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Biomedical subjects

J R Lackner

Publications and source records attributed to J R Lackner.

At least 109 records · Page 6Linked to original sources
PubMed1979

Parabolic flight: loss of sense of orientation.

On the earth, or in level flight, a blindfolded subject being rotated at constant velocity about his recumbent long body axis experiences illusory orbital motion of his body in the opposite direction. By contrast, during comparable rotation in the free-fall phase of parabolic flight, no body motion is perceived and all sense of external orientation may be lost; when touch and pressure stimulation is applied to the body surface, a sense of orientation is reestablished immediately. The increased gravitoinertial force period of a parabola produces an exaggeration of the orbital motion experienced in level flight. These observations reveal an important influence of touch, pressure, and kinesthetic information on spatial orientation and provide a basis for understanding many of the postural illusions reported by astronauts in space flight.

Acceleration↗
PubMed1979

Some influences of vision on susceptibility to motion sickness.

Two experiments were performed to evaluate the influence of vision on susceptibility to motion sickness during exposure to constant patterns of vestibular stimulation. The motion profile involved accelerating subjects at 20 degrees/s2 to 300 degrees/s, maintaining them at that constant velocity for 30 s, and decelerating them to a rapid stop in about 1.5 s. The number of stops tolerated by a subject before reaching the motion sickness endpoint served as his score. In Experiment 1, subjects were tested twice with their eyes open and twice with their eyes blindfolded. They tolerated fewer sudden stops when permitted sight of the experimental chamber. In Experiment 2, the effect of having the eyes-open or closed at different stages of the motion profile was evaluated. Having the eyes open during any stage of the test was more stressful than having the eyes closed, but this was especially true during the sudden stops. The findings are discussed in terms of their general implications for understanding a) situations in which vision alone elicits symptoms of motion sickness, and b) situations involving vestibular stimulation where vision heightens susceptibility.

Acceleration↗
PubMed1979

Changes in apparent body orientation and sensory localization induced by vibration of postural muscles: vibratory myesthetic illusions.

Illusions of continuous body tilt and rotation can be elicited by vibrating postural muscles of subjects standing in the dark. During such illusory motion, the apparent pivot point of the body can be influenced systematically by touch and pressure cues. Strong apparent movement is sometimes accompained by nystagmus of compensatory sign. If a small target light is visible during vibration, visual motion of like direction and velocity will accompany the illusory body motion. We have designated this pattern of apparent body and visual motion the "propriogyral illusion". Full room illumination abolishes both components of the propiogyral illusion. When the propriogyral illusion is being experienced, there is a dissociation between apparent displacement and apparent velocity; the extent of displacement is always less than would be expected on the basis of apparent velocity. The illusions of continuous body motion and the propriogyral illusion represent elements of a general set of vibratory myesthetic illusions that influence apparent posture, sensory, localization, and position sense of the body. These illusions demonstrate an important contribution of muscle afferent and touch-pressure information to the central mechanisms that determine apparent spatial orientation and visual localization. They also provide evidence that somatosensory information about orientation can influence oculomotor control.

Aerospace Medicine↗
PubMed1979

Rotation at 30 RPM about the A axis after 6 hours in the 10 degree head-down position: effect on susceptibility to motion sickness.

Intraindividual differences in susceptibility to motion sickness were measured in 14 subjects for two conditions of rotation at 30 rpm in the 10 degree head-down position. In one condition, subjects were in the 10 degree head-down position for 6 h prior to the onset of rotation; in the other condition, the delay was only 15 min. In both conditions, there were changes in vital capacity, indicating a redistribution of movable body fluids. Subjects tended to be less susceptible to motion sickness when they were recumbent for 6 h prior to rotation. These results are countervidence for the hypothesis that shifts of body fluid are responsible in large part for the motion sickness elicited in orbital space flight.

Aerospace Medicine↗
PubMed1978

Incremental exposure facilitates adaptation to sensory rearrangement.

The rate of adaptation to unusual patterns of vestibular stimulation is enhanced if the final stimulus level is achieved gradually rather than in a single step (6,7). Measurements of adaptation to visual rearrangement elicited by stepwise and single-step exposure indicate that incremental exposure also facilitates adaptation to visual rearrangement; adaptation is diminished when the optical displacement is varied nonsystematically during exposure. Enhancement of adaptation to unusual patterns of sensory stimulation by incremental exposure may reflect a general principle of sensorimotor function.

Adaptation, Ocular↗
PubMed1978

Postural illusions experienced during Z-axis recumbent rotation and their dependence upon somatosensory stimulation of the body surface.

A blindfolded recumbent subject experiences a variety of postural illusions when rotated about his Z axis. Initially, during the acceleratory phase of rotation turning about his Z axis is experienced; but, as rotary velocity increases, a spiraling of the body outward in the direction opposite to true rotation is experienced as well. Above 15-20 rpm, only orbital motion of the body is experienced, with the subject feeling that he is always facing in the same direction. One cycle of the apparent orbit is completed each time the subject actually rotates 360 degrees. The reverse sequence of illusory motion is experienced during deceleration. The illusory motion all subjects experience during Z-axis recumbent rotation is shown to depend upon the touch- and pressure-stimulation of the body surface generated by contact forces of support.

Acceleration↗
PubMed1978

Some influences of touch and pressure cues on human spatial orientation.

