Driving in the future: temporal visuomotor adaptation and generalization

Rapid and accurate visuomotor coordination requires tight spatial and temporal sensorimotor synchronization. The introduction of a sensorimotor or intersensory misalignment (either spatial or temporal) impairs performance on most tasks. For more than a century, it has been known that a few minutes of exposure to a spatial misalignment can induce a recalibration of sensorimotor spatial relationships, a phenomenon that may be referred to as spatial visuomotor adaptation. Here, we use a high-fidelity driving simulator to demonstrate that the sensorimotor system can adapt to temporal misalignments on very complex tasks, a phenomenon that we refer to as temporal visuomotor adaptation. We demonstrate that adapting on a single street produces an adaptive state that generalizes to other streets. This shows that temporal visuomotor adaptation is not specific to a single visuomotor transformation, but generalizes across a class of transformations. Temporal visuomotor adaptation is strikingly parallel to spatial visuomotor adaptation, and has strong implications for the understanding of visuomotor coordination and intersensory integration.     

Standardization and analysis of digitized photographic data in the longitudinal documentation of cataractous growth

Age-related cataract formation in man can be documented with slit and retroillumination photographs. With digitization and image analysis of such photographs a cataract may be characterized by a frequency distribution of picture elements over a 255 step gray scale spectrum. Transition from a clear to a cataractous lens may be manifested as a change from a unimodal, Gaussian to a multimodal, non Gaussian frequency distribution respectively. How should one compare and contrast these two distributions, so to accurately describe the extent and significance of a change in lens opacification? The in vitro system of cold cataract formation in the rabbit lens was used as a model of the much slower process of age-related cataract formation in man. As in the human lens undergoing progressive opacification, the frequency distribution (number of pixels vs. intensity of gray) for a digitized image of a clear lens at 26 degrees C is unimodal and Gaussian; that of a fully developed cold cataract at 10 degrees C is multimodal and non-gaussian. In spite of the increasing multimodality of the frequency distribution as the temperature dropped and the cataract grew in density and size, the mean gray density proved to be a valid and useful measure to characterize the distribution and to compare different unaligned images. The Wilcoxon Rank Sum Test proved to be useless in comparing the frequency distributions from cataract images because it proved to be too sensitive to subtle changes in the degree of opacification. Anomalous behavior of the opacification process--i.e. clarification as well as opacification of the lens during cold cataract formation caused all pairs to appear statistically significantly different when in appearance there was no difference. The mean of the frequency distribution is less sensitive to this anomalous behavior and is useful as a comparative index. The method of calculating the threshold of significant change in the mean density of a cataract image is presented.     

Anaphylatoxin levels in human aqueous humor

Radioimmunoassay was used to measure levels of C3a, C4a, and C5a in aqueous humor from 13 normal eyes, 8 noninflamed eyes with a history of surgery or inflammation, and 14 eyes with anterior uveitis. The authors were unable to measure levels of C3a, C4a, or C5a in normal aqueous humor. In noninflamed aqueous humor from eyes with a history of surgery or inflammation, the authors were unable to measure levels of C4a or C5a, but were able to measure low levels of C3a in 3/8 patients. In aqueous humor from eyes with anterior uveitis, the authors were able to measure levels of C3a in all 14 patients, C4a in 9/14 patients, and C5a in 5/14 patients. Patients with severe anterior uveitis had higher levels of C3a than those with moderate anterior uveitis. The higher ratios of anaphylatoxin to protein levels in inflamed aqueous humor, when compared to normal plasma or noninflamed aqueous humor, suggested that complement was being activated by either the classical or alternative pathways in inflamed aqueous humor. Measurable levels of C3a without detectable C4a in five patients with anterior uveitis suggested alternative pathway activation of complement.     

