Biomedical subjects

J C Johnston

Publications and source records attributed to J C Johnston.

At least 19 recordsLinked to original sources

PubMed2001

Switching between simple cognitive tasks: the interaction of top-down and bottom-up factors.

How do top-down factors (e.g., task expectancy) and bottom-up factors (e.g., task recency) interact to produce an overall level of task readiness? This question was addressed by factorially manipulating task expectancy and task repetition in a task-switching paradigm. The effects of expectancy and repetition on response time tended to interact underadditively, but only because the traditional binary task-repetition variable lumps together all switch trials, ignoring variation in task lag. When the task-recency variable was scaled continuously, all 4 experiments instead showed additivity between expectancy and recency. The results indicated that expectancy and recency influence different stages of mental processing. One specific possibility (the configuration-execution model) is that task expectancy affects the time required to configure upcoming central operations, whereas task recency affects the time required to actually execute those central operations.

Cognition↗

PubMed2001

A probabilistic approach to space-group determination from powder diffraction data.

An algorithm for the determination of the space-group symmetry of a crystal from powder diffraction data, based upon probability theory, is described. Specifically, the relative probabilities of different extinction symbols are assessed within a particular crystal system. In general, only a small number of extinction symbols are relatively highly probable and a single extinction symbol is often significantly more probable than any other. Several examples are presented to illustrate this approach.

Journal Article↗

PubMed2001

Attention and performance.

Recent progress in the study of attention and performance is discussed, focusing on the nature of attentional control and the effects of practice. Generally speaking, the effects of mental set are proving more pervasive than was previously suspected, whereas automaticity is proving less robust. Stimulus attributes (e.g. onsets, transients) thought to have a "wired-in" ability to capture attention automatically have been shown to capture attention only as a consequence of voluntarily adopted task sets. Recent research suggests that practice does not have as dramatic effects as is commonly believed. While it may turn out that some mental operations are automatized in the strongest sense, this may be uncommon. Recent work on task switching is also described; optimal engagement in a task set is proving to be intimately tied to learning operations triggered by the actual performance of a new task, not merely the anticipation of such performance.

Attention↗

PubMed2001

Why practice reduces dual-task interference.

M. A. Van Selst, E. Ruthruff, and J. C. Johnston (1999) found that practice dramatically reduced dual-task interference in a Psychological Refractory Period (PRP) paradigm with 1 vocal response and 1 manual response. Results from 3 further experiments using the highly trained participants of M. A. Van Selst et al. (1999) support 4 main conclusions: (a) A processing bottleneck exists even after extensive practice; (b) the principal cause of the reduction in PRP interference with practice is shortening of Task 1 bottleneck stages; (c) a secondary cause is that 1 or more, but not all, of the Task 2 substages that are postponed before practice are not postponed after practice (i.e., become automatized); and (d) the extent of PRP reduction with practice depends on the modalities of the 2 responses. A control experiment with 2 manual response tasks showed less PRP reduction with practice than that found by Van Selst et al.

Auditory Perception↗

PubMed2000

Visual search in complex displays: factors affecting conflict detection by air traffic controllers.

Recent free flight proposals to relax airspace constraints and give greater autonomy to aircraft have raised concerns about their impact on controller performance. Relaxing route and altitude restrictions would reduce the regularity of traffic through individual sectors, possibly impairing controller situation awareness. We examined the impact of this reduced regularity in four visual search experiments that tested controllers' detection of traffic conflicts in the four conditions created by factorial manipulation of fixed routes (present vs. absent) and altitude restrictions (present vs. absent). These four conditions were tested under varying levels of traffic load and conflict geometry (conflict time and conflict angle). Traffic load and conflict geometry showed strong and consistent effects in all experiments. Color coding altitude also substantially improved detection times. In contrast, removing altitude restrictions had only a small negative impact, and removing route restrictions had virtually no negative impact. In some cases conflict detection was actually better without fixed routes. The implications and limitations of these results for the feasibility of free flight are discussed. Actual or potential applications include providing guidance in the selection of free flight operational concepts.

