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Surgical treatment of macular holes with multiple recurrences.

PURPOSE: To evaluate the results of a third macular hole surgery in eyes with recurrent macular holes and two prior macular hole surgeries. DESIGN: Retrospective consecutive noncomparative case series. PARTICIPANTS: Sixteen eyes of sixteen patients with two prior macular hole surgeries with recurrent macular hole. INTERVENTION: A third vitreous surgery was performed in each eye using a long-acting gas bubble. MAIN OUTCOME MEASURE: Closure of the macular hole and change in visual acuity. RESULTS: The macular hole was closed in 12 of 16 eyes (75%) at 3 months after the third surgery. Visual acuity improved 2 or more Snellen lines in 9 of 16 eyes (56%), and 5 of 16 eyes (31%) achieved 20/40 or better vision. Six eyes (37.5%) had cataract surgery after the third macular hole surgery, and visual acuity results were similar in eyes with or without cataract surgery. Successful closure of the macular hole improved the visual acuity from 20/80 -1 to 20/50 +1 (P < 0.001). Eyes in which one of the previous surgeries had been temporarily successful in closing the macular hole improved from a mean of 20/80 to 20/40 (P = 0.003). Eyes in which both prior macular hole surgeries had been primary failures had minimal benefit with a preoperative visual acuity of 20/100 +1 and a postoperative visual acuity of 20/100 +2 (P = 0.67). CONCLUSIONS: Repeat macular hole surgery should be considered in eyes with recurrent macular holes and two prior surgeries when the macular hole was temporarily closed by at least one of the two previous surgeries. Successful closure of a macular hole in such cases usually results in significant visual acuity improvement.

Adult↗

Molecular dynamics simulation of bacteriorhodopsin's photoisomerization using ab initio forces for the excited chromophore.

Retinal proteins are photoreceptors found in many living organisms. They possess a common chromophore, retinal, that upon absorption of light isomerizes and thereby triggers biological functions ranging from light energy conversion to phototaxis and vision. The photoisomerization of retinal is extremely fast, highly selective inside the protein matrix, and characterized through optimal sensitivity to incoming light. This article describes the first report of an ab initio quantum mechanical description of the in situ isomerization dynamics of retinal in bacteriorhodopsin, a microbial retinal protein that functions as a light-driven proton pump. The description combines ab initio multi-electronic state molecular dynamics of a truncated retinal chromophore model (N-methyl-gamma-methylpenta-2,4-dieniminium cation fragment) with molecular mechanics of the protein motion and unveils in complete detail the photoisomerization process. The results illustrate the essential role of the protein for the characteristic kinetics and high selectivity of the photoisomerization: the protein arrests inhomogeneous photoisomerization paths and funnels them into a single path that initiates the functional process. Supported by comparison with dynamic spectral modulations observed in femtosecond spectroscopy, the results identify the principal molecular motion during photoisomerization.

Bacteriorhodopsins↗

Visuomotor integration is impaired in early stage Alzheimer's disease.

When the sensory information guiding a reach movement is dissociated from the required motor output, humans must integrate rule-based information in order to reach accurately. Here, we examine the accuracy of movements requiring a visuomotor transformation in neurologically healthy elderly subjects and patients diagnosed with probable Alzheimer's disease. Participants made sliding finger movements over a clear touch-sensitive screen positioned in three spatial planes to displace a cursor from a central target to one of four peripheral targets viewed on a monitor. These spatial plane conditions were repeated under conditions where the direction of cursor motion was rotated 180 degrees relative to the direction of hand motion. Significant main effects were observed between patient and control groups on reaction time and movement time measures. Also, significant increases in task completion errors were observed in the patient population. Further, performance was affected more by the visual feedback changes relative to the plane location changes. Notably, there were substantial performance deficits observed in the patient population, even those with minimal cognitive deficits. We suggest that the integration of eye and hand information may be impaired in these patients.

Aged↗

Effects of natural images on the detectability of simple and compound wavelet subband quantization distortions.