The tear ferning test: a simple clinical technique to evaluate the ocular tear film

A healthy tear film is very important for many major functions of the ocular surface. Dry eye disease is a significant clinical problem that needs to be solved but the poor correlation between clinical signs and reported symptoms makes it difficult for the clinician to apply a scientific basis to his clinical management. The problem is compounded by the difficulties of evaluating the tear film due to its transparency, small volume and complex composition. Practical insight into tear film composition would be very useful to the clinician for patient diagnosis and treatment but detailed analysis is restricted to expensive, laboratory‐based systems. There is a pressing need for a simple test. The tear ferning test is a laboratory test but it has the potential to be applied in the clinic setting to investigate the tear film in a simple way. Drying a small sample of tear fluid onto a clean, glass microscope slide produces a characteristic crystallisation pattern, described as a ‘tear fern’. This test is currently not widely used because of some limitations that need to be overcome but several studies have demonstrated its potential. Such limitations need to be resolved so that tear ferning could be used in the clinic setting to assess the tear film.     

Task-set switching with natural scenes: measuring the cost of deploying top-down attention

In many everyday situations, we bias our perception from the top down, based on a task or an agenda. Frequently, this entails shifting attention to a specific attribute of a particular object or scene. To explore the cost of shifting top-down attention to a different stimulus attribute, we adopt the task-set switching paradigm, in which switch trials are contrasted with repeat trials in mixed-task blocks and with single-task blocks. Using two tasks that relate to the content of a natural scene in a gray-level photograph and two tasks that relate to the color of the frame around the image, we were able to distinguish switch costs with and without shifts of attention. We found a significant cost in reaction time of 23-31 ms for switches that require shifting attention to other stimulus attributes, but no significant switch cost for switching the task set within an attribute. We conclude that deploying top-down attention to a different attribute incurs a significant cost in reaction time, but that biasing to a different feature value within the same stimulus attribute is effortless.     

Discrimination of single bars by the honeybee (Apis mellifera)

The bees learn to come for a reward to a very simple pattern, a black bar in a fixed position on a white background, in a Y-choice apparatus, with the targets presented in the vertical plane at a fixed range. They were trained on a number of different arrangements of a single bar on one or both targets. The trained bees were then given appropriate tests to discover what cues they had learned. A cue is an essential parameter that is recognized, not the whole pattern. At the choice point they learn exactly which way to look for consistent cues. After training on a single broad bar versus a blank target, they respond in tests to any area of black where they expect to see it, and are less able to detect it the more it has been displaced from the training position. They are more sensitive to vertical than to horizontal displacement of the bar. The cue is anything black of the right size. They do not recognize the shape or orientation of the bar. When trained to discriminate between two bars at right angles to each other, centred on the reward hole, the cue is the edge orientation at the expected places on the targets, and the bees are less able to discriminate the orientation cues the more they are displaced. When trained on a pair of broad black bars in different positions, the cues are the vertical positions of the centres. Division of the bar into squares, or making the edges stepped, removes the orientation cue but not the position cue. Addition of a large black spot or a checkerboard background to the original bar prevents discrimination, as if the spatial reference frame is disturbed. In training, or testing trained bees, parallax does not assist the discrimination of orientation.     

Countermanding saccades in humans.

We used a countermanding paradigm to investigate the relationship between conflicting cues for controlling human saccades. Subjects made a saccade to a target appearing suddenly in the periphery; but on some trials, after a delay, a stop-signal was presented that instructed subjects to inhibit the saccade. As we increased this delay, subjects increasingly failed to inhibit the movement. From measurements of this relationship, and of saccadic latency in control trials, we estimated the average time needed to inhibit the saccade (the stop-signal reaction time or SSRT). SSRTs were similar across subjects, between 125 and 145 ms, and did not vary with target luminance. We then investigated a race model in which the target initiates a response preparation signal rising linearly with a rate varying randomly from trial to trial, and racing against a similarly rising signal initiated by the cue to inhibit the saccade. The first process to cross a trigger threshold determines whether the saccade is initiated or not. In Monte Carlo simulations, this model correctly predicted the probability of successful saccade inhibition as a function of the stop-signal delay, and also the statistical distributions of saccadic latency during trials in which a stop-signal was presented but the subject failed to inhibit the saccade. These findings provide a comparison to results previously described in the monkey, and show that a simple race model with a linear rise to threshold may underlie behavioural performance in tasks of this kind.     

