Video Object Segmentation without Temporal Information.

Video Object Segmentation, and video processing in general, has been historically dominated by methods that rely on the temporal consistency and redundancy in consecutive video frames. When the temporal smoothness is suddenly broken, such as when an object is occluded, or some frames are missing in a sequence, the result of these methods can deteriorate significantly. This paper explores the orthogonal approach of processing each frame independently, i.e., disregarding the temporal information. In particular, it tackles the task of semi-supervised video object segmentation: the separation of an object from the background in a video, given its mask in the first frame. We present Semantic One-Shot Video Object Segmentation (OSVOS$^\mathrm {S}$S), based on a fully-convolutional neural network architecture that is able to successively transfer generic semantic information, learned on ImageNet, to the task of foreground segmentation, and finally to learning the appearance of a single annotated object of the test sequence (hence one shot). We show that instance-level semantic information, when combined effectively, can dramatically improve the results of our previous method, OSVOS. We perform experiments on two recent single-object video segmentation databases, which show that OSVOS$^\mathrm {S}$S is both the fastest and most accurate method in the state of the art. Experiments on multi-object video segmentation show that OSVOS$^\mathrm {S}$S obtains competitive results.

[Successful switch from originator to biosimilar growth hormone: patients' experiences]. / Succesvolle overgang van biological op biosimilar.

OBJECTIVE: To survey patients' experiences with the switch from an originator biologic to a biosimilar growth hormone. DESIGN: Questionnaire. METHOD: We developed a questionnaire in which patients were asked about their experiences with the switch from an originator biologic to a biosimilar growth hormone. The questionnaire was distributed to all 207 patients who were switched to the biosimilar in the Radboudumc since April 2014. The following topics were covered: (a) difficulties experienced in switching from originator to biosimilar; (b) patient education; (c) effectiveness of the biosimilar product; (d) possible adverse effects experienced; and (e) experience with application of the new injection system for the biosimilar. RESULTS: The questionnaire was completed by 79 patients (38.1%). Seventy-two percent of the patients indicated that before switching they had no concerns about switching. The other patients did have concerns beforehand, which were related to the different injection system (n=13), possible new adverse effects (n=13) and safety of the biosimilar (n=11). Before the switch was made, all patients had been informed in writing and also individually by endocrinologists and specialised nurses; 93% of the patients was satisfied with the counselling provided by Radboudumc. Concerning use of the new injection system, 95% of the patients indicated that they had received individual training and 98% was confident in using it. Patients rated the process of transition to the biosimilar at the Radboudumc an average of 7.8 (range: 1-10). CONCLUSION: Patients were satisfied with the switch to the biosimilar growth hormone and there were few side-effects. Some minor problems were encountered, but these could be solved. Extensive counselling of patients before switching to prescription of biosimilars proved to be worthwhile. The switch has led to a significant reduction in costs.

Minimal information to determine affine shape equivalence.

Participants judged the affine equivalence of 2 simultaneously presented 4-point patterns. Performance level (d') varied between 1.5 and 2.7, depending on the information available for solving the correspondence problem (insufficient in Experiment 1a, superfluous in Experiment 1b, and minimal in Experiments 1c, 2a, 2b) and on the exposure time (unlimited in Experiments 1 and 2a and 500 ms in Experiment 2b), but it did not vary much with the complexity of the affine transformation (rotation and slant in Experiment 1 and same plus tilt in Experiment 2). Performance in Experiment 3 was lower with 3-point patterns than with 4-point patterns, whereas blocking the trials according to the affine transformation parameters had little effect. Determining affine shape equivalence with minimal-information displays is based on a fast assessment of qualitatively or quasi-invariant properties such as convexity/ concavity, parallelism, and collinearity.

Overexpression of human poly(ADP-ribose) polymerase in transfected hamster cells leads to increased poly(ADP-ribosyl)ation and cellular sensitization to gamma irradiation.

