Salient distractors can induce saccade adaptation.

When saccadic eye movements consistently fail to land on their intended target, saccade accuracy is maintained by gradually adapting the movement size of successive saccades. The proposed error signal for saccade adaptation has been based on the distance between where the eye lands and the visual target (retinal error). We studied whether the error signal could alternatively be based on the distance between the predicted and actual locus of attention after the saccade.

Adaptation of naturally paced saccades.

In the natural environment, humans make saccades almost continuously. In many eye movement experiments, however, observers are required to fixate for unnaturally long periods of time. The resulting long and monotonous experimental sessions can become especially problematic when collecting data in a clinical setting, where time can be scarce and subjects easily fatigued.

In vitro effects of insulin and RPE on choroidal and scleral components of eye growth in chicks.

In chick eyes, exogenous insulin prevents the choroidal thickening caused by wearing positive lenses and increases ocular elongation and scleral glycosaminoglycan (GAG) synthesis, an indicator of eye growth. Using in vitro eye-cups, a novel experimental system, we examined the role of the retinal pigment epithelium (RPE) and insulin on choroidal thickness and scleral GAG synthesis. Specifically, we asked whether insulin causes the release of diffusible factors from the RPE that affect the choroid.

Effects of muscarinic agents on chick choroids in intact eyes and eyecups: evidence for a muscarinic mechanism in choroidal thinning.

Purpose: In chicks, ocular growth inhibition is associated with choroidal thickening and growth stimulation with choroidal thinning, suggesting a mechanistic link between the two responses. Because muscarinic antagonists inhibit the development of myopia in animal models by a non-accommodative mechanism, we tested the hypothesis that agonists would stimulate eye growth and thin the choroid. We also hypothesized that the effective growth-inhibiting antagonists would thicken the choroid.

Dynamics of active emmetropisation in young chicks--influence of sign and magnitude of imposed defocus.

Purpose: Young eyes compensate for the defocus imposed by spectacle lenses by changing their rate of elongation and their choroidal thickness, bringing their refractive status back to the pre-lens condition. We asked whether the initial rate of change either in the ocular components or in refraction is a function of the power of the lenses worn, a result that would be consistent with the existence of a proportional controller mechanism.

Methods: Two separate studies were conducted; both tracked changes in refractive errors and ocular dimensions.

End-point variability is not noise in saccade adaptation.

When each of many saccades is made to overshoot its target, amplitude gradually decreases in a form of motor learning called saccade adaptation. Overshoot is induced experimentally by a secondary, backwards intrasaccadic target step (ISS) triggered by the primary saccade. Surprisingly, however, no study has compared the effectiveness of different sizes of ISS in driving adaptation by systematically varying ISS amplitude across different sessions.

Eyes in various species can shorten to compensate for myopic defocus.

Purpose: We demonstrated that eyes of young animals of various species (chick, tree shrew, marmoset, and rhesus macaque) can shorten in the axial dimension in response to myopic defocus.

Methods: Chicks wore positive or negative lenses over one eye for 3 days. Tree shrews were measured during recovery from induced myopia after 5 days of monocular deprivation for 1 to 9 days.

Oscillatory alpha-band suppression mechanisms during the rapid attentional shifts required to perform an anti-saccade task.

Neuroimaging has demonstrated anatomical overlap between covert and overt attention systems, although behavioral and electrophysiological studies have suggested that the two systems do not rely on entirely identical circuits or mechanisms. In a parallel line of research, topographically-specific modulations of alpha-band power (~8-14 Hz) have been consistently correlated with anticipatory states during tasks requiring covert attention shifts. These tasks, however, typically employ cue-target-interval paradigms where attentional processes are examined across relatively protracted periods of time and not at the rapid timescales implicated during overt attention tasks.

Chicks use changes in luminance and chromatic contrast as indicators of the sign of defocus.

As the eye changes focus, the resulting changes in cone contrast are associated with changes in color and luminance. Color fluctuations should simulate the eye being hyperopic and make the eye grow in the myopic direction, while luminance fluctuations should simulate myopia and make the eye grow in the hyperopic direction. Chicks without lenses were exposed daily (9 a.

The relative importance of retinal error and prediction in saccadic adaptation.

When saccades systematically miss their visual target, their amplitude adjusts, causing the position errors to be progressively reduced. Conventionally, this adaptation is viewed as driven by retinal error (the distance between primary saccade endpoint and visual target). Recent work suggests that the oculomotor system is informed about where the eye lands; thus not all "retinal error" is unexpected.

Modification of saccadic gain by reinforcement.

Control of saccadic gain is often viewed as a simple compensatory process in which gain is adjusted over many trials by the postsaccadic retinal error, thereby maintaining saccadic accuracy. Here, we propose that gain might also be changed by a reinforcement process not requiring a visual error. To test this hypothesis, we used experimental paradigms in which retinal error was removed by extinguishing the target at the start of each saccade and either an auditory tone or the vision of the target on the fovea was provided as reinforcement after those saccades that met an amplitude criterion.

A novel instrument for logging nearwork distance.

Purpose: To validate a novel ultrasonic sensor for logging reading distances. In addition, this device was used to compare the habitual reading distances between low and high myopes.

Methods: First, the stability and sensitivity of the ultrasonic device were determined by repeated measures using artificial targets.

Saccade adaptation is unhampered by distractors.

Saccade adaptation has been extensively studied using a paradigm in which a target is displaced during the saccade, inducing an adjustment in saccade amplitude or direction. These changes in saccade amplitude are widely considered to be controlled by the post-saccadic position of the target relative to the fovea. However, because such experiments generally employ only a single target on an otherwise blank screen, the question remains whether the same adaptation could occur if both the target and a similar distractor were present when the saccade landed.