Variations in physician response to consultation requests for Hollenhorst plaques: a pilot study.

This is a report on physicians' response to a pilot survey regarding the method of management of a patient sent to them for a health evaluation because of a Hollenhorst plaque detected during a routine eye examination. Several specialties and sub-specialties were surveyed. The results demonstrate a wide variability in the methods chosen for management of the patient, indicating the need to consider standardizing the health evaluation. A review of literature suggests that the patient with a Hollenhorst plaque is at increased risk for both cardiovascular and cerebrovascular disease and appropriate measures should be taken to minimize the risk. The pilot survey suggests that more in-depth surveys are necessary to establish standards of care for the patient with Hollenhorst plaques as well as other ocular conditions related to systemic disorders.     

Interferon alfa-2a: a new treatment option for long lasting refractory cystoid macular edema in uveitis? A pilot study

PURPOSE: To perform a prospective pilot study to evaluate interferon alfa-2a (IFN alfa-2a) for the treatment of refractory cystoid macular edema (CME) in endogenous uveitis. METHODS: IFN alfa-2a was administered at an initial dose of 3 or 6 million IU (depending on body weight) per day subcutaneously. Afterwards IFN alfa-2a was tapered slowly over 6 months and finally discontinued. If CME relapsed IFN alfa-2a was reinstituted and tapered slowly again to evaluate the lowest maintenance dose to keep remission. RESULTS: A total of 15 eyes of 8 patients with refractory CME due to intermediate or posterior uveitis were included. Ineffective pretreatment consisted of systemic steroids and acetazolamide (all patients) and at least one additional immunosuppressant (6 patients). Six of 8 patients (11 eyes) responded well to IFN alfa-2a and CME resolved completely during 6 months treatment. One patient was lost to follow-up after IFN alfa-2a was stopped. In 1 patient (1 eye) even 19 months after cessation of IFN alfa-2a no recurrence of CME occurred. In 4 patients (8 eyes) IFN alfa-2a had to be reinstituted because CME relapsed. All 4 patients responded again. During a mean follow-up period of 16.4 months since restart of therapy we succeeded in all 4 patients to taper IFN alfa-2a to maintenance doses between 1.5 million IU every second and every sixth day without a recurrence of CME in any of the 8 eyes. CONCLUSION: IFN alfa-2a can be a treatment option for patients with otherwise treatment resistant uveitic CME.     

The efficacy of additional argon laser photocoagulation for persistent, severe proliferative diabetic retinopathy

Twenty-three eyes with severe proliferative diabetic retinopathy had failed to show a satisfactory response to initial panretinal photocoagulation of approximately 3000 burns. A satisfactory response was defined as two or less retinopathy risk factors as defined by the diabetic retinopathy study (DRS). These eyes were treated with additional, extensive ablative laser therapy. Twelve of the 23 eyes showed a satisfactory response after an average of 7550 burns. Eleven eyes failed to show a satisfactory response after an average of 7985 burns. Forty-five percent of eyes that failed to show a satisfactory response suffered a severe decrease in visual acuity to count fingers or less. Additional extensive laser therapy can induce a satisfactory response in approximately 50% of resistant nonresponder eyes. Failure to respond to such therapy indicates a poor prognosis.     

