Attentional demands of continuously monitoring orientation using vestibular information.

The aim of this series of experiments was to determine whether attention is normally required for continuously processing vestibular information concerning orientation, or is required only when orientation is disrupted (eg by vestibular dysfunction or by conflicting visual and vestibular orientation cues). In the first two studies, healthy subjects were passively oscillated, and indicated when they perceived they were passing through their starting position. There was only weak evidence for interference between performance on this 'continuous orientation monitoring task' and on concurrent mental tasks. However, a third study showed that when patients with vestibular imbalance carried out the continuous orientation monitoring task their performance on a concurrent mental arithmetic task was substantially impaired. This dual task interference was correlated with inaccuracy in judging orientation on the continuous orientation monitoring task, which in turn correlated with severity of recent vestibular symptomatology (assessed by questionnaire). In a fourth experiment, disorientation was induced in healthy subjects by rotating the visual field about the line of sight. Bidirectional interference was observed between monitoring orientation (assessed by accuracy in setting a rod to the perceived vertical) and performance of an arithmetic task. Dual task interference was correlated with baseline levels of disorientation induced by the visual field, as indicated by inaccuracy in judging the visual vertical. These findings suggest that monitoring orientation makes significant demands upon cortical processing resources when disorientation is induced, whether the disorientation results from deficient sensory functioning or from ambiguous perceptual information.     

Retained alloplastic temporomandibular joint disk implants: a retrospective study

The surgical treatment of intermediate- to late-stage temporomandibular joint disease often involves disk removal. In many instances, disks have not been replaced; long-term postsurgical findings of crepitation and osseous remodeling have been noted although subjective signs and symptoms have been few. Attempts to decrease the noises and bony changes, to enhance biologic resurfacing, and to prevent adhesions, recurrent pain, and dysfunction have prompted many surgeons to use various alloplastic materials to replace the disk, either in a planned permanent (retained) or a planned temporary (retrievable) manner. However, a certain degree of morbidity remains. This article reports clinical responses and radiographic findings in a series of patients who received retained alloplastic temporomandibular joint disk implants.     

Complications of needle localization of foreign bodies and nonpalpable breast lesions

Needle-wire localization of foreign bodies and nonpalpable breast lesions is commonly used to allow for more accurate excision or biopsy. We present three examples of complications of the localization procedure: (1) wire migration into the chest wall with retained fragment, (2) transection of a wire during biopsy with retained hook fragment, and (3) wire migration within the thigh soft tissues with breakage at the hooked end. Recommendations to minimize the incidence of these complications and their sequelae include (1) bending the hookwire 90 degree at the skin surface following localization, (2) transferring the patient between the radiology suite and the operating room via a stretcher, with minimal movement of the body part localized, and (3) accounting for the entire length of wire by the surgeon, pathologist, and radiologist following the procedure to exclude retained fragments.     

Eye movements induced by lateral acceleration steps Effect of visual context and acceleration levels

 Eye movement responses were obtained from six normal subjects exposed to randomly ordered rightwards/leftwards linear acceleration steps of 0.05 g, 0.1 g or 0.24 g amplitude and 650 ms duration along the inter-aural axis. With the instruction to gaze passively into the darkness, compensatory nystagmus was evoked with slow-phase velocity sensitivity of 49° s⁻¹ g ⁻¹. When subjects viewed earth-fixed targets at 30 cm, 60 cm or 280 cm, eye movements at 130 ms from motion onset were proportional to acceleration and inversely proportional to target distance, before the onset of visually guided eye movements. Our results show that a modulation with viewing distances of the earliest human otolith-ocular reflexes occurs in the presence of pure linear acceleration. However, full compensation was not attained for the nearer targets and higher accelerations. Received: 31 January 1996 / Accepted: 30 September 1996     

Horizontal ocular vergence and the three-dimensional response to whole-body roll motion

We evaluated the human binocular response to roll motion in the dark and during visual fixation with horizontal convergence. Six normal human subjects were exposed to manually driven, whole-body rotation about an earth-vertical, naso-occipital axis, under two conditions: (I) oscillation at 0.4 Hz (peak velocity 69+/-3.8 degree/s) in the dark, and whilst fixating an axial light-emitting diode at 48 cm ('near') and at 206 cm ('far'); (II) constant velocity rotation (56.5+/-3.1 degree/s) for 40 s, clockwise and counter-clockwise, in the dark, and sudden stops. Eye and head movements were monitored using scleral search coils. In head-fixed, angular velocity coordinates roll motion always evoked conjugate ocular torsion, with small conjugate horizontal and disconjugate vertical components. The resultant binocular eye responses were rotations about convergent axes. During oscillation with target fixation the convergence of the rotation axes was larger than that predicted by target geometry, producing disconjugate oscillations of vertical gaze about the target ('skewing'). Fast-phase eye movements were primarily resetting rotations about the same convergent rotation axes as the slow phases, but the small vertical velocity components had oscillatory, asymmetrical profiles. In response to velocity steps the slow-phase eye velocity decayed exponentially with time constants of 4.5+/-1.5 s for the torsional component and 5.8+/-1.9 s for the 'vertical vergence' component (right eye-left eye recordings). We conclude that in normal human subjects dynamic vertical canal stimulation with horizontal gaze convergence evokes rotation of the eyes about convergent axes and a small skewing of the eyes.     

