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M Bar

Publications and source records attributed to M Bar.

At least 19 recordsLinked to original sources
PubMed2006

The parahippocampal cortex mediates spatial and nonspatial associations.

The parahippocampal cortex (PHC) has been implicated in the processing of place-related information. It has also been implicated in episodic memory, even for items that are not related to unique places. How could the same cortical region mediate such seemingly different cognitive processes? Both processes rely on contextual associations, and we therefore propose that the PHC should be viewed not as exclusively dedicated for analyzing place-related information, or as solely processing episodic memories, but instead as more generally playing a central role in contextual associative processing. To test this proposal, we created a novel learning paradigm to form new associations among meaningless visual patterns. These new associations were created to emulate either spatial or nonspatial contexts. Both spatial and nonspatial associations activated the PHC more than noncontextual items. Moreover, items from spatial contexts activated the posterior part of the PHC, whereas items from nonspatial contexts activated the anterior PHC. Therefore, we show that the PHC plays a role of processing contextual associations in general, and that these associations are not restricted to spatial information. By modifying the existing view of the PHC function accordingly, the seemingly contradicting processes that activate it can be reconciled under one overarching framework.

Adult↗
PubMed2006

Top-down facilitation of visual recognition.

Cortical analysis related to visual object recognition is traditionally thought to propagate serially along a bottom-up hierarchy of ventral areas. Recent proposals gradually promote the role of top-down processing in recognition, but how such facilitation is triggered remains a puzzle. We tested a specific model, proposing that low spatial frequencies facilitate visual object recognition by initiating top-down processes projected from orbitofrontal to visual cortex. The present study combined magnetoencephalography, which has superior temporal resolution, functional magnetic resonance imaging, and a behavioral task that yields successful recognition with stimulus repetitions. Object recognition elicited differential activity that developed in the left orbitofrontal cortex 50 ms earlier than it did in recognition-related areas in the temporal cortex. This early orbitofrontal activity was directly modulated by the presence of low spatial frequencies in the image. Taken together, the dynamics we revealed provide strong support for the proposal of how top-down facilitation of object recognition is initiated, and our observations are used to derive predictions for future research.

Cerebral Cortex↗
PubMed2001

Viewpoint dependency in visual object recognition does not necessarily imply viewer-centered representation.

The nature of visual object representation in the brain is the subject of a prolonged debate. One set of theories asserts that objects are represented by their structural description and the representation is "object-centered." Theories from the other side of the debate suggest that humans store multiple "snapshots" for each object, depicting it as seen under various conditions, and the representation is therefore "viewer-centered." The principal tool that has been used to support and criticize each of these hypotheses is subjects' performance in recognizing objects under novel viewing conditions. For example, if subjects take more time in recognizing an object from an unfamiliar viewpoint, it is common to claim that the representation of that object is viewpoint-dependent and therefore viewer-centered. It is suggested here, however, that performance cost in recognition of objects under novel conditions may be misleading when studying the nature of object representation. Specifically, it is argued that viewpoint-dependent performance is not necessarily an indication of viewer-centered representation. An account for the neural basis of perceptual priming is first provided. In light of this account, it is conceivable that viewpoint dependency reflects the utilization of neural paths with different levels of sensitivity en route to the same representation, rather than the existence of viewpoint-specific representations. New experimental paradigms are required to study the validity of the viewer-centered approach.

Cerebral Cortex↗
PubMed2001

Inferior temporal neurons show greater sensitivity to nonaccidental than to metric shape differences.

