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PubMedDate not supplied

Visuo-tactile representation of near-the-body space.

Here we report findings from neuropsychological investigations showing the existence, in humans, of intersensory integrative systems representing space through the multisensory coding of visual and tactile events. In addition, these findings show that visuo-tactile integration may take place in a privileged manner within a limited sector of space closely surrounding the body surface, i.e., the near-peripersonal space. They also demonstrate that the representation of near-peripersonal space is not static, as objects in the out-of-reach space can be processed as nearer, depending upon the (illusory) visual information about hand position in space, and the use of tools as physical extensions of the reachable space. Finally, new evidence is provided suggesting the multisensory coding of peripersonal space can be achieved through bottom-up processing that, at least in some instances, is not necessarily modulated by more "cognitive" top-down processing, such as the expectation regarding the possibility of being touched. These findings are entirely consistent with the functional properties of multisensory neuronal structures coding near-peripersonal space in monkeys, as well as with behavioral, and neuroimaging evidence for the cross-modal coding of space in normal subjects. This high level of convergence ultimately favors the idea that multisensory space coding is achieved through similar multimodal structures in both humans and non-human primates.

Animals↗

PubMed2004

Gradients of detection in neglect: comparison of peripersonal and extrapersonal space.

Previous studies of target-cancellation performance in visuospatial neglect patients have reported lateral (left-right) and radial (near-far) gradients of attentional ability. The purpose of the present study was to replicate the reported attentional gradients in peripersonal space (within arms reach) and to examine whether lateral gradients of detection also appear in extrapersonal space (beyond arms reach), using equivalent tasks with no manual requirement. The relationship between radial gradients in peripersonal space and neglect severity (degree of lateral gradient) in extrapersonal space was also of interest. Right-hemisphere stroke subjects, with and without neglect, and healthy control subjects named visual targets on scanning sheets placed in peripersonal and extrapersonal space. The neglect group showed lateral gradients of increasing target detection from left to right in both peripersonal and extrapersonal space, which were not evident in the performance of either of the control groups. Double dissociations of neglect severity in peripersonal and extrapersonal space were also found in analyses of individual performance. Lesion analyses showed that peripersonal neglect was related to dorsal stream damage and extrapersonal neglect was related to ventral stream damage. Group analyses showed no significant radial gradients in peripersonal space in the three groups. In addition, while analyses of some individuals found significant near-far and far-near radial gradients, there was no correlation between radial gradients in peripersonal space and neglect severity in extrapersonal space. These results are discussed in terms of theorised hemispheric mechanisms of spatial attention and the relationship of neglect in the two co-ordinate spaces to the extent and location of damaged neurons in the right hemisphere.

Adult↗

PubMed2001

[Mechanism of development of space motion sickness].

Astronauts and scientists are scheduled to stay aboard the International Space Station (ISS) for three-month periods, and various problems relating to the human ability to live in space for such long periods of time, as well as medical problems, are being studied. For the crews that have operated and worked on the US space shuttle, the longest time spent in the gravity-free (accurately speaking, microgravity) environment of space has been about two weeks. Even such short periods have generated reports of various physical changes and symptoms caused by the absence of gravity. Particularly striking effects are circulatory system changes, muscular atrophy and decalcification of bones. In addition, serious problems arise during the time in space due to the symptoms of space motion sickness, caused by neuro-otological changes. Space motion sickness is experienced by nearly 70% of the first-time astronauts, in the form of such symptoms as nausea, and vomiting. It is said that space motion sickness develops at the time of adaptation of the body to the gravity-free environment. Unlike motion sickness on Earth, space motion sickness is characterized by a feeling of fullness of the head, a hot face and reduced sweating. The provocative factors include movement of the head in the pitch and roll directions and the unusual visual field. This paper reviews the research that has been carried out to date on space motion sickness, and its counter measures comprehensively, in terms of the changes in the otolith organ as well as asynchronization of information between the movements of the head and eyeballs, the deep sensations and body fluid shifts. Other problems, which may be encountered as a result of yet longer stays in space, are also discussed.

Adaptation, Physiological↗

PubMedDate not supplied

Canada and the International Space Station program: overview and status.

