FD) were measured as a function of forced vergence using binocular scleral search coils and simultaneously with nonius lines. The slope of the objective FD curve was significantly greater than the subjective FD curve for three of five subjects. This indicates an alteration in retinal correspondence of up to one degree, that shifts Panum's area to avoid the diplopia normally present with large disparities. This process allows for fusion in the presence of large objective fixation disparities which would normally cause diplopia. The shift in correspondence enhances the range of forced vergence, since the larger objective FDs serve as more effective stimuli to fusional vergence. The remaining subjects who lacked this effect had "flat" FD curves indicative of high vergence adaptation.
Topics: Adult; Convergence, Ocular; Fixation, Ocular; Humans; Mathematics; Methods; Models, Biological; Vision Disparity
PubMed: 9536364
DOI: 10.1016/s0042-6989(97)00142-9 -
Optometry and Vision Science : Official... May 1999This study compared the ability of myopes and emmetropes to detect subjectively the presence of retinal defocus. (Comparative Study)
Comparative Study
PURPOSE
This study compared the ability of myopes and emmetropes to detect subjectively the presence of retinal defocus.
METHODS
Subjects (12 myopes, 12 emmetropes) were cyclopleged and monocularly viewed a bipartite target through an appropriate near addition lens via a 2-mm artificial pupil. One-half of the target remained fixed while the other half was alternatively moved forward or backward until subjects first reported a difference in clarity between the two halves of the target.
RESULTS
The mean blur threshold for the emmetropes and myopes was +/-0.11 and +/-0.19 D, respectively (p = 0.0001).
CONCLUSIONS
These results demonstrate that myopes are less sensitive to the presence of blur, and may at least partially explain why previous reports have demonstrated a larger lag of accommodation in this refractive group. Additionally, the hyperopic retinal defocus resulting from the increased accommodative error may play a significant role in myopia development and progression.
Topics: Accommodation, Ocular; Adult; Contrast Sensitivity; Fixation, Ocular; Humans; Myopia; Retina
PubMed: 10375246
DOI: 10.1097/00006324-199905000-00018 -
Neuron Jan 2006Microsaccades are miniature eye movements produced involuntarily during visual fixation of stationary objects. Since their first description more than 40 years ago, the...
Microsaccades are miniature eye movements produced involuntarily during visual fixation of stationary objects. Since their first description more than 40 years ago, the role of microsaccades in vision has been controversial. In this issue, Martinez-Conde and colleagues present a solution to the long-standing research problem connecting this basic oculomotor function to visual perception, by showing that microsaccades may control peripheral vision during visual fixation by inducing flips in bistable peripheral percepts in head-unrestrained viewing. Their study provides new insight into the functional connectivity between oculomotor function and visual perception.
Topics: Eye Movements; Fixation, Ocular; Humans; Oculomotor Muscles; Saccades; Visual Perception
PubMed: 16423689
DOI: 10.1016/j.neuron.2006.01.005 -
Nature Jun 1994Steering a car requires visual information from the changing pattern of the road ahead. There are many theories about what features a driver might use, and recent...
Steering a car requires visual information from the changing pattern of the road ahead. There are many theories about what features a driver might use, and recent attempts to engineer self-steering vehicles have sharpened interest in the mechanisms involved. However, there is little direct information linking steering performance to the driver's direction of gaze. We have made simultaneous recordings of steering-wheel angle and drivers' gaze direction during a series of drives along a tortuous road. We found that drivers rely particularly on the 'tangent point' on the inside of each curve, seeking this point 1-2 s before each bend and returning to it throughout the bend. The direction of this point relative to the car's heading predicts the curvature of the road ahead, and we examine the way this information is used.
Topics: Automobile Driving; Computer Simulation; Eye Movements; Fixation, Ocular; Head; Humans; Videotape Recording; Visual Perception
PubMed: 8008066
DOI: 10.1038/369742a0 -
Journal of Vision Sep 2017Much effort has been made to explain eye guidance during natural scene viewing. However, a substantial component of fixation placement appears to be a set of consistent...
Much effort has been made to explain eye guidance during natural scene viewing. However, a substantial component of fixation placement appears to be a set of consistent biases in eye movement behavior. We introduce the concept of saccadic flow, a generalization of the central bias that describes the image-independent conditional probability of making a saccade to (xi+1, yi+1), given a fixation at (xi, yi). We suggest that saccadic flow can be a useful prior when carrying out analyses of fixation locations, and can be used as a submodule in models of eye movements during scene viewing. We demonstrate the utility of this idea by presenting bias-weighted gaze landscapes, and show that there is a link between the likelihood of a saccade under the flow model, and the salience of the following fixation. We also present a minor improvement to our central bias model (based on using a multivariate truncated Gaussian), and investigate the leftwards and coarse-to-fine biases in scene viewing.
Topics: Attention; Fixation, Ocular; Humans; Models, Theoretical; Probability; Saccades; Visual Perception
PubMed: 28973565
DOI: 10.1167/17.11.12 -
Experimental Brain Research Nov 2000We investigated the effect of strategic suppression of reflexive eye movements on external control over fixation using a fixation offset paradigm. A visual signal at...