Quantization of the coefficients within a discrete wavelet transform subband gives rise to distortions in the reconstructed image that are localized in spatial frequency and orientation and are spatially correlated with the image. We investigated the detectability of these distortions: Contrast thresholds were measured for both simple and compound distortions presented in the unmasked paradigm and against two natural-image maskers. Simple and compound distortions were generated through uniform scalar quantization of one or two subbands. Unmasked detection thresholds for simple distortions yielded contrast sensitivity functions similar to those reported for 1-octave Gabor patches. Detection thresholds for simple distortions presented against two natural-image backgrounds revealed that thresholds were elevated across the frequency range of 1.15-18.4 cycles per degree with the greatest elevation for low-frequency distortions. Unmasked thresholds for compound distortions revealed relative sensitivities of 1.1-1.2, suggesting that summation of responses to wavelet distortions is similar to summation of responses to gratings. Masked thresholds for compound distortions revealed relative sensitivities of 1.5-1.7, suggesting greater summation when distortions are masked by natural images.

Adult↗

The developing visual system and metamorphosis in the lamprey.

Metamorphosis of the sea lamprey, Petromyzon marinus, is a true metamorphosis. The larval lamprey is a filter-feeder who dwells in the silt of freshwater streams and the adult is an active predator found in large lakes or the sea. The transformation usually occurs in the fifth or sixth year of life. Enlargement of the eye has been long accepted as a distinctive indication of metamorphosis in the sea lamprey, but it had been thought that this was because eye development in the larva was arrested after the formation of only the small central region. Recent studies indicate that all of the retina begins its development in the larva and that ganglion, amacrine, and horizontal cells differentiate in the peripheral retina of the larva. Retinal development is arrested during the premetamorphic period, to be resumed during metamorphosis. Metamorphic contributions include the differentiation of photoreceptor and bipolar cells. With the early appearance of ganglion cells, retinal pathways to the thalamus and tectum are established in larvae, as is a centripetal pathway. Tectal development spans the larval period but a spurt in tectal growth and differentiation is correlated with the completion of the retinal circuitry late in metamorphosis. The metamorphic changes in retina and tectum complete the functional development of the visual system and provide for the adult lamprey's predatory and reproductive behavior.

Animals↗

Unilateral lattice corneal dystrophy associated with the novel His572del mutation in the TGFBI gene.

PURPOSE: To report a novel mutation in the TGFBI gene, c.1761_1763del (p.His572del), associated with a unilateral variant of lattice corneal dystrophy (LCD). METHODS: A 63-year-old man presenting with the complaint of decreased vision in one eye was noted to have a unilateral lattice corneal dystrophy. Examination of the patient's wife and two sons, ages 20 and 27 years old, failed to reveal the presence of any corneal opacities. Following the collection of DNA from the patient and his family members, the TGFBI gene was screened for mutations previously associated with lattice corneal dystrophy and any novel coding region changes. RESULTS: In the affected patient, none of the mutations previously associated with the classic and variant forms of LCD were identified. However, a novel mutation, c.1761_1763del (p.His572del), was identified in exon 13 of TGFBI in the patient and his sons. This mutation was not identified in the patient's wife or in 200 control chromosomes. CONCLUSIONS: The novel TGFBI gene mutation (p.His572del) is associated with a unilateral, late-onset variant of lattice corneal dystrophy. This case highlights the utility of molecular genetic analysis in differentiating corneal dystrophies associated with an atypical phenotype from nondystrophic conditions.

Adult↗

The Drosophila sine oculis locus encodes a homeodomain-containing protein required for the development of the entire visual system.

The transformation of an unpatterned epithelium into a patterned one is a fundamental issue in morphogenesis. This transformation occurs in a dramatic fashion in the developing eye imaginal disc, the primordium of the Drosophila compound eye. Molecular and developmental analyses reveals that the sine oculis (so) locus encodes a homeodomain-containing protein that is expressed and required in the unpatterned epithelium prior to morphogenesis. In mutants, cells undergo apoptosis. These findings argue that so plays an essential role in controlling the initial events of pattern formation in the eye disc. So is also expressed and required for the development of the rest of the fly visual system, including the optic lobes (i.e., those regions of the brain that process visual information). So is expressed in the optic lobe primordium prior to its invagination from the embryonic ectoderm; in so mutants, the optic lobe primordium fails to invaginate.

Alleles↗

Preferential looking acuity obtained with a staircase procedure in pediatric patients.