The twelve months since IAF 2000 have been perhaps the most exciting, challenging and rewarding months for Canada since the beginning of our participation in the International Space Station program in 1984. The highlight was the successful launch, on-orbit check out, and the first operational use of Canadarm2, the Space Station Remote Manipulator System, between April and July 2001. The anomalies encountered and the solutions found to achieve this success are described in the paper. The paper describes, also, the substantial progress that has been made, during the twelve months since IAF 2000, by Canada as it continues to complete work on all flight-elements of its contribution to the International Space Station and as we transition into real-time Space Station operations support and Canadian utilization. Canada's contribution to the International Space Station is the Mobile Servicing System (MSS), the external robotic system that is key to the successful assembly of the Space Station, the maintenance of its external systems, astronaut EVA support, and the servicing of external science payloads. The MSS ground segment that supports MSS operations, training, sustaining engineering, and logistics activities is reaching maturity. The MSS Engineering Support Center and the MSS Sustaining Engineering Facility are providing real-time support for on-orbit operations, and a Canadian Payloads Telescience Operations Center is now in place. Mission Controllers, astronauts and cosmonauts from all Space Station Partners continue to receive training at the Canadian Space Agency. The Remote Multi Purpose Room, one element of the MSS Operations Complex, will be ready to assume backroom support in 2002. Canada has completed work on identifying its Space Station utilization activities for the period 2000 through 2004. Also during the past twelve months the CSA drafted and is proceeding with the approval of a Canadian Space Station Commercialization Policy. Canadian astronauts have now participated in three ISS assembly missions--Julie Payette on STS-96, Marc Garneau on STS-97, and Chris Hadfield on STS-100 in April 2001 during which he performed Canada's first EVA and the successful installation of the Space Station Remote Manipulator System.

Astronauts↗

PubMedDate not supplied

CASH 2021: commercial access and space habitation.

Issues about commercialization of space have been a growing concern in the past decade for the space community. This paper focuses on the work from a team of 51 students attending the Summer Session Program of the International Space University in Bremen, Germany. CASH 2021 (Commercial Access and Space Habitation) documents a plan that identifies commercial opportunities for space utilization that will extend human presence in space, and will chart the way forward for the next 20 years. The group selected four commercial sectors that show the most promise for the future: tourism, entertainment, space system service, assembly and debris removal, and research and development/production. The content of this document presents the results of their research. Historical activities in each of the commercial sectors are reviewed along with the current market situation. To provide a coherent background for future commercialization possibilities a scenario has been developed. This scenario includes a postulated upon ideal future and includes social, political and economic factors that may affect the space industry over the timeline of the study. The study also presents a roadmap, within the limited optimistic scenario developed, for the successful commercialization of space leading to future human presence in space. A broad range of commercially viable opportunities, not only within the current limits of the International Space Station, but also among the many new developments that are expected by 2021 are discussed.

Agriculture↗

PubMedDate not supplied

On the contribution of space medicine in the public health care.

With the beginning of space era, a new branch of medicine has arisen and has been developing along with human exploration of outer space. And even though space medicine mainly faces the same problems as traditional medicine--cosmonauts health care and their high efficiency--this branch, has its own features, associated with the unusual factors of space flight, of which weightlessness is the major one. During the development of manned cosmonautics (duration of a human stay in space has reached already 438 days), methods of cosmonauts medical support and monitoring of their condition have been developed, knowledge of human possibilities and methods of process of organism adaptation to various and frequently severe conditions of external environment have increased. All this led to the fact that nowadays space medicine can become useful for improvement of human health care not only in space but also on the Earth. Moreover, the problem of implementation of cosmonautics achievements, and in particular of space medicine, in practice of public health care presents one of the most important issues concerning human health care. It is also connected with public opinion which is more and more concerned about the efficiency of significant expenses on space activities, especially lately. People often are set by the questions: what has space given, what fruits has space research provided to mankind, which results of this research can be used on the Earth already today for improvement of their life, for discussion of many difficult earthly problems? In terms of using cosmonautics possibilities, its achievements for health care and treatment, it is possible to define a few branches, in which purposeful studies are carried out.

