Mental rotation of the neuronal population vector.

A rhesus monkey was trained to move its arm in a direction that was perpendicular to and counterclockwise from the direction of a target light that changed in position from trial to trial. Solution of this problem was hypothesized to involve the creation and mental rotation of an imagined movement vector from the direction of the light to the direction of the movement. This hypothesis was tested directly by recording the activity of cells in the motor cortex during performance of the task and computing the neuronal population vector in successive time intervals during the reaction time. The population vector rotated gradually counterclockwise from the direction of the light to the direction of the movement at an average rate of 732 degrees per second. These results provide direct, neural evidence for the mental rotation hypothesis and indicate that the neuronal population vector is a useful tool for "reading out" and identifying cognitive operations of neuronal ensembles.

Sample design: Third National Health and Nutrition Examination Survey.

This report presents a detailed description of the sample design for the Third National Health and Nutrition Examination Survey, 1988-94, including a brief description of research that led to the choice of the final design. The National Health and Nutrition Examination Survey (NHANES) is one of the major surveys of the National Center for Health Statistics, Centers for Disease Control. Information on the health and nutritional status of the noninstitutionalized population of the United States is collected through the NHANES household interviews and standardized physical examinations.

A method for studying the control of three-dimensional isometric forces using dynamic stereogram.

A system has been developed for measuring the three-dimensional (3D) isometric forces produced by the arm in response to a visual stimulus. The output of 3 load cells is combined to determine the components of the 3D response force. The maximum force range of the load cells is 2000 g which can be read with a resolution of 4 g and with a measured accuracy of +/- 10 g. An overload stop protects the device to a load of 23 kg. The visual instruction to the subject concerning the direction and magnitude of the 3D force vector to be produced is presented using a vivid spherical stereogram. This stereogram is produced using the anaglyphic technique where the left and right images are separated by color filters. A dense aggregation of points defines the target cursor, which can be positioned anywhere inside or on the surface of the sphere. This cursor can represent a stationary or a moving target. A force feedback cursor can be provided to indicate to the subject his/her response. The color display on the cathode ray tube is produced by a display generator driven by a computer.

System for projection of a three-dimensional, moving virtual target for studies of eye-hand coordination.

Eye-hand tracking of moving visual objects in three-dimensional (3D) space is common in the behavioral repertoire of primates. However, behavioral and/or neurophysiological studies of this function are lacking mainly because devices do not exist that allow its investigation. We describe a device by which a spot of light can be presented in the immediate extrapersonal space of a subject and can be moved in various trajectories in 3D space. The target is a real image of a circular aperture produced by a system consisting of a light source, aperture, filters, several lenses and fold mirrors, and a large concave mirror to focus the final real image. Rapid, computer-controlled movement of the image is obtained by tilting a gimbal-mounted guide mirror (for x and y motion) and by translating a lens (for motion in the z direction). A second configuration of the system allows movement of a 3D image in the 3D space. Hand motion is monitored by means of a sonic, 3D, position-measurement system.

Static versus dynamic effects in motor cortex and area 5: comparison during movement time.

We examined the directionality of static and dynamic motor effects on cell discharge recorded during arm movements in motor cortex and area 5. Movements of 8 directions were performed by rhesus monkeys in a two-dimensional space ('movement task'). Static effects were determined using a static hold task in the same workspace ('static task'); they were adequately described as planar activity surfaces in 78/124 (63%) and 63/105 (60%) of motor cortical and area 5 cells, respectively, that showed statistically significant changes in steady-state activity associated with holding in different positions. The frequency of discharge expected during the movement time on the basis of the static effect alone was calculated for every trial using the static plane equation and the movement path. The difference between this value and the discharge rate observed in the movement task during the same period of time was taken as an estimate of the contribution of non-static, i.e. dynamic factors. Thus static and dynamic tuning curves were generated. These curves were compared with respect to depth of tuning and spatial congruence. The former was estimated by taking the difference between the maximum and minimum of the curve, and the latter by measuring the correlation between the static and dynamic curves. We found the following. First, the dynamic tuning curves were more deeply tuned than the corresponding static ones, by 1.51 and 1.59 times in motor cortex and area 5, respectively. This result was statistically significant in both areas (paired t-test, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Cognitive spatial-motor processes. 1. The making of movements at various angles from a stimulus direction.

