Head turning versus manual pointing to auditory targets in normal subjects and in subjects with right parietal damage.

Head turning and manual pointing to auditory targets have been studied in normal subjects and in subjects with right parietal damage. Important differences were found between these two types of movement. (1) In brain-damaged subjects, audiospatial manual pointing deficit patterns and audiospatial head turning deficit patterns were dissociated. Moreover, head turning deficits tended to appear peripherally in both auditory hemifields, while manual pointing deficits tended to appear unilaterally in the left hemifield. (2) In normal subjects, at all tested eccentricities in both hemifields, head turning performances showed a characteristic undershooting of auditory targets when compared to manual pointing. Results are discussed in terms of differences between the processes underlying audio-motor tasks that involve the head and tasks that involve the hands.     

The temporal organization of hand, eye, and head movements during reaching and pointing

Two experiments are reported that address the issue of coordination of the eyes, head, and hand during reaching and pointing. Movement initiation of the eyes, head, and hand were monitored in order to make inferences about the type of movement control used. In the first experiment, when subjects pointed with the finger to predictable or unpredictable locations marked by the appearance of a light, no differences between head and eye movement initiation were found. In the second experiment, when subjects pointed very fast with the finger, the head started to move before the eyes did. Conversely, when subjects pointed accurately, and thus more slowly, with the finger, the eyes started to move first, followed by the head and finger. When subjects were instructed to point to the same visual target only with their eyes and head, both fast and accurately, however, eye movement always started before head movement, regardless of speed-accuracy instructions. These results indicate that the behavior of the eye and head system can be altered by introducing arm movements. This, along with the variable movement initiation patterns, contradicts the idea that the eye, head, and hand system is controlled by a single motor program. The time of movement termination was also monitored, and across both experiments, the eyes always reached the target first, followed by the finger, and then the head. This finding suggests that movement termination patterns may be a fundamental control variable.     

Mechanisms controlling head stabilization in the elderly during random rotations in the vertical plane

Frequency-related response characteristics of the mechanisms controlling stabilization of the head in 10 elderly subjects were compared with response characteristics in 8 young adults. Angular velocity of the head with respect to the trunk and EMG responses of 2 neck muscles were recorded in 10 seated subjects during pseudorandom rotations of the trunk in the sagittal plane at frequencies of 0.35 to 3.05 Hz. Subjects were required to actively stabilize their heads with (VS) and without (NY) visual feedback so that voluntary mechanisms and the influence of vision could be tested. Reflex mechanisms were examined when subjects were distracted by a mental calculation task during rotations in the dark (MA). Age emerged as an influential factor in the performance of head stabilization mechanisms, and decrements in performance were even more pronounced in the older as compared with younger elderly subjects. Age effects could be seen in the (a) diminished ability to voluntarily stabilize the head, particularly with the absence of vision, (b) impaired ability to stabilize the head when cognitively distracted, and (c) appearance of a resonant response of the head. Control of head stabilization shifted from reflex mechanisms to system mechanics, probably as a result of age-related changes in the integrity of the sensory systems. The elderly's system mechanics could not effectively compensate for the disturbances, however, and instability was the result.     

Mechanisms Controlling Head Stabilization in the Elderly During Random Rotations in the Vertical Plane

Frequency-related response characteristics of the mechanisms controlling stabilization of the head in 10 elderly subjects were compared with response characteristics in 8 young adults. Angular velocity of the head with respect to the trunk and EMG responses of 2 neck muscles were recorded in 10 seated subjects during pseudorandom rotations of the trunk in the sagittal plane at frequencies of 0.35 to 3.05 Hz. Subjects were required to actively stabilize their heads with (VS) and without (NV) visual feedback so that voluntary mechanisms and the influence of vision could be tested. Reflex mechanisms were examined when subjects were distracted by a mental calculation task during rotations in the dark (MA). Age emerged as an influential factor in the performance of head stabilization mechanisms, and decrements in performance were even more pronounced in the older as compared with younger elderly subjects. Age effects could be seen in the (a) diminished ability to voluntarily stabilize the head, particularly with the absence of vision, (b) impaired ability to stabilize the head when cognitively distracted, and (c) appearance of a resonant response of the head. Control of head stabilization shifted from reflex mechanisms to system mechanics, probably as a result of age-related changes in the integrity of the sensory systems. The elderly's system mechanics could not effectively compensate for the disturbances, however, and instability was the result.     