Aerospace Medicine↗

PubMed1998

Development of space-fertilized eggs and formation of primordial germ cells in the embryos of Medaka fish.

In the second International Microgravity Laboratory (IML-2) mission in 1994, four small Japanese killifish (Medaka, Oryzias latipes) made a space travel of 15 days aboard a space shuttle. These four adult Medaka fish successfully mated in space for the first time among vertebrate animals. Moreover, the eggs they laid developed normally, at least in their external appearance, hatching as fry (baby fish) in space. Fish mated and laid eggs every day during the first week. Near the end of the mission most of the eggs had a well-developed body with two pigmented eyes. In total, 43 eggs were laid (detected), out of which 8 fry hatched in space, as truly 'space-originated' babies. A further 30 fry hatched within 3 days after landing. This is the normal hatching rate, compared with the ground-based data. Among the 8 space-originated fry, four were killed for histological sections, and germ cells at the gonadal region were counted for each fry. Their numbers were in the range of the germ cells of the normal control fry (ground-kept samples). Thus, as embryos developed normally in their external appearance, inside the embryos the formation of primordial germ cells took place normally in space, and their migration to the genital ridges was not hindered by microgravity. The two of the remaining space-originated fry have grown up and been creating their offspring in the laboratory. This proved that the primordial germ cells formed in space were also normal from a functional point of view. The four space-travelled adult fish re-started mating and laying eggs on the 7th day after landing and continued to do so every day afterward. Fertilization rate and hatchability of these eggs were as high as the eggs laid by the laboratory-kept fish. This fact implies that in gametogenesis of adult fish, there are no specific stages of germ cells extremely susceptible to microgravity.

Animals↗

PubMed2001

[Measurement of the Fowler dead space in patients with pulmonary emphysema using C18O2].

In patients with lung emphysema, changes in lung volumes as well as changes in airway resistance are well known. The change in airway resistance is caused by obstruction of central airways, which is supposed to reduce the respiratory dead space. Until now, it was not possible to measure the respiratory dead space in patients with lung emphysema using the method of Fowler [2], because in this method distinction of the three phases of an inert gas expirogram is essential. While this distinction is easy in healthy subjects (fig. 1; expirogram 3), the separation of the three phases in patients with lung emphysema is not possible due to gradual transition of phase II into phase III in these patients (fig. 1; expirogram 2). The use of C18O2 as tracer gas allows to separate phase II and phase III even if the patients have severe emphysema (fig. 1; expirogram 1). CO2 labeled with the stable oxygen isotope 18O (C18O2) is completely taken up in the gas exchanging region of the lung, but not from the conducting airways. Therefore C18O2 is only expired from the dead space of the lung, but not from the alveolar region. Hence, C18O2 allows exact measurement of the respiratory dead space in patients with lung emphysema. 21 healthy nonsmoking subjects and 29 patients with clinical signs of lung emphysema participated in this study. There was a good correlation between respiratory dead space, measured by the use of Ar-gas and C18O2-gas in healthy subjects (fig. 2). This indicates, that the use of C18O2 is a valid method to measure the functional dead space. As expected, there was also a correlation between the airway resistance and respiratory dead space in patients with lung emphysema (fig. 3), but not in healty subjects. There was no significant difference of the mean values of the respiratory dead space between these two groups (223 +/- 43 ml in healthy subjects vs. 227 +/- 52 ml in patients), even though there were large differences in airway resistance (0.20 +/- 0.10 kPa/l/s vs. 0.49 +/- 0.27 kPa/l/s). This may be due to a loss of alveolar function in the area of the terminal bronchioli, which is typical for emphysematous patients. This entails a shift of functional dead space towards lung periphery and therefore causes an increase of the volume of functional dead space. But this enlargement may be compensated by the volume reduction, caused by the airway obstruction. Hence, these two oppositional mechanisms may result in only minimal change of dead space volume.

Adult↗

PubMed1978

Space and frequency are represented separately in auditory midbrain of the owl.

