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PubMed1995

The role of attention in feature detection and conjunction discrimination: an electrophysiological analysis.

An electrophysiological probe technique was used to ascertain whether the same attentional mechanisms are employed for both the detection of simple visual features and the discrimination of conjunctions of features. Visual search arrays containing 14 grey items and 2 colored items were presented; one color was designated relevant for each trial block. Subjects were required to report the presence or absence of the relevant color (feature detection condition) or the shape of the relevantly-colored item (conjunction discrimination condition). Shortly after the onset of the search array, a task-irrelevant probe stimulus was flashed at the location of the relevant or irrelevant color and the event-related potential (ERP) produced by this stimulus was used to assess sensory processing at the probed location. Probes presented at the location of the relevant color were found to elicit enhanced ERP components and probes presented on the opposite side of the display from the relevant color elicited suppressed components. These effects were observed in both the detection and discrimination conditions, indicating that spatially restricted attentional processes are used for both the detection of simple features and the discrimination of conjunctions. However, one ERP component (the PI wave) exhibited these effects in the discrimination condition but not in the detection condition, indicating that conjunction discrimination utilizes additional attentional processes beyond those required for feature detection.

Attention↗
PubMed1999

Presentation of words to separate hemispheres prevents interword illusory conjunctions.

We tested the hypothesis that division of inputs between the hemispheres could prevent interword letter migrations in the form of illusory conjunctions. The task was to decide whether a centrally-presented consonant-vowel-consonant (CVC) target word matched one of four CVC words presented to a single hemisphere or divided between the hemispheres in a subsequent test display. During half of the target-absent trials, known as conjunction trials, letters from two separate words (e.g., "tag" and "cop") in the test display could be mistaken for a target word (e.g., "top"). For the other half of the target-absent trails, the test display did not match any target consonants (Experiment 1, N = 16) or it matched one target consonant (Experiment 2, N = 29), the latter constituting true "feature" trials. Bi- as compared to unihemispheric presentation significantly reduced the number of conjunction, but not feature, errors. Illusory conjunctions did not occur when the words were presented to separate hemispheres.

Adult↗
PubMed1991

Effect of feature similarity on illusory conjunctions.

In four experiments, we examined whether the phenomenon of illusory conjunctions is constrained by feature similarity. Specifically, are illusory conjunctions more likely to occur between items with similar features than between items with dissimilar features? Feature similarity was manipulated in two dimensions: color and shape. Experiment 1 demonstrated that more illusory conjunctions occur between items with similar colors than between items with dissimilar colors. A similar effect was found for letter similarity in Experiment 2. Experiments 3 and 4 demonstrated that the similarity effect is still obtained for illusory conjunctions even when identification of the relevant features is near perfect. These findings introduce a new constraint in the process of feature integration. Additional implications of the similarity constraint for theories of feature integration are discussed.

Attention↗
PubMed1998

"Transient structures": the effects of practice and distractor grouping on within-dimension conjunction searches.

It has been stated that whereas between-dimension (color x orientation) conjunctions can be searched in a "parallel" fashion, within-dimension (color x color) conjunctions are necessarily searched in a "serial self-terminating" fashion (Wolfe et al., 1990). We explored the effects of practice (within 1-h experimental session) and distractor grouping on within-dimension conjunction search tasks. In Experiments 1 and 3, the stimuli were rectangles formed by two adjacent squares; in Experiment 2, the stimuli were plus signs formed by two segments and an intersection. In Experiments 1 and 2, observers were assigned to one of two experimental conditions: In one, all the distractors shared a simple feature (the color blue); in the other, distractors did not share that simple feature. In the first condition, search became more efficient with practice and observers' performance was characterized by a shallow reaction time (RT) x set size slope; in the second condition, observers' performance did not improve as much with practice. We propose that the differential effects of practice between these two experimental conditions can be explained in terms of distractor grouping induced by the shared color of the distractors. Experiment 3 showed that, with practice, a shallow RT x set size slope characterized observers' search for a color x color target among four different distractors that shared a common color. The present results contradict a main tenet of some current visual search models--namely, that within-dimension conjunctions cannot be searched in parallel, and question the validity of using RT x set size slope functions to distinguish between preattentive versus attentive search.

Analysis of Variance↗
PubMed1995

Part-whole information is useful in visual search for size x size but not orientation x orientation conjunctions.