We investigated the effect of strategic suppression of reflexive eye movements on external control over fixation using a fixation offset paradigm. A visual signal at fixation facilitates the fixation reflex and inhibits eye movements. Certain preparatory states render the fixation reflex less reactive to visual stimulation at fixation, as evidenced by a reduction in the fixation offset effect (FOE). For example, past studies have suggested that the reduced FOE during anti-saccade tasks results from the requirement to inhibit reflexive eye movements. We tested whether suppressing reflexive saccades reduces external control over ocular fixation using a go-nogo saccade paradigm. During each trial, one of two targets appeared in the periphery. Participants were instructed to saccade to one target (go), but when the other target appeared they either had to maintain fixation (nogo) or move their eyes in the direction opposite the target (anti). When nogo trials were admixed with target-directed saccades a large FOE was observed compared to when target-directed saccades occurred alone (experiment 1); however, when anti-saccades were mixed with target-directed saccades, a small FOE was observed for both types of eye movements (experiment 2). We conclude that suppressing reflexive eye movements does not reduce external control over fixation. Further research is necessary to elucidate which other component of preparing to make an anti-saccade diminishes the FOE.
Topics: Adolescent; Adult; Analysis of Variance; Fixation, Ocular; Humans; Reaction Time; Saccades
PubMed: 11104129
DOI: 10.1007/s002210000494 -
Vision Research Feb 2006In a series of experiments, the currently fixated word (word n) and/or the word to the right of fixation (word n+1) either disappeared or was masked during readers' eye...
In a series of experiments, the currently fixated word (word n) and/or the word to the right of fixation (word n+1) either disappeared or was masked during readers' eye fixations. Consistent with prior research, when only word n disappeared or was masked, there was little disruption to reading. However, when word n+1 either disappeared or was masked (either at the onset of fixation on word n or after 60 ms), there was considerable disruption to reading. Independent of whether word n and/or word n+1 disappeared or was masked, there were robust frequency effects on the fixation on word n. These results not only confirm the robust influence of cognitive/linguistic processing on fixation times in reading, but also again confirm the importance of preprocessing the word to the right of fixation for fluent reading.
Topics: Fixation, Ocular; Humans; Perceptual Masking; Psychological Tests; Reading; Saccades; Time Factors
PubMed: 16085229
DOI: 10.1016/j.visres.2005.06.018 -
The Journal of Neuroscience : the... Jun 2009To explore the visible world, human beings and other primates often rely on gaze shifts. These are coordinated movements of the eyes and head characterized by...
To explore the visible world, human beings and other primates often rely on gaze shifts. These are coordinated movements of the eyes and head characterized by stereotypical metrics and kinematics. It is possible to determine the rules that the effectors must obey to execute them rapidly and accurately and the neural commands needed to implement these rules with the help of optimal control theory. In this study, we demonstrate that head-fixed saccades and head-free gaze shifts obey a simple physical principle, "the minimum effort rule." By direct comparison with existing models of the neural control of gaze shifts, we conclude that the neural circuitry that implements the minimum effort rule is one that uses inhibitory cross talk between independent eye and head controllers.
Topics: Animals; Attention; Biomechanical Phenomena; Fixation, Ocular; Head Movements; Humans; Models, Neurological; Orientation; Time Factors
PubMed: 19535584
DOI: 10.1523/JNEUROSCI.5518-08.2009 -
Reviews of Oculomotor Research 1990
Review
Topics: Eye Movements; Fixation, Ocular; Humans; Oculomotor Muscles; Posture; Reading; Visual Perception
PubMed: 7492534
DOI: No ID Found -
Perception & Psychophysics Aug 2000We studied the strategic (presumably cortical) control of ocular fixation in experiments that measured the fixation offset effect (FOE) while manipulating readiness to...
We studied the strategic (presumably cortical) control of ocular fixation in experiments that measured the fixation offset effect (FOE) while manipulating readiness to make reflexive or voluntary eye movements. The visual grasp reflex, which generates reflexive saccades to peripheral visual signals, reflects an opponent process in the superior colliculus (SC) between fixation cells at the rostral pole, whose activity helps maintain ocular position and increases when a stimulus is present at fixation, and movement cells, which generate saccades and are inhibited by rostral fixation neurons. Voluntary eye movements are controlled by movement and fixation cells in the frontal eye field (FEF). The FOE--a decrease in saccade latency when the fixation stimulus is extinguished--has been shown to reflect activity in the collicular eye movement circuitry and also to have an activity correlate in the FEF. Our manipulation of preparatory set to make reflexive or voluntary eye movements showed that when reflexive saccades were frequent and voluntary saccades were infrequent, the FOE was attenuated only for reflexive saccades. When voluntary saccades were frequent and reflexive saccades were infrequent, the FOE was attenuated only for voluntary saccades. We conclude that cortical processes related to task strategy are able to decrease fixation neuron activity even in the presence of a fixation stimulus, resulting in a smaller FOE. The dissociation in the effects of a fixation stimulus on reflexive and voluntary saccade latencies under the same strategic set suggests that the FOEs for these two types of eye movements may reflect a change in cellular activity in different neural structures, perhaps in the SC for reflexive saccades and in the FEF for voluntary saccades.
Topics: Adult; Fixation, Ocular; Humans; Random Allocation; Saccades
PubMed: 11019619
DOI: 10.3758/bf03212125