Aircraft↗

PubMed1999

Classification of small cell lung cancer and pulmonary carcinoid by gene expression profiles.

Small cell lung cancer is a common type of lung cancer that is generally classified within the spectrum of neuroendocrine lung neoplasms. Using high-density cDNA arrays, we profiled gene expression of small cell lung cancers and compared these expression profiles to those of normal bronchial epithelial cells and pulmonary carcinoids, which are classified as benign neuroendocrine tumors. We found the overall expression profiles of two small cell lung cancer cell lines, two microdissected tissue samples of primary small cell lung cancer, and cultured bronchial epithelial cells to be relatively similar to one another, with an average Pearson correlation coefficient for these comparisons of 0.63. However, we found the expression profiles of small cell lung cancers (and bronchial epithelial cells) to be surprisingly dissimilar to those of two samples of pulmonary carcinoid tumors, with an average correlation coefficient for these comparisons of 0.20. We then compared the pulmonary carcinoid expression profiles to those of two samples of infiltrating astrocytic brain cancers (oligodendroglioma and high-grade astrocytoma) and found similarity of gene expression among these four samples (average correlation coefficient, 0.57). These gene expression profiles suggest that small cell lung cancers are closely related to (and possibly derived from) epithelial cells, and that pulmonary carcinoids are related to neural crest-derived brain tumors. More generally, our results suggest that broad profiles of gene expression may reveal similarities and differences between tumors that are not apparent by traditional morphological criteria.

Carcinoid Tumor↗

PubMed1999

The S387Y mutations of the transforming growth factor-beta receptor type I gene is uncommon in metastases of breast cancer and other common types of adenocarcinoma.

Recently, mutations of the transforming growth factor-beta receptor type I gene have been reported to occur at high frequency in breast cancer metastases, with all mutations being an identical C to A transversion at nucleotide 1160 of the gene (T. Chen et al, Cancer Res., 58: 4805-4810, 1998). This mutation would result in a serine to tyrosine substitution at codon 387 (S387Y) and would reportedly disrupt receptor function. Because this mutation reportedly occurred at high frequency in breast cancer metastases (42%) and much less frequently in primary breast cancer tumors (6%), this would seem to represent a pivotal genetic alteration in breast cancer progression. To further investigate the possible role of this specific genetic alteration in the progression of breast cancer and other forms of adenocarcinoma, we analyzed 20 breast cancer metastases, 15 lung adenocarcinoma metastases, and 13 colorectal cancer metastases for possible mutations at this site. Using both single-strand conformation polymorphism screening and sequencing, we found no mutations of this gene in any of our samples. Our results suggest the S387Y mutation of the transforming growth factor-beta receptor type I gene is not common in these types of human cancers.

Activin Receptors, Type I↗

PubMed1999

Can practice eliminate the psychological refractory period effect?

Can people learn to perform two tasks at the same time without interference? To answer this question, the authors trained 6 participants for 36 sessions in a Psychological Refractory Period (PRP) experiment, where Task 1 required a speeded vocal response to an auditory stimulus and Task 2 required a speeded manual response to a visual stimulus. The large PRP effect found initially (353 ms in Session 1) shrank to only about 40 ms over the course of practice, disappearing entirely for 1 of the 6 participants. This reduction in the PRP effect with practice is considerably larger than has been previously reported. The obtained pattern of factor interactions between stimulus onset asynchrony and each of three task difficulty manipulations (Task 1 judgment difficulty, Task 2 stimulus contrast, and Task 2 mapping compatibility) supports a postponement (bottleneck) account of dual-task interference, both before and after practice.

Humans↗

PubMed1999

Minimum requirements for efficient transduction of dividing and nondividing cells by feline immunodeficiency virus vectors.

