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At least 469 records · Page 26Linked to original sources
PubMed2005

Amino acid supplementation, controlled oxygen limitation and sequential double induction improves heterologous xylanase production by Pichia stipitis.

Heterologous endo-beta-1,4-xylanase was produced by Pichia stipitis under control of the hypoxia-inducible PsADH2-promoter in a high-cell-density culture. After promoter induction by a shift to oxygen limitation, different aeration rates (oxygen transfer rates) were applied while maintaining oxygen-limitation. Initially, enzyme production was higher in oxygen-limited cultures with high rates of oxygen transfer, although the maximum xylanase activity was not significantly influenced. Amino acid supplementation increased the production of the heterologous endo-beta-1,4-xylanase significantly in highly aerated oxygen-limited cultures, until glucose was depleted. A slight second induction of the promoter was observed in all cultures after the glucose had been consumed. The second induction was most obvious in amino acid-supplemented cultures with higher oxygen transfer rates during oxygen limitation. When such oxygen-limited cultures were shifted back to fully aerobic conditions, a significant re-induction of heterologous endo-beta-1,4-xylanase production was observed. Re-induction was accompanied by ethanol consumption. A similar protein production pattern was observed when cultures were first grown on ethanol as sole carbon source and subsequently glucose and oxygen limitation were applied. Thus, we present the first expression system in yeast with a sequential double-inducible promoter.

Aerobiosis↗
PubMed2004

Measurement and numerical analysis of flammability limits of halogenated hydrocarbons.

Flammability limits measurement was made for a number of halogenated compounds by the ASHRAE method. Most of compounds measured are the ones for which discrepancy was noted between the literature values and predicted values of flammability limits. As a result, it has been found that most of the newly obtained values of flammability limits are not in accordance with the literature values. Numerical analysis was carried out for a set of flammability limits data including the newly obtained ones using a modified analytical method based on F-number scheme. In this method, fitting procedure was done directly to flammability limits themselves instead of fitting to F-number. After the fitting process, the average relative deviation between the observed and calculated values is 9.3% for the lower limits and 14.6% for the upper limits.

Fires↗
PubMed2004

Effect of repeal of the national maximum speed limit law on occurrence of crashes, injury crashes, and fatal crashes on Utah highways.

Speed limits were increased in Utah and other States after repeal of the national maximum speed limit law (NMSL) in 1995. This study analyzed effects of the increased speed limit on Utah highways on crash rates, fatality crash rates, and injury crash rates. Annual (1992-1999) rates of crashes, fatality crashes, and injury crashes for the following highway categories were calculated: urban Interstate segments (current speed limit 60-65 miles per hour (mph)); rural Interstate segments (current speed limit 70-75 mph); 55 mph rural non-Interstate highway segments; and high-speed non-Interstate highways (current speed limit 60-65 mph). Data were analyzed using autoregressive integrative moving average intervention time series analysis techniques. There were significant increases in total crash rates on urban (60-65 mph) Interstate segments (confounded by extensive ongoing highway construction on these highways), and in fatal crash rates on high-speed (60-65 mph) rural non-Interstate segments. The following variables were unaffected: total, fatality, and injury crash rates on rural Interstate segments; fatality and injury crash rates on urban Interstate segments; total and injury crash rates on high-speed non-Interstate segments. These results show an adverse effect on crash occurrence for subsets of crash types and highways, but do not show a major overall effect of NMSL repeal and increased speed limit on crash occurrence on Utah highways.

Accidents, Traffic↗
PubMed1994

Reduction-of-dimensionality kinetics at reaction-limited cell surface receptors.

It has been suggested for several years that reactions between ligands and cell surface receptors can be speeded up by nonspecific adsorption of the ligand to the cell surface followed by two-dimensional surface diffusion to the receptor, a mechanism referred to as "reduction-of-dimensionality" (RD) rate enhancement. Most of the theoretical treatments of this and related problems have assumed that the receptor is an irreversibly absorbing perfect sink. Such receptors induce a depletion zone of ligand probability density around themselves. The reaction rate in this case (called "diffusion-limited") is limited only by the time required for ligands to diffuse through this depletion zone. In some cases, however, the receptor may be far from "perfect" such that a collision with a ligand only rarely leads to binding. Receptors then do not create significant local depletion zones of ligand probability density, and the reaction rate becomes strongly affected by the (small) probability of reaction success per diffusive encounter (the "reaction-limited" case). This article presents a simple theory of RD rate enhancement for reaction-limited receptors that are either reversible or irreversible binders. In contrast to the diffusion-limited theories, the reaction-limited theory presented here: (a) differs quantitatively from diffusion-limited models; (b) is simple and algebraic in closed form; (c) exhibits significant rate enhancement in some realistic cases; (d) depends strongly on the actual Brownian rather than pure diffusive nature of the ligand's motion; (e) depends (for irreversibly binding receptors only) on the kinetic rates (not just equilibria) of reversible adsorption to nontarget regions, in contrast to some previous approximate theories of reduction of dimensionality; and (f) is applicable to actual ligand/receptor systems with binding success probabilities at the opposite extreme from the perfect sink/diffusion-limited models.