In visual search tasks, subjects look for a target among a variable number of distractor items. If the target is defined by a conjunction of two different features (e.g., color x orientation), efficient search is possible when parallel processing of information about orientation is used to guide the deployment of attention to the target. Another type of conjunction search has targets defined by two instances of one type of feature (e.g., a conjunction of two colors). In this case, search is inefficient when the target is an item defined by parts of two different colors but much more efficient if the target can be described as a whole item of one color with a park of another color (Wolfe, Friedman-Hill, & Bilsky, 1994). In this paper, we show that the same distinction holds for size. "Part-whole" size x size conjunction searches are efficient; "part-part" searches are not (Experiments 1-3). In contrast, all orientation x orientation searches are inefficient (Experiments 4-6). This difference between preattentive processing of color and size, on the one hand, and orientation, on the other, may reflect structural relationships between features in real-world objects.

Adolescent↗
PubMed1995

The eccentricity effect: target eccentricity affects performance on conjunction searches.

The serial pattern found for conjunction visual-search tasks has been attributed to covert attentional shifts, even though the possible contributions of target location have not been considered. To investigate the effect of target location on orientation x color conjunction searches, the target's duration and its position in the display were manipulated. The display was present either until observers responded (Experiment 1), for 104 msec (Experiment 2), or for 62 msec (Experiment 3). Target eccentricity critically affected performance: A pronounced eccentricity effect was very similar for all three experiments; as eccentricity increased, reaction times and errors increased gradually. Furthermore, the set-size effect became more pronounced as target eccentricity increased, and the extent of the eccentricity effect increased for larger set sizes. In addition, according to stepwise regressions, target eccentricity as well as its interaction with set size were good predictors of performance. We suggest that these findings could be explained by spatial-resolution and lateral-inhibition factors. The serial self-terminating hypothesis for orientation x color conjunction searches was evaluated and rejected. We compared the eccentricity effect as well as the extent of the orientation asymmetry in these three conjunction experiments with those found in feature experiments (Carrasco & Katz, 1992). The roles of eye movements, spatial resolution, and covert attention in the eccentricity effect, as well as their implications, are discussed.

Adult↗
PubMed1998

Response times and eye movements in feature and conjunction search as a function of target eccentricity.

In four experiments, saccadic eye movements, reaction times (RTs), and accuracy were measured as observers searched for feature or conjunction targets presented at several eccentricities. A conjunction search deficit, evidenced by a large eccentricity effect on RTs, accuracy, and number of saccades, was seen in Experiments 1A and 1B. Experiment 2 indicated that, when saccades were precluded, there was an even larger eccentricity effect for conjunction search targets. In Experiment 3, practice in a conjunction search task allowed both RT and number of saccades to become independent of eccentricity. Additionally, there was evidence of feature-based selectivity in that observers were more likely to fixate distractors that had the same contrast as the target. Results are consistent with the view that the oculomotor and attentional systems are functionally linked and provide constraints for models of visual attention and search.

Attention↗
PubMed1998

[The role of local conjunction in the integration process of shape and color].

It is an open question how simple features are integrated in the attention spotlight. In this paper, we examined two opposing models for the integration process of shape and color. One is a local conjunction model in which simple features of shape and color are combined directly. The other is a whole conjunction model in which simple features of shape are integrated into the whole shape and then it is combined with color. In Experiment 1, we measured the time required to search for a target defined by a conjunction of shape and color for five subjects with changing coloring of the figures. The slope of the search function was gentler when corners of figures were colored (p < 0.01). In Experiment 2, we measured the time required to integrate shape and color of figures presented in rapid serial visual presentation (RSVP) for five subjects. The presentation time required to answer the correct combination was shorter when corners were colored (p < 0.01). These results support the local conjunction model.

Adult↗
PubMed2001

Illusory conjunctions die hard: a reply to Prinzmetal, Diedrichsen, and Ivry (2001).

M. Donk (1999) showed that various data patterns that have been considered as evidence for the existence of illusory conjunctions may be due to errors of target-nontarget confusion, an account that challenges the mere existence of illusory conjunction. In a reply, W. Prinzmetal, J. Diedrichsen, and R. B. Ivry (2001) argued against this conclusion, claiming that some earlier findings can be explained only when one assumes that illusory conjunctions exist. The current article shows that Prinzmetal et al.'s claims cannot refute any of Donk's earlier conclusions, suggesting indeed that one can only conclude that "illusory conjunctions are an illusion."

Association Learning↗
PubMed2002

Conjunction error rates on a continuous recognition memory test: little evidence for recollection.

Two experiments examined conjunction memory errors on a continuous recognition task where the lag between parent words (e.g., blackmail, jailbird) and later conjunction lures (blackbird) was manipulated. In Experiment 1, contrary to expectations, the conjunction error rate was highest at the shortest lag (1 word) and decreased as the lag increased. In Experiment 2 the conjunction error rate increased significantly from a 0- to a 1-word lag, then decreased slightly from a 1- to a 5-word lag. The results provide mixed support for simple familiarity and dual-process accounts of recognition. Paradoxically, searching for an item in memory does not appear to be a good encoding task.

