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Biomedical subjects

S Edelman

Publications and source records attributed to S Edelman.

At least 19 recordsLinked to original sources
PubMed2001

Imperfect invariance to object translation in the discrimination of complex shapes.

The positional specificity of short-term visual memory for a variety of 3-D shapes was investigated in a series of 'same'/'different' discrimination experiments, with computer-rendered stimuli displayed either at the same or at different locations in the visual field. For animal-like shapes, we found complete translation invariance, regardless of the interstimulus similarity, and irrespective of direction and size of the displacement (experiments 1 and 2). Invariance to translation was obtained also with animal-like stimuli that had been 'scrambled' by randomizing the relative locations of their parts (experiment 3). The invariance broke down when the stimuli were made to differ in their composition, but not in the shapes of the corresponding parts (experiments 4 and 5). We interpret this pattern of findings in the context of several current theories of recognition, focusing in particular on the issue of the representation of object structure.

Analysis of Variance↗
PubMed2001

Detection of hypoglycemia with the GlucoWatch biographer.

OBJECTIVE: Hypoglycemia is a common acute complication of diabetes therapy. The GlucoWatch biographer provides frequent and automatic glucose measurements with an adjustable low-glucose alarm. We have analyzed the performance of the biographer low-glucose alarm relative to hypoglycemia as defined by blood glucose < or = 3.9 mmol/l. RESEARCH DESIGN AND METHODS: The analysis was based on 1,091 biographer uses from four clinical trials. which generated 14,487 paired (biographer and blood glucose) readings. RESULTS: The results show that as the low-glucose alert level of the biographer is increased, the number of true positive alerts (alarm sounds and blood glucose < or = 3.9 mmol/l) and false positive alerts (alarm sounds but blood glucose >3.9 mmol/l) increased. When analyzed as a function of varying low-glucose alert levels, the results show receiver operator characteristic curves consistent with a highly useful diagnostic tool. Setting the alert level from 1.1 to 1.7 mmol/l above the level of concern is likely to optimize the trade-off between true positives and false positives for each user. When the same blood glucose data are analyzed for typical monitoring practices (two or four measurements per day), the results show that fewer hypoglycemic events are detected than those detected with the biographer.

Automation↗
PubMed2000

Can psycotherapy increase the survival time of cancer patients?

OBJECTIVE: The aim of this paper was to review the evidence regarding the possibility of a relationship between psychological intervention and survival time of cancer patients. METHOD: A literature search was conducted using CD ROM databases to identify studies which have evaluated the effects of psychological interventions on the survival time of cancer patients. The identified studies were critically reviewed. RESULTS: Eight studies which used scientifically acceptable methodology to examine this question were identified. Three of these studies found evidence for a relationship between psychological intervention and patients' survival time, while five did not. Methodological issues and potentially confounding factors are discussed. CONCLUSION: To date, a direct relationship between psychological intervention and patient survival time has not been conclusively demonstrated. Large-scale replication studies which are currently under way will provide more conclusive evidence on this question within the next few years.

Depressive Disorder↗
PubMed2000

Prevalence of psychological distress and use of support services by cancer patients at Sydney hospitals.

OBJECTIVE: The study aimed to estimate the prevalence of anxiety and depression within a cross section of cancer patients in the Sydney region, and to assess the use of and degree of satisfaction with available support services. METHOD: A survey was conducted at oncology outpatient departments of four Sydney hospitals. Participants completed the Hospital Anxiety and Depression Scale (HADS) and a questionnaire seeking information on their use of patient support services, as well as demographic and clinical information. RESULTS: A total of 504 valid questionnaires were returned. Using a cut-off score of 11 on the HADS, the prevalence of clinically significant anxiety and depression was 11.5% and 7.1% respectively; 17% of patients had received individual counselling while 6.5% had attended support groups. The majority of patients who had attended counselling or support groups reported them to have been 'extremely' or 'reasonably' helpful (86% and 83% respectively). Of the patients who were experiencing clinically significant anxiety or depression, 75% had not received any counselling or psychological treatment. The main factors which predicted clinically significant anxiety or depression were: restricted activity levels, advanced disease, a non-English-speaking background and being female. CONCLUSIONS: While the prevalence of clinically significant anxiety or depression detected by the HADS was reasonably low, a substantial number of possible cases were identified. The majority of affected patients were not accessing counselling or psychological treatment. Systematic screening of oncology patients at hospital entry might enable more immediate identification of clinically affected patients, who could then be referred for further testing or psychological treatment.