Naive human subjects (N = 18) were asked to move a manipulandum on a phase in directions other than going straight towards a visual stimulus. They were instructed verbally to generate a movement at an angle from a stimulus direction which varied in 2-dimensional (2-D) space from trial to trial in a pseudorandom fashion. Each subject performed eight sets of twenty consecutive trials: one for moving in the stimulus direction and seven for moving in directions at an angle from it. The angles were 5, 10, 15, 35, 70, 105 and 140 degrees. Nine subjects were instructed to move in the clockwise (CW) departure and 9 to move in either (EI) the clockwise or the counterclockwise (CCW) departure, as they wished. The direction of the movement in 2-D space and the reaction time (RT) were measured. The mean angle achieved in a given set overshot the instruction angle, especially in the lower range (5-35 degrees). The reaction time, RT phi, of movements made at an angle from the stimulus direction showed two kinds of change; first, a step increase from the reaction time, RT0, of movements in the stimulus direction, and second, superimposed upon it, a linear increase with the amplitude of the angle. The slope of the line was similar for the CW (2.37 ms/degree) and the EI case (2.28 ms/degree), but the step increase (y-intercept) for the EI case (84 ms) was substantially less than that of the CW case (155 ms). The linear increase of the RT with angle is compatible with the idea that performance in the task may involve a mental rotation of the imagined movement vector about its origin. The rotation would begin from the stimulus direction and end when the required angle is judged to have been reached; in addition, corrections of this angle at the end of the rotation could be made. The slope of 2.37 ms/degree observed in the CW case would correspond to a rotation rate of 422 degrees/s. The finding of a similar rate for the EI case indicates a similarity in strategy with regard to achieving a desired angle. In contrast, the lower intercept observed for the EI case suggests significant savings in processing information which is unconstrained with regard to angular departure. Assuming this model of internal motion, we analyzed the amplitude-accuracy relations using Fitts' (1954) approach to real movements.(ABSTRACT TRUNCATED AT 400 WORDS)

Cognitive spatial-motor processes. 2. Information transmitted by the direction of two-dimensional arm movements and by neuronal populations in primate motor cortex and area 5.

We measured the amount of information transmitted by the direction of two-dimensional (2-D) arm movements of human subjects, and by neuronal populations in the motor cortex and area 5 of monkeys. We also compared the information transmitted by a motor cortical population when the predictability of the direction of movement was varied, i.e. when the target of the movement was the same, or different, in successive trials. The information transmitted by a neuronal population was measured using the "population vector" code (Georgopoulos et al. 1983, 1986) as the stimulated directional output of the population. We found the following. (a) The information transmitted per movement increased in all cases with input information but more slowly than the maximum possible. No asymptote had been reached at 6.64 bits of input information; the best human performance at that level was 4.5 bits. (b) The average information transmitted by a motor cortical population (N = 253 cells) was approximately 0.5 bits higher than that of best human performance at all levels of input information. These findings indicate that whereas information loss at the level of motor cortex, and during stages preceding it, increases with increasing input information, this loss remains constant at all levels of input information during processes intervening between motor cortex and movement. (c) The information transmitted by the neuronal population at a constant level of input information increased with the number of cells in the population and had not plateaued at the population size of 253 cells used in this study. (d) Consistently higher amounts of information were transmitted by motor cortical than by area 5 populations at all levels of input information (up to 7 bits) examined. The difference was approximately 0.16 bits. (e) Finally, the information transmitted by a motor cortical population was slightly higher (by 0.07 bits) when the movement was more than less predictable. Although this difference was small, it was consistent at all levels of input information (3-7 bits) and was statistically highly significant (p less than 0.005, paired t test). These results establish the information theoretical approach as a useful method for comparing (a) behavioral and neural data, (b) neural data between different brain areas, and (c) neural data obtained under different behavioral manipulations.