1. The influence of sound location and sound frequency on the responses of single units in the midbrain auditory area (MLD) of the owl (Tyto alba) were studied using a movable sound source under free-field conditions. With this technique, two functionally distinct regions in MLD have been identified: a tonotopic region and a space-mapped region. 2. MLD units were classified according to their receptive-field properties: 1) limited-field units responded only to sound from a small, discrete area of space; 2) complex-field units exhibited two to four different excitatory areas separated by areas of reduced response or inhibition: 3) space-preferring units responded best to a certain area of space, but their fields expanded considerably with increasing sound intensities; 4) Space-independent units responded similarly to a sound stimulus regardless of its location in space. 3. Limited-field units were located exclusively along the lateral and anterior borders of MLD. These units were tuned to sound frequencies at the high end of the owl's audible range (5-8.7 kHz). They usually responded only at the onset of a tonal stimulus; but most importantly, the units were systematically arranged in this region according to the azimuths and elevations of their receptive fields, thus creating a physiological map of auditory space. Because of this latter, dominant aspect of its functional organization, this region is named the space-mapped region of MLD. 4. The receptive fields of units in the larger, medial portion of MLD were of the space-independent, space-preferring, or complex-field types. These units tended to respond in a sustained fashion to tone and noise bursts, and these units were arranged in a strict frequency-dependent order. Based on this last property, this region is named the tonotopic region of MLD. 5. Because of the salient differences in the response properties of their constituent units, it is argued that the space-mapped region and the tonotopic region are involved in different aspects of sound analysis.

Acoustic Stimulation↗

PubMed2003

Chromosome aberration dosimetry in cosmonauts after single or multiple space flights.

BACKGROUND AND AIMS: Cosmic radiation is one of the main hazards for manned space exploration. Uncertainty in radiation risk estimates for crews of long-term missions are very high, and direct biological measurements are necessary. We measured chromosomal aberrations in peripheral blood lymphocytes from 33 cosmonauts involved in space missions during the past 11 years. METHODS: Blood lymphocytes from the cosmonauts were stimulated to grow in vitro and were harvested at their first mitosis. Slides were either stained with Giemsa stain for dicentrics analysis, or painted with whole-chromosome DNA probes for translocation analysis (FISH). RESULTS: A statistically significant increase in the yield of chromosomal aberrations was measured following long-term space missions in lymphocytes from cosmonauts at their first flight. No significant changes in aberration frequencies were observed for short-term taxi flights. The increase in long-term missions was consistent with the values calculated from physical dosimetry data. However, for cosmonauts involved in two or more space flights, the yield of interchromosomal exchanges was not related to the total duration of space sojourn or integral absorbed dose. Indeed, the yield of aberrations at the end of the last mission was generally in the range of background frequencies measured before the first mission. CONCLUSIONS: Chromosome aberration dosimetry can detect radiation damage during space flight, and biological measurements support the current risk estimates for space radiation exposure. However, for cosmonauts involved in multiple space missions the frequency of chromosomal aberrations is lower than expected, suggesting that the effects of repeated space flights on this particular endpoint are not simply additive. Changes in the immune system in microgravity and/or adaptive response to space radiation may explain the apparent increase in radioresistance after multiple space flights.

Astronauts↗

PubMed1998

Plants and somatic embryos in space: what have we learned?

Space provides a unique environment that can affect the interplay between cell cycle controls and environment and can thus modify the processes of cell division, development and growth. It is proposed that the chromosomal and nuclear abnormalities frequently encountered in cells of various plants exposed to space are due to a combination of factors including the biological status of the systems and the way in which they are grown, exposed to, and ultimately, the way in which they experience multiple stresses. The extent to which space-specific changes become manifest is dependent on the extent of pre-existing stresses in the system. This has become evident in a variety of plant species grown in space but has been particularly amenable to study using in vitro systems, especially in developing embryoids. The following observations allow us to harmonize disparate results from a variety of space experiments:- (a) the more completely developed a system, the less likely it is to show cell stress during growth; the less morphologically complex, the greater the vulnerability; (b) the size/"packaging" of the genome (karyotype) are significant experimental variables; plants with larger genomes (e.g. polyploids) seem to be more space-stress tolerant; (c) a single space-associated stress is inadequate to produce a significant adverse response unless the stress is severe, or a biological parameter necessary to 'amplify' it exists. On this view, an appropriate "stress match" with other non-equilibrium determinants, much like a 'tug of war', can result in genomic variations in space. All this emphasizes that fastidiously-controlled growing environments must be devised if one is to resolve the matter of direct versus indirect effects of space. Better understanding of the novel physico-chemical equilibrium phenomena associated with space will allow those interested in space cell and developmental biology to pick and choose procedures best suited to their exploitation for specific objectives.