The development of gene delivery vectors based on feline immunodeficiency virus (FIV) is an attractive alternative to vectors based on primate sources for the delivery of genes into humans. To investigate the requirements for efficient transduction of dividing and nondividing cells by vector particles based on FIV, a series of packaging and vector constructs was generated for which viral gene expression was minimized and from which unnecessary cis-acting sequences were deleted. Pseudotyped vector particles produced in 293T cells were used to transduce various target cells, including contact-inhibited human skin fibroblasts and growth-arrested HT1080 cells. FIV vectors in which the U3 promoter was replaced with the cytomegalovirus promoter gave rise to over 50-fold-higher titers than FIV vectors containing the complete FIV 5' long terminal repeat (LTR). Comparison of the transduction efficiencies of vectors containing different portions of the FIV Gag coding region indicates that at least a functional part of the FIV packaging signal (Psi) is located within an area which includes the 5' LTR and the first 350 bp of gag. Transduction efficiencies of vectors prepared without FIV vif and orf2 accessory gene expression did not differ substantially from those of vectors prepared with accessory gene expression in either dividing or nondividing cells. The requirement for FIV rev-RRE was, however, demonstrated by the inefficient production of vector particles in the absence of rev expression. Together, these results demonstrate the efficient transduction of nondividing cells in vitro by a multiply attenuated FIV vector and contribute to an understanding of the minimum requirements for efficient vector production and infectivity. In addition, we describe the ability of an FIV vector to deliver genes in vivo into hamster muscle tissue.

Animals↗

PubMed1999

Feline immunodeficiency virus vectors persistently transduce nondividing airway epithelia and correct the cystic fibrosis defect.

Several problems limit the application of gene transfer to correct the cystic fibrosis (CF) Cl(-) transport defect in airway epithelia. These include inefficient transduction with vectors applied to the apical surface, a low rate of division by airway epithelial cells, failure of transgene expression to persist, and immune responses to vectors or vector-encoded proteins. To address these issues, we used a feline immunodeficiency virus-based (FIV-based) vector. FIV vector formulated with a calcium chelator transduced fully differentiated, nondividing human airway epithelia when applied to the apical surface. FIV-based vector encoding the cystic fibrosis transmembrane conductance regulator cDNA corrected the Cl(-) transport defect in differentiated CF airway epithelia for the life of the culture (>3 months). When this approach was applied in vivo, FIV vector expressing beta-galactosidase transduced 1-14% of adult rabbit airway epithelia. Transduced cells were present in the conducting airways, bronchioles, and alveoli. Importantly, gene expression persisted, and cells with progenitor capacity were targeted. FIV-based lentiviral vectors may be useful for the treatment of genetic lung diseases such as CF. This article may have been published online in advance of the print edition.

Animals↗

PubMed1998

The psychological refractory period effect following callosotomy: uncoupling of lateralized response codes.

A callosotomy patient was tested in 2 dual-task experiments requiring successive speeded responses to lateralized stimuli. The patient showed a robust psychological refractory period (PRP) effect. Three aspects of the data indicate that, unlike for the control participants, the PRP effect for the split-brain patient should not be attributed to a response selection bottleneck. First, the patient did not show an increase in reaction time (RT) when the 2 tasks required responses from a common output system compared with when different output systems were used. Second, inconsistent stimulus-response mappings for the 2 tasks increased RTs for the control participants but had minimal effect on the performance of the split-brain patient. Third, the consistency manipulation was underadditive with stimulus onset asynchrony but was additive or overadditive for the normal participants. These results suggest that the persistent PRP effect following callosotomy should be attributed to a bottleneck associated with response initiation, a strategy adopted to comply with the task demands, or a combination of these factors.

