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PubMedDate not supplied

Serial and parallel processing of visual feature conjunctions.

Treisman and others have reported that the visual search for a target distinguished along a single stimulus dimension (for example, colour or shape) is conducted in parallel, whereas the search for an item defined by the conjunction of two stimulus dimensions is conducted serially. For a single dimension the target 'pops out' and the search time is independent of the number of irrelevant items in the set. For conjunctions, the search time increases as the set becomes larger. Thus, it seems that the visual system is incapable of conducting a parallel search over two stimulus dimensions simultaneously. Here we extend this conclusion for the conjunction of motion and colour, showing that it requires a serial search. We also report two exceptions: if one of the dimensions in a conjunctive search is stereoscopic disparity, a second dimension of either colour or motion can be searched in parallel.

Color↗
PubMed1992

Use and understanding of adverbial conjuncts: a developmental study of adolescents and young adults.

The use and understanding of two types of adverbial conjuncts, concordant (e.g., similarly, moreover, consequently) and discordant (e.g., contrastively, rather, nevertheless), was examined developmentally in 120 adolescents and young adults. Four groups of 30 students participated. Mean ages of the groups were 12:9, 15:10, 19:2, and 23:8 (years:months). The results demonstrated an increasing ability to use and understand these words in the written mode. An interesting discrepancy emerged between the use and the understanding of adverbial conjuncts, a finding that resembled the well-documented discrepancy between the use and the understanding of spoken words in young children. Although young adults had mastered the words in terms of their understanding, they continued to show some difficulty using the words correctly. It was also found that the two types of conjuncts were equally difficult, a result that failed to support Piaget's (1928) hypothesis concerning the greater difficulty of discordant connectives. Factors that may contribute to the development of adverbial conjuncts are discussed.

Adolescent↗
PubMed1999

Parallel search for conjunctions with stimuli in apparent motion.

A series of experiments was conducted to determine whether apparent motion tends to follow the similarity rule (i.e. is attribute-specific) and to investigate the underlying mechanism. Stimulus duration thresholds were measured during a two-alternative forced-choice task in which observers detected either the location or the motion direction of target groups defined by the conjunction of size and orientation. Target element positions were randomly chosen within a nominally defined rectangular subregion of the display (target region). The target region was presented either statically (followed by a 250 ms duration mask) or dynamically, displaced by a small distance (18 min of arc) from frame to frame. In the motion display, the position of both target and background elements was changed randomly from frame to frame within the respective areas to abolish spatial correspondence over time. Stimulus duration thresholds were lower in the motion than in the static task, indicating that target detection in the dynamic condition does not rely on the explicit identification of target elements in each static frame. Increasing the distractor-to-target ratio was found to reduce detectability in the static, but not in the motion task. This indicates that the perceptual segregation of the target is effortless and parallel with motion but not with static displays. The pattern of results holds regardless of the task or search paradigm employed. The detectability in the motion condition can be improved by increasing the number of frames and/or by reducing the width of the target area. Furthermore, parallel search in the dynamic condition can be conducted with both short-range and long-range motion stimuli. Finally, apparent motion of conjunctions is insufficient on its own to support location decision and is disrupted by random visual noise. Overall, these findings show that (i) the mechanism underlying apparent motion is attribute-specific; (ii) the motion system mediates temporal integration of feature conjunctions before they are identified by the static system; and (iii) target detectability in these stimuli relies upon a nonattentive, cooperative, directionally selective motion mechanism that responds to high-level attributes (conjunction of size and orientation).

Adult↗
PubMed1998

Perceptual learning in visual conjunction search.

Perceptual learning in colour/orientation visual conjunction search was examined in five experiments. Good transfer occurred to other conjunction arrays when only one element of the conjunction (either colour or orientation) was changed. When both elements (colour and orientation) were changed, but the same feature spaces were used (i.e. other colours and orientations) or when a new dimension was introduced to the transfer task (shapes instead of orientation), transfer was poor. The results suggest that perceptual learning of visual conjunction search is constrained mainly by stimulus parameters rather than by changes in cognitive strategies which are common to all search tasks. Contrary to other reports we found little evidence of long-term retention of learning.

Discrimination Learning↗
PubMed2004

Memory conjunction errors for autobiographical events: more than just familiarity.