Cell Physiological Phenomena↗

PubMed1991

Making arm movements within different parts of space: the premotor and motor cortical representation of a coordinate system for reaching to visual targets.

The activity of 156 individual arm-related neurons was studied in the premotor cortex (area 6) while monkeys made arm movements of similar directions within different parts of 3-dimensional space. This study was aimed at describing the relationship between premotor cortical cell activity and direction of arm movement and assessing the coordinate system underlying this relationship. We found that the activity of 152 (97.4%) cells varied in an orderly fashion with the direction of movement, in at least some region of the work space. Premotor cortical cells fired most for a given preferred direction and less for other directions of movement. These preferred directions covered the directional continuum in a uniform fashion across the work space. It was found that, as movements of similar directions were made within different parts of the work space, the cells' preferred directions changed their orientation. Although these changes had different magnitudes for different cells, at the population level, they followed closely the changes in orientation of the arm necessary to move the hand from one to another part of the work space. This shift of cells' preferred direction with the orientation of the arm in space has been observed with similar characteristics in the motor cortex (see Caminiti et al., 1990). In both premotor and motor cortices, neuronal movement population vectors provide a good description of movement direction. Unlike the individual cell preferred directions upon which they are based, movement population vectors did not change their spatial orientation across the work space, suggesting that they remain good predictors of movement direction regardless of the region of space in which movements are made. The firing frequency of both premotor and motor cortical neurons varied significantly with the position occupied by the hand in space. These static positional effects were observed in 88.5% of premotor and 91.8% of motor cortical cells. In a second task, monkeys made movements from differing origins to a common end point. This task was performed within 3 different parts of space and was aimed at dissociating movement direction from movement end point. It was found that in both premotor and motor cortices virtually all cells were related to the direction and not to the end point of movement. These data suggest that premotor and motor cortices use common mechanisms for coding arm movement direction. They also provide a basis for understanding the coordinate transformation required to move the hand toward visual targets in space.

Analysis of Variance↗

PubMed2005

Competitive strategies in adult beech and spruce: space-related foliar carbon investment versus carbon gain.

In Central Europe, Fagus sylvatica and Picea abies represent contrasting extremes in foliage type, crown structure and length of growing season. In order to examine the competitive strategies of these two co-occurring species, we tested the following hypotheses: (1) the space occupied by the foliage of sun branches is characterized by greater foliar mass investment compared to shade branches, (2) the carbon (C) gain per unit of occupied space is greater in sun than in shade branches, and (3) annual C and water costs of the foliage for sustaining the occupied space are low, wherever C gain per unit of occupied space is low. These were investigated in a mature forest in Southern Germany. The examination was based on the annual assessment of space-related resource investments and gains of the foliage. The foliated space around branches was regarded as the relevant volume with respect to aboveground resource availability. Occupied crown space per standing foliage mass was higher in shade compared to sun branches of beech, whereas no difference existed in crown volume per foliage mass between sun and shade branches of spruce (hypothesis 1 accepted for beech but rejected for spruce). However, beech occupied more space per foliage mass than spruce. The C gain per occupied crown volume was greater in sun than in shade branches (hypothesis 2 accepted) but did not differ between species. The amount of occupied space per respiratory and transpiratory costs did not differ between species or between sun and shade branches. In beech and spruce, the proportion of foliage investment in the annual C balance of sun and shade branches remained rather stable, whereas respiratory costs distinctly increased in shade foliage. Hence, shade branches were costly structures to occupy space, achieving only low and even negative C balances (rejection of hypothesis 3), which conflicts with the claimed C autonomy of branches. Our findings suggest that competitiveness is determined by the standing foliage mass and the annual branch volume increment rather than annual investments in foliage. Expressing competitiveness in terms of space-related resource investments versus returns, as demonstrated here, has the potential of promoting mechanistic understanding of plant-plant interactions.