It has long been known that macaque inferior temporal (IT) neurons tend to fire more strongly to some shapes than to others, and that different IT neurons can show markedly different shape preferences. Beyond the discovery that these preferences can be elicited by features of moderate complexity, no general principle of (nonface) object recognition had emerged by which this enormous variation in selectivity could be understood. Psychophysical, as well as computational work, suggests that one such principle is the difference between viewpoint-invariant, nonaccidental (NAP) and view-dependent, metric shape properties (MPs). We measured the responses of single IT neurons to objects differing in either a NAP (namely, a change in a geon) or an MP of a single part, shown at two orientations in depth. The cells were more sensitive to changes in NAPs than in MPs, even though the image variation (as assessed by wavelet-like measures) produced by the former were smaller than the latter. The magnitude of the response modulation from the rotation itself was, on average, similar to that produced by the NAP differences, although the image changes from the rotation were much greater than that produced by NAP differences. Multidimensional scaling of the neural responses indicated a NAP/MP dimension, independent of an orientation dimension. The present results thus demonstrate that a significant portion of the neural code of IT cells represents differences in NAPs rather than MPs. This code may enable immediate recognition of novel objects at new views.

Animals↗
PubMed2001

Cortical mechanisms specific to explicit visual object recognition.

The cortical mechanisms associated with conscious object recognition were studied using functional magnetic resonance imaging (fMRI). Participants were required to recognize pictures of masked objects that were presented very briefly, randomly and repeatedly. This design yielded a gradual accomplishment of successful recognition. Cortical activity in a ventrotemporal visual region was linearly correlated with perception of object identity. Therefore, although object recognition is rapid, awareness of an object's identity is not a discrete phenomenon but rather associated with gradually increasing cortical activity. Furthermore, the focus of the activity in the temporal cortex shifted anteriorly as subjects reported an increased knowledge regarding identity. The results presented here provide new insights into the processes underlying explicit object recognition, as well as the analysis that takes place immediately before and after recognition is possible.

Adult↗
PubMed2001

FLP/FRT-mediated restoration of normal phenotypes and clonal sectors formation in rolC transgenic tobacco.

Site-specific recombination systems have been shown to excise transgene DNA sequences positioned between their cognate target sites, and thus be used to generate clonal sectors in transgenic plants. Here we characterized clonal sectors derived from genetic reversion of rolC (A. rhizogenes)--induced vegetative and reproductive phenotypes, mediated by FLP recombinase from S. cerevisiae, in tobacco. The constitutive expression of rolC induces pleiotropic effects including reduced apical dominance and plant height, lanceolate and pale green leaves and small, male-sterile flowers. Two transgenic male-sterile tobacco lines (N. tabacum, Samsun NN) expressing a 35sP-rolC gene construct flanked by two FRT (FLP recombinase target) sites, were cross-pollinated with pollen from a constitutive 35sP-FLP expressing line. Three main phenotypes were generated in result of recombinase-mediated excision of the 35sP-rolC locus in the F1 (FLP x FRT-35sP-rolC-FRT) hybrid progenies: (a) restoration of male fertility, associated with reversion to normal leaf phenotypes prior to flower bud formation, (b) development of normal and fertile lateral shoot sectors on the background of rolC-type plants, (c) restoration of partially fertile flowers, associated with display of peripheral normal leaf sectors surrounding rolC-type inner-leaf tissues, consistent with periclinal chimeras. These results, supported by DNA molecular analysis, indicate that site-specific recombination might be used as a relatively efficient tool for generation of transgenic periclinal chimeric plants.

Blotting, Southern↗
PubMed2000

Differentiation of human cytomegalovirus genotypes in immunocompromised patients on the basis of UL4 gene polymorphisms.

The variety of clinical manifestations of human cytomegalovirus infection probably results from both viral and host factors. Because genetic markers that span the viral genome are needed to identify such viral factors, polymorphisms at the UL4 gene locus were analyzed. DNA sequence analyses revealed 4 UL4-based genotypes, 2 of which were closely related but distinguishable by an uncommon polymorphism that results in overexpression of gpUL4. Similarities in the spectra of polymorphisms detected in various sets of samples reveal that all UL4 types infect a diversity of organs in different patient groups and in different geographic locales. Simultaneous infection by >1 UL4 type is common in AIDS patients. Data from sequencing analyses and from a rapid and simple UL4 typing assay did not detect linkage between UL4 and glycoprotein B types, which suggests that UL4 genotyping should be useful for studies that attempt to identify cytomegalovirus genes involved in disease pathogenesis.

