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M J Tarr

Publications and source records attributed to M J Tarr.

At least 37 records · Page 2Linked to original sources
PubMed1997

Levels of categorization in visual recognition studied using functional magnetic resonance imaging.

BACKGROUND: Recent functional neuroimaging results implicate part of the ventral temporal lobe of the brain in face recognition, and have, together with neurophysiological findings, been used as evidence for a face-specific neural module in the brain. Experimental designs, however, have often failed to distinguish between the class of the object used as the stimulus (face or non-face) and the level of categorization at which the stimulus is recognized (the 'basic' level, such as 'bird', at which familiar objects are first recognized, or more subordinate levels - 'sparrow', for example - which require additional perceptual processing). We have used echo-planar functional magnetic resonance imaging to compare brain activation for the matching of non-face objects with subordinate-level and basic-level descriptors. RESULTS: The additional visual processing required to verify the subordinate level of a picture over its basic level was associated with activation of the fusiform and inferior temporal gyri (FIT) as well as the temporal poles. These areas correspond closely to those previously implicated in the processing of facial images. CONCLUSIONS: Our results indicate that areas of the ventral visual pathway that have been associated with face recognition are sensitive to manipulations of the categorization level of non-face objects. This idea offers an alternative to the dominant view that FIT may be organized according to conceptual categories, and our results establish the importance of manipulating task requirements when evaluating a 'neural module' hypothesis.

Brain Mapping↗
PubMed1997

Becoming a "Greeble" expert: exploring mechanisms for face recognition.

Sensitivity to configural changes in face processing has been cited as evidence for face-exclusive mechanisms. Alternatively, general mechanisms could be fine-tuned by experience with homogeneous stimuli. We tested sensitivity to configural transformations for novices and experts with nonface stimuli ("Greebles"). Parts of transformed Greebles were identified via forced-choice recognition. Regardless of expertise level, the recognition of parts in the Studied configuration was better than in isolation, suggesting an object advantage. For experts, recognizing Greeble parts in a Transformed configuration was slower than in the Studied configuration, but only at upright. Thus, expertise with visually similar objects, not faces per se, may produce configural sensitivity.

Discrimination, Psychological↗
PubMed1997

Testing conditions for viewpoint invariance in object recognition.

Based on the geon structural description approach, I. Biederman and P.C. Gerhardstein (1993) proposed 3 conditions under which object recognition is predicted to be viewpoint invariant. Two experiments are reported that satisfied all 3 criteria yet revealed performance that was clearly viewpoint dependent. Experiment 1 demonstrated that for both sequential matching and naming tasks, recognition of qualitatively distinct objects became progressively longer and less accurate as the viewpoint difference between study and test viewpoints increased. Experiment 2 demonstrated that for single-part objects, larger effects of viewpoint occurred when there was a change in the visible structure, indicating sensitivity to qualitative features in the image, not geon structural descriptions. These results suggest that the conditions proposed by I. Biederman and P.C. Gerhardstein are not generally applicable, the recognition of qualitatively distinct objects often relies on viewpoint-dependent mechanisms, and the molar features of view-based mechanisms appear to be image features rather than geons.

Adult↗
PubMed1997

Structural processing and implicit memory for possible and impossible figures.

Previous investigations have shown that participants are biased to respond "possible" to studied items when asked to decide whether objects could or could not exist in an object possibility test. The present study clarified and extended the concept of bias in implicit memory research in two ways. First, the authors showed that participants were biased to respond "possible" (rather than "impossible") on the object possibility test because structural processing was facilitated by prior study of possible, but not impossible, portions of objects. Second, the authors demonstrated that bias in this context was a form of, not an alternative to, implicit memory, by showing priming effects in response times when accuracy scores for studied and unstudied items were equated. The authors concluded by comparing proceduralist and memory-systems accounts of implicit memory effects and suggested that the two approaches could be seen as complementary rather than conflicting.

Humans↗
PubMed1997

Orientation priming of novel shapes in the context of viewpoint-dependent recognition.

Can visual similarity between shapes facilitate orientation priming? Five experiments are reported in which this possibility was explored by using novel two-dimensional shapes that formed homogeneous stimulus classes. After training on individual shapes in a canonical view, the recognition of these shapes was tested in several picture-plane orientations. In experiments 1 and 2 an identification task was used to replicate the classic finding obtained with the mirror-judgment task-that prior orientation cueing does not reduce the magnitude of orientation dependence in processing rotated shapes. The results of experiment 3, however, indicate that blocking trials by orientation is one condition in which orientation priming may be obtained. Experiment 4 builds on this result, and it is suggested that awareness of the blocking manipulation is not required to obtain orientation priming. In experiment 5 the mechanisms underlying this finding are explored, and evidence is offered that orientation priming is a consequence of representations that encode both shape and orientation. Such results may be considered as an extension to the 'image-based' approach to object recognition, demonstrating that generalization across exemplars may occur within recognition mechanisms that are viewpoint dependent.

