Search PubMed⌕ Search

Biomedical subjects

J McIntyre

Publications and source records attributed to J McIntyre.

102 records · Page 6Linked to original sources
PubMedDate not supplied

Internal reference frames for representation and storage of visual information: the role of gravity.

Experimental studies of visual mechanisms suggests that the CNS represents image information with respect to preferred horizontal and vertical axes, as shown by a phenomenon known as the "oblique effect". In the current study we used this effect to evaluate the influence of gravity on the representation and storage of visual orientation information. Subjects performed a psychophysical task in which a visually-presented stimulus line was aligned with the remembered orientation of a reference stimulus line presented moments before. The experiments were made on 5 cosmonauts during orbital space flight and additionally on 13 subjects in conditions of normal gravity with a tilting chair. Data were analyzed with respect to response variability and timing. On earth, these measurements for this task show a distinct preference for horizontally and vertically oriented stimuli when the body and gravitational axes were aligned. This preference was markedly decreased or disappeared when the body axis was tilted with respect to gravity; this effect was not connected with ocular counter-rolling nor could we find a preference of any other intermediate axis between the gravity and body aligned axes. On the other hand, the preference for vertical and horizontal axes was maintained for tests performed in microgravity over the course of a 6 month flight, starting from flight day 6. We concluded that subjects normally process visual orientation information in a multi-modal reference frame that combines both proprioceptive and gravitational cues when both are available, but that a proprioceptive reference frame is sufficient for this task in the absence of gravity after a short period of adaptation. Some of the results from this study have been previously published in a preliminary report. Grant numbers: 99-04-48450.

Adult↗
PubMedDate not supplied

Does gravity play an essential role in the asymmetrical visual perception of vertical and horizontal line length?

The eye perceives the length of vertical and horizontal lines with an inherent asymmetry. A vertical line having the same length as a horizontal one is usually perceived to be longer. In this experimental investigation we tested the hypothesis that gravity has a direct role in producing the observed perceptual asymmetry. To this end we performed experiments in weightlessness during long-orbital space flights onboard the MIR station. Subjects performed a psychophysical task in which the length of a visually-presented vertical line was adjusted to match the length of a horizontal reference. On Earth, almost all subjects produce errors in adjusting the length of the vertical line, consistently under-estimating the length of the horizontal reference. The asymmetry of perception of the line lengths persisted in weightlessness. From these results we conclude that the phenomena of asymmetry of perception of the lengths of vertical and horizontal lines is not dependent on gravity, but is instead defined by properties of the system of internal representation. Grant numbers: 99-04-48450.

Adaptation, Physiological↗
PubMedDate not supplied

A 6 D.O.F. opto-inertial tracker for virtual reality experiments in microgravity.

Gravity plays a role in many different levels of human motor behavior. It dictates the laws of motion of our body and limbs, as well as of the objects in the external world with which we wish to interact. The dynamic interaction of our body with the world is molded within gravity's constraints. The role played by gravity in the perception of visual stimuli and the elaboration of human movement is an active research theme in the field of Neurophysiology. Conditions of microgravity, coupled with techniques from the world of virtual reality, provide a unique opportunity to address these questions concerning the function of the human sensorimotor system. The ability to measure movements of the head and to update in real time the visual scene presented to the subject based on these measurements is a key element in producing a realistic virtual environment. A variety of head-tracking hardware exists on the market today, but none seem particularly well suited to the constraints of working with a space station environment. Nor can any of the existing commercial systems meet the more stringent requirements for physiological experimentation (high accuracy, high resolution, low jitter, low lag) in a wireless configuration. To this end, we have developed and tested a hybrid opto-inertial 6 degree-of-freedom tracker based on existing inertial technology. To confirm that the inertial components and algorithms will function properly, this system was tested in the microgravity conditions of parabolic flight. Here we present the design goals of this tracker, the system configuration and the results of 0g and 1g testing.

Acceleration↗
PubMedDate not supplied

Technical evolutions of the French multipurpose instruments for Cognitive Neurosciences.

Since the first French flight in space in 1982, the CNES has developed a wide range of instruments, especially in the field of Neurosciences. The design of these instruments has considerably evolved from rather simple equipment up to much more sophisticated tools that are being specially tailored for these missions. Four major phases can be identified: -a simple adaptation of an echographe leading to the first neurosciences experiments (the ARAGATZ'88 mission), -the ILLUSIONS and VIMINAL instruments used during the ANTARES'92 and ALTAIR'93 missions, -the COGNILAB instrument developed for the CASSIOPEE'96 mission, to be re-used in 1997 and in 1999, -a preliminary design of the 1999 mission payload, including virtual reality concepts, in a modular design to adapt to the European COF. Aside from the evolution of scientific requirements, the experience gained during the flights led to progressive improvements in the different technical parts, including visual system, body restraint systems, accessories, such as a force feedback joystick, computer and software, etc. This paper describes the technical evolutions in the CNES Neurosciences program.

Cognition↗
PubMedDate not supplied

Arm end-point trajectories under normal and micro-gravity environments.