The multifunctional choroid.

The choroid of the eye is primarily a vascular structure supplying the outer retina. It has several unusual features: It contains large membrane-lined lacunae, which, at least in birds, function as part of the lymphatic drainage of the eye and which can change their volume dramatically, thereby changing the thickness of the choroid as much as four-fold over a few days (much less in primates). It contains non-vascular smooth muscle cells, especially behind the fovea, the contraction of which may thin the choroid, thereby opposing the thickening caused by expansion of the lacunae.

Chick eyes compensate for chromatic simulations of hyperopic and myopic defocus: evidence that the eye uses longitudinal chromatic aberration to guide eye-growth.

Longitudinal chromatic aberration (LCA) causes short wavelengths to be focused in front of long wavelengths. This chromatic signal is evidently used to guide ocular accommodation. We asked whether chick eyes exposed to static gratings simulating the chromatic effects of myopic or hyperopic defocus would "compensate" for the simulated defocus.

Saccade adaptation specific to visual context.

When saccades consistently overshoot their targets, saccade amplitudes gradually decrease, thereby maintaining accuracy. This adaptive process has been seen as a form of motor learning that copes with changes in physical parameters of the eye and its muscles, brought about by aging or pathology. One would not expect such a motor-repair mechanism to be specific to the visual properties of the target stimulus.

Opposite effects of glucagon and insulin on compensation for spectacle lenses in chicks.

Purpose: Chick eyes compensate for the defocus imposed by positive or negative spectacle lenses. Glucagon may signal the sign of defocus. Do insulin (or IGF-1) and glucagon act oppositely in controlling eye growth, as they do in metabolic pathways and in control of retinal neurogenesis?

Methods: Chicks, wearing lenses or diffusers or neither over both eyes, were injected with glucagon, a glucagon antagonist, insulin, or IGF-1 in one eye (saline in the other eye).

Temporal properties of compensation for positive and negative spectacle lenses in chicks.

Purpose: Chicks' eyes rapidly compensate for defocus imposed by spectacle lenses by changing their rate of elongation and their choroidal thickness. Compensation may involve internal emmetropization signals that rise and become saturated during episodes of lens wear and decline between episodes. The time constants of these signals were measured indirectly by measuring the magnitude of lens compensation in refractive error and ocular dimensions as a function of the duration of episodes and the intervals between the episodes.

Cone signals for spectacle-lens compensation: differential responses to short and long wavelengths.

Chick eyes compensate for defocus imposed by spectacle lenses by making compensatory changes in eye length and choroidal thickness, a laboratory model of emmetropization. To investigate the roles of longitudinal chromatic aberration and of chromatic mechanisms in emmetropization, we examined the participation of different cone classes, and we compared the efficacy of lens compensation under monochromatic illumination with that under white light of the same illuminance to the chick eye. Chicks wore positive or negative 6D or 8D lenses on one eye for 3 days, under either blue (460 nm) or red (620 nm) light at 0.

The spatial scale of attention strongly modulates saccade latencies.

We have previously shown that when a stimulus consisting of two concentric rings moves, saccade latencies are much longer (by 150 ms) when attention is directed to the larger ring than to the smaller ring. Here, we investigated whether this effect can be explained by a deferral of the "cost" of making a saccade while the target remains inside the attentional field, or by purely visual factors (eccentricity or contrast). We found 1) latencies were shorter when attention was directed to small features irrespective of retinal eccentricity; 2) saccade latency distributions were systematically determined by the ratio between the amplitude of the stimulus step and the diameter of the attended ring: stimulus steps that were larger than the attended ring resulted in short latencies, whereas steps smaller than the attended ring resulted in proportionally longer and more variable latencies; 3) this effect was not seen in manual reaction times to the same target movement; and 4) suprathreshold changes in the contrast of targets, mimicking possible attentional effects on perceived contrast and saliency, had little effect on latency.

Temporal constraints on experimental emmetropization in infant monkeys.

Purpose: To characterize the temporal integration properties of the emmetropization process, the authors investigated the effects of brief daily interruptions of lens wear on the ocular compensation for negative lenses in infant rhesus monkeys.

Methods: Eighteen monkeys wore -3 D lenses binocularly starting from approximately 3 weeks of age. Six of these monkeys wore the lenses continuously.

Acute effects of dietary retinoic acid on ocular components in the growing chick.

When the eyes of chicks are induced to grow toward myopia or hyperopia by having them wear spectacle lenses or diffusers, opposite changes take place in the retina and choroid in the synthesis and levels of all-trans Retinoic Acid (RA). To explore whether RA plays a causal role in the regulation of eye growth, we fed young chicks RA (doses 0.5 to 24 mg/kg) either twice a day or on alternate days or only once.

Spatial deployment of attention influences both saccadic and pursuit tracking.

We examined the effects of changing spatial aspects of attention during oculomotor tracking. Human subjects were instructed to make a discrimination on either the small (0.8 degrees ) central or the large (8 degrees ) peripheral part of a compound stimulus (two counter-rotating concentric rings) while the stimulus either translated across the screen or was stationary.

In a matter of minutes, the eye can know which way to grow.

Purpose: The fitting of chick eyes with positive or negative lenses causes eye growth to decelerate or accelerate, respectively, thereby minimizing the imposed blur. This study was conducted to determine whether the eye can initially assess the correct direction of growth or whether it relies on trial and error, reversing its direction if the magnitude of blur increases. The rapid changes in choroidal thickness in response to brief periods of defocus were measured.