Humans↗
PubMed1995

Spatial language and spatial representation.

This study explores the commonalities between linguistic and visual representations of space. In particular, because common types of spatial relations, specifically closed-class spatial forms in language and qualitative spatial relations in perception, have been proposed in both representational systems, we investigate whether they share underlying structural similarities. Moreover, while visual spatial relations are a basic element of several theories of object representation, they have been characterized mainly in terms of their linguistic counterparts and without direct evidence about their organization. In order to illuminate the nature of these structures, as well as demonstrate possible correspondences between the two systems, we compare how the spatial relationship between pairs of objects in a scene is encoded linguistically and visually. Spatial language was investigated by having subjects either generate (Experiment 1) or rate the applicability of (Experiment 2) spatial terms for describing the spatial relationship between object pairs. Both the frequency of use and the applicability of spatial terms were highest when the two objects were in vertical or in horizontal alignment. Spatial representation was investigated by paradigms in which subjects either recalled the position of one object relative to the other (Experiment 3) or judged whether one object presented sequentially was in the same or a different position relative to the other (Experiment 4). The accuracy of position estimates and the sensitivity to shifts in position were both highest when the rated object was in a spatial location where spatial terms had been judged to have high applicability in Experiments 1 and 2. These results indicate that the structure of space as encoded by language may be determined by the structure of spatial relations in visual representation.

Adult↗
PubMed1995

Is human object recognition better described by geon structural descriptions or by multiple views? Comment on Biederman and Gerhardstein (1993).

Is human object recognition viewpoint dependent or viewpoint invariant under "everyday" conditions? I. Biederman and P.C. Gerhardstein (1993) argued that viewpoint-invariant mechanisms are used almost exclusively. However, our analysis indicates that (a) their conditions for immediate viewpoint invariance lack the generality to characterize a wide range of recognition phenomena, (b) the extensive body of viewpoint-dependent results cannot be dismissed as processing "by-products" or "experimental artifacts," and (c) geon structural descriptions cannot coherently account for category recognition, the domain they are intended to explain. The weight of current evidence supports an exemplar-based multiple-views mechanism as an important component of both exemplar-specific and categorical recognition.

Cognition↗
PubMed1992

Effect of 1,1-dimethylhydrazine (UDMH) on Corynebacterium parvum-associated immunosuppression in mice.

These studies further investigate the immunoenhancement properties of UDMH by utilizing Corynebacterium parvum-induced immunosuppressed mice as well as evaluating activated macrophage production of reactive oxygen intermediates or their effects. Forty-eight hour Con A-induced lymphoblastogenic responses from splenocytes isolated from C. parvum and UDMH-treated Balb/C mice were significantly increased compared with C. parvum alone, although less than normal control mice (no treatment). In vitro bioassay of IL-2 production in cell culture supernatant isolated from these same treatment groups exhibited a pattern of stimulation similar to that of lymphocyte blastogenesis. In addition, UDMH did not interfere with H2O2-mediated suppression of either Con A- or LPS-induced lymphocyte blastogenesis and actually enhanced suppression of Con A-induced lymphocyte cultures at 25 micrograms/ml. We also report that production of superoxide anion from TPA-activated peritoneal macrophages exposed to various concentrations of UDMH in vitro was not affected. Although in vivo exposure to UDMH partially reversed C. parvum-induced immunosuppression in mice, the exact mechanism by which UDMH acts to reverse this immune suppression is not clear. UDMH does not appear to interfere with either activated peritoneal macrophage production of superoxide anion or H2O2-induced suppression of lymphocyte blastogenesis to elicit immune enhancement.

Animals↗
PubMed1992

Evaluation of murine lymphocyte membrane potential, intracellular free calcium, and interleukin-2 receptor expression upon exposure to 1,1-dimethylhydrazine.

The effects of 1,1-dimethylhydrazine (UDMH) on several early events associated with lymphocyte activation were examined. The concentration of intracellular calcium ([Ca2+]i) and membrane potential of murine lymphocytes were found to be altered upon exposure to UDMH; [Ca2+]i was increased in murine thymocytes, while splenocytes exhibited membrane hyperpolarization. In addition, interleukin-2 receptor expression induced by in-vitro concanavalin A stimulation of murine splenocytes at 24 and 48 h in the presence of UDMH was not affected. UDMH may interfere with the ability of these two distinct lymphocyte populations to regulate normal ionic fluctuations, thus contributing to altered immune responsiveness.

Animals↗
PubMed1992

The effects of perfluorodecanoic acid (PFDA) on humoral, cellular, and innate immunity in Fischer 344 rats.