Two diary studies investigated the prevalence of memory conjunction errors for real-life events. In both studies, participants completed detailed diary pages over the course of several weeks. Participants in both diary studies committed memory conjunction errors on a later recognition memory test. In the second diary study participants also made remember/know judgements. For a large proportion of their memory conjunction errors participants indicated that they "remembered" the event occurring in that context. These diary studies demonstrate that memory conjunction errors do occur for autobiographical memories, and these errors can seem compelling.

Analysis of Variance↗
PubMed2005

Study repetition and the rejection of conjunction lures.

Four experiments were conducted to provide further support for a dual-process approach to conjunction errors in recognition memory over a single-process approach. In Experiments 1, 2a, and 2b study words were repeated once (2 presentations) or several times (8 or 16 presentations), and a response signal delay (RSD) was manipulated (short vs long). Short RSD groups produced lower hit rates but higher conjunction error rates compared to long RSD groups. Repetition effects on conjunction errors occurred for short RSD but not long RSD groups. In Experiment 3, additional judgements on new items were solicited to show that the "null" effects for long RSD groups in the earlier experiments were, in fact, illusory. Together, the experiments provide evidence for recollection-based rejections of conjunction lures and support a dual-process theory of recognition memory over a single-process model.

Cognition↗
PubMed2001

Changes in acoustic features and their conjunctions are processed by separate neuronal populations.

We investigated the relationship between the neuronal populations involved in detecting change in two acoustic features and their conjunction. Equivalent current dipole (ECD) models of the magnetic mismatch negativity (MMNm) generators were calculated for infrequent changes in pitch, perceived sound source location, and the conjunction of these two features. All of these three changes elicited MMNms that were generated in the vicinity of auditory cortex. The location of the ECD best describing the MMNm to the conjunction deviant was anterior to those for the MMNm responses elicited by either one of the constituent features. The present data thus suggest that at least partially separate neuronal populations are involved in detecting change in acoustic features and feature conjunctions.

Adult↗
PubMed2004

Amelioration of hyperglycemia in streptozotocin-induced diabetic mice with fetal pancreatic allografts: prevention of rejection by donor specific transfusion in conjunction with CTLA4Ig.

INTRODUCTION: Fetal pancreas has been considered as an alternative donor source for islet transplantation since it has potent capacity for beta cell differentiation and proliferation. However, prevention of fetal pancreatic allograft rejection can be hardly achieved compared with adult islet allografts. AIMS: The aim of the study is to determine whether donor specific transfusion (DST) in conjunction with CTLA4Ig has any favorable effect on prevention of fetal pancreatic allograft rejection in mice. METHODS: BALB/c splenocytes (SPC, 1 x 10) were injected iv into C57BL/6 mice in conjunction with CTLA4Ig (ip, 50 microgram, day 0, 2, and 4). Fourteen days later, the mice were made diabetic with streptozotocin (STZ, iv) and donor specific or third party pancreatic allografts were transplanted beneath the kidney capsule. RESULTS: Morphologically, it was found that rejection of fetal pancreatic allografts can be prevented at 30 days after transplantation only when donor specific allografts were grafted into the mice treated with DST in conjunction with CTLA4Ig. Functionally, 3 out of 9 diabetic mice became normoglycemic by 120 days after transplantation of fetal pancreatic allografts. CONCLUSION: DST in conjunction with CTLA4Ig can have a favorable effect on prevention of fetal pancreatic allograft rejection resulting in amelioration of STZ-induced diabetes in mice.

Abatacept↗
PubMedDate not supplied

Bilateral nodular lymphocytic conjunctivitis in a horse.

A Russian jumper horse presented because of an ocular perilimbal conjunctival mass and, on clinical examination, two bilateral conjunctival masses were found, of different size and conformation. Attempts at complete excision of the left eye mass and excisional biopsy of the right eye mass were performed. The left eye mass recurred rapidly, but resolved completely after topical corticosteroid therapy. The two lesions had similar histopathologic features, characterized by focal, chronic, primarily lymphocytic conjunctivitis with follicular lymphoid hyperplasia. Special histopathologic staining techniques (Gomori methenamine silver and acid fast stains) and immunohistochemistry (for CD3, BLA36 and lysozyme) failed to reveal any etiologic agents and indicated an inflammatory lesion composed of a heterogeneous population of lymphocytes and macrophages (nodular lymphocytic conjunctivitis). The lesions were indistinguishable, clinically and behaviorally, from what has been reported as 'conjunctival pseudotumor' in the horse. Equine conjunctival pseudotumor/nodular lymphocytic conjunctivitis has been reported to be unilateral and have a good prognosis after partial or complete surgical excision. This is the first reported case of bilateral nodular lymphocytic conjunctivitis in a horse and for which surgical excision alone was not curative.