AIDS-Related Opportunistic Infections↗
PubMed2000

Modulated amplitude waves and the transition from phase to defect chaos

The mechanism for transitions from phase to defect chaos in the one-dimensional complex Ginzburg-Landau equation (CGLE) is presented. We describe periodic coherent structures of the CGLE, called modulated amplitude waves (MAWs). MAWs of various periods P occur in phase chaotic states. A bifurcation study of the MAWs reveals that for sufficiently large period, pairs of MAWs cease to exist via a saddle-node bifurcation. For periods beyond this bifurcation, incoherent near-MAW structures evolve towards defects. This leads to our main result: the transition from phase to defect chaos takes place when the periods of MAWs in phase chaos are driven beyond their saddle-node bifurcation.

Journal Article↗
PubMed2000

High-dose chemotherapy and stem cell transplantation for patients with stage IV breast cancer without clinically evident disease: correlation of CD34+ selection to clinical outcome.

Forty-five patients with metastatic breast cancer without clinically evident disease were treated with thiotepa 750 mg/m2, mitoxantrone 40 mg/m2 and carboplatin 1000 mg/m2 followed by stem cell transplantation to determine the safety and efficacy of CD34+ selection of peripheral blood stem cells. Of these, 15 patients' (group I) stem cells were processed through Baxter Isolex 300 device for CD34+ selection, whereas 30 patients (group II) received unmanipulated stem cells. Toxicity, progression-free survival and survival were compared between these two groups. There was no difference in transfusion requirements, white cell count and platelet recovery and non-hematologic toxicity between the two groups. The survival of patients in group I was 27 months compared to 38 months in group II (P = 0.8). The progression-free survival was 12 months and 13.5 months for group I and group II patients, respectively (P = 0.6). Our results indicate that while there is no adverse effect, there is also no significant advantage of CD34+ selection in terms of progression-free survival and survival in patients with metastatic breast cancer without clinically evident disease. Bone Marrow Transplantation (2000).

Adult↗
PubMed2000

Front propagation and pattern formation in anisotropic bistable media

The effects of diffusion anisotropy on pattern formation in bistable media are studied using a FitzHugh-Nagumo reaction-diffusion model. A relation between the normal velocity of a front and its curvature is derived and used to identify distinct spatiotemporal patterns induced by the diffusion anisotropy. In a wide parameter range anisotropy is found to have an ordering effect: initial patterns evolve into stationary or breathing periodic stripes parallel to one of the principal axes. In a different parameter range, anisotropy is found to induce spatiotemporal chaos confined to one space dimension, a state we term "stratified chaos."

Journal Article↗
PubMed1999

Localizing the cortical region mediating visual awareness of object identity.

Presentations of pictures that are too brief to be recognized, or even guessed above chance on a forced-choice test, nonetheless can facilitate the recognition of the same pictures many trials later. This subliminal visual priming was compared for images translated 4. 8 degrees either Within or Between quadrants of the visual field. Priming was evident only for images that remained within the same quadrant in priming and test trials. Consequently, subliminal visual priming is likely mediated by cortical areas in which cells have receptive fields large enough to respond to both presentations of a stimulus translated almost 5 degrees, yet where the receptive fields are confined to a single quadrant, namely, the human homologue of macaque V4 or TEO (the posterior part of the inferior temporal cortex). Awareness of object identity might therefore be associated exclusively with activity at or beyond the anterior part of the inferior temporal cortex, namely, area TE.

Adolescent↗
PubMed1999

Subordinate-level object classification reexamined.

