Vasudevan Lakshminarayanan

Electromyographic Evidence of Neurological Controller Signals with Viscous Load

Ensemble averaging after pre-editing of surface EMG potentials has enabled construction of underlying controller signals from stereotyped head movements. Carefully controlled, intended time-optimal movements by trained, actively participating human subjects have been found to yield repeatable, multi-pulse controller signals. Also, adaptive changes in these horizontal head movements in response to added viscous loads showed further causal relationships between movement dynamics and EMG signals from left and right splenius muscles. These experimental results are a base from which modeling studies can be performed to explicate the neurological control strategies used in the performance of this class of movements.

DISCRIMINATION OF RELATIVE SPATIAL POSITION

Subjects can accurately discriminate small changes in the relative position of features within a pattern. Simple patterns (intersected line segments) can undergo magnification and a variety of transformations without significantly affecting the discrimination thresholds. Features to be localized and compared need not be similar. We suggest that such relative position discriminations could support complex object identification.

Optokinetic and vection responses to apparent motion in man

Apparent motion was investigated as a stimulus for optokinetic nystagmus (OKN) and self-motion perception (vection). Apparent motion was stimulated by stroboscopically illuminating vertical stripes on the interior of a large drum that rotated about the observer at 20, 40 and 60 deg/sec. We determined threshold stroboscopic frequencies (f) for the appearance of smooth continuous apparent motion and measured responses of pursuit, OKN, optokinetic after nystagmus (OKAN) and vection, to stroboscopic frequencies at, above and below f. Pursuit occurred for all of these stimuli. However OKN, OKAN and vection only occurred for frequencies equal to or greater than the threshold for continuous apparent motion. Our results suggest that pursuit can occur as a response to apparent motion generated by both small and large image displacements, while OKN and vection are responses to apparent motion generated by small image displacements only. These results suggest that different afferent sources are utilized for the control of pursuit and of the slow phase of OKN.

Initial field and energy flux in absorbing optical waveguides. II. Implications

We present here numerical estimates of the density and flux of energy based on physical parameters associated with the absorption properties of certain types of absorbing optical waveguides. These results are based on a theoretical formalism established previously for the initial field incident upon the entrance pupil of an absorbing optical waveguide. Based on these results, the mechanisms of confined energy transmission and possible cross talk between neighboring waveguides are discussed. Some comments on the behavior of Bessel functions with complex arguments are also included in the discussion.

Visual field defects detected in patients with Gilles de la Tourette syndrome: Preliminary report

The presence of visual field anomalies was measured using Goldmann kinetic perimetry in twelve patients, age 7 to 39 with Gilles de la Tourette syndrome. Refraction to the cupola was carefully controlled.The visual acuity of the group was good to excellent. Visual field alterations were prechiasmal, generally non-symmetric, and best described as arcuate defects, steps, baring of the blind spot and enlargement of the blind spot. Central fields were most commonly affected, i.e., I/2e to I/1B isopters.There was no evidence of glaucoma in any of the patients although two patients exhibited keratoconus and another one manifested moderate to high astigmatism.Visual involvement other than ocular and lid tics have not been reported in Tourette syndrome. This research represents clear evidence of additional physical components in this condition.Automated visual field measurements are not recommended in this population because of the presence of non-predictable tic and vocal behavior (both may result in head/eye movements). Suppression of tic behavior can be very fatiguing. (Eight of twelve of the patients reported exhibited signs of marked fatigue during testing.)

The Stiles—Crawford Effect of the First Kind (SCE I): Studies of SCE I in an Aniridic Observer

The Stiles—Crawford effect of the first kind (SCE I), discovered in 1933, represented a major breakthrough in our understanding of retinal physiology and the modern beginning of the science of photoreceptor optics. The current status of knowledge in this area is briefly reviewed. A study is presented of a white adult female observer with aniridia, clear media, only traces of nystagmus, rather good visual acuity, and good fixation. It is shown that this individual exhibits approximate alignment of her photoreceptors with the center of the retinal sphere, clear evidence of side lobes on functions, and surprisingly steep SCE I functions. The implications of these findings are considered.

Gilles De La Tourette Syndrome: Genetic Marker?

In An Accompanying Paper (And In Other Reports), Visual Field Defects In Gilles De La Tourette Syndrome (Ts), A Complex Neuropsychiatric Condition Involving Motor, Vocal And Behavioral Anomalies Have Been Described. Tourette Syndrome Is Thought To Be A Dominant Trait Passed Preferentially From Fathers To Sons Over Daughters. In This Paper, Visual Field Studies Of Families Which Include A Proband Who Has A Confirmed Diagnosis Of Ts Are Presented. To Date, All Ts Patients, All Fathers And A Majority Of Mothers Of Probands Show Characteristic Visual Field Alterations. It Will Be Important To Determine Whether These Visual Field Determinations Serve As A Genetic Marker For This Complex Of Traits.

The vestibular ocular reflex in Alzheimer's disease

The vestibular ocular reflex (VOR) and VOR suppression in both light and dark- ness were tested in subjects with probable Alzheimers disease of mild to moderate severity. It is found that mechanisms responsible for VOR and VOR suppression are apparently intact in early stages of this disease.

An analysis of step-like field defects in Gilles de la Tourette syndrome

Step-like visual field defects have been found in 37 individuals exhibiting Gilles de la Tourette syndrome (TS). The authors present an analysis of these step-like field defects. There is a near equal distribution of nasal and temporal steps in this group of individuals. The majority (76%) of steps face upwards. These results are independent of age and sex. However, drugs used in management of TS have a quantitative effect on visual fields. Drug therapy reduces the number of steps detected and also reduces areas of sensitivity difference at the horizontal meridian. Analysis also suggests that plotting at least two isopters will result in detection of a step-like field defect in all individuals exhibiting TS and in 91% of the eyes of such individuals.It is difficult to determine the underlying pathophysiology for these types of visual field defects. It is suggested that dopamine, a neurotransmitter of the retina might be involved in some manner in the pathogenesis of the visual field defects.

Initial field and energy flux in absorbing optical waveguides. I. Theoretical formalism.

An exact formulation of the electromagnetic field striking an optical waveguide is presented and compared with the decomposition relationship used in the literature. The expression for the critical angle is derived as a natural consequence of this formulation. Equations for the total fraction of power confined within a waveguide are derived and analyzed for the special case of absorbing waveguides. An explicit expression is derived for the fraction of energy confined within a waveguide supporting two sets of modes.