Adsorption↗
PubMed1994

Flow limitation during tidal expiration in symptom-free infants and the subsequent development of asthma.

During a longitudinal study of lung function and airway responsiveness in a cohort of healthy infants, we identified a subgroup of symptom-free infants at the age of 1 month with flow limitation during tidal expiration. We report a 2-year follow-up of 252 infants who were first studied at 1 month of age. Maximal flow at functional residual capacity (VmaxFRC) was measured from a forced expiratory flow-volume curve by the rapid thoracic compression technique. The pattern of tidal breathing was assessed with the ratio of the time to reach maximal expiratory flow during expiration to the total expiratory time (Tme/Te ratio). Histamine inhalation challenge was used to determine the level of airway responsiveness. Compliance and resistance of the total respiratory system were measured from a passive expiration after occlusion at end inspiration. Data regarding the family history of asthma, atopy, and parental smoking were obtained by questionnaire. Flow limitation was considered present when the forced expiratory flow did not exceed tidal flow at functional residual capacity. Nineteen infants were identified with flow limitation at 5 weeks of age; all had a family history of asthma, atopy, and/or parental smoking. These 19 infants were compared with 35 infants with no family history of asthma or parental smoking and 38 gender-, history-, and age-matched control infants without flow limitation during tidal expiration. At the age of 1 month, the flow-limited group had reduced VmaxFRC, Tme/Te, and respiratory compliance and increased respiratory resistance. At 6 and 12 months of age, although no longer flow limited, these infants still had significantly reduced lung function and increased airway responsiveness. Flow limitation in early life was also significantly associated with the development of physician-diagnosed asthma by the age of 2 years (odds ratio, 7.4; 95% confidence interval, 1.4 to 35.2). Infants with abnormal lung function soon after birth may have a genetic predisposition to asthma or other airway abnormalities that predict the risk of subsequent lower respiratory tract illness.

Asthma↗
PubMed1982

Limited joint mobility in diabetes mellitus of childhood: natural history and relationship to growth impairment.

We report a prospective study of the recently recognized complication of limited joint mobility in childhood diabetes, summarizing data collected over the seven years after the initial description of this sign. Of 309 patients, ranging in age from 1 to 28 years, 30% had limited joint mobility. No race or sex influence on expression of limited joint mobility was found; its appearance was temporally more influenced by age than by duration of diabetes. Of 142 patients with diabetes onset before puberty and of longer than three years' duration, 74 had limited joint mobility. Disproportionate distribution of height percentiles for age characterized this entire group, but those with limited joint mobility had four times the skewing of those without (74 vs 37% below the twenty-fifth percentile). The presence or absence of thyroid microsome or islet cell antibodies did not relate significantly to limited joint mobility. Diabetes control, assessed subjectively by clinical estimation and objectively by hemoglobin A1 levels, was generally unrelated to the joint findings. For patients with diabetes duration less than five years, there was a significant association between hemoglobin A1 and limited joint mobility, but the variability in values explained by this association was small (11%).

Adolescent↗
PubMed2002

Photosynthetic energy conversion under extreme conditions--I: important role of lipids as structural modulators and energy sink under N-limited growth in Antarctic sea ice diatoms.