The classification of a table as round rather than square, a car as a Mazda rather than a Ford, a drill bit as 3/8-inch rather than 1/4-inch, and a face as Tom have all been regarded as a single process termed "subordinate classification." Despite the common label, the considerable heterogeneity of the perceptual processing required to achieve such classifications requires, minimally, a more detailed taxonomy. Perceptual information relevant to subordinate-level shape classifications can be presumed to vary on continua of (a) the type of distinctive information that is present, nonaccidental or metric, (b) the size of the relevant contours or surfaces, and (c) the similarity of the to-be-discriminated features, such as whether a straight contour has to be distinguished from a contour of low curvature versus high curvature. We consider three, relatively pure cases. Case 1 subordinates may be distinguished by a representation, a geon structural description (GSD), specifying a nonaccidental characterization of an object's large parts and the relations among these parts, such as a round table versus a square table. Case 2 subordinates are also distinguished by GSDs, except that the distinctive GSDs are present at a small scale in a complex object so the location and mapping of the GSDs are contingent on an initial basic-level classification, such as when we use a logo to distinguish various makes of cars. Expertise for Cases 1 and 2 can be easily achieved through specification, often verbal, of the GSDs. Case 3 subordinates, which have furnished much of the grist for theorizing with "view-based" template models, require fine metric discriminations. Cases 1 and 2 account for the overwhelming majority of shape-based basic- and subordinate-level object classifications that people can and do make in their everyday lives. These classifications are typically made quickly, accurately, and with only modest costs of viewpoint changes. Whereas the activation of an array of multiscale, multiorientation filters, presumed to be at the initial stage of all shape processing, may suffice for determining the similarity of the representations mediating recognition among Case 3 subordinate stimuli (and faces), Cases 1 and 2 require that the output of these filters be mapped to classifiers that make explicit the nonaccidental properties, parts, and relations specified by the GSDs.

Classification↗
PubMed1999

One-shot viewpoint invariance in matching novel objects.

Humans often evidence little difficulty at recognizing objects from arbitrary orientations in depth. According to one class of theories, this competence is based on generalization from templates specified by metric properties (MPs), that were learned for the various orientations. An alternative class of theories assumes that non-accidental properties (NAPs) might be exploited so that even novel objects can be recognized under depth rotation. After scaling MP and NAP differences so that they were equally detectable when the objects were at the same orientation in depth, the present investigation assessed the effects of rotation on same-different judgments for matching novel objects. Judgments of a sequential pair of images of novel objects, when rendered from different viewpoints, revealed relatively low costs when the objects differed in a NAP of a single part, i.e. a geon. However, rotation dramatically reduced the detectability of MP differences to a level well below that expected by chance. NAPs offer a striking advantage over MPs for object classification and are therefore more likely to play a central role in the representation of objects.

Adolescent↗
PubMed1997

Sporadic phaeochromocytomas are rarely associated with germline mutations in the von Hippel-Lindau and RET genes.

OBJECTIVE: von Hippel-Lindau (VHL) disease and multiple endocrine neoplasia type 2 (MEN2) are autosomal dominant cancer syndromes. In both conditions, phaeochromocytoma is a prominent feature. It has recently been suggested that phaeochromocytoma can be the presenting and sole clinical manifestation of these multi-organ syndromes. The aim of this study was to ascertain the incidence of VHL and MEN2 among patients with sporadic phaeochromocytoma by mutational analysis. PATIENTS: Twenty-seven unrelated patients with biochemically and/or anatomically proven sporadic phaeochromocytoma were evaluated. DESIGN AND MEASUREMENTS: Constitutional DNA obtained from the patients was analysed by single stranded conformational analysis (SSCP) for mutations within the VHL gene coding sequence and by denaturing gradient gel electrophoresis (DGGE) for predominant mutations in exons 10, 11 and 16 of the RET proto-oncogene. The incidence of patients positive for either VHL or RET germline mutations was assessed. RESULTS: Twenty-six of 27 patients had normal SSCP patterns in all three VHL gene exon segments and only one patient, with an atypical clinical presentation, had an aberrant pattern in exon 3 which upon DNA sequencing was shown to harbor a G to A transversion mutation at nucleotide 695. All patients had normal RET exon 10, 11 and 16 DGGE migration patterns. CONCLUSION: Most, if not all, patients with typical unilateral sporadic phaeochromocytoma do not have von Hippel-Lindau disease or MEN2. Thus, clinical and/or molecular investigation for von Hippel-Lindau disease and MEN2 in this patient population does not appear to be indicated.