Adult↗
PubMed2000

Evidence for physiological coupling of insulin-mediated glucose metabolism and limb blood flow.

We hypothesized that the vasodilation observed during insulin stimulation is closely coupled to the rate of glucose metabolism. Lean (L, n = 13), obese nondiabetic (OB, n = 13), and obese type 2 diabetic subjects (Type 2 DM, n = 16) were studied. Leg blood flow (LBF) was examined under conditions of euglycemic hyperinsulinemia (EH) and hyperglycemic hyperinsulinemia (HH), which produced a steady-state whole body glucose disposal rate (GDR) of approximately 2,000 micromol. m(-2). min(-1). At this GDR, under both conditions, subjects across the range of insulin sensitivity exhibited equivalent LBF (l/min EH: L, 0.42 +/- 0.03; OB, 0.43 +/- 0. 03; Type 2 DM, 0.38 +/- 0.07; P = 0.72 by ANOVA. HH: L, 0.44 +/- 0. 04; OB, 0.39 +/- 0.05; Type 2 DM, 0.41 +/- 0.04; P = 0.71). The continuous relationship between LBF and GDR did not differ across subject groups [slope x 10(-5) l/(micromol. m(-2). min(-1)) by ANOVA. EH: L, 8.6; OB, 9.2; Type 2 DM, 7.9; P = 0.91. HH: L, 4.2; OB, 2.5; Type 2 DM, 4.1; P = 0.77], although this relationship did differ between the EH and HH conditions (P = 0.001). These findings support a physiological coupling of LBF and insulin-mediated glucose metabolism. The mechanism(s) linking substrate delivery and metabolism appears to be intact in insulin-resistant states.

Adult↗
PubMed2000

(Coarse coding of shape fragments) + (retinotopy) approximately = representation of structure.

The ability to deal with object structure--to determine what is where in a given object, rather than merely to categorize or identify it--has been hitherto considered the prerogative of 'structural description' approaches, which represent shapes as categorical compositions of generic parts taken from a small alphabet. In this note, we propose a simple extension to a theoretically motivated and extensively tested appearance-based model of recognition and categorization, which should make it capable of representing object structure. We describe a pilot implementation of the extended model, survey independent evidence supporting its modus operandi, and outline a research program focused on achieving a range of object processing capabilities, including reasoning about structure, within a unified appearance-based framework.

Animals↗
PubMed1999

Differential processing of objects under various viewing conditions in the human lateral occipital complex.

The invariant properties of human cortical neurons cannot be studied directly by fMRI due to its limited spatial resolution. Here, we circumvented this limitation by using fMR adaptation, namely, reduction of the fMR signal due to repeated presentation of identical images. Object-selective regions (lateral occipital complex [LOC]) showed a monotonic signal decrease as repetition frequency increased. The invariant properties of fMR adaptation were studied by presenting the same object in different viewing conditions. LOC exhibited stronger fMR adaptation to changes in size and position (more invariance) compared to illumination and viewpoint. The effect revealed two putative subdivisions within LOC: caudal-dorsal (LO), which exhibited substantial recovery from adaptation under all transformations, and posterior fusiform (PF/LOa), which displayed stronger adaptation. This study demonstrates the utility of fMR adaptation for revealing functional characteristics of neurons in fMRI studies.

Adaptation, Physiological↗
PubMed1999

Effects of parametric manipulation of inter-stimulus similarity on 3D object categorization.