The purpose of the present experiment was to study the way in which the CNS represents gravitational force during vertical arm pointing movements. Movements in upward and downward directions were executed by two cosmonauts in normal-gravity and weightlessness. Analyses focused upon finger kinematics in the sagittal plane. In normal-gravity, downward direction movements showed smaller curvatures and greater relative times to peak velocity (AT/MT) when compared with upward direction movements. Data from the weightlessness experiments showed that whilst downward movements decreased their curvature during space flight, curvatures of upward movements changed slightly. Furthermore, AT/MT was modified during the first days in micro-gravity for both directions, recovering, however, to pre-flight values after 18 days in space. Results from the present study, provide evidence that gravitational force is centrally treated constituting an important component of the motor plan for vertical arm movements.

Aerospace Medicine↗
PubMedDate not supplied

The Kinelite Project: a new powerful motion analyser for Spacelab and space station.

The goal of the Kinelite Project is to develop a space qualified motion analysis system to be used in space by the scientific community, mainly to support neuroscience protocols. The measurement principle of the Kinelite is to determine, by triangulation mean, the 3D position of small, lightweight, reflective markers positioned at the different points of interest. The scene is illuminated by Infra Red flashes and the reflected light is acquired by up to 8 precalibrated and synchronized CCD cameras. The main characteristics of the system are: Camera field of view: 45 degrees; Number of cameras: 2 to 8; Acquisition frequency: 25, 50, 100, or 200 Hz; CCD format: 256 x 256; Number of markers: up to 64; 3D accuracy: 2mm; Main dimensions: 45 cm x 45 cm x 30 cm; Mass: 23 kg; Power consumption: less than 200 W. The Kinelite will first fly aboard the NASA Spacelab; it will be used, during the NEUROLAB mission (4/98), to support the "Frames of References and Internal Models" (Principal Investigator: Pr. A. Berthoz, Co Investigators: J. McIntyre, F. Lacquaniti).

Aerospace Medicine↗
PubMedDate not supplied

Rice as a vehicle for dietary fluoride uptake.

The objective of this study was to analyze aspects of the metabolism and bio-availability of fluoride after consumption of a sample of polished white rice containing 5.6 ppm fluoride ion. Up to 400 g of fluoridated rice was consumed by three volunteer adult subjects over specific time periods on two separate occasions. Saliva concentrations were elevated immediately and remained so 90 minutes following ingestion, among other indications. It was concluded that polished rice has the potential to be a useful vehicle for dietary fluoride transport.

Adult↗
PubMedDate not supplied

Dynamic internal compliance of a vascular prosthesis.

A new technique was used to measure dynamic internal compliance of a blood vessel or vascular graft subjected to dynamic internal pressure. The internal compliance can be broken into three categories: the volumetric compliance (CV), defined as (dV/V)/dP; the longitudinal compliance (CL), defined as (dL/L)/dP; and radial compliance (CR), defined as (dR/R)/dP. It can be shown mathematically that CV = 2 CR + CL. Thus, measuring any two of the three entities will also give the value for the third. A Dynatek DCT1 dynamic compliance tester was used for measuring the compliance of DenaflexTM biologic grafts and fresh bovine internal thoracic arteries, from which the Denaflex grafts were obtained by fixation. Volumetric compliance was obtained with the test sample mounted in a loose loop that allowed the sample to move both radially and longitudinally. By mounting the sample in a straight fashion that limited longitudinal movement, the radial compliance was determined. The longitudinal compliance was then calculated from the above relationship. Test results show that the fresh bovine artery had an average volumetric compliance of 26.1%/100 mmHg, radial compliance of 9.5%/100 mmHg, and longitudinal compliance of 7.2%/100 mmHg. The Denaflex vascular graft showed a reduction in longitudinal and radial compliance, compared to the fresh raw artery, as a result of extensive fixation.

Animals↗
PubMedDate not supplied

Dynamic internal compliance measurements of fresh and fixed artery.

A new device is used to compare dynamic internal compliance of biologic vascular prostheses derived from bovine artery. These grafts were prepared using dialdehyde starch (DS), and a polyepoxy polyether compound (PC), as crosslinking agents. Internal compliance was measured using the Dynatek DCT1 Dynamic Compliance Tester, developed by Dynatek Laboratories. This device utilizes a variable speed DC motor coupled to miniature bellows, which displace a stroke volume controllable to within 0.5 microliter. The bellows displace fluid into and out of the graft, resulting in a sinusoidal change in internal pressure. Volumetric displacement is monitored by a linear voltage displacement transducer (LVDT) mounted on the motor coupling, whereas internal graft pressure is monitored by a miniature pressure transducer mounted on the closed end of the graft. For this series of experiments, a pressure range of 80-120 mmHg was used, with a cycle speed of 80 cycles/min. Preliminary results indicate that PC fixation of bovine artery results in a vascular graft with internal compliance somewhere between fresh tissue and DS fixation. This data confirms qualitative assessment. The DCT1 provides valuable comparative information on the dynamic internal compliance of vascular prostheses. These measurements reflect what occurs in the graft lumen, since they take into account wall compression and axial deformation. Further development is required to separate radial and longitudinal compliance components.

Animals↗