Adolescent↗
PubMed1996

Spatial context in recognition.

In recognizing objects and scenes, partial recognition of objects or their parts can be used to guide the recognition of other objects. Here, the role of individual objects in the recognition of complete figures and the influence of contextual information on the identification of ambiguous objects were investigated. Configurations of objects that were placed in either proper or improper spatial relations were used, and response times and error rates in a recognition task were measured. Two main results were obtained. First, proper spatial relations among the objects of a scene decrease response times and error rates in the recognition of individual objects. Second, the presence of objects that have a unique interpretation improves the identification of ambiguous objects in the scene. Ambiguous objects were recognized faster and with fewer errors in the presence of clearly recognized objects compared with the same objects in isolation or in improper spatial relations. The implications of these findings for the organization of recognition memory are discussed.

Adult↗
PubMed1995

Prophylactic intervention in radiation-leukemia-virus-induced murine lymphoma by the biological response modifier polysaccharide K.

Polysaccharide K (PSK) is a biological response modifier used for adjuvant immunotherapy of malignant diseases. We studied the potential applicability of PSK for preventing tumor progression using an experimental model of murine lymphoma. Mice inoculated with the radiation leukemia virus (RadLV) develop thymic lymphomas after a latency of 3-6 months. However, 2 weeks after virus inoculation, prelymphoma cells can already be detected in the thymus. We found that PSK treatment induced hyperresponsiveness to concanavalin A and heightened production of interleukin-2 (IL-2) and IL-4 in spleen cells of both control and prelymphoma mice. The response was transient and was accompanied with a dominant usage of T cells expressing V beta 8, but other T cell subsets were also stimulated by PSK. T lymphoma cells expressing V beta 8.2 underwent apoptosis when incubated with PSK. Treatment of RadLV-inoculated mice with PSK delayed the onset of overt lymphoma (and mortality) but could not protect the mice from the disease. Combined treatment with PSK and a RadLV-specific immunotoxin prevented synergistically the progression of the prelymphoma cells to frank lymphoma. The results suggest that PSK contains a superantigen-like component that selectively activates V beta 8+ T cells. Its administration prelymphoma mice interfered with the process of lymphoma progression.

Adjuvants, Immunologic↗
PubMed1995

Impact of a coordinated tuberculosis Team in an inner-city hospital in New York City.

OBJECTIVE: To evaluate the impact of a coordinated approach for the isolation, diagnosis, and treatment of patients with tuberculosis. DESIGN: Retrospective cohort study. SETTING: Bronx-Lebanon Hospital Center, an inner-city hospital in the South Bronx, New York City. PATIENTS: Patients with smear-positive, culture-confirmed pulmonary tuberculosis. INTERVENTIONS: Institution of a coordinated tuberculosis team. RESULTS: Admissions of 46 patients before and 39 patients after the formation of a tuberculosis team were reviewed. Before institution of the tuberculosis team, 35% of patients were isolated within 24 hours of presentation, 41% never were isolated, and the mean number of days patients were not isolated was 19. After implementation of the tuberculosis team, 59% of patients were isolated within 24 hours, only 5% were never isolated, and the mean number of days patients were not isolated was 3.5. These differences were statistically significant. There also was a corresponding decrease in length of hospitalization. In addition, there were noticeable improvements in patient and staff morale and attitudes. CONCLUSIONS: The tuberculosis team likely has decreased the risk of nosocomial tuberculosis transmission by increasing the proportion of infectious tuberculosis patients admitted into AFB isolation and by reducing (by 780) the number of days out of isolation while smear positive. There also were concomitant financial savings.

Adolescent↗