The availability of dissolved nutrients such as nitrate under extreme low temperatures is a strong determinant in the development and growth of ice diatoms. Consequently we investigated regulation of photosynthesis in a mixed culture of three diatom species, which grew in chemostats at -1 degrees C, 15 micromol photons m(-2) s(-1) under N-limitation. When nitrogen is limiting, pigment-protein complexes are one of the most affected structures under low-light conditions. The loss of integral polar thylakoid components destabilized the bilayer structure of the membrane with consequences for lipid composition and the degree of fatty acid desaturation. N-Limitation caused a decrease in monogalactosydiacylglycerol (MGDG) and a simultaneous increase in bilayer forming digalactosyldiacylglycerol (DGDG). Their ratio MGDG:DGDG decreased from 3.4 +/- 0.1 to 1.1 +/- 0.4, while 20:5 n-3 fatty acids of chloroplast related phospholipid classes such as phosphatidylglycerol (PG) increased under N-limitation. These data reveal that lipids are important components, required to sustain membrane structure under a deficiency of integral membrane bound proteins and pigments. Nonetheless, energy conversion at photosystem II is still affected by N-limitation despite this structural regulation. Photosynthetic quantum yield (F(v)/F(m)) and electron transport rates decreased under N-limitation caused by an increasing amount of electron acceptors (second stable electron acceptor = Q(B)) which had slower reoxidation kinetics. The energy surplus under these conditions is stored in triacylglycerols, the main energy sink in Antarctic sea ice diatoms under N-limitation.

Antarctic Regions↗
PubMed2003

Normal limits of the electrocardiogram in Chinese subjects.

BACKGROUND: Accurate normal limits of the electrocardiogram (ECG) are the basis on which diagnostic criteria are developed. The ECG, however, is subject to age- and sex-variations and may also be racially determined. Studies into normal ECG limits for the Chinese, comprising one fifth of the world population, are few and have their limitations. We have undertaken to establish normal limits of the ECG from a large sample of healthy Chinese subjects. METHODS: Standard simultaneous 12-lead ECGs from 5360 apparently healthy Chinese subjects (3614 men and 1746 women, ages ranging from 18 to 84 years) were collected with a modern digital recorder and processed with a well-validated ECG computer program. The medians, lower limits (2nd percentile) and upper limits (98th percentile) of various ECG measurements were calculated and age and sex differences examined. RESULTS: Significant age trends were present in, for example, P-wave duration, QTc interval, and frontal QRS axis, with concomitant changes of R amplitudes in the extremity leads. Sex differences existed for heart rate, interval durations, the Sokolow and Cornell indices, and QRS and ST-T amplitudes in different leads. Notably, left-precordial R-wave amplitudes in women increased with age; the Sokolow index showed a clearer age trend for men than for women, the reverse being true for the Cornell index. Some of these findings are at odds with established diagnostic ECG criteria. CONCLUSIONS: Normal ECG limits of Chinese subjects show marked age and sex differences. This merits the definition and use of age- and sex-specific ECG criteria for a Chinese population.

Adolescent↗
PubMed2003

Gender differences in pain characteristics of chronic stable angina and perceived physical limitation in patients with coronary artery disease.

Chronic stable angina pectoris, the chest pain associated with reversible myocardial ischemia has detrimental effects on health-related quality of life, particularly in women. The limited research on gender differences in chronic stable angina suggests that angina may be experienced differently in women and that women report greater functional disability related to angina symptoms. No studies have examined gender differences in chronic stable angina from a multidimensional pain perspective or have included reliable and valid measures of pain that would facilitate comparing chronic angina patients with other chronic pain populations. The purpose of this descriptive study was to examine gender differences in characteristics of chronic stable angina using the short-form McGill pain questionnaire (SF-MPQ) and to explore relationships among these pain characteristics and perceived limitation in performing physical activities in patients with coronary artery disease (CAD) (physical limitation subscale of the Seattle angina questionnaire). One hundred and twenty-eight subjects (30.5% women) with stable CAD and angina pectoris documented by a cardiologist completed study questionnaires in an outpatient cardiology clinic. Results of the study suggest that men and women with chronic stable angina had more similarities than differences in chest pain characteristics. No significant gender differences were demonstrated in total sensory or affective intensity scores, the present pain intensity index, or the number of pain words chosen. However, women did report significantly greater pain intensity on the SF-MPQ visual analogue scale. Women were also significantly more likely to describe their chronic angina as 'hot-burning' and 'tender' and to have greater intensity of pain for these two descriptors. Despite the similarities in pain characteristics, women reported greater physical limitation related to anginal pain. The variables of social status and years diagnosed with CAD significantly interacted with gender in predicting physical limitation suggesting that gender-specific models of physical limitation in angina patients need to be explored. To our knowledge, this is one of the first studies that has assessed chronic anginal pain using a reliable and valid generic pain instrument. More research is needed to better understand the nature of gender differences in functional limitation secondary to anginal pain and the physiologic, cognitive-perceptual and psychosocial mechanisms that lead to angina-related functional disability.

