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At least 973 records · Page 54Linked to original sources
PubMed2006

Enterococci predictions from partial least squares regression models in conjunction with a single-sample standard improve the efficacy of beach management advisories.

Beach health advisories are issued if enterococci (ENT) densities exceed the 30-d geometric mean or single-sample water quality criteria. Current ENT enumeration procedures require 1 day of incubation; therefore, beach managers make policy decisions using 1-day-old data. This is tantamount to using a model that assumes ENT density on day t is equal to ENT density on day t-1. Research has shown that ENT densities vary over time scales shorterthan a day, calling into question the usefulness of the current model for decision-making. We created Dynamic Partial Least Square Regression (DPLSR) models for ENT at water quality monitoring stations within two adjacent marine recreational sites, Huntington State Beach (HSB) and Huntington City (HCB) Beach, California, using publicly available environmental data and tested whether these models overcome the drawbacks of the current model. The DPLSR models provide a better prediction of ENT than the current models based on comparisons of root-mean-square errors of prediction and the numbers of type 1 and 2 errors. We compared outcomes in terms of predicted illness, swimmers deterred from entering the water, and net benefits to swimmers for hypothetical management scenarios where beach advisories were issued based on (a) the previously collected sample's ENT density in conjunction with the two water quality criteria, and (b) predictions from DPLSR models in conjunction with the single-sample standard. At both HSB and HCB the DPLSR scenario produced a more favorable balance between illness prevention and recreational access. The results call into question the current method of beach management and show that model-informed decision-making and elimination of the geometric mean standard will aid beach managers in achieving more favorable outcomes in terms of illness and access than are presently achieved using 1-day-old measurements, especially at beaches where water quality problems are chronic.

Animals↗
PubMed1998

Attomole detection of 3H in biological samples using accelerator mass spectrometry: application in low-dose, dual-isotope tracer studies in conjunction with 14C accelerator mass spectrometry.

This is the first demonstration of the use of accelerator mass spectrometry (AMS) as a tool for the measurement of 3H with attomole (10(-18) mol) sensitivity in a biological study. AMS is an analytical technique for quantifying rare isotopes with high sensitivity and precision and has been most commonly used to measure 14C in both the geosciences and more recently in biomedical research. AMS measurement of serially diluted samples containing a 3H-labeled tracer showed a strong correlation with liquid scintillation counting. The mean coefficient of variation of 3H AMS based upon the analysis of separately prepared aliquots of these samples was 12%. The sensitivity for 3H detection in tissue, protein, and DNA was approximately 2-4 amol/mg of sample. This high sensitivity is comparable to detection limits for 14C-labeled carcinogens using 14C AMS and demonstrates the feasibility of 3H AMS for biomedical studies. One application of this technique is in low-dose, dual-isotope studies in conjunction with 14C AMS. We measured the levels of 3H-labeled 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 14C-labeled 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) in rat liver tissue and bound to liver DNA and protein 4.5 h following acute administration of individual or coadministered doses in the range of 4-5100 pmol/kg of body weight. Levels of PhIP and MeIQx in whole tissue and bound to liver protein were dose-dependent. MeIQx-protein and -DNA adduct levels were higher than PhIP adduct levels, which is consistent with their respective carcinogenicity in this organ. Coadministration of PhIP and MeIQx did not demonstrate any measurable synergistic effects compared to administration of these compounds individually. These studies demonstrate the application of AMS for the low-level detection of 3H in small biological samples and for its use in conjunction with 14C AMS for dual-labeling studies.

Animals↗
PubMed1986

Conjunction of color and form without attention: evidence from an orientation-contingent color aftereffect.

According to feature-integration theory (Treisman & Gelade, 1980), separable features such as color and shape exist in separate maps in preattentive vision and can be integrated only through the use of spatial attention. Many perceptual aftereffects, however, which are also assumed to reflect the features available in preattentive vision, are sensitive to conjunctions of features. One possible resolution of these views holds that adaptation to conjunctions depends on spatial attention. We tested this proposition by presenting observers with gratings varying in color and orientation. The resulting McCollough aftereffects were independent of whether the adaptation stimuli were presented inside or outside of the focus of spatial attention. Therefore, color and shape appear to be conjoined preattentively, when perceptual aftereffects are used as the measure. These same stimuli, however, appeared to be separable in two additional experiments that required observers to search for gratings of a specified color and orientation. These results show that different experimental procedures may be tapping into different stages of preattentive vision.

Adolescent↗
PubMed1991

Density effects in conjunction search: evidence for a coarse location mechanism of feature integration.