To explore the nature of the representation space of 3D objects, we studied human performance in forced-choice categorization of objects composed of four geon-like parts emanating from a common center. Two categories were defined by prototypical objects, distinguished by qualitative properties of their parts (bulging vs waist-like limbs). Subjects were trained to discriminate between the two prototypes (shown briefly, from a number of viewpoints, in stereo) in a 1-interval forced-choice task, until they reached a 90% correct-response performance level. After training, in the first experiment, 11 subjects were tested on shapes obtained by varying the prototypical parameters both orthogonally (ORTHO) and in parallel (PARA) to the line connecting the prototypes in the parameter space. For the eight subjects who performed above chance, the error rate increased with the ORTHO parameter-space displacement between the stimulus and the corresponding prototype; the effect of the PARA displacement was weaker. Thus, the parameter-space location of the stimuli mattered more than the qualitative contrasts, which were always present. To find out whether both prototypes or just the nearest one to the test shape influenced the decision, in the second experiment we varied the similarity between the categories. Specifically, in the test stage trials the distance between the two prototypes could assume one of three values (FAR, INTERMEDIATE, and NEAR). For the 13 subjects who performed above chance, the error rate (on physically identical stimuli) in the NEAR condition was higher than in the other two conditions. The results of the two experiments contradict the prediction of theories that postulate exclusive reliance on qualitative contrasts, and support the notion of a representation space in which distances to more than one reference point or prototype are encoded (Edelman, 1998).

Humans↗
PubMed1998

Representation of objective similarity among three-dimensional shapes in the monkey.

Humans have been recently shown to represent parameterized three-dimensional objects in a manner that preserves relative similarities (as measured by parameter-space distances) among the objects (Cutzu and Edelman 1996). We show that the representation of objects in the monkey visual system is similarly faithful to the parametric variation built into the stimulus set. A monkey (Macaca fuscata) performed a delayed matching-to-sample task with 28 images (4 views x 7 objects). Stimuli in each of the two experiments were seven computer-rendered parameterized animal-like shapes, arranged in a low-dimensional configuration (namely, a two-dimensional TRIANGLE) in a common 56-dimensional parameter space. The monkey's task was to match objects (not views). Each experiment lasted for 3-4 weeks after the introduction of the stimulus set to the subject. Error rates were entered into a 7 x 7 object confusion matrix and submitted to nonmetric multidimensional scaling (MDS). In both experiment 1 (mean correct rate 69.7%) and experiment 2 (mean correct rate 59.9%), the MDS solutions resembled closely the low-dimensional parameter-space patterns built into the stimuli, in the sense that the point corresponding to the central one in the original pattern was inside the other six points and that the order of the six points in angular positions around the center point was preserved. A simulation study showed that the resemblance could not be due to chance. These results demonstrate the possibility of veridical representation of parametric similarity among complex objects in the monkey.

Animals↗
PubMed1998

Representation of object similarity in human vision: psychophysics and a computational model.

We report results from perceptual judgment, delayed matching to sample and long-term memory recall experiments, which indicate that the human visual system can support metrically veridical representations of similarities among 3D objects. In all the experiments, animal-like computer-rendered stimuli formed regular planar configurations in a common 70-dimensional parameter space. These configurations were fully recovered by multidimensional scaling from proximity tables derived from the subject data. We show that such faithful representation of similarity is possible if shapes are encoded by their similarities to a number of reference (prototypical) shapes, as in the computational model that accompanies the psychophysical data.

Computer Simulation↗
PubMed1998

Stimulus-specific effects in face recognition over changes in viewpoint.