Orbital Inflammation Secondary to a Delayed Hypersensitivity Reaction to Sub-Tenon’s Hyaluronidase

Abstract

We report a rare case of a delayed orbital inflammation with raised intraocular pressure as a result of hyluronidase allergy following sub-Tenon’s anaesthesia. Here, we have shown evidence to prove the orbital inflammation to be an allergic response to hyluronidase with a skin patch test. This is the first case to our knowledge of a delayed hypersensitivity reaction to sub-Tenon’s hyluronidase comprising of an initial exposure to hyluronidase in the fellow eye with no subsequent allergic response, but with a subsequent delayed reaction to hyluronidase during a second eye cataract surgery. This case demonstrates hyaluronidase allergy should be considered as a differential diagnosis among patients presenting with acute post-operative orbital inflammation, even if there is a history of previous exposure to hyaluronidase in the fellow eye with no subsequent allergic response.     

Counterphase dichoptic flicker is seen as its own second harmonic

If a patternless field is modulated sinusoidally in time so that the luminance change in one eye is in counterphase to that in the other, the resulting flicker appears faster than if the modulation to both eyes has the same phase. If observers set the frequency and the amplitude of a comparison in-phase field so that it matches a neighbouring counterphase field, modulated at, say, 2.5 x its threshold, they set the frequency to twice the counterphase frequency, and the amplitude to a value that is, for a given frequency, a constant ratio of the modulation of the counterphase field. Counterphase stimulation thus appears to cause an internal second-harmonic signal. However, it is not possible to cancel this by adding a second harmonic component to the stimulus.     

Examination of different pointwise linear regression methods for determining visual field progression

PURPOSE: To compare the specificity and sensitivity of several different methods for using pointwise linear regression (PLR) to detect progression (deterioration) in visual fields. METHODS: First, theoretical results were derived to predict which of the considered PLR methods would be the most specific and hence the least sensitive. Then, a "Virtual Eye" simulation model was developed that simulates series of sensitivity readings for a point over time. The model adds normally distributed noise (estimated from published results) to the sensitivity at each point to produce a series of fields to be analyzed using each method. Stable and deteriorating eyes were simulated, with the latter defined to have a noise-free loss of 2 dB/y at a significant cluster of points over the series. RESULTS: The most sensitive method tested was to flag a visual field as progressing if it had a point that exhibited a statistically significant slope (at the 1% level) of at least -1 dB/y in the sensitivity. The most specific was a new "Three-Omitting" method that is being proposed, using two confirmation fields in a novel way. Current methods of using confirmation fields to verify a significant slope incorrectly flagged up to twice as many stable eyes as having progressing fields as did our new method. CONCLUSIONS: Using the new proposed PLR method is recommended in preference to current PLR methods in any applications when a high degree of specificity is the main priority.     

Do people match surface reflectance fundamentally differently than they match emitted light?

We compared matches between colours that were both presented on a computer monitor or both as pieces of paper, with matching the colour of a piece of paper with a colour presented on a computer monitor and vice versa. Performance was specifically poor when setting an image on a computer monitor to match the colour of a piece of paper. This cannot be due to any of the individual judgments because subjects readily selected a matching piece of paper to match another piece of paper and set the image on the monitor to match another image on a monitor. We propose that matching the light reaching the eye and matching surface reflectance are fundamentally different judgments and that subjects can sometimes but not always choose which to match.     

Color and luminance share a common motion pathway

Following exposure to a moving grating of bars differing only in luminance, a motion aftereffect (MAE) is observed on a stationary grating of bars differing only in chrominance. This suggests that the motion of equiluminous chromatic stimuli is sensed by a channel that responds to both luminance and chrominance and not by a separate channel specialized for the motion of colored stimuli. However, adding color to a low contrast luminance stimulus actually reduces its effectiveness at creating or nulling a MAE, indicating that the response of the motion pathway to color is qualitively different from its response to luminance. In addition, a chromatic stimulus demonstrates a dissociation between perceived speed, MAE speed and speed required to null the MAE that is absent for a luminance stimulus.     

Capsulorhexis assisted by slit illuminator for white cataract without a red reflex.