Components of analogical reasoning in a mildly head injured population

This study sought to investigate the effects of mild head injury on a particular type of cognitive ability, verbal analogical reasoning. The performance of 19 individuals with head injuries was compared to a group of 30 control subjects matched for age, education, and gender on 100 verbal analogies. Solution times and error rates were modeled. Unstandardized regression weights for individual subjects were correlated with subjects’ performance on a number of standardized ability tests. Results showed that compared to the control subjects, the head injured subjects: (a) were significantly slower to solve the analogies, and were particularly slow to perform certain processes: encoding/inference and comparison; (b) tended to show greater variability in performance; and (c) had data that had a poorer componential model fit. The data suggest that analogical reasoning is affected by a head injury, and that certain information processes may be responsible for performance deficits.     

Further experiments on the perception of growth in three dimensions

Mark and Todd (1983) reported an experiment in which the cardioidal strain transformation was extended to three dimensions and applied to a three-dimensional (3-D) representation of the head of a 15-year-old girl in a direction that made the transformed head appear younger to the vast majority of their subjects. The experiments reported here extend this research in order to examine whether subjects are indeed detecting cardioidal strain in three dimensions, rather than detecting changes in head slant or making 2-D comparisons of the shape of the occluding contour. Three-dimensional surfaces were obtained by measuring a real head manually (Experiment 1) and with a laser scanner (Experiment 2), and transformed to different age levels using the 3-D strain transformation described by Mark and Todd (1983). There were no statistically significant differences in the accuracy with which relative age judgments could be made in response to pairs of profiles, pairs of 3/4 views, or pairs of mixed views (profile plus 3/4 view), suggesting that subjects can indeed extract the cardioidal strain level of the head in three dimensions. However, an additional effect that emerged in these studies was that judgments were crucially affected by the instructions given to subjects, which suggests that factors other than cardioidal strain are important in making judgments about rich data structures.     

Adaptation to altered visual—vestibular feedback: Mechanisms of maintenance and recovery

Adaptation of perceived movement during head motion (apparent concomitant motion, ACM) and the subsequent elimination of adaptation were studied in two experiments. During the adaptation phase of both experiments, subjects performed voluntary 1-Hz head oscillations for 6 min while fixating a stimulus moving either in the same (with) direction as or the opposite (against) direction of head movements. In Experiment 1, ACM adaptation was measured following either a 1- or a 4-min delay after the adaptation phase. Results indicated some loss of adaptation during the additional 3-min delay, demonstrating a tendency of the system linking head and image to return to its preadaptation state following removal of an adaptation stimulus. In Experiment 2, subjects viewed a stimulus after adaptation that appeared to move minimally in the same manner as the adaptation stimulus during 3 min of head oscillations. No loss of adaptation was measured in these subjects between the beginning and the end of the 3-min interval. In another condition, subjects viewed a stimulus that appeared to move alternately in the same direction as and in the opposite direction of the adaptation stimulus during a similar 3-min interval following adaptation. ACM adaptation was substantially reduced during this 3-min interval. These results implicate two mechanisms that operate to either maintain or eliminate ACM adaptation. One is passive and operates in the absence of visual feedback to eliminate the short-term adapted state, and the other responds to postadaptation visual feedback.     

Haptic cues for orientation and postural control

Haptic cues from fingertip contact with a stable surface attenuate body sway in subjects even when the contact forces are too small to provide physical support of the body. We investigated how haptic cues derived from contact of a cane with a stationary surface at low force levels aids postural control in sighted and congenitally blind individuals. Five sighted (eyes closed) and five congenitally blind subjects maintained a tandem Romberg stance in five conditions: (1) no cane; (2, 3) touch contact (<2 N of applied force) while holding the cane in a vertical or slanted orientation; and (4, 5) force contact (as much force as desired) in the vertical and slanted orientations. Touch contact of a cane at force levels below those necessary to provide significant physical stabilization was as effective as force contact in reducing postural sway in all subjects, compared to the no-cane condition. A slanted cane was far more effective in reducing postural sway than was a perpendicular cane. Cane use also decreased head displacement of sighted subjects far more than that of blind subjects. These results suggest that head movement control is linked to postural control through gaze stabilization reflexes in sighted subjects; such reflexes are absent in congenitally blind individuals and may account for their higher levels of head displacement.     

Responses to a virtual reality grocery store in persons with and without vestibular dysfunction.