Individual faces vary considerably in both the quality and quantity of the information they contain for recognition and for viewpoint generalization. In the present study, we assessed the typicality, recognizability, and viewpoint generalizability of individual faces using data from both human observers and from a computational model of face recognition across viewpoint change. The two-stage computational model incorporated a viewpoint alignment operation and a recognition-by-interpolation operation. An interesting aspect of this particular model is that the effects of typicality it predicts at the alignment and recognition stages dissociate, such that face typicality is beneficial for the success of the alignment process, but is adverse for the success of the recognition process. We applied a factor analysis to the covariance data for the human- and model-derived face measures across the different viewpoints and found two axes that appeared consistently across all viewpoints. Projection scores for individual faces on these axes (i.e. the extent to which a face's 'performance profile' matched the pattern of human- and model-derived scores on that axis), correlated across viewpoint changes to a much higher degree than did the raw recognizability scores of the faces. These results suggest that the stimulus information captured in the model measures may underlie distinct and dissociable aspects of the recognizability of individual faces across viewpoint change.

Computer Simulation↗
PubMed1998

Cue-invariant activation in object-related areas of the human occipital lobe.

The extent to which primary visual cues such as motion or luminance are segregated in different cortical areas is a subject of controversy. To address this issue, we examined cortical activation in the human occipital lobe using functional magnetic resonance imaging (fMRI) while subjects performed a fixed visual task, object recognition, using three different primary visual cues: motion, texture, or luminance contrast. In the first experiment, a region located on the lateral aspect of the occipital lobe (LO complex) was preferentially activated in all 11 subjects both by luminance and motion-defined object silhouettes compared to full-field moving and stationary noise (ratios, 2.00+/-0.19 and 1.86+/-0.65, respectively). In the second experiment, all subjects showed enhanced activation in the LO complex to objects defined both by luminance and texture contrast compared to full-field texture patterns (ratios, 1.43+/-0.08 and 1.32+/-0.08, respectively). An additional smaller dorsal focus that exhibited convergence of object-related cues appeared to correspond to area V3a or a region slightly anterior to it. These results show convergence of visual cues in LO and provide strong evidence for its role in object processing.

Adult↗
PubMed1998

Representation is representation of similarities.

Advanced perceptual systems are faced with the problem of securing a principled (ideally, veridical) relationship between the world and its internal representation. I propose a unified approach to visual representation, addressing the need for superordinate and basic-level categorization and for the identification of specific instances of familiar categories. According to the proposed theory, a shape is represented internally by the responses of a small number of tuned modules, each broadly selective for some reference shape, whose similarity to the stimulus it measures. This amounts to embedding the stimulus in a low-dimensional proximal shape space spanned by the outputs of the active modules. This shape space supports representations of distal shape similarities that are veridical as Shepard's (1968) second-order isomorphisms (i.e., correspondence between distal and proximal similarities among shapes, rather than between distal shapes and their proximal representations). Representation in terms of similarities to reference shapes supports processing (e.g., discrimination) of shapes that are radically different from the reference ones, without the need for the computationally problematic decomposition into parts required by other theories. Furthermore, a general expression for similarity between two stimuli, based on comparisons to reference shapes, can be used to derive models of perceived similarity ranging from continuous, symmetric, and hierarchical ones, as in multidimensional scaling (Shepard 1980), to discrete and nonhierarchical ones, as in the general contrast models (Shepard & Arabie 1979; Tversky 1977).

Cognition↗
PubMed1998

Double-blind randomized trial of tramadol for the treatment of the pain of diabetic neuropathy.

OBJECTIVE: The objective of this study was to evaluate the efficacy and safety of tramadol in treating the pain of diabetic neuropathy. BACKGROUND: The pain of diabetic neuropathy is a major cause of morbidity among these patients and treatment, as with other small-fiber neuropathies, is often unsatisfactory. Tramadol is a centrally acting analgesic for use in treating moderate to moderately severe pain. METHODS: This multicenter, outpatient, randomized, double-blind, placebo-controlled, parallel-group study consisted of a washout/screening phase, during which all analgesics were discontinued, and a 42-day double-blind treatment phase. A total of 131 patients with painful diabetic neuropathy were treated with tramadol (n=65) or placebo (n=66) tramadol, which were administered as identical capsules in divided doses four times daily. The primary efficacy analysis compared the mean pain intensity scores in the tramadol and placebo groups obtained at day 42 of the study or at the time of discontinuation. Secondary efficacy assessments were the pain relief rating scores and a quality of life evaluation based on daily activities and sleep characteristics. RESULTS: Tramadol, at an average dosage of 210 mg/day, was significantly (p < 0.001) more effective than placebo for treating the pain of diabetic neuropathy. Patients in the tramadol group scored significantly better in physical (p=0.02) and social functioning (p=0.04) ratings than patients in the placebo group. No statistically significant treatment effects on sleep were identified. The most frequently occurring adverse events with tramadol were nausea, constipation, headache, and somnolence. CONCLUSIONS: The results of this placebo-controlled trial showed that tramadol was effective and safe in treating the pain of diabetic neuropathy.