Carbon↗

PubMed1999

Teaching of space life sciences.

Space life sciences is not really a new life sciences discipline such as immunology was some decades ago and it may never be so. Rather it is a field that will provide each existing life sciences discipline with new and more information gathered from space research. In fact, the danger is that space research will be confined in a separate discipline, and thus it will be cut off from classical ground research. Conversely, scientists should increasingly consider spaceflight as a tool and should integrate the findings of space research into their traditional disciplines. A brief survey of topics and main findings in the various subdisciplines of space life sciences is provided. This is followed by a discussion of typical problems encountered such as access to space, controls, ground-based simulations, medical care in space, extravehicular activity, and environmental control and life support. As many space life sciences courses are initiated around the world either by space agencies or universities or jointly, there is a need to consider the international, intercultural, and interdisciplinary aspects of such programs. It is argued that the growing knowledge derived from space research should be integrated into the regular teaching of life sciences rather than leaving it confined to a separate field. Teaching of space life sciences is a prime candidate for the application of the new techniques of "cyberspace education", where interactive learning and globalization of the learning process will take a leading place. The experts and student body are dispersed over many nations, research is of necessity conducted on a basis of international cooperation. The conduct of tele-education is discussed and existing information sources and courses are listed.

Biological Science Disciplines↗

PubMed2000

Radiographic joint space in rheumatoid glenohumeral joints. A 15-year prospective follow-up study in 74 patients.

OBJECTIVE: To evaluate radiographically the glenohumeral (GH) joint space in patients with long-term rheumatoid arthritis (RA). METHODS: A cohort of 74 patients with RA were followed prospectively for 15 yr. At the end point, 148 shoulders were radiographed using a standard method. The GH joint space was examined from the radiographs using a method developed previously for population studies; the joint space was measured at three different sites and the average of the three measurements, the integral space, was calculated. Destruction of the GH joints was assessed with the Larsen method on a scale of 0-5 and compared with the joint space measurements. RESULTS: The mean GH joint space in RA patients was 3. 1 (S.D. 3.3), range -17.3 to 5.7 mm; 2.7 mm (S.D. 4.5) in men and 3. 2 mm (S.D. 2.8) in women. The mean of the affected joints (Larsen grades 2-5), 1.7 mm (S.D. 4.5), was notably narrower than the mean 4. 4 mm (S.D. 0.6) of the non-affected (Larsen grades 0-1) joints. Pathological GH joint space, less than 2 mm, was found in five (15%) of 36 joints in men and in 14 (13%) of 112 joints in women. All the joints graded as Larsen 4 and 5 (n = 17) fulfilled this pathological criterion. Joint space narrowing was associated [r = - 0.66, 95% confidence interval (CI): -0.56 to -0.75] with increasing destruction (Larsen grading) of the joint. The narrowing was significant between non- (Larsen 0, 1), moderately (Larsen 2, 3) and severely (Larsen 4, 5) affected joints (P < 0.001). However, a remarkable step in this process occurred between Larsen grades 3 and 4 when the mean joint space diminished from 3.1 to 0.3 mm. CONCLUSIONS: Joint space narrowing is a frequent consequence of GH joint rheumatoid affection. However, joint space narrowing is a late phenomenon occurring not until after marked erosive destruction, which should be noted when using the Larsen method for GH joints.

Adolescent↗

PubMed1999

Cochlear fluid space dimensions for six species derived from reconstructions of three-dimensional magnetic resonance images.