Visual acuity of infants and young children with ophthalmologic disorders was assessed by adapting a transformed up-down staircase to preferential looking (PL) procedures. Eighty-five percent of pediatric patients between 11 days and 5 years of age were tested successfully. Acuity of infants and young children with normal eyes obtained by the PL staircase procedure agreed well with acuities obtained previously by the method of constant stimuli. In children with anisometropia, differences in acuity between eyes varied systematically with the amount of anisometropia. Monocular acuities of untreated patients with strabismus did not always agree with fixation preference. In general, test results from pediatric patients with structural ocular abnormalities were consistent with the severity of the disorder. By means of serial measurement of PL acuity, the therapy of patients with amblyopia was monitored. In our young patients, anisometropic amblyopia affected grating acuity differently than did strabismic amblyopia, as others have reported in older patients with these conditions. Our results indicate that the PL staircase procedure provides a useful measure of visual acuity in pediatric ocular disorders that can complement the clinical evaluation of infants and young children.

Age Factors↗

Trade-off between achromatic colour and perceived illumination as revealed by the use of pseudoscopic inversion of apparent depth.

The albedo hypothesis was tested under apparent transformations of perceived illumination and achromatic colour induced by pseudoscopic inversion of apparent depth. Looking through a pseudoscope made a cone attached to a vertical white screen look like a conical hole in the screen. This in turn caused the shadow which the now 'invisible' cone cast on the screen to change its appearance and to look like a darkly pigmented area. The darkness of the shadow before the pseudoscopic reversal and greyness of colour afterwards were measured by means of psychophysical scales for darkness and greyness set by the bisection method. Contrast of the shaded area was varied from 0.17 to 0.96 in 7 steps, the mean illuminance of the screen having been maintained at 40 1x. Although the albedo hypothesis in its classical form was not confirmed, it was found that darkness of shadow varied linearly in inverse proportion to greyness of colour within the entire contrast range. This is in agreement with the hypothesis that achromatic colour and perceived illumination are inversely proportional to each other while the retinal illumination is constant.

Color Perception↗

Time-varying, slow-phase component interaction in congenital nystagmus.

We investigated the nystagmus of a 12-year-old boy with suspected X-linked congenital nystagmus (CN) and exophoria to determine the underlying mechanisms and component signals in the 'dual-velocity' and other slow phases of his Asymmetric (a)Periodic Alternating Nystagmus (APAN). Fast Fourier transforms (FFT) were performed on the waveforms and residual data after subtracting a sawtooth waveform whose amplitude and frequency matched those of the jerk nystagmus. The FFT analyses identified two frequency components (jerk--4 Hz and pendular--4 and 8 Hz, variable) that varied differently in intensity and frequency/phase over the time-course of the APAN. We synthesized each of the patient's slow phases using summation of sawtooth and sinusoidal waveforms. The resulting waveforms included jerk (with different slow-phase appearances), dual jerk, and pendular. We demonstrated that the pendular nystagmus seen during the neutral phase of APAN and the appearance of either decelerating (mimicking latent nystagmus), dual-velocity, or dual-jerk slow phases can be explained and produced by the summation of linear and pendular components of variable amplitudes and frequencies/phases. Thus, one mechanism may be responsible for all the variation seen in this patient's slow phases, rather than the less parsimonious hypothesis of a switched-tonic-imbalance mechanism that we had originally suggested to simulate the dual-velocity waveform.

Child↗

Computing relief structure from motion with a distributed velocity and disparity representation.

Recent psychophysical experiments suggest that humans can recover only relief structure from motion (SFM); i.e., an object's 3D shape can only be determined up to a stretching transformation along the line of sight. Here we propose a physiologically plausible model for the computation of relief SFM, which is also applicable to the related problem of motion parallax. We assume that the perception of depth from motion is related to the firing of a subset of MT neurons tuned to both velocity and disparity. The model MT neurons are connected to each other laterally to form modulatory interactions. The overall connectivity is such that when a zero-disparity velocity pattern is fed into the system, the most responsive neurons are not those tuned to zero disparity, but instead are those having preferred disparities consistent with the relief structure of the velocity pattern. The model computes the correct relief structure under a wide range of parameters and can also reproduce the SFM illusions involving coaxial cylinders. It is consistent with the psychophysical observation that subjects with stereo impairment are also deficient in perceiving motion parallax, and with the physiological data that the responses of direction- and disparity-tuned MT cells covary with the perceived surface order of bistable SFM stimuli.