The authors investigated the clinical efficacy of a slit illuminator in a surgical microscope during capsulorhexis for white cataract. After staining the anterior capsule, the slit illuminator was adjusted to a width of 3 mm and a height of 12 mm using the slider to obtain a high-contrast image of the anterior capsule, and an angle of 30 degrees to both the left and right was possible using the arc guide. After the anterior capsular puncture was done, a capsulorhexis forceps was used to grasp the capsular edge and a continuous curvilinear capsulorhexis was successfully performed in all 10 cases. Using a slit illuminator in a surgical microscope seems to be a valuable technique for performing a continuous curvilinear capsulorhexis on a mature or intumescent cataract that has no red reflex and high intralenticular pressure.     

TTT as rescue treatment for choroidal melanoma not controlled with iodine-125 brachytherapy

Purpose: To describe the use of transpupillary thermotherapy in the management of two small choroidal melanomas that continued to grow following Iodine-125 brachytherapy. Methods: Case reports from a tertiary care center. Results: One small growing choroidal melanoma showed a partial response to Iodine-125 brachytherapy; four years later, it regrew to a thickness of 2.7mm. After transpupillary thermotherapy (TTT), the tumor regressed to a flat scar and has remained inactive for more than three years. A second small melanoma failed to show regression after Iodine-125 brachytherapy; it progressively grew to 3.6mm. TTT was used to treat the tumor on two successive occasions six weeks apart. The tumor regressed to a flat scar within three months and has remained inactive for 2.5 years. Conclusion: TTT may be considered as a rescue treatment for small choroidal melanomas that have failed to respond satisfactorily to brachytherapy.     

A hypothesis on the pathogenesis of pterygiums.

All true pterygiums are attracted to a specific site at the corneoscleral junction along the 3 to 9 o'clock meridian. The pathogenesis of a pinguecula-pterygium is postulated to be due to a noninfected inflammation at the junction of the conjunctival blood vessels and Bowman's membrane where the autolytic process of inflammation results in a protein degradation amino acid mixture which has the ability of attracting conjunctival blood vessels on the cornea. This amino acid mix is hypothesized to contain a pterygium angiogenesis factor.     

Progressive orbital granular cell tumour associated with medial rectus

Granular cell tumour is a rare soft tissue tumour that can occur in any part of the body, but seldom in ocular adnexa. It usually behaves in a benign fashion. We report a case of a 54-year-old man with a well-demarcated, solitary, slow-growing orbital tumour which lead to significant ocular symptoms. The case was a diagnostic and therapeutic challenge due to its location and difficulty in obtaining tissue for a histological diagnosis. Surgical biopsy attempts were made but they all failed to uncover the true identity of the lesion. A definitive diagnosis was revealed with complete surgical excision of the tumour, which was challenging due to its size and close association with rectus muscle. This case has highlighted that orbital granular cell tumour may result in significant ocular symptoms. Adequate exposure to the anatomical site is the key to obtaining diagnosis and complete excision of a lesion.     

Cataract Extraction in an Eye with a Filtering Bleb

Seventy-two ophthalmologists with a major interest in glaucoma (glaucoma surgeons) responded to a questionnaire as to how they would remove a cataract from a hypothetical 60-year-old patient with a functioning filtering bleb in the superior nasal quadrant. The majority recommended an intracapsular cataract extraction through a lateral or inferolateral limbal incision or a superior corneal incision anterior to the bleb. Most of the glaucoma surgeons preferred to close the wound with five to nine interrupted 10—0 nylon sutures. Estimates of the percentage of blebs failing after cataract extraction ranged from zero to more than 50%, with a median of 30%. The majority of the glaucoma surgeons stated that they would never, or only under exceptional circumstances, implant an intraocular lens in an eye with a filtering bleb. Twelve ophthalmologists with a major interest in intraocular lens implantation (implant surgeons) responded to the same questionnaire. They were more likely than the glaucoma surgeons to recommend extracapsular cataract extraction and to implant an intraocular lens in an eye with a filtering bleb.