Biomedical subjects

Joseph McIntyre

Publications and source records attributed to Joseph McIntyre.

5 recordsLinked to original sources

PubMed2005

Anticipating the effects of gravity when intercepting moving objects: differentiating up and down based on nonvisual cues.

Intercepting an object requires a precise estimate of its time of arrival at the interception point (time to contact or "TTC"). It has been proposed that knowledge about gravitational acceleration can be combined with first-order, visual-field information to provide a better estimate of TTC when catching falling objects. In this experiment, we investigated the relative role of visual and nonvisual information on motor-response timing in an interceptive task. Subjects were immersed in a stereoscopic virtual environment and asked to intercept with a virtual racket a ball falling from above or rising from below. The ball moved with different initial velocities and could accelerate, decelerate, or move at a constant speed. Depending on the direction of motion, the acceleration or deceleration of the ball could therefore be congruent or not with the acceleration that would be expected due to the force of gravity acting on the ball. Although the best success rate was observed for balls moving at a constant velocity, we systematically found a cross-effect of ball direction and acceleration on success rate and response timing. Racket motion was triggered on average 25 ms earlier when the ball fell from above than when it rose from below, whatever the ball's true acceleration. As visual-flow information was the same in both cases, this shift indicates an influence of the ball's direction relative to gravity on response timing, consistent with the anticipation of the effects of gravity on the flight of the ball.

Attention↗

PubMed2005

Do novel gravitational environments alter the grip-force/load-force coupling at the fingertips?

In this experiment we examined the coupling between grip force and load force observed during cyclic vertical arm movements with a hand-held object, performed in different gravitational environments. Six subjects highly experienced in parabolic flight participated in this study. They had to continuously move a cylindrical object up and down in the different gravity fields (1g, 1.8 g and 0 g) induced by parabolic flights. The imposed movement frequency was 1 Hz, the object mass was either 200 or 400 g, the amplitude of movement was either 20 or 40 cm and an additional mass of 200 g could be wound around the forearm. Each subject performed the task during 15 consecutive parabolas. The coordination between the grip force normal to the surface and the tangential load force was examined in nine loading conditions. We observed that the same normal grip force was used for equivalent loads generated by changes of mass, gravity or acceleration despite the fact that these loads required different motor commands to move the arm. Moreover, our results suggest that the gravitational and inertial components of the load are treated adequately and independently by the internal models used to predictively control the required grip force. These results indicate that the forward internal models used to control precision grip take into account the dynamic characteristics of the upper limb, the object and the environment to predict the object's acceleration and, in turn, the load force acting at the fingertips.

Adult↗

PubMed2005

Two reference frames for visual perception in two gravity conditions.

The processing and storage of visual information concerning the orientation of objects in space is carried out in anisotropic reference frames in which all orientations are not treated equally. The perceptual anisotropies, and the implicit reference frames that they define, are evidenced by the observation of 'oblique effects' in which performance on a given perceptual task is better for horizontally and vertically oriented stimuli. The question remains how the preferred horizontal and vertical reference frames are defined. In these experiments cosmonaut subjects reproduced the remembered orientation of a visual stimulus in 1g (on the ground) and in 0g, both attached to a chair and while free-floating within the International Space Station. Results show that while the remembered orientation of a visual stimulus may be stored in a multimodal reference frame that includes gravity, an egocentric reference is sufficient to elicit the oblique effect when all gravitational and haptic cues are absent.

Analysis of Variance↗

PubMed2003

Estimating time to contact and impact velocity when catching an accelerating object with the hand.

To catch a moving object with the hand requires precise coordination between visual information about the target's motion and the muscle activity necessary to prepare for the impact. A key question remains open as to if and how a human observer uses velocity and acceleration information when controlling muscles in anticipation of impact. Participants were asked to catch the moving end of a swinging counterweighted pendulum, and resulting muscle activities in the arm were measured. The authors also simulated muscle activities that would be produced according to different tuning strategies. By comparing data with simulations, the authors provide evidence that human observers use online information about velocity but not acceleration when preparing for impact.

Adult↗

PubMed2003

Gravity and spatial orientation in virtual 3D-mazes.

In order to bring new insights into the processing of 3D spatial information, we conducted experiments on the capacity of human subjects to memorize 3D-structured environments, such as buildings with several floors or the potentially complex 3D structure of an orbital space station. We had subjects move passively in one of two different exploration modes, through a visual virtual environment that consisted of a series of connected tunnels. In upright displacement, self-rotation when going around corners in the tunnels was limited to yaw rotations. For horizontal translations, subjects faced forward in the direction of motion. When moving up or down through vertical segments of the 3D tunnels, however, subjects facing the tunnel wall, remaining upright as if moving up and down in a glass elevator. In the unconstrained displacement mode, subjects would appear to climb or dive face-forward when moving vertically; thus, in this mode subjects could experience visual flow consistent with rotations about any of the 3 canonical axes. In a previous experiment, subjects were asked to determine whether a static, outside view of a test tunnel corresponded or not to the tunnel through which they had just passed. Results showed that performance was better on this task for the upright than for the unconstrained displacement mode; i.e. when subjects remained "upright" with respect to the virtual environment as defined by subject's posture in the first segment. This effect suggests that gravity may provide a key reference frame used in the shift between egocentric and allocentric representations of the 3D virtual world. To check whether it is the polarizing effects of gravity that leads to the favoring of the upright displacement mode, the experimental paradigm was adapted for orbital flight and performed by cosmonauts onboard the International Space Station. For these flight experiments the previous recognition task was replaced by a computerized reconstruction task, which proved to be more efficient in terms of the time required to achieve reliable results. Suppressing gravity did not immediately affect relative performance between the two modes, indicating that on-line graviceptor information is not directly responsible for this differential effect. Trends in the evolution of responses over the course of a 10-day mission, however, suggest that human subjects might adapt their ability to represent internally complex 3D displacements.

Gravitation↗