Cues↗

Off-axis aberrations of a wide-angle schematic eye model.

A schematic eye model based on anatomical data, which had been previously designed to reproduce image quality on axis, has been transformed into a wide-angle model by simply adding a spherical image surface that plays the role of the retina. This model captures the main features of the wide-angle optical design of the human eye with minimum complexity: four conic optical surfaces plus a spherical image surface. Seidel aberrations (spherical aberration, coma, astigmatism, field curvature, and distortion), longitudinal and transverse chromatic aberrations, and overall monochromatic spot diagrams have been computed for this eye model and for field angles ranging from 0 degree to 60 degrees by both finite and third-order ray tracing. The modulation transfer function for each field angle has been computed as well. In each case our results have been compared with average experimental data found in the literature, showing a reasonably good agreement. The agreement between the model and experimental data is better off axis, mainly at moderate (10 degrees-40 degrees) field angles, than on axis. The model has been applied to simulate a variety of experimental methods in which image aberrations are estimated from measurements taken in the object space. Our results suggest that for some types of aberration, these methods may yield biased estimates.

Astigmatism↗

Colorimetry for CRT displays.

We analyze the sources of error in specifying color in CRT displays. These include errors inherent in the use of the color matching functions of the CIE 1931 standard observer when only colorimetric, not radiometric, calibrations are available. We provide transformation coefficients that prove to correct the deficiencies of this observer very well. We consider four different candidate sets of cone sensitivities. Some of these differ substantially; variation among candidate cone sensitivities exceeds the variation among phosphors. Finally, the effects of the recognized forms of observer variation on the visual responses (cone excitations or cone contrasts) generated by CRT stimuli are investigated and quantitatively specified. Cone pigment polymorphism gives rise to variation of a few per cent in relative excitation by the different phosphors--a variation larger than the errors ensuing from the adoption of the CIE standard observer, though smaller than the differences between some candidate cone sensitivities. Macular pigmentation has a larger influence, affecting mainly responses to the blue phosphor. The estimated combined effect of all sources of observer variation is comparable in magnitude with the largest differences between competing cone sensitivity estimates but is not enough to disrupt very seriously the relation between the L and M cone weights and the isoluminance settings of individual observers. It is also comparable with typical instrumental colorimetric errors, but we discuss these only briefly.

Colorimetry↗

Food insecurity, malnutrition and mortality in Maewo and Ambae Islands, Vanuatu.

CONTEXT: This paper reports on findings from the ex-post evaluation of the Maewo Capacity Building project in Maewo Island, Vanuatu, which was funded by World Vision Australia. OBJECTIVES: To examine the extent to which the infrastructure and systems left behind by the project contributed to the improvement of household food security and health and nutritional outcomes in Maewo Island, using Ambae Island as a comparator. SETTING: Two-stage cluster survey conducted from 6 to 20 July 2004, which included anthropometric measures and 4.5-year retrospective mortality data collection. PARTICIPANTS: A total of 406 households in Maewo comprising 1623 people and 411 households in Ambae comprising 1799 people. MAIN OUTCOME MEASURES: Household food insecurity, crude mortality rate (CMR), under-five mortality rate (U5MR) and malnutrition prevalence among children. RESULTS: The prevalence of food insecurity without hunger was estimated at 15.3% (95% confidence interval (CI): 12.1, 19.2%) in Maewo versus 38.2% (95% CI: 33.6, 43.0%) in Ambae, while food insecurity with hunger in children did not vary by location. After controlling for the child's age and gender, children in Maewo had higher weight-for-age and height-for-age Z-scores than children of the same age in Ambae. The CMR was lower in Maewo (CMR = 0.47/10 000 per day, 95% CI: 0.39, 0.55) than in Ambae (CMR=0.59/10 000 per day, 95% CI: 0.51, 0.67) but no difference existed in U5MR. The major causes of death were similar in both locations, with frequently reported causes being malaria, acute respiratory infection and diarrhoeal disease. CONCLUSIONS: Project initiatives in Maewo Island have reduced the risks of mortality and malnutrition. Using a cross-sectional 'external control group' design, this paper demonstrates that it is possible to draw conclusions about project effectiveness where baseline data are incomplete or absent. Shifting from donor-driven evaluations to impact evaluations has greater learning value for the organisation, and greater value when reporting back to the beneficiaries about project impact and transformational development in their community. Public health nutritionists working in the field are well versed in the collection and interpretation of anthropometric data for evaluation of nutritional interventions such as emergency feeding programmes. These same skills can be used to conduct impact evaluations, even some time after project completion, and elucidate lessons to be learned and shared. These skills can also be applied more widely to projects which impact on the longer-term nutritional status of communities and their food security.