During constant velocity rotation about his recumbent Z axis, a blindfolded subject feels as if he were on an orbital path in the same direction. This experienced motion results from the pattern of touch and pressure stimulation of the body surface. If the subject changes the pressure pattern on his body by bracing himself in the rotating apparatus in different ways, it is possible for him to influence profoundly and systematically his apparent orientation. For example, pressure on the top of his head while he is rotating can make the subject feel he is upside down on a cylindrical path. The changes in apparent ongoing posture elicited by different patterns of pressure cues are very similar for different subjects and are constant for the same subject over time. During experienced orbital motion, a subject will hear a continuously emitting sound source--one that is stationary in the external environment--as circling his head in the direction opposite that of his true rotation. If the rotating subject is permitted unrestricted sight of his surroundings, he neither experiences orbital motion nor mislocalizes sounds. These observations provide insight into the spatial orientation mechanisms that normally allow an organism to distinguish accurately between those changes in activity at its receptors contingent on its own movements, and those resulting from movement within the environment. They also provide a way of understanding some of the postural illusions experienced during exposure to unusual force environments, including free fall.

Adolescent↗
PubMed1977

Some aspects of the psychological representation of speech sounds.

If one listens to a meaningless syllable that is repeated over and over, he will hear it undergo a variety of changes that can be described systematically in terms of reorganization of the phones constituting the syllable and changes in a restricted set of phonetic distinctive features. When the repeated syllable is followed by a different syllable but in the same voice, the new (test) syllable will be misperceived in a manner related to the perceptual misrepresentation of the repeated syllable. In the present experiment subjects (N = 24) listened to 72 different experimental sequences of repeated syllables in a male voice followed by test syllables in a female voice. Identification of penultimate and test syllables was independent and in no instance were the phone constituting the syllables reorganized. These results are interpreted as evidence against both auditory and phonetic feature detector theories of speech perception.

Auditory Perception↗
PubMed1977

Some factors affecting the perceived ordering of natural speech stimuli.

Primary auditory stream segregation--the perceptual segregation of acoustically related elements of a continuous auditory sequence into spatially distinct streams--disrupts recovery of the relative temporal order of repeated sequences of consonant and vowel syllables. Three experiments were performed to determine why the apparent temporal order of natural speech is not similarly disrupted. Exp. 1 (N =24) showed that the disruption is not dependent on repetition of the 32 experimental sequences of consonant and vowel syllables. Exps. 2 (N = 48) and 3 (N = 20) showed that when 4 English monosyllables are used as stimuli and syntactic and intonational structure is present then the temporal integrity of the acoustic signal is preserved perceptually. Despite accurate resolution of order for the 40 experimental sequences, errors of words were common. These errors often imposed a syntactic organization on the resulting sequence.

Auditory Perception↗
PubMed1977

Comparison of susceptibility to motion sickness during rotation at 30 rpm in the earth-horizontal, 10 degrees head-up, and 10 degrees head-down positions.

Normal persons rotated about an Earth-horizontal axis vary in their susceptibility to motion sickness. The purpose of this experiment was to measure, intraindividual differences in susceptibility in 12 subjects when rotated 10 degrees head up and 10 degrees head down as well as in the horizontal position. Subjects assumed the test-position 60 min prior to rotation, thus providing an opportunity for translocation of body fluids. Physiological and psychophysical measurements were conducted throughout the experiment. There were no intraindividual differences in susceptibility to motion sickness in the three positions tested, although there were significant differences in vital capacity, demonstrating the expected fluid shifts. It was concluded that, in the sample of subjects tested, short-term effects of fluid shifts greater than those that would be manifested in zero gravity had no definite effect on motion sickness susceptibility.

Adult↗
PubMed1977

Optokinetic motion sickness: continuous head movements attenuate the visual induction of apparent self-rotation and symptoms of motion sickness.

Symptoms of motion sickness are sometimes experienced during exposure to optokinetic stimulation. Two experimetns were performed to compare the symptoms of motion sickness elicited when subjects were exposed to incremental changes in optokinetic stimulation while sitting passively and while continuously executing shoulder-to-shoulder head movements. In the first experiment, a fixed head-movement frequency (20 cpm) was used, wheras in the second the subjects varied the frequency of their head movements in order to maintain suppression of illusory self-rotation. In both experiments, subjects in the head-moving condition had fewer and less severe symptoms of motion sickness and experienced illusory self-rotation after longer exposure times and at higher optokinetic velocities than in the head-stationary condition. Subjects in th- head-movement condition of the second experiment increased the frequency of their head movements as the velocity of optokinetic stimulation increased. The symptoms of motion sickness elicited during optokinetic stimulation tended to be dizziness, headache, eye-strain, and stomach awareness appearing in no fixed order. The pattern and constellation of symptoms are unlike those elicited by vestibular stimulation.

Eye Movements↗
PubMed1977

Induction of illusory self-rotation and nystagmus by a rotating sound-field.

Subjects seated in darkness often experience illusory self-rotation when exposed to a rotating sound field. Compelling illusions of self-rotation are generally accompanied by nystagmoid movements of the eyes with the slow phase in the direction opposite that of the experienced self-rotation. These phenomena are related to the functioning of a spatial constancy mechanism by which a stable distinction is normally maintained between movements of self and movements of the environment. The appearance of nystagmus during illusory self-rotation indicates that apparent body orientation can influence oculomotor control.

Acoustic Stimulation↗
PubMed1977

Somatosensory motion after-effect following earth-horizontal rotation about the Z-axis: a new illusion.

During rotation about the Z-axos while recumbent one is exposed to a changing pattern of pressure cues over the body surface. If the body is only loosely padded in the experimental apparatus, then apparent motion of part of the body surface may be experienced sometime after rotation has been terminated. This somatosensory motion aftereffect of opposite sign is temporarily abolished if one looks at the affected body area, but is again re-experienced when the gaze is shifted elswhere. The similarity of this motion aftereffect to those contingent on vestibular and visual stimulation is discussed.

Humans↗