People with vestibular dysfunction often complain of having difficulty walking in visually complex environments. Virtual reality (VR) may serve as a useful therapeutic tool for providing physical therapy to these people. The purpose of this pilot project was to explore the ability of people with and without vestibular dysfunction to use and tolerate virtual environments that can be used in physical therapy. We have chosen grocery store environments, which often elicit complaints from patients. Two patients and three control subjects were asked to stand and navigate in VR grocery stores while finding products. Perceived discomfort, simulator sickness symptoms, distance traveled, and speed of head movement were recorded. Symptoms and discomfort increased in one subject with vestibular dysfunction. The older subjects traveled a shorter distance and had greater speed of head movements compared with young subjects. Environments with a greater number of products resulted in more head movements and a shorter distance traveled.     

Inhibitory control differences following mild head injury

Complex inhibitory control, defined as the ability to inhibit a planned or ongoing action, was assessed in a sample of individuals with a history of mild head injury, case-matched with normal control subjects for age and gender. This central act of control was assessed using a modification of the stop-signal paradigm. The group with mild head injury took longer to inhibit their on going action and reported more accidents than the normal control subjects. The group that reported having had a mild head injury did not differ in terms of their go reaction time, number of correct responses, handedness, education level, or reported learning disabilities. Limitations of this design and directions for future research are discussed.     

Illusory visual direction during and after backward head tilts

When the head is returned to upright after prolonged backward tilt, people who are asked to look straight ahead look higher than they did before the backward tilting. One explanation attributes the illusory visual direction to a change in muscle responsiveness which develops after the head is returned to upright. According to this explanation, the illusory shift should be absent, or at least reduced, if the subjects are not returned to upright before testing. In the present study, the illusion was the same whether subjects remained tilted for testing or were returned to upright.     

Extinction of conditioned sexual responses in male Japanese quail (Coturnix japonica): role of species-typical cues

The authors examined how a conditioned stimulus (CS) that included species-typical cues affected the acquisition and extinction of conditioned sexual responses in male quail (Coturnix japonica). Some subjects were conditioned with a CS that supported sexual responses and included a taxidermic head of a female quail. Others were conditioned with a similar CS that lacked species-typical cues. Pairing the CSs with access to live females increased CS-directed behavior, with the head CS eliciting significantly more responding than the no-head CS. Responding to the head CS persisted during the 42-day, 126-trial extinction phase; responses to the no-head CS extinguished. Responding declined when the cues were removed or the subjects were sexually satiated. Possible functions and mechanisms of these effects are discussed.     

Shape from shading in different frames of reference

It has often been reported that, in the absence of information about the direction of illumination, people interpret surface convexities and concavities in accordance with the assumption that illumination comes from above. However, 'above' could mean with reference to gravity, the head or the retina. Yonas et al reported that four-year-old infants use the head more than gravity as the frame of reference in interpreting surface relief but that seven-year-olds make about equal use of the two frames of reference. The potency of these two frames of reference when acting separately and when pitted against each other was measured on adult subjects. For all subjects the 'assumption' about the direction of illumination was predominantly with respect to the head. The gravitational frame was used only when the headcentric frame was irrelevant, and then not consistently.     

Contextual conditioning and the control of copulatory behavior by species-specific sign stimuli in male Japanese quail

Three experiments were conducted to identify species-specific sign stimuli sufficient to elicit copulatory behavior in male Japanese quail and to determine how learning is involved in the control of behavior by these sign stimuli. In Experiment 1, sexually experienced subjects were tested for copulatory behavior with a live female quail and with a model consisting of a female quail's head and neck mounted in front of a foam pad. Comparable levels of copulatory behavior were observed in the two tests, indicating that static visual cues provided by a female quail's head and neck are sufficient to elicit copulatory behavior in this species. Experiment 2 showed that male birds that previously received numerous opportunities to copulate with a live female quail in the test situation were significantly more likely to copulate with the head + neck model than were sexually inexperienced subjects. Experiment 3 showed that prior sexual experience with live quail facilitated responding to the head + neck model only if the sexual experience was provided in the same place where subjects were later tested with the model. This last finding suggests that sexual experience facilitates control of copulatory behavior by species-specific sign stimuli through contextual conditioning. Contextual conditioning may lower the threshold for sexual behavior with the result that a stimulus as impoverished as an immobile model containing only the head and neck of a female quail becomes sufficient to elicit normal levels of copulatory behavior. The results are also discussed as an example of conditioned stimulus facilitation of responding to an unconditioned stimulus.     

Exploration of head injury without medical attention.