Anthropometry↗

[The origin of informed consent].

The principle of informed consent, aimed at the lawfulness of health assistance, tends to reflect the concept of autonomy and of decisional autodetermination of the person requiring and requesting medical and/or surgical interventions. This legal formula, over the last few years, has gained not only considerable space but also importance in the doctrinal elaboration and approaches, as well as juridical interpretations, thereby influencing the everyday activities of the medical profession. Informed consent is still the object of continuous explorations, not only asfar as concerns the already confirmed theoretical profile but, instead, the ambiguous practical and consequential aspect. Analysing how the concept and role of consensus was born and developed with the more adequate and reasonable excursions to make it valid and obtain it, it is impossible not to take into consideration, on the one hand, the very ancient philosophical origins and, on the other, the fact that it was conditioned by religion with the moral aspects and the accelerated deontological evolution with pathways parallel to the needs and the progress offered by new forms of treatment and novel biotechnological applications. The principle of consent is a relatively new condition. In fact, already in the times of not only the Egyptian civilisation, but also the Greek and Roman, documents have been found which show how the doctor's intervention had, in some way, first to be approved by the patient. Plato (law IV) had already foreseen the problems, the procedures and the modes of information which are, in synthesis, at the root of the principles of the present formula of informed consent and correlated the practice of the information and consensus with the quality and social position of the patient. The only guarantee that the patient might have, derived from a fundamental principle of medicine of all times: "in disease, focus on two aims, to improve and not to cause damage". A figure can be recognised, in the Hippocratic physician, that cared about the patient's suffering, but never neglected looking after his own outcome, endeavouring to avoid becoming involved in lack of success and death of a patient. The concept of consensus is inexistent, albeit, there is an awareness of the presence of precautious and preventive information. In the behaviour of doctors, in ancient times, it is not difficult to recognize the true motives and the real reasons that, already in those days, give rise to the necessary "defensive medicine" particularly as far as concerns the social status of the patient. Already from the early origins, continuing the Hippocratic tradition, the relationship between doctor and patient was consolidated, based upon two very definite criteria, represented, on the one hand, by the professional duty of the physician to do what is bestfor the patient and, on the other, the duty of the patient to completely accept the physician's decisions and intervention. The Hippocratic physician respected a principle of professional responsibility which was more religious and of a moral type, but, from a legal point of view, very weak inasmuch as it depended upon regulations elaborated by human beings. The conviction and certainty that the physician acted, in the interest of his patient's well-being, has been passed down over the centuries endowing the physician with moral authority and a kind of legal impunity, conditions which corresponded, in an almost reflection-likefashion, with the duty of obedience and subjection, on the part of the patient. Christianity was grafted into this consolidated vision of the sacral character of medicine and medical practice, which did not substantially change the Hippocratic type of ethical behaviour. Non only the population but also the Christian physician was aware of the religious importance of his intense activity as a mission and compared to a special kind of priesthood in safe-guarding health, considered as a gift of God. Therefore, invested with this authority which derived from his professional role and from his very work, he felt it his duty to guide the patient, deciding and for him. The patient is an ignorant person who does not have the knowledge, the intellectual capacity or moral authority to oppose or disagree with the wishes and decisions of the physician who, instead, on account of his doctrine, knows exactly what is goodfor him. In this regard, if we were to speak of consensus concerning the physician's intervention, he would be considered useless in as much as obvious and understood when seeking help. The attitude of the patient towards the physician has always tended to one of strong faith and characterized by psychological subjection borne out by traditions thousands of years old. A patient who was sick, again, as an attitude of respect and gratitude, followed the treatment but never asked for any explanations regarding the therapeutic