The in vivo effects of perfluorodecanoic acid (PFDA) exposure on antibody production, delayed type hypersensitivity (DTH), and natural killer (NK) cell activity were determined. Fischer 344 rats were injected with PFDA (20 mg/kg or 50 mg/kg, 8 days or 30 days prior to sacrifice) and were immunized with keyhole limpet hemocyanin (KLH). Pair-fed and ad libitum-fed control rats were included to evaluate effects of PFDA-induced anorexia. KLH-specific IgG2a production was significantly decreased (p < 0.05) in PFDA-treated rats when compared to ad libitum-fed and pair-fed controls at 8 days but not at 30 days following PFDA treatment. The DTH response of PFDA-treated rats was decreased 8 days and 30 days after PFDA treatment when compared to ad libitum-fed and pair-fed controls, however, the decrease was not statistically significant. NK activity 30 days after PFDA treatment was significantly elevated (p < 0.05) when compared to ad libitum-fed controls, but pair-fed controls had similarly elevated NK activity. NK activity at 8 days after PFDA treatment was not significantly altered. In conclusion, PFDA has been demonstrated to have immunomodulatory effects, some of which may be associated with drug-induced anorexia.

Animals↗
PubMed1991

The in vitro and in vivo effects of 1,1-dimethylhydrazine (UDMH) on murine lymphocyte subsets and Ia antigen expression.

1,1-Dimethylhydrazine or unsymmetrical dimethylhydrazine (UDMH) is a highly volatile and reactive compound used primarily as a liquid rocket propellant. Previous studies found UDMH to possess immunomodulatory activity similar to other hydrazine derivatives. Modulation of T lymphocyte subpopulations and Major Histocompatibility Complex Class II or Ia antigen were evaluated as possible mechanisms for this UDMH-induced immunomodulation. Murine lymphoid cell populations were examined by flow cytometry for changes in their cell surface marker percentages or relative number upon exposure to UDMH either in vitro or in vivo. The results show UDMH caused significant suppression of the T helper cell population derived from the thymus at the 75 mg/kg dose in vivo, but did not affect other lymphocyte subpopulations isolated from mesenteric lymph node, spleen or thymus at this or any other dose. In vivo exposure of mice at all doses of UDMH did not significantly alter expression of Ia antigens on adherent cell populations and expression of the Ia antigen following in vitro UDMH exposure was not affected as well. Results indicate that the immunomodulatory effects of UDMH are not mediated by phenotypic alteration of T lymphocyte subpopulations or Ia antigen.

Adjuvants, Immunologic↗
PubMed1990

Familial renal amyloidosis in Chinese Shar Pei dogs.

Renal amyloidosis was diagnosed in 14 young Chinese Shar Pei dogs, all of which were related. Clinical signs were those of renal failure and included vomiting, anorexia, lethargy, polydipsia, polyuria, weight loss, and dehydration. Some dogs had a history of intermittent fever and joint swelling. Laboratory findings also were compatible with renal failure and included azotemia, hyperphosphatemia, low total CO2 content in serum, isosthenuria, proteinuria, and hypercholesterolemia. All dogs had medullary deposition of amyloid, and 9 of 14 (64%) had glomerular involvement. The remaining renal lesions were typical of end-stage renal disease. In some dogs, amyloid deposits were found in other tissues (eg, liver, spleen, stomach, small intestine, myocardium, lymph node, prostate gland, thyroid gland, and pancreas). Amyloid deposits were sensitive to potassium permanganate oxidation, suggesting the presence of amyloid protein AA.

Amyloidosis↗
PubMed1990

In vitro and in vivo evidence that the antiviral activity of 2',3'-dideoxycytidine is target cell dependent in a feline retrovirus animal model.