Poly(ADP-ribosyl)ation is a posttranslational modification of nuclear proteins catalyzed by poly(ADP-ribose) polymerase (PARP), an enzyme which uses NAD+ as substrate. Binding of PARP to DNA single-strand or double-strand breaks leads to enzyme activation. Inhibition of poly(ADP-ribose) formation impairs the cellular recovery from DNA damage. Here we describe stable transfectants of the Chinese hamster cell line CO60 that constitutively overexpress human PARP (COCF clones). Immunofluorescence analysis of gamma-irradiation-stimulated poly(ADP-ribose) synthesis revealed consistently larger fractions of cells positive for this polymer in the COCF clones than in control clones, which failed to express human PARP. HPLC-based quantitative determination of in vivo levels of poly(ADP-ribose) confirmed this result and revealed that the basal polymer levels of undamaged cells were significantly higher in the COCF clones. The COCF clones were sensitized to the cytotoxic effects of gamma irradiation compared with control transfectants and parental cells. This effect could not be explained by depletion of cellular NAD+ or ATP pools. Together with the well-known cellular sensitization by inhibition of poly(ADP-ribosyl)ation, our data lead us to hypothesize that an optimal level of cellular poly(ADP-ribose) accumulation exists for the cellular recovery from DNA damage.

Shape equivalence under perspective and projective transformations.

When a planar shape is viewed obliquely, it is deformed by a perspective deformation. If the visual system were to pick up geometrical invariants from such projections, these would necessarily be invariant under the wider class of projective transformations. To what extent can the visual system tell the difference between perspective and nonperspective but still projective deformations of shapes? To investigate this, observers were asked to indicate which of two test patterns most resembled a standard pattern. The test patterns were related to the standard pattern by a perspective or projective transformation, or they were completely unrelated. Performance was slightly better in a matching task with perspective and unrelated test patterns (92.6%) than in a projective-random matching task (88.8%). In a direct comparison, participants had a small preference (58.5%) for the perspectively related patterns over the projectively related ones. Preferences were based on the values of the transformation parameters (slant and shear). Hence, perspective and projective transformations yielded perceptual differences, but they were not treated in a categorically different manner by the human visual system.

Detection of poly(ADP-ribose) polymerase and its reaction product poly(ADP-ribose) by immunocytochemistry.

Poly(ADP-ribose) polymerase catalyses the formation of ADP-ribose polymers covalently attached to various nuclear proteins, using NAD+ as substrate. The activity of this enzyme is strongly stimulated upon binding to DNA single or double strand breaks. Poly(ADP-ribosyl)ation is an immediate cellular response to DNA damage and is thought to be involved in DNA repair, genetic recombination, apoptosis and other processes during which DNA strand breaks are formed. In recent years we and others have established cell culture systems with altered poly(ADP-ribose) polymerase activity. Here we describe immunocytochemistry protocols based on the use of antibodies against the DNA-binding domain of human poly(ADP-ribose) polymerase and against its reaction product poly(ADP-ribose). These protocols allow for the convenient mass screening of cell transfectants with overexpression of poly(ADP-ribose) polymerase or of a dominant-negative mutant for this enzyme, i.e. the DNA-binding domain. In addition, the immunocytochemical detection of poly(ADP-ribose) allows screening for cells with altered enzyme activity.

Qualitative cues in the discrimination of affine-transformed minimal patterns.

An important factor in judging whether two retinal images arise from the same object viewed from different positions may be the presence of certain properties or cues that are 'qualitative invariants' with respect to the natural transformations, particularly affine transformations, associated with changes in viewpoint. To test whether observers use certain affine qualitative cues such as concavity, convexity, collinearity, and parallelism of the image elements, a 'same-different' discrimination experiment was carried out with planar patterns that were defined by four points either connected by straight line segments (line patterns) or marked by dots (dot patterns). The first three points of each pattern were generated randomly; the fourth point fell on their diagonal bisector. According to the position of that point, the patterns were concave, triangular (three points being collinear), convex, or parallel sided. In a 'same' trial, an affine transformation was applied to one of two identical patterns; in a 'different' trial, the affine transformation was applied after the point lying on the diagonal bisector was perturbed a short, fixed distance along the bisector, inwards for one pattern and outwards for the other. Observers' ability to discriminate 'same' from 'different' pairs of patterns depended strongly on the position of the fourth, displaced, point: performance varied rapidly when the position of the displaced point was such that the patterns were nearly triangular or nearly parallel sided, consistent with observers using the hypothesised qualitative cues. The experimental data were fitted with a simple probabilistic model of discrimination performance that used a combination of these qualitative cues and a single quantitative cue.

Molecular genetic systems to study the role of poly(ADP-ribosyl)ation in the cellular response to DNA damage.