Four experiments used the visual search paradigm to examine feature integration mechanisms. Reaction time to determine the presence or absence of a conjunctive target is relatively fast and exhaustive for low-density displays. Search rate is slow and self-terminating for high-density displays. Density effects do not arise when the target is defined by a unique feature. Two mechanisms are proposed for feature integration. A fast mechanism integrates features on the basis of coarse location information coded with the initial registration of the features. This coarse location mechanism requires that display items be spaced apart. A second, slower mechanism is used when objects are clumped together. The 2-mechanism hypothesis provides a resolution to conflicting findings in the visual search and illusory-conjunction literature. A possible interpretation of the findings with a single guided search mechanism for feature integration is also discussed.

Adult↗
PubMed1994

Stages of auditory feature conjunction: an event-related brain potential study.

Auditory event-related brain potentials (ERPs) were recorded to tones of different frequencies and locations in a dichotic selective attention task in which Ss responded to occasional deviant tones of a prespecified location and frequency. Attention effects were isolated as negative difference (Nd) waves by subtracting ERPs to tones with no attended features from ERPs to the same tones when they shared target frequency, location, or both cues. The N1/P90 (latency 80-100 ms), originating in a tonotopically organized generator, was enhanced for all tones in the attended ear. Nd waves, beginning at 80 ms and lasting up to 700 ms, were seen to tones with either attended feature. Nd waves to frequency and location features had different scalp distributions consistent with generation in different cortical fields. Conjunction-specific Nds began 30-50 ms after Nds to individual features. The relative timing suggests that feature conjunction began before the analysis of individual features was complete.

Acoustic Stimulation↗
PubMed1995

Loosening the constraints on illusory conjunctions: assessing the roles of exposure duration and attention.

Illusory conjunctions are the incorrect combination of correctly perceived features, such as color and shape. They have been found to occur using a brief exposure (under 200 ms) and a dual task designed to divert attention. The present study investigated the roles of exposure duration and attention in obtaining illusory conjunctions. Several mathematical models of the feature integration task were also assessed. Experiment 1 tested participants' accuracy at combining features using a long exposure and an attention-diverting taks. Experiment 2 compared performance with and without the attention-diverting task. The final experiment compared performance using a brief (0.15 s) and a long (1.5 s) exposure duration without an attention-diverting task. Neither attention nor exposure duration had a significant effect on feature integration.

Attention↗
PubMed1997

Goal-directed guidance of attention: evidence from conjunctive visual search.

Conjunctive visual search is most difficult when distractor types are in equal proportions and gets easier as the proportions diverge (e.g., E. Zohary & S. Hochstein, 1989). This may reflect restriction of search to the feature shared by the target and the less-frequent distractor. Alternatively, such effects could reflect target salience, which varies with distractor ratio. In 2 experiments, 60 participants searched 64-element displays for a conjunctive target among distractors of 2 types in various proportions. Participants were correctly informed (Experiment 1) or misinformed (Experiment 2) about which distractor type would be less frequent on most trials. In both experiments, the distractor-ratio effect was significantly influenced by the information provided to participants. These findings demonstrate the efficacy of top-down information in guiding attention and show that it can be applied flexibly, weighted toward particular target features.

Attention↗
PubMed2001

Illusory conjunctions of pitch and duration in unfamiliar tone sequences.

In 3 experiments, the authors examined short-term memory for pitch and duration in unfamiliar tone sequences. Participants were presented a target sequence consisting of 2 tones (Experiment 1) or 7 tones (Experiments 2 and 3) and then a probe tone. Participants indicated whether the probe tone matched 1 of the target tones in both pitch and duration. Error rates were relatively low if the probe tone matched 1 of the target tones or if it differed from target tones in pitch, duration, or both. Error rates were remarkably high, however, if the probe tone combined the pitch of 1 target tone with the duration of a different target tone. The results suggest that illusory conjunctions of these dimensions frequently occur. A mathematical model is presented that accounts for the relative contribution of pitch errors, duration errors, and illusory conjunctions of pitch and duration.

Adolescent↗
PubMed2001

Storage of features, conjunctions and objects in visual working memory.

Working memory can be divided into separate subsystems for verbal and visual information. Although the verbal system has been well characterized, the storage capacity of visual working memory has not yet been established for simple features or for conjunctions of features. The authors demonstrate that it is possible to retain information about only 3-4 colors or orientations in visual working memory at one time. Observers are also able to retain both the color and the orientation of 3-4 objects, indicating that visual working memory stores integrated objects rather than individual features. Indeed, objects defined by a conjunction of four features can be retained in working memory just as well as single-feature objects, allowing many individual features to be retained when distributed across a small number of objects. Thus, the capacity of visual working memory must be understood in terms of integrated objects rather than individual features.

Cues↗
PubMed2001

Interactions between search mechanisms in conjunction search.