Animals↗
PubMed2004

The sequential processing of visual feature conjunction mismatches in the human brain.

To clarify the brain mechanism for multifeature stimulus comparison, subjects matched the features of two serial visual stimuli in pairs. Stimulus pairs were of four categories: C-S-, color same, shape same (match); C-S+, color same, shape different (shape mismatch); C+S-, color different, shape same (color mismatch); C+S+, color different, shape different (conjunction mismatches). Subjects matched the stimuli in three different sessions according to different attention tasks: attending to color (Ac), attending to shape (As), or attending to both color and shape (Acs). A negative one-peak brain potential, N270, was elicited in all the mismatch conditions with amplitude enhanced in the task-relevant mismatch. Negative potential with two peaks, N270 and N400, appeared when attending to the conjunction mismatches concurrently. The two serial negativities in response to attended feature conjunctions might reflect the temporal different stages for processing conjunction mismatches or conflicts.

Adult↗
PubMedDate not supplied

The Relationship between chlamydia trachomatis and chlamydia pneumoniae as the cause of neonatal conjunctivitis (ophthalmia neonatorum).

The authors examined 130 newborns and nursery children from September 1999 till May 2003 from the Prague district for the surmise of chlamydial conjunctivitis. Chlamydia infections were detected in conjunctival smears. Chlamydia trachomatis was confirmed in 20 (15.3%) using ligase chain reaction and C. pneumoniae in 16 (12.3%) children using an indirect immunofluorescent method. Direct captures of chlamydial infections of newborns were included in the study. The authors had also examined 671 newborns in a maternity hospital from January 2002 till May 2003. Conjunctival scraping had been done in 29 (4.3%) cases mainly for mucopurulent conjunctivitis. Chlamydial conjunctivitis was identified only in 4 (0.6%) cases, i.e. C. trachomatis and C. pneumoniae in 2 cases each. Initial clinical symptoms of both types of chlamydial conjunctivitis were similar (mucous discharge with various degrees of eyelid effusion and chemosis mainly on the tarsal conjunctiva). Clinical symptoms of the C. pneumoniae infection were later accompanied by pseudofollicular changes on the tarsal conjunctiva. The complication of this infection was lacrimal obstruction among half of newborns. Clarithromycin in syrup at a dose of 15 mg/kg/per day for 14 days ensured effective treatment of both chlamydial infections. Control scrapings were always negative and simultaneously the pathological conjunctival finding disappeared.

Anti-Bacterial Agents↗
PubMed1992

Conjunctive enhancement of enzymatic thrombolysis and prevention of thrombotic reocclusion with the selective factor Xa inhibitor, tick anticoagulant peptide. Comparison to hirudin and heparin in a canine model of acute coronary artery thrombosis.