Activities of Daily Living↗
PubMed1998

A sequence of object-processing stages revealed by fMRI in the human occipital lobe.

Functional magnetic resonance imaging was used in combined functional selectivity and retinotopic mapping tests to reveal object-related visual areas in the human occipital lobe. Subjects were tested with right, left, up, or down hemivisual field stimuli which were composed of images of natural objects (faces, animals, man-made objects) or highly scrambled (1,024 elements) versions of the same images. In a similar fashion, the horizontal and vertical meridians were mapped to define the borders of these areas. Concurrently, the same cortical sites were tested for their sensitivity to image-scrambling by varying the number of scrambled picture fragments (from 16-1,024) while controlling for the Fourier power spectrum of the pictures and their order of presentation. Our results reveal a stagewise decrease in retinotopy and an increase in sensitivity to image-scrambling. Three main distinct foci were found in the human visual object recognition pathway (Ungerleider and Haxby [1994]: Curr Opin Neurobiol 4:157-165): 1) Retinotopic primary areas V1-3 did not exhibit significant reduction in activation to scrambled images. 2) Areas V4v (Sereno et al., [1995]: Science 268:889-893) and V3A (De Yoe et al., [1996]: Proc Natl Acad Sci USA 93:2382-2386; Tootell et al., [1997]: J Neurosci 71:7060-7078) manifested both retinotopy and decreased activation to highly scrambled images. 3) The essentially nonretinotopic lateral occipital complex (LO) (Malach et al., [1995]: Proc Natl Acad Sci USA 92:8135-8139; Tootell et al., [1996]: Trends Neurosci 19:481-489) exhibited the highest sensitivity to image scrambling, and appears to be homologous to macaque the infero-temporal (IT) cortex (Tanaka [1996]: Curr Opin Neurobiol 523-529). Breaking the images into 64, 256, or 1,024 randomly scrambled blocks reduced activation in LO voxels. However, many LO voxels remained significantly activated by mildly scrambled images (16 blocks). These results suggest the existence of object-fragment representation in LO.

Adult↗
PubMed1997

A model of visual recognition and categorization.

To recognize a previously seen object, the visual system must overcome the variability in the object's appearance caused by factors such as illumination and pose. Developments in computer vision suggest that it may be possible to counter the influence of these factors, by learning to interpolate between stored views of the target object, taken under representative combinations of viewing conditions. Daily life situations, however, typically require categorization, rather than recognition, of objects. Due to the open-ended character of both natural and artificial categories, categorization cannot rely on interpolation between stored examples. Nonetheless, knowledge of several representative members, or prototypes, of each of the categories of interest can still provide the necessary computational substrate for the categorization of new instances. The resulting representational scheme based on similarities to prototypes appears to be computationally viable, and is readily mapped onto the mechanisms of biological vision revealed by recent psychophysical and physiological studies.

Animals↗
PubMed1997

Similarity, connectionism, and the problem of representation in vision.

A representational scheme under which the ranking between represented similarities is isomorphic to the ranking between the corresponding shape similarities can support perfectly correct shape classification because it preserves the clustering of shapes according to the natural kinds prevailing in the external world. This article discusses the computational requirements of representation that preserves similarity ranks and points out the relative straightforwardness of its connectionist implementation.

Form Perception↗