Humans↗
PubMed1984

Microbial causes of neonatal conjunctivitis.

We assessed the microbial causes of neonatal conjunctivitis by comparing 55 infants with purulent conjunctivitis and 60 healthy control infants. A mean of greater than 5 leukocytes per 1000X microscopic field was seen in Gram-stained smears obtained from the more inflamed eye in 77% of 30 untreated patients but none of 57 controls. Pathogens isolated more often from untreated patients than from controls included Haemophilus spp. (17% vs 2%, P = 0.01), Staphylococcus aureus (17% vs 2%, P = 0.01), Chlamydia trachomatis (14% vs 0%, P = 0.01), enterococci (8% vs 0%, P = 0.05), and Streptococcus pneumoniae (11% vs 2%, P = 0.06). One or more of these pathogens were isolated from the conjunctivae in 58% of patients and 5% of controls (P less than 0.001). Bacterial morphology seen on smear correlated with the pathogens cultured. Isolation of Haemophilus spp. or S. pneumoniae was associated with dacryostenosis. We conclude that several microbial pathogens are implicated in neonatal conjunctivitis. These organisms have differing susceptibilities to antimicrobial agents, so culture and sensitivity testing are required as a guide to therapy.

Bacterial Infections↗
PubMed1987

Adult follicular conjunctivitis and neonatal ophthalmia in a Liverpool eye hospital, 1980-1984.

In the five year period between 1980 and 1984, 2146 adults and 172 neonates suffering from acute conjunctivitis underwent laboratory investigation for Chlamydia trachomatis (CT), Adenoviruses (AV), Herpes Simplex Virus (HSV) and pathogenic bacteria. Epidemiology and clinical features are presented and discussed. CT was detected in 29 per cent of neonates with conjunctivitis. 5.6 per cent of adults and older children investigated for follicular conjunctivitis were CT positive. There was a significant female preponderance among CT positive neonates of 1.9:1 (p less than 0.02). 91 per cent of neonates and 62 per cent of adults in whom CT was detected were receiving some sort of treatment. Serotypes 7, 3, 10, 4 and 8 were responsible in decreasing order of frequency for 96 per cent of AV infections. Serotype 7 was seen for the first time in an adult age distribution. HSV was isolated in 1.3 per cent of cases in the absence of typical lid or corneal lesions. Viral infection was not detected in any neonate. Bacterial infection was a more likely cause than CT in neonates if infection had persisted longer than 5 weeks (p much less than 0.001). Neonates with Staph aureus infection tended to present earlier in the course of disease than those with Haemophilus sp or Pneumococcus (p less than 0.05).

Adenoviridae Infections↗
PubMed1989

Viral and bacterial conjunctivitis. Prevention of disastrous results.

Conjunctivitis has many bacterial and viral causes. If the cause is bacterial, treatment with a broad-spectrum antibiotic resolves the problem in 1 to 3 days in almost all cases. If signs and symptoms persist, referral to an ophthalmologist is wise. Most cases of viral conjunctivitis are accompanied by follicular reactions in the inferior fornix, as observed with adult inclusion disease. If dendrites are seen, trifluridine (Viroptic) is preferred for treatment. Referral to an ophthalmologist is advisable because recurrence with scarring and permanent loss of vision is possible. Many topical antibiotics include a corticosteroid component that never should be used unless the conjunctivitis or keratitis is proven to be nonherpetic.

Adult↗
PubMed1984

A study of the incidence of neonatal conjunctivitis and of its bacterial causes including Chlamydia trachomatis. Clinical examination, culture and cytology of tear fluid.

Out of 300 newborn infants who had conjunctival swabs inoculated for detection of Chlamydia trachomatis and other bacteria, 72% had bacteria isolated 4 to 6 days after birth. Of these, Staph. albus constituted 51% and Staph. aureus 19%. None of the infants were Chlamydia positive. Five out of 112 mothers (4.5%) were Chlamydia positive from the cervix just before delivery. Nineteen of the neonates were treated for conjunctivitis within the first month of life. Chlamydia trachomatis was isolated from 2, and Staph. aureus, alpha-Streptococci, Pneumococci and Haemophilus influenzae from some of the other infants. A likely diagnosis could be made in 46% of these cases, while the remaining cultures showed only apathogenic bacteria or no growth. There was a fairly good accordance with observation of inflammatory cells in the tear fluid and the clinical picture, 17/19 = 90% showing neutrophilia. Despite failing aetiological diagnosis in several cases, the infants responded satisfactorily to local antibiotic treatment. 75% of the parents replied to questionnaires 2 months after birth concerning conjunctivitis within the first month of life. The replies showed that 58 = 25% had had conjunctivitis, of whom 17% had been treated with antibiotics.