BACKGROUND: Effective thrombolytic recanalization of an occluded coronary vessel is often limited by acute thrombotic reocclusion, which has galvanized the search for effective adjunctive or conjunctive antithrombotic agents. METHODS AND RESULTS: Recombinant versions of tick anticoagulant peptide (rTAP) and hirudin (rHIR) are highly selective and potent polypeptide inhibitors of factor Xa and thrombin, respectively. The comparative antithrombotic efficacies of rTAP, rHIR, and heparin, administered conjunctively with recombinant tissue-type plasminogen activator (rt-PA), on thrombolytic reperfusion and reocclusion, were determined in a canine model of occlusive coronary artery thrombosis with a superimposed critical stenosis. In this model, a platelet-rich occlusive thrombus was formed after damage to the intimal surface of the left circumflex coronary artery induced by electrolytic injury. Fifteen minutes after occlusion, the dogs received a systemic intravenous administration of either saline (control), heparin (200 units/kg bolus + 2 units/kg/min, heparin (HEP) 200 or 100 units/kg bolus + 1 unit/kg/min, HEP 100), rHIR (50 or 100 micrograms/kg/min, rHIR 50 or 100, respectively), or rTAP (100 micrograms/kg/min, rTAP 100) followed 15 minutes later by rt-PA (100 micrograms/kg bolus + 10 micrograms/kg/min over 90 minutes). Infusions of the conjunctive agents were discontinued 60 minutes after termination of rt-PA. The incidence and time (mean +/- SEM) to thrombolytic reperfusion were determined for control (five of 12; 68.0 +/- 7.8 minutes), HEP 100 (six of eight; 40.1 +/- 8.3 minutes), HEP 200 (six of eight; 39.8 +/- 9.5 minutes), rHIR 50 (six of eight; 51.7 +/- 14.6 minutes), rHIR 100 (eight of eight; 19.5 +/- 4.2 minutes), and rTAP 100 (eight of eight; 22.8 +/- 10.0 minutes). The incidence and time to reocclusion after rt-PA were determined for control (four of five; 45.7 +/- 12.5 minutes), HEP 100 (four of six; 18.2 +/- 10.7 minutes), HEP 200 (five of six; 26.2 +/- 20.7 minutes), rHIR 50 (four of six; 47.3 +/- 21.6 minutes), rHIR 100 (six of eight; 89.8 +/- 5.9 minutes), and rTAP 100 (three of eight; 54.0 +/- 16.3 minutes). All of the dogs that reoccluded in the rHIR 100 group did so after termination of the inhibitor infusion, whereas two of the three dogs in the rTAP 100 group that reoccluded did so during the inhibitor infusion. Coronary artery blood flow was characterized by intermittent periods of reocclusion and recanalization in all groups except rTAP 100. CONCLUSIONS: The potent antithrombotic effects of rTAP in this model directly implicate de novo thrombin formation as a major source of thrombin activity within the highly thrombogenic residual thrombus. These findings suggest that direct inhibition of prothrombinase activity may be an effective strategy in the development of a new class of conjunctive agents.

Animals↗
PubMed2000

Minimizing binding errors using learned conjunctive features.

We have studied some of the design trade-offs governing visual representations based on spatially invariant conjunctive feature detectors, with an emphasis on the susceptibility of such systems to false-positive recognition errors-Malsburg's classical binding problem. We begin by deriving an analytical model that makes explicit how recognition performance is affected by the number of objects that must be distinguished, the number of features included in the representation, the complexity of individual objects, and the clutter load, that is, the amount of visual material in the field of view in which multiple objects must be simultaneously recognized, independent of pose, and without explicit segmentation. Using the domain of text to model object recognition in cluttered scenes, we show that with corrections for the nonuniform probability and nonindependence of text features, the analytical model achieves good fits to measured recognition rates in simulations involving a wide range of clutter loads, word size, and feature counts. We then introduce a greedy algorithm for feature learning, derived from the analytical model, which grows a representation by choosing those conjunctive features that are most likely to distinguish objects from the cluttered backgrounds in which they are embedded. We show that the representations produced by this algorithm are compact, decorrelated, and heavily weighted toward features of low conjunctive order. Our results provide a more quantitative basis for understanding when spatially invariant conjunctive features can support unambiguous perception in multiobject scenes, and lead to several insights regarding the properties of visual representations optimized for specific recognition tasks.

Artificial Intelligence↗
PubMed2000

Minimizing binding errors using learned conjunctive features.

We have studied some of the design trade-offs governing visual representations based on spatially invariant conjunctive feature detectors, with an emphasis on the susceptibility of such systems to false-positive recognition errors-Malsburg's classical binding problem. We begin by deriving an analytical model that makes explicit how recognition performance is affected by the number of objects that must be distinguished, the number of features included in the representation, the complexity of individual objects, and the clutter load, that is, the amount of visual material in the field of view in which multiple objects must be simultaneously recognized, independent of pose, and without explicit segmentation. Using the domain of text to model object recognition in cluttered scenes, we show that with corrections for the nonuniform probability and nonindependence of text features, the analytical model achieves good fits to measured recognition rates in simulations involving a wide range of clutter loads, word size, and feature counts. We then introduce a greedy algorithm for feature learning, derived from the analytical model, which grows a representation by choosing those conjunctive features that are most likely to distinguish objects from the cluttered backgrounds in which they are embedded. We show that the representations produced by this algorithm are compact, decorrelated, and heavily weighted toward features of low conjunctive order. Our results provide a more quantitative basis for understanding when spatially invariant conjunctive features can support unambiguous perception in multiobject scenes, and lead to several insights regarding the properties of visual representations optimized for specific recognition tasks.