We report the results of a technique designed to measure interactions between different visual search processes. We interrupted pop-out search before it produced a detection response, by adding extra distractors to the display so that a target initially defined by a single feature difference (e.g., a yellow horizontal line among yellow vertical lines) could then only be found on the basis of the conjunction of two features (a yellow horizontal line among yellow vertical lines and pink horizontal lines; difficult search). This technique has been used to measure the duration of the perceptual components of pop-out search, independent of over-all response time, for targets presented among different sets of distractors. In addition, when pop-out failed because it was interrupted, past work has shown that it nevertheless provided useful information to the processes responsible for difficult search. That is, partial pop-out assisted difficult search, when extra distractors made search difficult because the target was between the two types of distractors in the relevant feature space (Olds, Cowan, & Jolicoeur, 2000a,b,c). The present results demonstrate that partial pop-out also assists difficult search when difficult search is a conjunction search, and therefore these interactions may occur at a stage where information from different feature dimensions is combined.

Adult↗
PubMed2003

Guidance of eye movements during conjunctive visual search: the distractor-ratio effect.

The distractor-ratio effect refers to the finding that search performance in a conjunctive visual search task depends on the relative frequency of two types or subsets of distractors when the total number of items in a display is fixed. Previously, Shen, Reingold, and Pomplun (2000) examined participants' patterns of eye movements in a distractor-ratio paradigm and demonstrated that on any given trial saccadic endpoints were biased towards the smaller subset of distractors and participants flexibly switched between different subsets across trials. The current study explored the boundary conditions of this tendency to flexibly search through a smaller subset of distractors by examining the influence of several manipulations known to modulate search efficiency, including stimulus discriminability (Experiment 1), within-dimension versus cross-dimension conjunction search and distractor heterogeneity (Experiment 2). The results indicated that the flexibility of visual guidance and saccadic bias exemplified by the distractor-ratio effect is a robust phenomenon that mediates search efficiency by adapting to changes in the relative informativeness of stimulus dimensions and features.

Cues↗
PubMed1988

Visual search for a conjunction of movement and form is parallel.

Treisman has proposed when a human subject performs a visual search, the search is parallel for targets defined by a single feature, and serial for targets defined by a conjunction of features. Here we report that this is not true for targets defined by a conjunction of the features movement and form. Detection of a moving X among randomly distributed moving Os and static Xs is parallel. Search is uninfluenced by the stationary stimuli despite their spatial intermingling with the moving items. Thus, attention can be restricted to a spatially dispersed perceptual group, defined by common movement. This contradicts previous conclusions from visual search experiments that attention can only be assigned to contiguous regions of visual space. The search process first segregates the array into moving and stationary items, and then examines the moving group for the target form. Cells in the middle temporal region (cortical area MT) have the properties required to perform these operations.

Color Perception↗
PubMed1997

The capacity of visual working memory for features and conjunctions.

Short-term memory storage can be divided into separate subsystems for verbal information and visual information, and recent studies have begun to delineate the neural substrates of these working-memory systems. Although the verbal storage system has been well characterized, the storage capacity of visual working memory has not yet been established for simple, suprathreshold features or for conjunctions of features. Here we demonstrate that it is possible to retain information about only four colours or orientations in visual working memory at one time. However, it is also possible to retain both the colour and the orientation of four objects, indicating that visual working memory stores integrated objects rather than individual features. Indeed, objects defined by a conjunction of four features can be retained in working memory just as well as single-feature objects, allowing sixteen individual features to be retained when distributed across four objects. Thus, the capacity of visual working memory must be understood in terms of integrated objects rather than individual features, which places significant constraints on cognitive and neurobiological models of the temporary storage of visual information.

Color Perception↗
PubMed2002

Treatment of port-wine stain birthmarks using the 1.5-msec pulsed dye laser at high fluences in conjunction with cryogen spray cooling.

BACKGROUND: The majority of port-wine stain (PWS) patients treated with the pulsed dye laser (PDL) do not achieve complete blanching. Safe administration of higher fluences has been proposed as a means of improving treatment efficacy. OBJECTIVE: To determine the safety and efficacy of PWS treatment with the 1.5-msec PDL at high fluences in conjunction with cryogen spray cooling. METHODS: Twenty PWS patients were treated with the PDL in combination with cryogen spray cooling utilizing a 7 or 10 mm spot size and fluences ranging from 6 to 15 J/cm2. Before and after treatment photographs were compared on a blinded basis. RESULTS: No scarring or skin textural changes occurred. Blanching scores were as follows: 20% of patients achieved 75% or greater blanching after an average of 3.3 treatments, 30% achieved 50-74% blanching, 20% achieved 25-49% blanching, and 30% achieved less than 25% blanching. CONCLUSION: In conjunction with cryogen spray cooling, the PDL can be safely used at high fluences. At this time it is not clear that the use of higher fluences improves treatment efficacy; however, as other aspects of PWS laser treatment are optimized, safe administration of higher fluences is likely to be advantageous.