effects and the physician refrained from taking any initiative to inform the patient or his/her family. Each phenomenon, therefore, has a precise origin, a well-defined history and when its importance tends to significantly condition the activities concerning Man, a desire emerges to learn the origin and the history. As is well known, a trial commenced in Nuremberg, on December 19, 1946, of Nazi doctors and a code was defined in which the judges, all Americans, clearly emphasized a view of medical research and technology: science should never transform or consider human beings as an instrument to be employed for scientific purposes. In actual fact, documents exist providing evidence that a few decades before the drawing up of the Nuremberg Code, the need had been expressed, in Germany itself to somehow make medical interventions and actions legal by means of the use and practice of consensus. The moral and ethical principles in those documents, even if not available as bibliographic references in the English literature, certainly merit, from a historical viewpoint to be considered as conceptual elements and doctrinal and socio-cultural products, even if at that time, of little practical importance, which belong to the European culture and, in particular, and almost paradoxically, in the light of what happened, to the German culture. The United States of America is held to be the country of origin of informed consent, the initial aim of which was make sure that the correct dignity of the patient's independence be reserved at the time of decision making and choice of medical options. Reports on this topic, in fact, first appeared in the USA, at the beginning of the 18th Century, with problems focusing on and limited to only the simple rights of the patient in giving his/her approval of the health intervention later to be conceptually developed, along the lines of an itinerary with, at intervals, famous legal actions, until in the 20th Century, informed consent was reached, a criterion that, as is well known, foresees and includes not only the important and fundamental autonomy of the patient to decide, which stems ones personal rights, but also the essential objective element, which is, information. The expression informed consent has simply been transposed in Italian and roughly translated in an ambiguous fashion into "consenso informato" when, on the contrary, it should be referred to as "informazione per il consenso" "information for consensus" not only to respect the concept but, surely, for a more correct deciphering and a more precise interpretation related to the numerous concepts it presupposes and implies. Information and consent may be compared to the two sides of the same coin. These are the two important pillars that coincide and are joined giving weight to the medical responsibility, as far as concerns consent to the health intervention: on the one hand, having obtained consent,following correct and sincere information interpreted and deciphered as an important phase and an essential indicator of correct, scrupulous medico-professional procedure and, on the other, the consensus itself conceived as a duty aiming at the maximum respect of the rights to autodetermination, independence and autonomy of the patient, as a person. At the beginning of the Nineties, as we have seen, we were made aware of a series of legal actions regarding medical responsibility which was greatly conditioned by the Anglosaxon influence which initially induced many Italian magistrates and forensic physicians to adopt an extremely rigid attitude with no attempt to comply, in any way, with the culture and traditions of our country and our tradition which has always been inspired by good common sense, both medical and human. The American experience has been very rapidly adopted, by some, without a profound, complete and necessary historical and evolutional analysis aimed at those intertwined principles that have been motifs that have gradually led to the legal references in those emblematic cases referred to, the conclusions of which continue to attract a great deal of attention. In Italy, the legal and doctrinal evolution of informed consent, even if following a little more rapidly the traces, steps, problems and interpretations of the various aspects drawn up, characterized and applied in the United States, has not only occurred at a later time, but, despite reaching the same meaningful objectives, the same considerations, the same importance, and, unfortunately, the same inconveniences, has had quite different aims, approaches and articulations. In this respect, it is enough to focus attention on the different cultural traditions and religious routes, on the different doctrinal background, the particular historical origins and the individual legal aspects, all extremely different one from the other. (ABSTRACT TRUNCATED)

Christianity↗

The interaction of depth parameters in motion integration with polar plaids.