Adult↗

PubMed1997

Dependence by any other name smells just as sweet: reply to van der Velde and van der Heijden (1997)

The hypothesis that people selectively attend to entire objects predicts that all attributes of an object will be reported either very accurately (if the object was attended) or very inaccurately (if it was unattended). Hence, reports of object attributes should show positive dependence. M. Monheit and J. Johnston (1994) have confirmed this prediction. F. van der Velde and A. H. C. van der Heijden (1997), however, have argued that dependence in the overall data is spurious. They advocate a model that partitions the data into 2 subsets, 1 for perception trials and 1 for guessing trials, each of which separately exhibits independence. Here, the authors argue that this treatment of guessing is misguided because, in effect, guesses are discarded rather than treated as failures of perception. The Monheit and Johnston analysis, on the other hand, is fundamentally sound and demonstrates precisely the kind of dependence predicted by the spatial attention hypothesis.

Attention↗

PubMed1996

Both codon context and leader length contribute to efficient expression of two overlapping open reading frames of a cucumber necrosis virus bifunctional subgenomic mRNA.

The importance of codon context and leader length in the translational regulation of p20 and p21 from the bifunctional 0.9-kb subgenomic mRNA cucumber necrosis virus was investigated. Nucleotide substitutions introduced into the -3 and +4 positions of the p21 AUG codon (where the A of the AUG is +1) verified that purines in these positions are favored and demonstrated the similar contribution of the -3 and +4 positions to the efficiency of initiation codon selection in plants. The effect of nucleotide substitutions in the +5 position, most clearly demonstrated when pyrimidines occupy the -3 and +4 positions, also provided direct insight into the influence of the +5 position in plants. The codon context of the upstream p21 initiation codon affected expression from the downstream p20 AUG codon. In addition, an increase in the length of the subgenomic mRNA leader decreased expression from the downstream p20 initiation site. These latter observations are in accordance with the "Kozak rules" for accession of internal AUG codons by leaky ribosomal scanning and provide the first example of an effect of leader length on the efficiency of translation initiation in a plant (viral) mRNA.

Base Sequence↗

PubMed1996

Perceptual repetition blindness effects.

Repetition blindness (RB) may reveal a new limitation on human perceptual processing. Recently, however, researchers have attributed RB to postperceptual processes. The standard rapid serial visual presentation (RSVP) paradigm used in most RB studies is open to such objections. The "single-frame" paradigm introduced by J. C. Johnston and B. L. Hale (1984) allowed investigation of RB with minimal memory demands. Participants made a judgment about whether 1 masked target word was the same or different than a posttarget probe. Confidence ratings permitted use of signal detection methods. In the critical condition for RB, a precue of the posttarget word was provided prior to the target stimulus so that the required judgment amounted to whether the target did or did not repeat the precue word. In control treatments, the precue was an unrelated word or a dummy. Results showed that perceptual sensitivity was significantly reduced in the RB condition relative to baseline control conditions. The data showed that RB can be obtained under conditions in which memory problems are minimal and perceptual sensitivity is assessed independently of biases. RB therefore can be a perceptual phenomenon.

Adult↗

PubMed1996

Laparoscopic cholecystectomy in the geriatric population.

OBJECTIVE: To assess effectiveness and conversion rates of inpatient laparoscopic cholecystectomy in older people living in the community. SETTING AND SUBJECTS: All acute care hospitals providing cholecystectomy in a single state. Medicare patients who underwent inpatient cholecystectomy in fiscal year 1994 in Arkansas. METHODS: A random sample comprising 449 of 2182 geriatric patients who underwent inpatient cholecystectomy in fiscal year 1994, stratified by hospital bed size, had charts reviewed for type of cholecystectomy performed, occurrence of conversion from a laparoscopic to an open cholecystectomy, surgical complications, and need for transfusion. RESULTS: Eighty-two percent of nonincidental cholecystectomies were initially laparoscopic. Total conversion rate for all inpatient laparoscopic cases was 20%. Forty-two percent of this group suffered acute cholecystitis with male patients exhibiting a higher rate of acute cholecystitis than female patients. Conversion rates for elective cholecystectomy for both sexes was between 13 and 14%. Conversion rate to an open procedures was 28% for patients with acute disease, with male patients again having a higher rate than female patients (40% vs 19%, P < .001). Surgical complications and intraoperative transfusions were rare. Conversion rates did not vary between large and small hospitals or among different age groups within the older population. CONCLUSIONS: Inpatient laparoscopic cholecystectomy is common in older people both for acute and chronic gallbladder conditions. Conversion rates ranged from 13% for elective cholecystectomy to 28% for acute disease. These rates are higher than published literature, which focuses on younger populations undergoing elective procedures. Audit committees need to be aware of this higher conversion rate in older people when assessing surgical proficiency.