In surveys of prison inmates and four other populations, 1,055 subjects reported having a history of 489 head injuries, with 31% of these "unattended" by a physician and 60% "undocumented" in that they were not hospitalized. The prison inmates did not have a history of more unattended injuries or undocumented injuries than the other groups of subjects as was predicted. However, the inmates reported more permanent effects from their unattended and undocumented injuries. Also, the inmates had more permanent effects and longer unconsciousness than did the other groups for their attended and documented head injuries.     

The effect of head turn on auditory asymmetry

In two experiments, right-handed men and women were tested for ear differences in report of dichotically presented digits, with their heads straight ahead, turned 90 degrees to the left, and turned 90 degrees to the right. In Experiment 1, head turn was controlled simply by asking the subjects to fixate an appropriately located point; a right-ear advantage occurred under all conditions of head turn among the men, but only in the head-straight condition among the women. In Experiment 2, head turn was controlled by having the subjects direct a flashlight attached to their heads toward the fixation point. This eliminated the right-ear advantage under all head conditions for the men, but for the women the right-ear advantage was, if anything, more pronounced when their heads were turned than when straight. These results suggest that auditory asymmetry depends in part on whether space is perceived as divided into left and right sides, and in part of the balance between spatial and verbal requirements. Both factors, and the asymmetry itself, may interact with sex.     

What’s up in mental rotation?

We report two experiments on the influence of head tilt on mental rotation. In Experiment I, subjects decided whether dot patterns were or were not repeated about a line. Their reaction times (RTs) were consistent with the interpretation that they mentally rotated the patterns so that the line was subjectively vertical before making their decisions. When the subjects tilted their heads, the RT functions shifted in the direction of the tilt, indicating that the subjective vertical lay closer to the retinal than to the gravitational vertical. In Experiment II, subjects decided whether singly presented alphanumeric characters in various orientations were standard or backward (mirror-reversed). Again, analysis of their RTs suggested mental rotation to the standard upright, but the function was unaffected by head tilt; in this case, the subjects operated in subjective gravitational rather than retinal coordinates. The choice of retinal or gravitational coordinates may depend on whether the stimuli are interpreted egocentrically or as part of the external world.     

Rapid adaptation to a prismatic distortion

Among several shape distortions caused by a wedge prism is one where a pattern of evenly spaced lines that are parallel to the prism base reaches the eye with distances seen through the base region contracted and distances seen through the apex region expanded. Rapid partial adaptation to this distortion was obtained by having subjects who wore the prism in vertical orientation move the head up and down during the exposure period. The head movements caused the distortion to shift up and down through the line pattern. When, with subjects’ heads stationary, the distortion was made to shift up and down by artificial means, rapid adaptation failed to develop. It is proposed that head movements are here needed for adaptation to develop, because the covariance between them and the shifting of the distortion serves as a signal that the distortions are not objective facts and causes the initiation of the adaptation process.     

The role of head-centric spatial reference with a static and kinetic visual disturbance

A static or kinetic visual disturbance affects subjects’ ability to estimate the direction of the gravitational vertical. This kind of error is increased by a head roll inclination. In two experiments, we combined head orientation with a static (Experiment 1: tilted frame) versus kinetic (Experiment 2: rotating disk) visual disturbance. The results showed that with a static visual disturbance, the increase of errors in the inclined head condition was mainly the consequence of a postural head effect like an Aubert effect. On the contrary, with a kinetic visual disturbance, it appears that the disk effect increases with head inclination. However, individual errors observed with the head inclined in front of a stationary disk were systematically correlated with the errors triggered by the same head inclination in front of a rotating disk. These observations confirm that the head axis spatial reference plays an important role in orientation perception, whatever the head position and the kind of visual display.     

Wrinkling and head shape as coordinated sources of age-level information

Changes in the shape of a human head and the development of facial wrinkles were examined as potential sources of information about age level. In Experiment 1, subjects estimated the ages of faces that had been produced by systematically manipulating characteristic head shapes and levels of wrinkles associated with ages 15, 30, 50, and 70 years. The results indicated that observers used both sources of craniofacial change in making age estimates; but the effect of either source of change on perceived age depended upon the level of the other source of change. In Experiment 2, subjects’ ratings of the apparent conflict between levels of head shape and wrinkles further substantiated the conclusion that observers are sensitive to the coordination of products of the two sources of change. These findings suggest that the information specifying perceived age level is a complexrelationship among different types of craniofacial change.