To study biological functions of poly(ADP-ribose) polymerase (PARP), low-molecular-mass inhibitors have been used extensively, and the experimental results obtained led to the view that PARP plays a role in DNA repair as well as in other cellular processes, eg DNA replication, cell proliferation, and differentiation. Accumulating evidence that these inhibitors have side effects on other metabolic pathways prompted us to develop two molecular genetic systems for the modulation of poly(ADP-ribosyl)ation in living cells: i) the first approach is centered on the DNA-binding domain (DBD) of PARP, which recognizes DNA strand breaks through its zinc fingers, leading to enzyme activation. We have established stable cell culture systems for either constitutive or inducible overexpression of the DBD. In these cells we observe a drastic trans-dominant inhibition of poly(ADP-ribosyl)ation which is associated with sensitization of cells to gamma-irradiation; and ii) in an attempt to specifically increase the poly(ADP-ribose) formation capacity in living cells, the hamster cell line CO60 was stably transfected to obtain constitutive overexpression of full-length human PARP. These molecular genetic systems may be useful for the elucidation of the precise role of poly(ADP-ribosyl)ation in the biological response to DNA damage.

Invariance from the Euclidean geometer's perspective.

It is remarkable how well the human visual system can cope with changing viewpoints when it comes to recognising shapes. The state of the art in machine vision is still quite remote from solving such tasks. Nevertheless, a surge in invariance-based research has led to the development of methods for solving recognition problems still considered hard until recently. A nonmathematical account explains the basic philosophy and trade-offs underlying this strand of research. The principles are explained for the relatively simple case of planar-object recognition under arbitrary viewpoints. Well-known Euclidean concepts form the basis of invariance in this case. Introducing constraints in addition to that of planarity may further simplify the invariants. On the other hand, there are problems for which no invariants exist.

Higher-order structure in regularity detection.

In three experiments a simple Euclidean transformation (reflection, translation, rotation) was applied to collections of twelve dots in such a way that they contained equal lower-order structure, defined on the pairwise grouping of elements with their partner following transformation (e.g. parallel virtual lines), but differed in the presence vs absence of higher-order structure, defined on pairs of pairwise groupings (e.g. virtual quadrangles with correlated angles). Based on the much better performance levels (d') in the case of additional higher-order structure, we conclude that global regularities are easier to detect when the local correspondences are supported by higher-order ones formed between them. These enable the lower-order groupings to spread out across the whole pattern very rapidly (called bootstrapping). As a preliminary attempt to specify these principles, we proposed a working model with two basic components: first, a function expressing the cost of a perceptual grouping or the lack of regularity, and, secondly, an algorithm based on simulated annealing to minimize the cost function. The simulation results obtained with our current implementation of these principles showed satisfactory qualitative agreement with human regularity detection performance. Finally, the theory was shown to capture the essence of a large number of grouping phenomena taken from diverse domains such as detection of symmetry in dot patterns, global structure in Glass and vector patterns, correspondence in stereoscopic transparency and apparent motion. Therefore, we are convinced that, in principle, the mechanism used by the human visual system to detect regularity incorporates something like bootstrapping based on higher-order structure. We regard this as a promising step towards unraveling the intriguing mechanisms of classic Gestalt phenomena.

Detection of symmetry in tachistoscopically presented dot patterns: effects of multiple axes and skewing.

We examined the effects of multiple axes and skewing on the detectability of symmetry in tachistoscopically presented (100-msec) dot patterns to test the role of normal grouping processes based on higher order regularities in element positions. In addition to the first-order regularities of orientational uniformity and midpoint collinearity (Jenkins, 1983), bilateral symmetry (BS) gives rise to second-order relations between two pairs of symmetric elements (represented by correlation quadrangles). We suggest that they allow the regularity (i.e., BS) to emerge simply as a result of the position-based grouping that takes place normally, so that no special symmetry-detection mechanism has to be postulated. In combination with previously investigated variables--number and orientation of axes--we introduced skewing (resulting from orthographic projection of BS) to manipulate the kind and number of higher order regularities. In agreement with our predictions, the data show that the effect of skewing angle (varied at three 15 degrees steps, clockwise and counterclockwise) on the preattentive detectability of symmetry (measured with d') increases as the number of axes decreases. On the basis of some more specific findings, we suggest that it is not as much the number of correlation quadrangles that determines the saliency of a regularity as it is the degree to which they facilitate or "bootstrap" each other.