Publications from 1993-1994

Titles:

Alternating Prism Exposure Causes Dual Adaptation and Generalization to a Novel Displacement

Performance and mood state parameters during 30 day 6° head down bed rest with exercise training

Cerebral blood flow velocity in humans exposed to 24 h of head-down tilt

New Findings Regarding Light Intensity and Its Effects as a Zeitgeber in the Sprague-Dawley Rat

Multiple Concurrent Visual-Motor Mappings: Implications for Models of Adaptation

The Possible Role of Nystagmus in Motion Sickness: a Hypothesis

Alternating Prism Exposure Causes Dual Adaptation and Generalization to a Novel Displacement

Robert B. Welch, Bruce Bridgeman, Sulekha Anand, and Kaitlin E. Brownman

In two experiments, we examined the hypothesis that repeatedly adapting and readapting to two mutually conflicting sensory environments fosters the development of a separate adaptation to each situation (dual adaptation) as well as an increased ability to adapt to a novel displacement (adaptive generalization). In the preliminary study, subjects alternated between adapting their visuomotor coordination to 30-diopter prismatic displacement and readapting to normal vision. Dual adaptation was observed by the end of 10 alternation cycles. However, an unconfounded test of adaptive generalization was prevented by an unexpected prism-adaptive shift in preexposure baselines for the dual-adapted subjects. In the primary experiment, the subjects adapted and readapted to opposite 15-diopter displacements for a total of 12 cycles. Both dual adaptation and adaptive generalization to a 30-diopter displacement were obtained. These findings may be understood in terms of serial reversal learning and "learning to learn."

Perception & Psychophysics 1993, 54 (2), 195-204

Performance and mood state parameters during 30 day 6° head down bed rest with exercise training

The study was designed to determine if performance and mood impairments occur in long duration weightlessness simulated by bed rest (BR), and if different exercise-training regimens modify or prevent them. Eighteen normal, healthy men were divided into three similar groups: no exercise, isotonic exercise, and isokinetic exercise. A 15-min battery (Automated Portable Testing System, Essex Corp.) of 10 cognitive performance tests and 8 mood and 2 sleep scales were administered daily during ambulatory control, 30 d of absolute BR, and 4 d of ambulatory recovery. Performance test proficiency increased (P< 0.05) for all three groups during BR in 7 of 10 tests and there were no consistent significant differences between the three exercise groups. We conclude that mood and performance did not deteriorate in response to prolonged BR and were not altered by exercise training. Previous studies of weightlessness simulated by bed rest, mostly performed in the Soviet Union, reported progressive deterioration, manifested by fatigue and lack of energy, emotional lability, sleep disturbances, neurological changes, and inconsistent performance. In contrast, affective mood and performance actually improved in our study from the onset to the end of bed rest. The unexpectedly high degree of subject adaptability to the conditions in our study was attributed to selection of subjects with optimal characteristics for adaptation to isolation, confinement, and restricted mobility, and to highly favorable environmental habitability factors in our study, relative to the previous studies. These habitability factors included maintenance of a stimulating environment, access to communications with friends and relatives, absence of staff/subject conflicts, and absence of strict immobilization. The importance of this research was in providing evidence that appropriate crew selection procedures and the provision of favorable habitability countermeasures can prevent deterioration in the psychological status and performance of space crews during long-duration space missions.

Aviat. Space Environ. Med. 64: 522 527, 1993.

Cerebral blood flow velocity in humans exposed to 24 h of head-down tilt

This study investigates cerebral blood flow (CBF) velocity in humans before, during, and after 24 h of 6 degree head-down tilt (HDT), which is a currently accepted experimental model to simulate microgravity. CBF velocity was measured by use of the transcranial Doppler technique in the right middle cerebral artery of eight healthy male subjects. Mean CBF velocity increased from the pre-HDT upright seated baseline value of 55.5 +/- 3.7 (SE) cm/s to 61.5 +/- 3.3 cm/s at 0.5 h of HDT (P < 0.05), reached a peak value of 63.2 +/- 4.1 cm/s at 3 h of HDT, and remained significantly above the pre-HDT baseline for > or = 6 h of HDT. During upright seated recovery (1-5 h post-HDT), mean CBF velocity decreased to 87% of the pre-HDT baseline value (P < 0.05). Mean CBF velocity correlated well with calculated intracranial arterial pressure (IAP) (r = 0.54, P < 0.001). As analyzed by linear regression, mean CBF velocity = 29.6 + 0.32IAP. These results suggest that HDT increases CBF velocity by increasing IAP during several hours after the onset of microgravity. Importantly, the decrease in CBF velocity after HDT may be responsible, in part, for the increased risk of syncope observed in subjects after prolonged bed rest and also in astronauts returning to Earth.

J Appl Physiol. 1993 Jun;74(6):3046-51.

New Findings Regarding Light Intensity and Its Effects as a Zeitgeber in the Sprague-Dawley Rat

In most mammals, the suprachiasmatic nucleus of the anterior hypothalamus has been implicated as the central driving mechanism of circadian rhythmicity. The photic input from the retina, via the retino-hypothalamic tract, and modulation from the pineal gland help regulate the clock. In this study, we investigated the effects of low light intensity on the circadian system of the Sprague-Dawley rat. A series of light intensity experiments were conducted to determine if a light level of 0.1 Lux will maintain entrained circadian rhythms of feeding, drinking, and locomotor activity.

The Physiologist 36: (Suppl.): S 125 to S 126, 1993

Multiple Concurrent Visual-Motor Mappings: Implications for Models of Adaptation

H. A. Cunningham, Robert B. Welch

Previous research on adaptation to visual-motor rearrangement suggests that the central nervous system represents accurately only 1 visual-motor mapping at a time. This idea was examined in 3 experiments where subjects tracked a moving target under repeated alternations between 2 initially interfering mappings (the "normal" mapping characteristic of computer input devices and a 108° rotation of the normal mapping). Alternation between the 2 mappings led to significant reduction in error under the rotated mapping and significant reduction in the adaptation aftereffect ordinarily caused by switching between mappings. Color as a discriminative cue, interference versus decay in adaptation aftereffect, and intermanual transfer were also examined. The results reveal a capacity for multiple concurrent visual-motor mappings, possibly controlled by a para netric process near.

Journal of Experimental Psychology: Copyright 1994 by the American Psychological Association, Inc. Human Perception and Performance 1994, Vol 20, No. 5, 987-999

The Possible Role of Nystagmus in Motion Sickness: a Hypothesis

Sheldon M. Ebenholtz, Malcolm M. Cohen, Barry J. Linder

An alternative hypothesis to that provided by conflict theory is formulated to account for motion sickness. The new approach is predicated on the oculocardiac reflex (i.e., bradycardia produced by extra-ocular muscle traction) and empirical evidence that retrobulbar anesthesia significantly lowers the incidence of emesis after strabismus surgery. Eye muscle traction is presumed to elicit afferent signals that ultimately stimulate the vagus nerve. The same neuromuscular sequence is presumed to occur during reflexive eye movements under vestibular control and during more complicated combinations of reflexive and voluntary eye movements. It is proposed that the blocking of afferent signals from extra-ocular muscle in an otherwise intact vestibulo-ocular system will eliminate the signs and symptoms of motion sickness normally produced in a provocative environment.

Aviation Space & Environmental Medicine, 1994, 65(11): 1032-1035.