Bacteria↗
PubMed2006

Acute haemorrhagic conjunctivitis outbreak in the city of Fortaleza, northeast Brazil.

BACKGROUND/AIM: Between February and May 2003 an epidemic of acute haemorrhagic conjunctivitis affected more than 200 000 people in all five geographic regions of Brazil (north, south, midwestern, southeast, and northeast). The aim was to identify the aetiological agent and to describe clinical aspects of this outbreak in a group of patients treated at the ophthalmology department of the Hospital Walter Cantídio (OD-HWC) at the Universidade Federal do Ceará, in the city of Fortaleza, capital of the state of Ceará, northeastern Brazil. METHODS: Conjunctival swabs were collected from patients who spontaneously went to the laboratory of virology. Specimens were inoculated in HEp-2 and RD cell lines. The viral isolation was confirmed by performing reverse transcriptase polymerase chain reaction and indirect immunofluorescence assay. RESULTS: Viral conjunctivitis was diagnosed in 56 patients but only 24 of them allowed the collection of samples. Of 24 conjunctival swabs tested, 11 were positive for a variant of coxsackie virus A24 (CA24v) and one of the isolates reacted with anti-adenovirus monoclonal antibodies. CONCLUSION: CA24v was confirmed as the aetiological agent of this outbreak of acute haemorrhagic conjunctivitis in the city of Fortaleza.

Adolescent↗
PubMed2003

A phase III, placebo controlled clinical trial of 0.5% levofloxacin ophthalmic solution for the treatment of bacterial conjunctivitis.

AIM: To compare the efficacy and safety of levofloxacin 0.5% ophthalmic solution (Quixin) with placebo for treatment of bacterial conjunctivitis. METHODS: In this prospective, randomised, placebo controlled, double masked, multicentre study, 249 patients with bacterial conjunctivitis received either 0.5% levofloxacin (n = 126) or placebo (n = 123) for 5 days, administered every 2 hours on days 1-2, then every 4 hours on days 3-5. Cultures were obtained and signs/symptoms evaluated at baseline, interim, and final visits. The end point was the last evaluable observation. Primary microbial outcomes were based on culture results; clinical outcomes were based on resolution of cardinal signs. RESULTS: 117 patients (60 levofloxacin, 57 placebo) were evaluated. Microbial eradication rates were significantly greater with levofloxacin at all time points, reaching 90% at end point. In a subgroup analysis, differences in eradication rates at end point were most pronounced in children but were also statistically significant for levofloxacin in adults. Clinical cure rates were significantly greater with levofloxacin at final visit and end point. Statistically significant differences favouring levofloxacin were measured at end point for resolution of conjunctival discharge, bulbar conjunctival injection, palpebral conjunctival injection, burning/stinging, itching, and photophobia. Adverse events were similar between groups. Safety composite scores analysed by age indicated significantly fewer children on levofloxacin experienced worsening symptoms. CONCLUSIONS: Levofloxacin 0.5% ophthalmic solution is safe and effective for treatment of bacterial conjunctivitis.

Adolescent↗
PubMed2000

Tolerance of N-chlorotaurine, a new antimicrobial agent, in infectious conjunctivitis - a phase II pilot study.

N-Chlorotaurine (NCT) is an endogenous microbicidal oxidant. This open pilot study (phase IIa) with 9 patients was done to gain first knowledge on the tolerance of NCT in infectious conjunctivitis. By application of 1% NCT 5 times a day, no adverse effects could be observed. All 6 subjects with bacterial conjunctivitis were cured within 3-5 days. Two subjects with epidemic keratoconjunctivitis were treated for 7-10 days and 1 subject with herpes simplex blepharitis for 3 days with no rapid improvement but probable mitigation of inflammation. Therefore, NCT seems to be useful in the treatment of infectious conjunctivitis, and further investigation on its therapeutic efficacy is suggested.

Adolescent↗
PubMed1979

Conjunctivitis in children. A refresher survey of diagnosis and contemporary treatment.

The management of acute conjunctivitis need not be confusing. In the newborn period the common etiologic agents are chemical, TRIC, and bacterial. The latter two causes are effectively treated with sulfacetamide ophthalmic preparations. Dacryostenosis should be suspected in any child with recurrent conjunctivitis in the first six months of life. With older children the major causes can be classified as viral, allergic, foreign bodies, and bacterial. Bacterial conjunctivitis almost always responds to sulfacetamide ophthalmic preparations.

Anti-Bacterial Agents↗