Asymmetries in oriented-line detection indicate two orthogonal filters in early vision.

Visual detection of a line target differing in orientation from a background of lines may be achieved speedily and effortlessly. Such performance is assumed to occur early in vision and to involve filter mechanisms acting in parallel over the visual field. This study establishes orientational limits on this performance and analytically derives some generic properties of the underlying filters. It was found that, in brief displays, target orientation detection thresholds increased approximately linearly with background orientation, from minima at 0 degree (vertical) and 90 degrees, whereas background orientation detection thresholds decreased approximately linearly with target orientation, from maxima at 0 degree and 90 degrees. Target and background threshold functions were exactly antisymmetric. These data are shown to indicate a model of early line processing dominated by two classes of orientation-sensitive filter with axes close to the vertical and horizontal and orientation-tuning half-widths each of approximately 30 degrees at half-height.     

Effect of phrenic afferent stimulation on pattern of respiratory muscle activation.

Ventilation and electromyogram (EMG) activities of the right hemidiaphragm, parasternal intercostal, triangularis sterni, transversus abdominis, genioglossus, and alae nasi muscles were measured before and during central stimulation of the left thoracic phrenic nerve in 10 alpha-chloralose anesthetized vagotomized dogs. Pressure in the carotid sinuses was fixed to maintain baroreflex activity constant. The nerve was stimulated for 1 min with a frequency of 40 Hz and stimulus duration of 1 ms at voltages of 5, 10, 20, and 30 times twitch threshold (TT). At five times TT, no change in ventilation or EMG activity occurred. At 10 times TT, neither tidal volume nor breathing frequency increased sufficiently to reach statistical significance, although the change in their product (minute ventilation) was significant (P less than 0.05). At 20 and 30 times TT, increases in both breathing frequency and tidal volume were significant. At these stimulus intensities, the increases in ventilation were accompanied by approximately equal increases in the activity of the diaphragm, parasternal, and alae nasi muscles. The increase in genioglossus activity was much greater than that of the other inspiratory muscles. Phrenic nerve stimulation also elicited inhomogeneous activation of the expiratory muscles. The transversus abdominis activity increased significantly at intensities from 10 to 30 times TT, whereas the activity of the triangularis sterni remained unchanged. The high stimulation intensities required suggest that the activation of afferent fiber groups III and IV is involved in the response. We conclude that thin-fiber phrenic afferent activation exerts a nonuniform effect on the upper airway, rib cage, and abdominal muscles and may play a role in the control of respiratory muscle recruitment.     

Tolerance and upregulation of acetylcholine receptors follow chronic infusion of d-tubocurarine.

The hypothesis that chronic competitive antagonism of nicotinic acetylcholine receptors (nAChR), even in the absence of immobilization or paralysis, induces proliferation of the receptor and tolerance to the competitive antagonist was tested. Chronic antagonism of the nAChR was achieved in rats by an infusion of d-tubocurarine (dTC) via subcutaneously placed osmotic pumps. After 2 wk of dTC or saline, the neuromuscular pharmacodynamics and nAChR number were examined. No differences in weight gain or mobility were observed between groups. Chronic dTC infusion at 2 wk resulted in a baseline concentration of 0.41 +/- 0.07 (SE) micrograms/ml, which, if achieved acutely, would cause a depression of the twitch tension to 60% of control twitch height. Moreover the experimental group was able to develop a baseline twitch tension of 50 g, similar to that of controls. Despite the baseline dTC concentration in the experimental group, the effective doses of dTC for twitch depression were similar to those of controls. The plasma dTC concentration required for steady-state twitch inhibition was significantly (P less than 0.05) higher in the experimental group (0.83 +/- 0.04 vs. 0.50 +/- 0.15 micrograms/ml) as were the extrajunctional nAChR (19.76 +/- 1.77 vs. 13.37 +/- 1.82 fmol/mg protein). The diaphragmatic nAChR were unaltered. This study confirms that chronic doses of dTC cause tolerance to its effects and proliferation of nAChR even in the absence of immobilization. The absence of nAChR changes in the diaphragm may be due to the higher margin of safety of the diaphragm for muscle relaxants than for peripheral muscles. Intensive Care Unit patients receiving chronic infusions of dTC to facilitate mechanical ventilation will require increased doses with time.     