Adolescent↗
PubMed2004

Does previewing one stimulus feature help conjunction search?

We examined the effects of previewing one aspect of a search display, in order to determine what subset of display information is most useful as a prelude to a search task. Observers were asked to indicate the presence or absence of a known target, in a conjunction search where the target was defined by the combination of colour and orientation (a yellow horizontal line presented among yellow vertical and pink horizontal distractors). In the colour preview condition of experiment 1, observers were first shown a 1 s preview of the locations and colours of the search items before the actual search set was presented. That is, search items first appeared as yellow and pink squares for 1 s, which each then turned into yellow and pink oriented lines (in the same locations) which comprised the display to be searched. In the orientation preview condition, observers were first shown a 1 s preview of the locations and orientations of the search items before the actual search display was presented. These two conditions were compared to a control condition consisting of standard conjunction search without any preview display. There was no effect of colour preview; there was a marginal effect of orientation preview, but in the opposite direction from what was expected reaction time increased for orientation preview searches. In experiment 2 these previews were compared to two spatial cueing conditions; in this experiment the colour preview did provide a small amount of help. Finally, in experiment 3 both previews were presented in succession, and increased facilitation was found, in particular when the colour preview preceded the orientation preview. These findings are discussed in relation to the literature, in particular the Guided Search model (Wolfe et al 1989 Journal of Experimental Psychology: Human Perception and Performance 15 419-433; Wolfe 1994 Psychonomic Bulletin & Review 1 202-238).

Adaptation, Psychological↗
PubMedDate not supplied

The effects of age on guided conjunction search.

The effect of age on top-down guidance in visual search for conjunctions of form and motion was examined with a task developed by Driver et al. (1992). Young (mean age = 19.2 years) and old (mean age = 77.3 years) adults searched for a vertically oscillating X among varying numbers of vertically oscillating Os and horizontally oscillating Xs. The ease with which subjects could use top-down guidance to improve search efficiency was manipulated by varying the motion coherence of display items. Overall, older adults produced steeper response-time-display-size slopes than did young adults, and both age groups showed significant reductions in slopes when distractors oscillated coherently. Older adults, however, produced proportionally smaller reductions in slope than did younger adults, suggesting that age affects the efficiency of top-down guidance in conjunction search for form and motion.

Adult↗
PubMed2003

Methemoglobinemia induced by refrigerated vegetable puree in conjunction with supraventricular tachycardia.

UNLABELLED: We report on a case of methemoglobinemia in conjunction with supraventricular tachycardia. A 6-mo-old infant was admitted to hospital with perioral cyanosis three hours after eating a refrigerated mixed-vegetable puree. The patient developed supraventricular tachycardia (SVT) and had a heart rate of 230 beats/min. The arrhythmia resolved spontaneously. A chemical analysis showed oxygen saturation of 85% and a methemoglobin level of 25%. The infant was treated with oxygen and referred to the Pediatric Intensive Care Unit. The patient had two additional short episodes of SVT, which were resolved spontaneously without treatment. She received oxygen for 8 h until the methemoglobin level dropped to 1%. CONCLUSION: Long-term storage of refrigerated vegetables can cause methemoglobinemia in infants. Methemoglobinemia can appear in conjunction with SVT, but it is also possible that in a child with a tendency to develop SVT, methemoglobinemia involved hypoxemia, which then triggers SVT.

Female↗
PubMed1995

Jun-B expression in Purkinje cells by conjunctive stimulation of climbing fibre and AMPA.

Co-application of alpha-amino-3-hydro-5-methyl-4-isoxazole-propionate (AMPA) and 8-bromo cGMP (8-Br-cGMP) which cause long-term desensitization also induces c-Fos and Jun-B expression in Purkinje cells of cerebellar slices [Nakazawa K, Karachot L, Nakabeppu Y et al. NeuroReport 4, 1275-1278 (1993)]. Here, we report an increased local induction of Jun-B immunoreactivity in Purkinje cells in vivo when electrical stimulation of the inferior olive nucleus (IOn) was conjunctively applied with AMPA on the vermis. The present data further supports the idea that conjunctive heterosynaptic inputs to cerebellar Purkinje cells can trigger active gene transcription thus possibly contributing to cerebellar long-term plasticity. They also demonstrate that Jun-B may be a useful transcriptional marker to study cerebellar coincidence phenomena.

Afferent Pathways↗