Algorithms↗
PubMed2000

Conjunctions of colour, luminance and orientation: the role of colour and luminance contrast on saliency and proximity grouping in texture segregation.

To examine whether perceptual grouping on the basis of orientation can be performed simultaneously with or only subsequently to grouping according to colour or luminance, we tested whether subjects are able to segregate arrays of texture elements that differ from surrounding elements by conjunctions of either (i) colour and orientation, or (ii) luminance contrast and orientation, or (iii) luminance contrast polarity and orientation. Subjects were able to use conjunctions between luminance and orientation for segregation but not conjunctions between colour or contrast polarity and orientation. Our results suggest that (i) in agreement with earlier findings, there seem to exist no specific conjunction detectors for colour and orientation or contrast polarity and orientation, and (ii) when orientation defined textures are to be distinguished by virtue of differences in luminance, colour, or contrast polarity, luminance provides a much stronger cue than colour or contrast polarity for saliency-based orientation grouping.

Adaptation, Ocular↗
PubMed1984

Evaluation of drugs used in the prophylaxis of neonatal conjunctivitis.

Administration of silver nitrate 1% solution into the eyes of the newborn has proven effective in the prophylaxis of gonococcal neonatal conjunctivitis. Silver nitrate, however, is not active against Chlamydia trachomatis, the most common cause of neonatal conjunctivitis. Also, silver nitrate commonly is associated with substantial chemical irritation. For these reasons, alternative agents are receiving increasing attention. Recently, erythromycin 0.5% and tetracycline 1% ophthalmic ointments were recommended by the Centers for Disease Control Venereal Disease Control Division for prophylaxis of neonatal conjunctivitis. Erythromycin has proven at least as effective as silver nitrate for gonococcal prophylaxis, can prevent chlamydial conjunctivitis in infants born to Chlamydia-positive mothers, and is associated with minimal complications. Clinical studies, however, demonstrating significant differences between erythromycin and tetracycline ophthalmic ointments are lacking. Well-controlled clinical studies comparing silver nitrate, erythromycin, and tetracycline prophylaxis are needed to determine the relative effectiveness of these agents.

Chlamydia Infections↗
PubMed2006

Working memory for conjunctions relies on the medial temporal lobe.

A prominent theory of hippocampal function proposes that the hippocampus is importantly involved in relating or binding together separate pieces of information to form an episodic representation. This hypothesis has only been applied to studies of long-term memory because the paradigmatic view of the hippocampus is that it is not critical for short-term forms of memory. However, relational processing is important in many working memory tasks, especially tasks using visual stimuli. Here, we test the hypothesis that the medial temporal lobes are important for relational memory even over short delays. The task required patients with medial temporal lobe amnesia and controls to remember three objects, locations, or object-location conjunctions over 1 or 8 s delays. The results show that working memory for objects and locations was at normal levels, but that memory for conjunctions was severely impaired at 8 s delays. Additional analyses suggest that the hippocampus per se is critical for accurate conjunction working memory. We propose that the hippocampus is critically involved in memory for conjunctions at both short and long delays.

Aged↗
PubMed1982

Human performance on conjunctive fixed-interval fixed-ratio schedules.

Eighteen young adults performed a lever-pulling task for money. Subjects were initially exposed to a fixed-interval 80-second schedule and subsequently to one of three conjunctive schedules in which the added fixed-ratio requirement was set at either 10, 80, or 120 responses. Three fixed-interval response patterns emerged: high constant rate, intermediate rate, or low rate, with most subjects displaying the last. Conjunctive performance was related to the subjects' prior fixed-interval patterns and the conjunctive ratio requirements. Low-rate subjects tended to optimize reinforcement (maximum reinforcers for minimum responses) on conjunctive schedules. Response rate was directly related to ratio requirements. Subjects' performance closely corresponded to their verbal statements of the contingencies.

Journal Article↗