Management of traumatic intracranial haematoma.

Deciding which head-injured patients should be transferred to a neurosurgical unit can be difficult. Traditional criteria emphasise the development of deteriorating responsiveness but lead to delayed diagnosis and to avoidable mortality and morbidity. To discover if a more liberal admission policy improved results a study was conducted analysing data collected prospectively from 683 patients who had a traumatic intracranial haematoma evacuated in the Glasgow neurosurgical unit between 1974 and 1980. In the first four years, before the change in policy, mortality was 38% but decreased to 29% afterwards. This reflected a reduction in the proportion of patients who talked after injury but who deteriorated into coma before operation--that is, 31% before the change in policy, 16% afterwards. If the potential benefits of CT scanning in the management of head injuries are to be realised patients must be scanned sooner than in the past. This will usually mean that more patients should go to a neurosurgical unit and that simple criteria for transfer should be established.     

Chiasma frequency and distribution in a maize family segregating for k10 and trisomy 10

Chiasma frequency was determined from total chiasma counts, and the distribution of these exchanges was determined by the ratio of proximal to distal chiasmata. No effect of trisomy 10 could be demonstrated. Confirmation was obtained of earlier work showing more proximal and fewer distal chiasmata in K10 plants than in controls. However, diakinesis data failed to confirm the ability of K10 to increase total chiasmata as suggested from metaphase I results.     

A Comparison of the Genetic Infrastructure of the Ye''Cuana and the Yanomama: A Likelihood Analysis of Genotypic Variation among Populations

A general procedure is described for measuring and testing population differences in gametic frequencies. The total dispersion among populations is subdivided in hierarchical fashion. The multiple-locus treatment is simply the sum of the single-locus analyses, provided gametic equilibrium obtains among the loci. In the event that gametic equilibrium does not obtain, correlations among loci need to be dealt with.—The analysis is then used to examine the genetic infrastructure of two Indian tribes from South America, the Ye'cuana (Makiritare) and the Yanomama. From historical evidence, we may identify several "clusters" of villages within each tribe. The demographic and cultural practices affecting village formation and the maintenance of peer integrity are rather different in these tribes, however, and lead us to postulate rather different patterns of genetic variation among villages. Analyses of five codominant two-allele loci, four dominant two-allele loci and two complex loci (with four codominant haplotypes each) demonstrate that Yanomama clusters are more disparate than Ye'cuana clusters, as would have been predicted on sociocultural grounds.     

HL-A antigens in North American black families

The polymorphic HL-A histocompatibility system has been studied in North American black families. The family studies show that haplotype frequencies differ between black and white populations. Seven haplotypes (W28,W5; W28,W17; W28, undefined four; W23,W5; W19,W5; undefined LA,W5; and undefined LA, undefined four) were significantly more frequent in blacks than whites, while haplotypes 1,8 and 3,7 were significantly less frequent. Some of these differences may be accounted for by differences in gene frequencies between the two groups; other differences may be explained by linkage disequilibrium in the white population. No significant linkage disequilibrium between the LA and FOUR loci was found in the black population.     

Studies on the swimming musculature of the rainbow trout I. Fibre types

A histochemical study has been made on the myotomal musculature of the rainbow trout Salmo gairdneri Richardson. Four main types of fibre can be distinguished on the basis of differences in fibre size, lipid content and succinic dehydrogenase and myofibrillar adenosine triphosphatase activity (ATPase activity). Early histological studies have concluded that in addition to a superficial strip of muscle small diameter 'red' fibres occur throughout the trout myotome. These small diameter fibres occurring in the bulk of the myotome are shown to differ from the superficial fibres with respect to their oxidative metabolism and myofibrillar ATPase. The relevance of this finding to studies on the energetics and swimming efficiency of this species are discussed.