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S Edelman

Publications and source records attributed to S Edelman.

16 recordsLinked to original sources
PubMed1992

Fast perceptual learning in visual hyperacuity.

In many different spatial discrimination tasks, such as in determining the sign of the offset in a vernier stimulus, the human visual system exhibits hyperacuity by evaluating spatial relations with the precision of a fraction of a photoreceptor's diameter. It is proposed that this impressive performance depends in part on a fast learning process that uses relatively few examples and that occurs at an early processing stage in the visual pathway. This hypothesis is given support by the demonstration that it is possible to synthesize, from a small number of examples of a given task, a simple network that attains the required performance level. Psychophysical experiments agree with some of the key predictions of the model. In particular, fast stimulus-specific learning is found to take place in the human visual system, and this learning does not transfer between two slightly different hyperacuity tasks.

Algorithms↗
PubMed1992

Psychophysical support for a two-dimensional view interpolation theory of object recognition.

Does the human brain represent objects for recognition by storing a series of two-dimensional snapshots, or are the object models, in some sense, three-dimensional analogs of the objects they represent? One way to address this question is to explore the ability of the human visual system to generalize recognition from familiar to unfamiliar views of three-dimensional objects. Three recently proposed theories of object recognition--viewpoint normalization or alignment of three-dimensional models [Ullman, S. (1989) Cognition 32, 193-254], linear combination of two-dimensional views [Ullman, S. & Basri, R. (1990) Recognition by Linear Combinations of Models (Artificial Intelligence Laboratory, Massachusetts Institute of Technology, Cambridge), A. I. Memo No. 1152], and view approximation [Poggio, T. & Edelman, S. (1990) Nature (London) 343, 263-266]--predict different patterns of generalization to unfamiliar views. We have exploited the conflicting predictions to test the three theories directly in a psychophysical experiment involving computer-generated three-dimensional objects. Our results suggest that the human visual system is better described as recognizing these objects by two-dimensional view interpolation than by alignment or other methods that rely on object-centered three-dimensional models.

Computer Graphics↗
PubMed1992

Orientation dependence in the recognition of familiar and novel views of three-dimensional objects.

We report four experiments that investigated the representation of novel three-dimensional (3D) objects by the human visual system. In the first experiment, canonical views were demonstrated for novel objects seen equally often from all test viewpoints. The next two experiments showed that the canonical views persisted under repeated testing, and in the presence of a variety of depth cues, including binocular stereo. The fourth experiment probed the ability of subjects to generalize recognition to unfamiliar views of objects previously seen at a limited range of attitudes. Both mono and stereo conditions yielded the same increase in the error rate with misorientation relative to the training attitude. Taken together, these results support the notion that 3D objects are represented by multiple specific views, possibly augmented by partial viewer-centered 3D information.

Computer Simulation↗
PubMed1991

A self-organizing multiple-view representation of 3D objects.

We explore representation of 3D objects in which several distinct 2D views are stored for each object. We demonstrate the ability of a two-layer network of thresholded summation units to support such representations. Using unsupervised Hebbian relaxation, the network learned to recognize ten objects from different viewpoints. The training process led to the emergence of compact representations of the specific input views. When tested on novel views of the same objects, the network exhibited a substantial generalization capability. In simulated psychophysical experiments, the network's behavior was qualitatively similar to that of human subjects.

Cybernetics↗
PubMed1991

Models of object recognition.

Progress in the understanding of visual recognition in the past year has been signified by the demonstration of computational feasibility of and psychophysical support for two-dimensional view-interpolation methods.

Animals↗
PubMed1990

A network that learns to recognize three-dimensional objects.

The visual recognition of three-dimensional (3-D) objects on the basis of their shape poses at least two difficult problems. First, there is the problem of variable illumination, which can be addressed by working with relatively stable features such as intensity edges rather than the raw intensity images. Second, there is the problem of the initially unknown pose of the object relative to the viewer. In one approach to this problem, a hypothesis is first made about the viewpoint, then the appearance of a model object from such a viewpoint is computed and compared with the actual image. Such recognition schemes generally employ 3-D models of objects, but the automatic learning of 3-D models is itself a difficult problem. To address this problem in computational vision, we have developed a scheme, based on the theory of approximation of multivariate functions, that learns from a small set of perspective views a function mapping any viewpoint to a standard view. A network equivalent to this scheme will thus 'recognize' the object on which it was trained from any viewpoint.

Artificial Intelligence↗
PubMed1987

A model of handwriting.