OBJECTIVES: To establish the dimensions and volumes of the cochlear fluid spaces. STUDY DESIGN: Fluid space volumes, lengths, and cross-sectional areas were derived for the cochleas from six species: human, guinea pig, bat, rat, mouse, and gerbil. METHODS: Three-dimensional reconstructions of the fluid spaces were made from magnetic resonance microscopy (MRM) images. Consecutive serial slices composed of isotropic voxels (25 microm3) representing the entire volume of fixed, isolated cochleas were obtained. The boundaries delineating the fluid spaces, including Reissner's membrane, were resolved for all specimens, except for the human, in which Reissner's membrane was not consistently resolved. Three-dimensional reconstructions of the endolymphatic and perilymphatic fluid spaces were generated. Fluid space length and variation of cross-sectional area with distance were derived by an algorithm that followed the midpoint of the space along the length of the spiral. The total volume of each fluid space was derived from a voxel count for each specimen. RESULTS: Length, volume, and cross-sectional areas are provided for six species. In all cases, the length of the endolymphatic fluid space was consistently longer than that of either perilymphatic scala, primarily as a result of a greater radius of curvature. For guinea pig specimens, the measured volumes of the fluid spaces were considerably lower than those suggested by previous reports based on histological data. CONCLUSIONS: The quantification of cochlear fluid spaces provided by this study will enable the more accurate calculation of drug and other solute movements in fluids of the inner ear during experimental or clinical manipulations.

Animals↗

PubMed2004

Reading speed benefits from increased vertical word spacing in normal peripheral vision.

PURPOSE: Crowding, the adverse spatial interaction due to proximity of adjacent targets, has been suggested as an explanation for slow reading in peripheral vision. The purposes of this study were to (1) demonstrate that crowding exists at the word level and (2) examine whether or not reading speed in central and peripheral vision can be enhanced with increased vertical word spacing. METHODS: Five normal observers read aloud sequences of six unrelated four-letter words presented on a computer monitor, one word at a time, using rapid serial visual presentation (RSVP). Reading speeds were calculated based on the RSVP exposure durations yielding 80% correct. Testing was conducted at the fovea and at 5 degrees and 10 degrees in the inferior visual field. Critical print size (CPS) for each observer and at each eccentricity was first determined by measuring reading speeds for four print sizes using unflanked words. We then presented words at 0.8x or 1.4x CPS, with each target word flanked by two other words, one above and one below the target word. Reading speeds were determined for vertical word spacings (baseline-to-baseline separation between two vertically separated words) ranging from 0.8x to 2x the standard single-spacing, as well as the unflanked condition. RESULTS: At the fovea, reading speed increased with vertical word spacing up to about 1.2x to 1.5x the standard spacing and remained constant and similar to the unflanked reading speed at larger vertical word spacings. In the periphery, reading speed also increased with vertical word spacing, but it remained below the unflanked reading speed for all spacings tested. At 2x the standard spacing, peripheral reading speed was still about 25% lower than the unflanked reading speed for both eccentricities and print sizes. Results from a control experiment showed that the greater reliance of peripheral reading speed on vertical word spacing was also found in the right visual field. CONCLUSIONS: Increased vertical word spacing, which presumably decreases the adverse effect of crowding between adjacent lines of text, benefits reading speed. This benefit is greater in peripheral than central vision.

Adolescent↗

PubMed1971

Determination of extracellular space and intracellular electrolytes in rat liver in vivo.

1. Uptake of a number of isotopically labelled extracellular tracers by rat liver in vivo was studied.2. A residual intravascular space of 3.0-3.5% following exsanguination was measured by use of [(51)Cr]red cells. This space was significantly greater than that of skeletal muscle and was also greater in nephrectomized as compared to intact rats.3. [(131)I]albumin and polyvinylpyrolidine (PVP) were found to distribute initially in a space of 6-7% and this was followed by a delayed rise that was greater for PVP. The extravascular portion of this space is termed the large-molecule accessible space and is believed to correspond to the histological space of Disse.4. [(14)C]sucrose and inulin initially distribute in a space of 10-12% followed by a continued late increase. This initial space is termed the small molecule accessible space and is thought to include most of interstitial space.5. (36)Cl(-) and stable Na(+) and Cl(-) spaces were constant at 19-21% and can be used to put an upper limit on extracellular space.6. Operationally, the 1 hr inulin space in the nephrectomized rat was felt to be the best indicator of extracellular space.7. Total electrolytes were measured and intracellular values of 22, 165 and 22 m-mole/l. cell water for Na(+), K(+) and Cl(-), respectively, were calculated.8. By use of [(14)C]DMO, an intracellular pH of 7.25 and an intracellular HCO(3) (-) of 13 m-mole/l. cell water were calculated.

Albumins↗