Activities of Daily Living↗
PubMedDate not supplied

[Limiting factors of exercise capacity in patients with COPD].

Chronic Obstructive Pulmonary Disease (COPD) is a major cause of morbidity and mortality worldwide. Moderate to severe COPD patients demonstrate severe impairments in exercise performance in daily activities, significantly affecting their quality of life. There are several causes for this limitation found in literature: air-flow limitation, lung hyperinflation, respiratory and peripheral muscles weakness, among others. In this study we intended to identify the potentially relevant factors that influence exercise performance in a group of moderate to severe COPD patients. We studied 24 male patients, 64,13 + 8,46 years old (46-83 years), FEV1: 46,96 + 12,99% predicted, FRC: 144,71 + 26,86% predicted, DLCO: 69,88 + 16,49 % predicted, PaO2: 78,25 + 7,82 mmHg, PaCO2: 40,78 + 4,28 mmHg. Patients performed an incremental symptom-limited cycle exercise. We correlated rest and exercise lung function parameters with peak oxygen uptake, maximal work rate and time span to exertion. The main contributors to exercise limitation were gas exchange abnormalities, ventilatory limitation and smaller values of body mass index. Rest lung hyperinflation didn't correlate with exercise performance. Dynamic exercise hyperinflation contributed greatly to exercise intolerance, through progressive restriction to tidal volume expansion necessary to deal with increasing exercise metabolic demands. Rest lung function parameters didn't correlate with exercise performance, stressing the importance of cardio-pulmonary exercise testing in the detection of exercise limitation factors in each patient. The identification of exercise limitation factors will certainly contribute to towards defining the best therapeutic approach in COPD patients.

Adaptation, Physiological↗
PubMed2005

Influence of the limited interchange rule on injury rates in sub-elite Rugby League players.

This study investigated the incidence of injury in sub-elite Rugby League players before and after the introduction of the limited interchange rule. The incidence of injury was prospectively studied in one sub-elite Rugby League club over three competitive seasons. Two seasons were played under the unlimited interchange rule, while the third season was played under the limited interchange rule. Players participated in 91 matches under the unlimited interchange rule and 44 matches under the limited interchange rule. Injury was defined as any pain, disability or injury that occurred as a result of a competition game that caused the player to miss a subsequent game. The relative risk (RR) of injury significantly decreased (RR = 0.70 [0.65 to 0.75], P<0.05) following the introduction of the limited interchange rule, with the incidence of injury decreasing from 72.5 (58.2 to 86.8) per 1000 playing hr under the unlimited interchange rule to 51.0 (33.8 to 68.1) per 1000 playing hr under the limited interchange rule. The risk of sustaining thigh and calf injuries (RR= 0.27 [0.12 to 0.59], P < 0.05), muscular strains (RR= 0.23 10.17 to 0.31]., P<0.05), and high intensity running injuries (RR= 0.16 [0.04 to 0.691, P<0.05) was significantly reduced following the introduction of the limited interchange rule. These findings demonstrate that the risk of injury in sub-elite Rugby League players is significantly reduced following the introduction of the limited interchange rule. The reduced injury risk may reflect a fatigue-induced reduction in match speed and impact forces associated with physical collisions and tackles.

Athletic Injuries↗
PubMed2004

Neuropsychology of academic and behavioural limitations in school-age survivors of bacterial meningitis.

Neuropsychological impairments possibly underlying academic and/or behavioural limitations were studied in 149 school-age survivors of bacterial meningitis, 68 with and 81 without academic and/or behavioural limitations. Academic limitations affected mathematics, reading, and writing. Behavioural limitations were inferred from scores in the clinical range on the Child Behaviour Checklist. These children had been selected from a cohort of 674 children (57% males) who had recovered from non-Haemophilus influenzae type B bacterial meningitis and who had a mean age at infection of 2 years 4 months (range 1mo to 9y 5mo). They had neither 'complex onset' meningitis, prior cognitive or behavioural problems, nor severe disease sequelae. They were assessed with standardized assessment methods a mean of 7.8 years (range 4 to 10.4) after meningitis. Children with limitations (32% of the cohort) performed generically poorly on measures of cognitive functioning, speed, and motor steadiness, rather than having impairments in specific neuropsychological domains. The presence of two or more minor neurological signs was more frequent in the group with than in the group without limitations (30% versus 9%); this may explain the relatively poor speed and motor steadiness of the group with limitations.