The research reported here is concerned with hand trajectory planning for the class of movements involved in handwriting. Previous studies show that the kinematics of human two-joint arm movements in the horizontal plane can be described by a model which is based on dynamic minimization of the square of the third derivative of hand position (jerk), integrated over the entire movement. We extend this approach to both the analysis and the synthesis of the trajectories occurring in the generation of handwritten characters. Several basic strokes are identified and possible stroke concatenation rules are suggested. Given a concise symbolic representation of a stroke shape, a simple algorithm computes the complete kinematic specification of the corresponding trajectory. A handwriting generation model based on a kinematics from shape principle and on dynamic optimization is formulated and tested. Good qualitative and quantitative agreement was found between subject recordings and trajectories generated by the model. The simple symbolic representation of hand motion suggested here may permit the central nervous system to learn, store and modify motor action plans for writing in an efficient manner.

Cybernetics↗
PubMed1987

Progression of hypertrophic cardiomyopathy into a hypokinetic left ventricle: higher incidence in patients with midventricular obstruction.

The development of segmental or generalized left ventricular hypokinesia is an unusual occurrence in patients with hypertrophic cardiomyopathy. To determine the incidence and possible pathophysiologic mechanisms responsible for this process, the serial clinical and laboratory data of 62 patients with the diagnosis of hypertrophic cardiomyopathy were analyzed. During a mean follow-up period of 8 years (range 2 to 21), 5 patients (Group A) developed left ventricular hypokinesia, whereas the remaining 57 patients (Group B) continued to exhibit the clinical and laboratory findings of hypertrophic cardiomyopathy. Three patients developed a dilated left ventricle with generalized hypokinesia; two other patients had segmental left ventricular wall motion abnormalities. None of these five patients who developed left ventricular hypokinesia had fixed coronary artery disease. The mean age, sex, mean duration of follow-up, presence of coronary myocardial bridges and angina pectoris, and an interventricular gradient were all similar in Groups A and B. Midventricular obliteration was seen in 4 (80%) of the 5 patients in Group A and in 4 (7%) of the 57 patients in Group B (p less than 0.001). Findings from this study reveal that segmental or generalized left ventricular hypokinesia can develop in patients with hypertrophic cardiomyopathy in the absence of fixed coronary artery disease. Such hypokinesia can occur after an acute myocardial infarction or it can develop gradually without clinical or electrocardiographic evidence of infarction. Patients with the mid-ventricular obliteration variant of hypertrophic cardiomyopathy are at a higher risk of developing segmental or diffuse left ventricular hypokinesia.

Adolescent↗
PubMed1985

Safety of outpatient cardiac catheterization.

In this study, we compared the procedure-related complications of inpatient and outpatient cardiac catheterization when performed at the same institution by the same group of cardiologists. The majority of the studies were done using a brachial arterial cutdown approach. The mean age, sex, cardiac diagnosis, mean left ventricular ejection fraction, and the distribution of coronary arterial lesions were similar in both groups. There were relatively more patients in the New York Heart Association's class 4 in the inpatient group (p less than 0.01). In the outpatient group (676 patients), there were no major complications, and the rate of minor complications was 1 percent. In the inpatient group (1,106 patients), the rate of major complications was 0.4 percent and of minor complications 1.4 percent. The rates of major, minor, and total complications were statistically similar between the two groups. In the outpatient group the presence of left main coronary arterial disease, triple-vessel coronary disease, a left ventricular ejection fraction less than 30 percent, or a history of a recent myocardial infarction did not alter rates of complications. The hospital-related cost of the procedure on an outpatient basis was 26 percent less than on an inpatient basis. Our findings indicate that outpatient cardiac catheterization, using a brachial cutdown approach, is safe even in a higher risk subgroup of patients and provides significant financial savings.

Adolescent↗
PubMed1976

Primary torsion of the greater omentum mimicking duodenal ulcer.

The diagnosis of primary torsion of the omentum is a diagnostic enigma and is made almost exclusively at laparotomy. The difficulty is enhanced when the patient has a chronic problem mimicking a specific entity, e.g. peptic ulcer disease. The case presented is an example of this situation. The patient's history and acute presentation were compatible with chronic peptic ulcer disease with acute perforation. At laparotomy, the findings of torsion of the right lower omentum with infarction, along with marked scarring of the remainder of the greater omentum explained the clinical picture. Torsion of the greater omentum, therefore, must be added to the list of differential diagnoses when one is considering peptic ulcer disease.

Adult↗