Many parameters have been investigated as to their effect on the way in which the visual system is able to integrate different motion directions at the same visual location. Of special interest have been parameters that determine the depth relationship between surfaces, such as disparity, relative contrast, and occlusion versus transparency. The preferred stimulus for this research has been the 'plaid', usually constructed from two linear gratings. The present study concentrated not on these Cartesian plaids, but on polar plaids, made from a combination of concentric circles and radial gratings. These kinds of plaids also have a special theoretical significance: within the Lie Transformation Group approach to visual pattern processing, Cartesian and polar stimuli represent different invariances in the visual world. This study compared Cartesian, polar and hybrid plaids as to their propensity to be perceived as coherently moving stimuli. Cartesian and polar plaids were similar in terms of the effects of intersection luminance and relative contrast on coherence, polar plaids being consistently less coherent. Hybrid plaids did not usually cohere at all. Adaptation to an unambiguously coherent plaid decreased perceived coherence when tested with a bistable plaid from the same, and not from the other Lie group, i.e. there was within-group adaptation but no between-group adaptation. Polar plaids also offer the possibility of studying the influence of another depth parameter on motion integration: expansion or contraction of circular gratings, which represent motion-in-depth toward or away from the observer. This motion-in-depth was tested for interaction with disparity or relative contrast in the determination of motion integration. The results were negative under the present conditions. Thus not all depth parameters contribute equally to the determination of the stimulus depth relations affecting the motion integration process.

Depth Perception↗

Objective assessment of image quality. III. ROC metrics, ideal observers, and likelihood-generating functions.

We continue the theme of previous papers [J. Opt. Soc. Am. A 7, 1266 (1990); 12, 834 (1995)] on objective (task-based) assessment of image quality. We concentrate on signal-detection tasks and figures of merit related to the ROC (receiver operating characteristic) curve. Many different expressions for the area under an ROC curve (AUC) are derived for an arbitrary discriminant function, with different assumptions on what information about the discriminant function is available. In particular, it is shown that AUC can be expressed by a principal-value integral that involves the characteristic functions of the discriminant. Then the discussion is specialized to the ideal observer, defined as one who uses the likelihood ratio (or some monotonic transformation of it, such as its logarithm) as the discriminant function. The properties of the ideal observer are examined from first principles. Several strong constraints on the moments of the likelihood ratio or the log likelihood are derived, and it is shown that the probability density functions for these test statistics are intimately related. In particular, some surprising results are presented for the case in which the log likelihood is normally distributed under one hypothesis. To unify these considerations, a new quantity called the likelihood-generating function is defined. It is shown that all moments of both the likelihood and the log likelihood under both hypotheses can be derived from this one function. Moreover, the AUC can be expressed, to an excellent approximation, in terms of the likelihood-generating function evaluated at the origin. This expression is the leading term in an asymptotic expansion of the AUC; it is exact whenever the likelihood-generating function behaves linearly near the origin. It is also shown that the likelihood-generating function at the origin sets a lower bound on the AUC in all cases.

Area Under Curve↗

Brain imaging in a patient with hemimicropsia.

Hemimicropsia is an isolated misperception of the size of objects in one hemifield (objects appear smaller) which is, as a phenomenon of central origin, very infrequently reported in literature. We present a case of hemimicropsia as a selective deficit of size and distance perception in the left hemifield without hemianopsia caused by a cavernous angioma with hemorrhage in the right occipitotemporal area. The symptom occurred only intermittently and was considered the consequence of a local irritation by the hemorrhage. Imaging data including a volume-rendering MR data set of the patient's brain were transformed to the 3-D stereotactic grid system by Talairach and warped to a novel digital 3-D brain atlas. Imaging analysis included functional MRI (fMRI) to analyse the patient's visual cortex areas (mainly V5) in relation to the localization of the hemangioma to establish physiological landmarks with respect to visual stimulation. The lesion was localized in the peripheral visual association cortex, Brodmann area (BA) 19, adjacent to BA 37, both of which are part of the occipitotemporal visual pathway. Additional psychophysical measurements revealed an elevated threshold for perceiving coherent motion, which we relate to a partial loss of function in V5, a region adjacent to the cavernoma. In our study, we localized for the first time a cerebral lesion causing micropsia by digital mapping in Talairach space using a 3-D brain atlas and topologically related it to fMRI data for visual motion. The localization of the brain lesion affecting BA 19 and the occipitotemporal visual pathway is discussed with respect to experimental and case report findings about the neural basis of object size perception.

Adult↗