Acute Disease↗

PubMed1995

Deletion analysis of the promoter for the cucumber necrosis virus 0.9-kb subgenomic RNA.

Sequences comprising the core promoter for the cucumber necrosis virus (CNV) 0.9-kb subgenomic RNA have been determined using deletion analysis and site-directed mutagenesis. The deletion studies indicate that the promoter lies within a region located 20 nucleotides upstream and 6 nucleotides downstream and including the subgenomic start site. Sequences further upstream or downstream of the core promoter do not appear to strongly affect promoter activity or viral RNA accumulation. Results of site-directed mutagenesis studies indicate that nucleotides immediately surrounding the subgenomic start site regulate promoter activity. Comparison of sequences within the CNV promoter region with the corresponding region of other tombusviruses shows that the tombusvirus promoter shares a region of near complete identity in 14 of the 26 core promoter nucleotides. Little similarity exists between the CNV 0.9-kb subgenomic RNA promoter and the region surrounding the transcription initiation site for the CNV 2.1-kb subgenomic RNA. Likewise, limited similarity occurs with the 5' region of CNV genomic RNA. Sequences similar to the ICR2-like motifs found in the promoters of several alphavirus-like (supergroup III) plant and animal viruses are not apparent. This study represents the first analysis of a subgenomic promoter from a member of supergroup II of positive-strand RNA viruses.

Base Sequence↗

PubMed1995

Mutational analysis of the cucumber necrosis virus coat protein gene.

A series of frameshift, deletion, and inversion mutations were made in the coat protein (CP) gene of the icosahedral cucumber necrosis tombusvirus (CNV) to investigate the role of the CP protruding (P) domain in the production of virus particles and, also, to investigate the basis for the accumulation of CP deletion derivatives previously reported in plants inoculated with PD(-), a P-domainless CNV CP mutant. P-domainless coat protein subunit could be detected in extracts of CP mutant-infected plants; however, virus-like particles could not, suggesting that the P domain is essential for tombusvirus particle assembly and/or stability. In addition, each of the P-domain mutants analyzed invariably produced coat protein deletion derivatives in infected plants whereas shell domain mutants rarely produced deletion derivatives. Finally, P-domain inversion and deletion mutants accumulated deletion derivatives very rapidly in comparison to P-domain frameshift mutants. Protoplast studies show that PD(-) RNA inoculum does not undergo further deletion in infected protoplasts, suggesting that PD(-) CP deletion derivatives preferentially accumulate in plants because they have a greater capacity for cell-to-cell movement.

Base Sequence↗

PubMed1994

Spatial attention to arrays of multidimensional objects.

Encoding briefly displayed arrays of multidimensional objects appears to require selective attention, but this hypothesis is challenged by M. J. Nissen's (1985) finding that properties of an object are reported independently. Selective attention to some objects but not others should produce positive dependence. Theoretical analysis shows that deviations from independence would have been difficult to observe in Nissen's data because of high guessing rates and small sample sizes. Four new experiments showing strong positive dependence in property reports are described. Deviations from independence were highly significant for most Ss. Quantitative modeling shows that selective attention to subsets of objects would produce about the amount of dependence obtained. Rather than challenging attention theories, the amount of dependence in encoding multidimensional objects is consistent with selective attention to either objects or locations.

Attention↗