Achievement↗
PubMed2002

Steady-state limiting currents at finite conical microelectrodes.

The investigation of steady-state diffusion-limiting currents at finite conical microelectrodes is reported. Such electrodes are of particular interest as probes in studies of kinetic reactions, measurements in microenvironments, and high-resolution electrochemical imaging. The diffusion-limiting currents were calculated using numerical (finite element) analysis and compared to those obtained at inlaid disk and hemispheroidal microelectrodes. Time-dependent simulations demonstrating the approach of the diffusion current to a steady-state value are also reported. The steady-state diffusion-limiting currents obtained were found to be a strong function of the electrode geometry, including the aspect ratio of the cone and the thickness of the insulating sheath. Thus, simple, approximate analytical expressions which account for these geometrical dependencies in the simulated steady-state diffusion-limited currents are also reported. As a limiting case, an analytical approximation was obtained for the steady-state current to a microdisk as a function of the insulator thickness. The use of these approximate equations in calculating electrode radii from steady-state diffusion-limiting currents is demonstrated, and good agreement was found with previously reported experimental studies. Use of the frequently implemented hemispherical theory to analyze steady-state diffusion-limiting currents obtained with finite conical microelectrodes is shown to result in an experimentally acceptable underestimation of the electrode radius.

Journal Article↗
PubMed1983

Rate-limiting step: a quantitative definition. Application to steady-state enzymic reactions.

The generality of the concept of a rate-limiting step in enzymic reactions recently has been questioned [Northrop, D. B. (1981) Biochemistry 20, 4056-4061] because, in simulated isotopic experiments, alterations of the step identified as rate limiting by current definitions do not consistently affect Vmax in the expected manner. In this paper a definition for a rate-limiting step is posed that eliminates such inconsistencies while the thrust of the original concept is retained. Thus, for any steady-state process involving a linear reaction sequence the rate-limiting step is taken as the "most sensitive" step, or the step which, if perturbed, causes the largest change in overall velocity, v. In both V and V/K enzymic systems the most sensitive step is identified by the relative magnitude of the sensitivity function, SFj, for the various forward steps. If forward steps are identified by kj, SFj is equal to delta(1/v)/[delta(1/kj)/(1/kj)], when the equilibrium constant for the step involving kj is maintained constant. The corresponding sensitivity index, SIj, is a normalized function of SFj (the normalizing factor is v) such that the sum of the values for SIj is equal to 1. In addition, there is an exact relationship between the sensitivity index for the isotopic step and the fraction of the intrinsic isotopic effect that is expressed in the overall rate of the reaction (when the intrinsic effect is taken as the fractional difference in reciprocal rate constant produced by the isotope). A procedure is described for approximating the sensitivity function for the various steps in a reaction sequence on the basis of the Gibbs energy profile for that reaction and thus identifying the most sensitive step. This approach also is used to consider the general question of whether a rate-limiting step should be specified for a multistep enzymic reaction. Identifying the rate-limiting step as the most sensitive step in a reaction sequence means that no aspect of the concept of minimal rate should be automatically considered as a property of a rate-limiting step.

Enzymes↗
PubMed2001

Impact of a 10-year nation-wide alcohol campaign on knowledge of sensible drinking limits in Denmark.

In Great Britain and in Denmark, strong efforts have been made to influence knowledge on upper threshold for hazardous drinking. In Denmark, a campaign has been repeated every week 40 from 1990 to 2000 with information on the sensible drinking limits of 21 drinks per week for men and 14 drinks per week for women. The aim of this study was to examine the effect of this ongoing campaign on the level of knowledge of sensible drinking limits for men and women. Random representative samples of 1030 adult Danes were telephone interviewed each year during 1994-1999. Our main finding was that the level of knowledge of sensible drinking limits for own sex increased in all subsets of the population throughout the period. However, at the end of the study period (1999) a total of 80% of highly educated young (18-25 years) men knew sensible drinking limits for own sex, while only 35% of uneducated older (more than 65 years) men had knowledge on sensible drinking limits. The proportions were similar among women. Subjects admitting an intake higher than sensible for own sex, i.e. 21 and 14 drinks per week, respectively, had the highest knowledge of these drinking limits. We conclude that public health campaigns, such as the sensible drinking limit campaign, certainly has an impact on level of awareness in the general population. Furthermore, those drinking more than 21 and 14 drinks per week, respectively, are reached by these campaigns.