Monitoring data quality through comparisons between data systems.

Since its creation in 1960, the National Center for Health Statistics (NCHS) has placed a high value on the quality of the information and statistics collected and published by its data systems. An important component of a comprehensive data quality monitoring system for a statistical agency such as NCHS is the comparison of statistics between data systems. Between-data-systems comparisons are used to monitor the consistency and comparability of statistics across data systems and between NCHS data systems and outside sources of data. This paper focuses on between-data-systems comparisons and describes a number of methodological analyses that can be used to evaluate data quality. The methodological analyses presented include the evaluation of time trends, the estimation of survey method effects, the evaluation of response error, the measurement of definitional and concept effects, and the detection of inconsistencies between data systems. The paper concludes with a discussion of the complexities of the between-data-systems comparisons and an assessment of the net benefits from such comparisons.

Cognitive spatial-motor processes. 5. Specification of the direction of visually guided isometric forces in two-dimensional space: time course of information transmitted and effect of constant force bias.

The effects of an external constant force bias on the information transmitted (Ti) by the direction of isometric force exerted in 2-dimensional (2-D) space by human subjects were studied using an isometric manipulandum and random dot stereograms generated in a color display (Massey et al. 1988, Massey et al. 1990). Subjects exerted force on the manipulandum such that a visual force-feedback cursor would move in the direction of a visually defined stimulus in the stereo display. The time course of force development and the gain of directional information during increasing force intensity were also studied. We found the following. (a) When no bias force was applied, the force exerted by the subject increased from near zero to greater than 200 gram-force at the end of a trial and was close to the visually defined direction. When a constant bias force of 110 gram-force was applied in various directions in blocks of trials, the force exerted by the subject increased in time, as above; however, its direction also changed in time so that the instantaneous vector sum of the bias force and the force exerted by the subject pointed close to the visually defined direction. The Ti and the reaction time (RT) did not differ significantly in the two experimental conditions. These results suggest that the directional control of isometric forces is very efficient, especially in relation to visuomotor coordination. (b) The Ti was calculated at various levels of force intensity, as the latter increased from approximately 50 gram-force to 200 gram-force.(ABSTRACT TRUNCATED AT 250 WORDS)

Cognitive spatial-motor processes. 4. Specification of the direction of visually guided isometric forces in two-dimensional space: information transmitted and effects of visual force-feedback.

The information transmitted (Ti) by the direction of two-dimensional (2-D) isometric forces at different stereoscopic depths was studied in 50 naive human subjects using an isometric manipulandum and random dot stereograms generated in a color display (Massey et al. 1988). Subjects viewed the display through appropriate color filters and perceived the image of a disk rotated about a horizontal axis on the frontal plane; the top of the disk was rotated around that axis by 15, 45, 60 and 80 degrees away from the subject. Each of these disks involved a different amount of stereoscopic depth perception which was lowest for the 15 degrees and highest for the 80 degrees tilt. Subjects were instructed to exert force in the direction of a visual target presented on the disk in a reaction time task. The instantaneous force exerted by the subjects on the manipulandum was shown on the disk in the form of a feedback cursor. Information transmitted, reaction time (RT) and systematic directional deviations were calculated. We found the following. (a) Ti increased with input information but at a lower rate; at the highest level of input information studied (5.91 bits), Ti was 4.1 bits at the 15 degrees tilt. This high value of Ti suggests that directional information for isometric force is processed very efficiently. However, this Ti was consistently lower than that transmitted by the direction of movement (Georgopoulos and Massay, 1988). (b) Ti did not differ significantly among the 15-60 degrees tilt but was 0.19 bits less for the 80 degrees tilt. RT did not differ among the 15-80 degrees tilts.(ABSTRACT TRUNCATED AT 250 WORDS)

On the relations between the direction of two-dimensional arm movements and cell discharge in primate motor cortex.