2',3'-Dideoxycytidine (DDC) was evaluated for prophylactic antiviral activity in vitro and in vivo, using the feline leukemia virus (FeLV)-cat animal model. In vitro antiviral activity of DDC against FeLV was dependent upon the target cell used for infection. DDC (5 to 10 microM) inhibited FeLV infection of feline lymphoid cells by greater than 80%, while 6.07 to 12.13 microM DDC was required to similarly inhibit infection of feline fibroblasts. However, 43 to 384 microM DDC was needed to inhibit FeLV infection of primary bone marrow cells by greater than 80%. These in vitro results suggest that, although relatively low doses of DDC may be adequate to prevent infection of feline lymphoid cells, 8- to 80-times-higher doses may be necessary to block infection of bone marrow cells, a primary target cell type for FeLV infection. In vivo studies with DDC consisted of pharmacokinetic and toxicity determinations and evaluation of the prophylactic antiviral activity against FeLV in cats. Clearance and half-life values for DDC in cats were 6.5 ml/min per kg and 54.7 min, respectively. In the prophylactic studies, DDC was administered by continuous intravenous infusion at doses of 22, 15, 10, and 5 mg/kg per h for 28 days in most animals. Cats were challenged intravenously with FeLV 1 to 3 days after drug treatment began. Doses of 22 and 15 mg/kg per h were extremely toxic, causing death in 8 of 10 cats. The mg/kg per h dose was slightly toxic, causing chronic progressive thrombocytopenia over the 28-day treatment period. Of 10 cats given 10 to 5 mg of DDC per kg per h, only one was completely protected from FeLV antigenemia. However, conversion to positive FeLV antigenemia status was delayed by 2 to 7 weeks in seven of nine remaining animals. Interestingly, FeLV infection of bone marrow cells, as indicated by FELV antigen in peripheral blood neutrophils, was only slightly delayed by 0 to 2 weeks, except in the case of the one protected cat, and usually preceded conversion to antigenemia. This pattern of neutrophils becoming antigen positive before detection of antigenemia was not seen in FeLV challenge control animals and indicates that the antiviral activity of DDC may be incomplete during DDC treatment. Results of our in vitro and in vivo studies suggest that feline bone marrow cells may remain partially susceptible to FeLV infection at tolerated doses, while other somatic target tissues (i.e., lymphoid or epithelial tissues) may be protected from infection. Incomplete inhibition of FeLV infection permitted focal bone marrow infection to develop in cats given DDC. These loci of infection served as virus reservoirs which, subsequent to discontinuation of DDC treatment, permitted spread of infection to tissues previously protected during treatment.

Animals↗
PubMed1990

Renal excretion of creatinine, electrolytes, protein, and enzymes in healthy sheep.

Urinary indices of renal function and damage were measured in 6 healthy, mature ewes over a 48-hour period. Endogenous creatinine clearance, total and fractional electrolyte excretion rates, protein excretion, urine volume, and urine gamma-glutamyltransferase and beta-glucuronidase activities were measured. Significant variations in the excretion rates of creatinine, electrolytes, and protein were not found between intervals within the 48-hour urine collection period. Total urinary electrolyte excretion rates were significantly (P less than 0.001) correlated with fractional electrolyte excretion rates normalized for creatinine concentration; however, coefficient of determination was low.

Animals↗
PubMed1989

Clinicopathologic findings in dogs with renal amyloidosis: 59 cases (1976-1986).

The medical records of 59 dogs with renal amyloidosis were reviewed. Most dogs with amyloidosis were greater than 6 years old, and females were affected more often than males. Beagles, Collies, and Walker Hounds were at increased risk, whereas German Shepherd Dogs and mixed-breed dogs were at decreased risk. Common historical findings were anorexia, polyuria, polydipsia, lethargy, vomiting, and weight loss. Common laboratory findings were leukocytosis, lymphopenia, nonregenerative anemia, hypercholesterolemia, azotemia, hyperphosphatemia, metabolic acidosis, isosthenuria, cylindruria, and proteinuria. Proteinuria was moderate to severe in most dogs, as assessed by qualitative determination of urine protein concentration, urine protein/urine creatinine ratio, and 24-hour urine protein excretion. Conservative medical management was of little value, and survival ranged from 3 to 20 months in 12 dogs for which this information was available. Moderate to severe diffuse global glomerular amyloidosis was detected in all dogs. Medullary amyloid deposition was multifocal and less severe, but was evident in most dogs. Secondary tubulointerstitial and glomerular lesions were mild or absent in most dogs. Thromboembolism was identified in approximately 14% of affected dogs, underlying inflammatory disease in 37%, and neoplasia in 20%. Laboratory indicators of renal function correlated poorly with histologic lesions, with the exception of glomerular amyloid deposition and "chronic renal disease" index with endogenous creatinine clearance.

Age Factors↗
PubMed1988

Veno-occlusive disease of the liver in captive cheetah.

Liver tissues from 126 captive cheetah were evaluated by light microscopy and histochemistry; eight animals were evaluated by electron microscopy. The main hepatic lesion, a vascular lesion resembling veno-occlusive disease (VOD) of the liver and characterized by subendothelial fibrosis and proliferation of smooth muscle-like cells in the central veins, was seen in 60% of the sexually mature cheetah. Although this hepatic vascular lesion was seen in cheetah as young as 1 year of age, the most severe lesions, usually associated with liver failure, were found in cheetah between the ages of 6 and 11. There was no sex predisposition, and in approximately 40% of the VOD cases, liver disease was not suspected clinically or at necropsy. VOD was found in other felidae, especially in the snow leopard. High levels of vitamin A in livers, as well as in diets of the cheetah, could be a contributing factor in the development of VOD in some groups of cheetah.

Acinonyx↗