Adult↗
PubMed2004

AT1 receptor blockade limits myocardial injury and upregulates AT2 receptors during reperfused myocardial infarction.

Persistent left ventricular (LV) dysfunction after reperfused myocardial infarction (RMI) is a significant problem and angiotensin II (AngII) type 1 receptor (AT1R) blockers (ARBs) may limit reperfusion injury involving upregulation of AngII type 2 receptors (AT2R). To determine whether ARBs valsartan and irbesartan limit reperfusion injury and upregulate AT2R protein during RMI, we randomized dogs with anterior RMI (90 min ischemia; 120 min reperfusion) to 4 groups [valsartan (n = 6); irbesartan (n = 9); vehicle controls (n = 8); and sham (n = 6)] and measured serial in vivo hemodynamics, LV systolic and diastolic function, and inhibition of AngII pressor responses to the ARBs, and ex vivo infarct size, and regional AT1R and AT2R protein expression at the end of the reperfusion. Compared to the control group, both ARBs significantly limited the increase in left atrial pressure, promptly limited the deterioration of LV dP/dtmax, dP/dtmin, ejection fraction and diastolic function, limited infarct expansion and thinning, and limited infarct size. Importantly, both ARBs increased AT2R protein in the postischemic reperfused zone, with no change in AT1R protein. There were no changes in the sham group. The results suggest that limitation of myocardial injury associated with AT1R blockade combined with upregulation of AT2R protein expression contributes to the cardioprotective effects of ARBs during RMI. This beneficial effect of ARBs on persistent LV dysfunction after RMI should be evaluated in the clinical setting to determine the relative benefit of ARBs in patients who undergo reperfusion therapy for acute coronary syndromes.

Angiotensin II Type 1 Receptor Blockers↗
PubMed2000

Detection of inspiratory flow limitation during sleep by computer assisted respiratory inductive plethysmography.

The potential of respiratory inductive plethysmography (RIP) to detect inspiratory flow limitation during sleep was investigated. Sixteen sleep apnoea patients underwent polysomnography. Airflow by a flowmeter attached to a nasal mask, oesophageal and mask pressure were recorded along with calibrated RIP. Presence of inspiratory flow limitation was defined by constant or decreasing flow without pressure dependence throughout significant portions of inspiration, its absence by a linear or mildly alinear pressure:airflow relationship. Based on this standard, three of various computerized RIP derived parameters, with highest performance to detect flow limitation, were identified. They were combined to an inspiratory flow limitation, (IFL)-Index(RIP), which was validated prospectively in another 10 sleep apnoea patients. RIP derived fractional inspiratory time, peak to mean inspiratory flow ratio, and ribcage contribution to tidal volume had the highest accuracy to detect flow limitation (area under the receiver operating characteristic (ROC) curves 0.81, 0.76, 0.76, respectively, 160 comparisons). Prospective validation revealed an area under the ROC curve for the IFL-Index(RIP) to detect flow limitation of 0.89 (95% confidence interval 0.85 to 0.93, 200 comparisons) with sensitivity and specificity at the point of equality of 80%. It is concluded that inspiratory flow limitation may be assessed by computer assisted analysis of respiratory inductive plethysmography derived breathing patterns with clinically acceptable accuracy.

Adult↗
PubMed1978

Letter identification as a function of type of perceptual limitation and type of attribute.

It is argued that the distribution of errors in letter identification depends on two factors: (a) whether the set of letters is defined by features that exist or do not exist or by dimensions that exist at some positive value, and (b) whether errors are produced by process limitation in which the letter patterns are distorted or by state limitation in which there is inadequate energy. A specific hypothesis tested was that error distributions reflect the attribute structure under both types of limitation if dimensions define the letter set, but only under a process limitation if features define the letter set. Under a state limitation, feature set errors are primarily produced by a loss of features, so that a letter with more features is called a letter with fewer features more often than conversely. An experiment completely validated the hypothesis under test. In addition, the relative discriminabilities of two dimensions defining a dimension set of letters was reversed from state to process limitation. Thus the attribute structure derived from error distributions is not invariant across types of perceptual limitation, nor are distances between letter pairs always symmetric.

Discrimination, Psychological↗