The activity of single cells in the motor cortex was recorded while monkeys made arm movements in eight directions (at 45 degrees intervals) in a two-dimensional apparatus. These movements started from the same point and were of the same amplitude. The activity of 606 cells related to proximal arm movements was examined in the task; 323 of the 606 cells were active in that task and were studied in detail. The frequency of discharge of 241 of the 323 cells (74.6%) varied in an orderly fashion with the direction of movement. Discharge was most intense with movements in a preferred direction and was reduced gradually when movements were made in directions farther and farther away from the preferred one. This resulted in a bell-shaped directional tuning curve. These relations were observed for cell discharge during the reaction time, the movement time, and the period that preceded the earliest changes in the electromyographic activity (approximately 80 msec before movement onset). In about 75% of the 241 directionally tuned cells, the frequency of discharge, D, was a sinusoidal function of the direction of movement, theta: D = b0 + b1 sin theta + b2cos theta, or, in terms of the preferred direction, theta 0: D = b0 + c1cos (theta - theta0), where b0, b1, b2, and c1 are regression coefficients. Preferred directions differed for different cells so that the tuning curves partially overlapped. The orderly variation of cell discharge with the direction of movement and the fact that cells related to only one of the eight directions of movement tested were rarely observed indicate that movements in a particular direction are not subserved by motor cortical cells uniquely related to that movement. It is suggested, instead, that a movement trajectory in a desired direction might be generated by the cooperation of cells with overlapping tuning curves. The nature of this hypothetical population code for movement direction remains to be elucidated.

A dual frame design for sampling elderly minorities and persons with disabilities.

Multiple data sources are sometimes available as potential sampling frames for population surveys, and in some situations the use of a multiple frame sample design is more advantageous than using a single sampling frame. The use of multiple sampling frames, however, has variance and bias implications, as well as sampling, data collection, and logistical considerations. These issues are addressed for a proposed dual frame sampling approach in the National Health Interview Survey (NHIS). The results of an investigation of the sampling efficiencies and operational issues in supplementing the NHIS area frame sample with a sample of elderly African and Hispanic Americans and persons with disabilities selected from Social Security Administration files are presented.

Three-dimensional drawings in isometric conditions: planar segmentation of force trajectory.

Normal human subjects grasped an isometric handle with an unrestrained, pronated hand. They were asked to exert forces continuously to draw lemniscates (figure eights) in specified or self-chosen planes and in the presence or absence of a three-dimensional visual feedback cursor and a visual template. In every condition, the mean plane orientation in the force space differed appreciably between the two loops of the figure, as described previously by Soechting and Terzuolo (1987a) for free drawing arm movements. These findings suggest that the planar segmentation of the motor trajectory is not a consequence of joint motion but arises from central constraints related to the production of motor trajectory in space.

Interruption of motor cortical discharge subserving aimed arm movements.

Can evolving motor commands be interrupted by changes in sensory signals that triggered them? We investigated this problem by observing the changes in single cell activity in the motor cortex of monkeys, changes that preceded movement of the hand toward a visual target. We found that this activity was interrupted following a shift of the target during the reaction or movement time and replaced by the pattern activity related to the movement towards the new target. This suggests that motor cortical commands subserving aimed arm movements are processes that can be interrupted in the course of their formation and/or execution by changes in afferent controlling inputs.

Three-dimensional drawings in isometric conditions: relation between geometry and kinematics.

Normal human subjects grasped a 3-D isometric handle with an otherwise unrestrained, pronated hand and exerted forces continuously to draw circles, ellipses and lemniscates (figure-eights) in specified planes in the presence or absence of a 3-D visual force-feedback cursor and a visual template. Under any of these conditions and in all subjects, a significant positive correlation was observed between the instantaneous curvature and angular velocity, and between the instantaneous radius of curvature and tangential velocity; that is, when the force trajectory was most curved, the tangential velocity was lowest. This finding is similar to that obtained by Viviani and Terzuolo (1982) for 2-D drawing arm movements and supports the notion that central constraints give rise to the relation between geometric and kinematic parameters of the trajectory.