Compensatory eye movements in the presence of conflicting canal and otolith signals

Summary Orbital motion of the head with the face directed towards the axis of rotation is a stimulus to the otolith organs which is in the opposite rightwards-leftwards sense to the rotational stimulus to the semicircular canals. This can be experienced, for example, by a child held at arms length en face and swung from side to side. As one swings, say to the right, the child's head rotates to its right yet moves linearly to its left. Eye movement responses to a transient orbital movement were observed whilst subjects fixated earth-fixed targets, i) a near target placed between the head and the axis whose relative displacement is in the same direction as head rotation, and ii) a far target placed beyond the axis whose relative motion is in the opposite direction to head rotation. The motion stimuli evoked slow phase eye movements at 45 ms latency, always in the opposite direction to head rotation, thus compensating for the motion of the far target but in the wrong direction for fixating the near target. Theoretically, fixating the near target demands a predominance of the otolith ocularreflex, which would give an eye movement in the correct direction. However, despite visual cues, it seems that if the canal and otolith-ocular reflexes are evoked in opposing directions, the otolith reflex fails to operate at a sensitivity sufficiently high to reverse the direction of the canal-reflex.     

Percept-related changes in horizontal optokinetic nystagmus at different body orientations in space

Large-field motion of the visual environment is a powerful stimulus to induce the perception of contra-directional self-motion in a stationary observer. We investigated the interrelations between horizontal optokinetic nystagmus and subjective states of motion perception under variation of subjects' orientation with respect to gravity. Subjects were tested sitting upright and lying supine, and signalled transitions between object- and self-motion perception whilst viewing an optokinetic stimulus rotating about the subjects' longitudinal axis at a range of angular velocities. Optokinetic stimulation in the supine condition resulted in subjects perceiving a graviceptive conflict and the illusory perception of whole body tilt in a direction opposite to optokinetic stimulus rotation, whereas during upright viewing the axis of stimulus rotation was aligned with the direction of gravity and thus did not result in a conflict or perception of tilt. In both postures, self-motion perception coincided with an increased deviation of mean horizontal gaze position in the perceived direction of heading with a concurrent reduction in optokinetic nystagmus slow-phase gain. Slow-phase gain was also significantly reduced in the supine position as well as at increasing stimulus velocities. The results demonstrate that spontaneous transitions between the perception of object-motion and that of self-motion consistently coincide with spatial attentional and orientational strategies, shifting from passive monitoring to active oculomotor exploration and anticipation.     

Stabilizing seizure disorders

Scientific understanding of seizures and epilepsy is rapidly evolving. Recent advances in diagnosis, classification, and medical and surgical treatment have significantly altered our approach to patients with these conditions.     

Low Prenatal Weight Gain Among Adult WIC Participants Delivering Term Singleton Infants: Variation by Maternal and Program Participation Characteristics

Objective: To determine the association of maternal and prenatal WIC program participation characteristics with low prenatal weight gain among adult women delivering liveborn, singleton infants at term. Methods: WIC program data for 19,017 Black and White Alabama women delivering in 1994 were linked with birth certificate files to examine the association of anthropometric, demographic, reproductive, hematologic, behavioral and program participation characteristics with low prenatal weight gain. Results: One third (31.0%) had low prenatal weight gain as defined by the Institute of Medicine. The incidence of low weight gain was increased among women who had < 12 years of education, were single, Black, anemic, had low or normal pre-pregnancy body mass index (BMI), increased parity, interpregnancy intervals 24 months, used tobacco or alcohol, or entered prenatal care or WIC programs after the first trimester. After adjusting for selected maternal characteristics, the adjusted odds ratios (AOR) for low weight gain were increased with short interpregnancy intervals (AOR 1.21 to 2.20); tobacco use (AOR 1.16 to 1.40), anemia (AOR 1.20 to 1.25), and second trimester entry into prenatal care (AOR 1.14 to 1.20); the size of the AORs and 95% confidence intervals varied by BMI and racial subgroup. Conclusions: The results of this study suggest that WIC interventions targeting low prenatal weight gain be focused on risk factors present not only during pregnancy, but during the pre- and interconceptional periods as well. Interventions should target low BMI, tobacco use, and anemia, and include attention to nutrition screening and risk reduction among women in postpartum and family planning clinic settings.