Showing papers by "McGill University published in 1976"

Evidence for an endogenous ultradian rhythm governing growth hormone secretion in the rat.

Abstract: Sequential blood samples were obtained from undisturbed freely-behaving male rats bearing chronic intracardiac venous cannulae. Blood was withdrawn every 15 min for periods of 4–24 h; plasma was separated, and saline-resuspended red cells were reinjected. Plasma GH was determined by radioimmunoassay. Pulsatile GH secretion was evident in each animal with most peak values >200 ng/ml and most trough values <1 ng/ml. The GH secretory episodes occurred at approximately 3 h intervals, and this rhythmic pattern of GH secretion persisted unchanged across all phases of a 12-h lightdark (L-D) cycle. Seven major episodes of GH secretion were observed during a single 24-h period. The mean period, or time interval between episodes, in 24 animals was 3.32 ± 0.07 (SEM) h. The timing of the pulses with respect to the L-D cycle was similar in most animals, indicating that the rhythm may be entrained to the L-D cycle. The role of environmental lighting was further assessed in 14 animals exposed to constant light for 7 wee...

A contingency framework for the design of accounting information systems

Abstract: Most of the research to date concerning the design of an accounting information system has taken a rather narrow and inflexible view of accounting information. The primary intent of this paper is to provide a broader and more adaptive framework for designing such systmes. A contingency approach, which takes into account the environment, organizational attributes, and managerial decision making styles, is advocated. In this context, several hypotheses are offered concerning the requisites of an accounting information system.

Extreme vestibulo-ocular adaptation induced by prolonged optical reversal of vision.

Abstract: 1. These experiments investigated plastic changes in the vestibulo-ocular reflex (VOR) of human subjects consequent to long-term optical reversal of vision during free head movement. Horizontal vision-reversal was produced by head-mounted dove prisms. Four normal adults were continuously exposed to these conditions during 2, 6, 7 and 27 days respectively. 2. A sinusoidal rotational stimulus, previously shown to be nonhabituating (1/6 Hz; 60°/sec amplitude), was used to test the VOR in the dark at frequent intervals both during the period of vision-reversal and an equal period after return to normal vision. D.c. electro-oculography (EOG) was used to record eye movement, taking care to avoid changes of EOG gain due to light/dark adaptation of the retina. 3. All subjects showed substantial reduction of VOR gain (eye velocity/head velocity) during the first 2 days of vision-reversal. The 6-, 7- and 27-day subjects showed further reduction of gain which reached a low plateau at about 25% the normal value by the end of one week. At this time the attenuation of some EOG records was so marked as to defy extraction of a meaningful sinusoidal signal. 4. After removal of the prisms VOR gain recovered along a time course which approximated that of the original adaptive attenuation. 5. In the 27-day experiment large changes of phase developed in the VOR during the second week of vision-reversal. These changes generally progressed in a lagging sense, to reach 130° phase lag relative to normal by the beginning of the third week. Accompanying this was a considerable restoration of gain from 25 to 50% the normal value. These adapted conditions, which approximate functional reversal of the reflex, were then maintained steady, even overnight, until return to normal vision on the 28th day. 6. Thereafter, whereas VOR phase returned to near-normal in 2 hr, restoration of gain occupied a further 2-3 weeks. 7. There was a highly systematic relation between instantaneous gain and phase, even during periods of widely fluctuating change associated with transition from one steady state to another. During such transition there was a tendency for directional preponderance to occur in the VOR. 8. All the observed changes were highly specific to the plane of vision-reversal, no VOR changes being observed in the sagittal plane. 9. VOR changes were adaptive, in the sense that they were always goal-directed towards the requirements of retinal image stabilization during head movement. They were plastic to the extent that there was extensive and retained remodelling of the reflex towards this goal. 10. It is inferred that all the observed changes in gain and phase are compatible with a simple neural network employing known vestibulo-ocular projections via brainstem and cerebellar pathways, providing that the reversed visual tracking task can produce plastic modulation of efficacy in the cerebellar pathway and that this pathway exhibits a dynamic characteristic producing moderate phase lead in a sinusoidal signal at 1/6 Hz.

The psychology of left and right

Abstract: Originally published in 1976, this title deals with the problem of how we tell left from right. The authors argue that the ability to tell left from right depends ultimately on a bodily asymmetry, such as preference for one or the other hand, or dominance of one side of the brain. This has implications for child development, reading disability, navigation, art, and culture.

The lateral migration of a spherical particle in two-dimensional shear flows

Abstract: The lateral migration of a solid spherical particle suspended in a fluid flowing between parallel vertical walls is investigated theoretically using a method developed by Cox & Brenner (1968) Buoyant and neutrally buoyant, freely rotating and non-rotating particles in the fluid flow are considered as is also the case of a sedimenting particle in a quiescent fluid The results obtained are applied to the special cases of plane Poiseuille flow and of plane shear flow, these situations being investigated in detail

Liquid Crystalline Structure In Aqueous Hydroxypropyl Cellulose Solutions

Abstract: Concentrated aqueous solutions of hydroxypropyl cellulose form lyotropic mesophases displaying a range of iridescent colors. Evidence from light microscopy and optical rotatory dispersion suggests that the mesophase has helicoidal structure, resembling in some respects that of cholesteric liquid crystals.

Short-term adaptive changes in the human vestibulo-ocular reflex arc.

Abstract: 1. Two sets of experiments have examined the vestibulo-ocular response (VOR) to repeated sinusoidal rotation (A) in the dark and (B) after attempting visual tracking of a mirror-reversed image of the visual surround. 2. In both A and B a horizontal sinusoidal rotational stimulus of 1/6 Hz and 60°/sec angular velocity amplitude was employed, specifically chosen to lie within the presumed range of natural stimulation of the semicircular canals. 3. In A each of seven subjects underwent ten 2-min runs of the standard stimulus in the dark on each of three consecutive days, with 3-min rest periods between runs. Using d.c. electro-oculography (EOG) the VOR gain was measured throughout as eye velocity/head velocity. Mental arousal was maintained by competitive mental arithmetic. Constancy of EOG gain was assured by 50 min dark adaptation before experimentation. 4. The results of A showed no consistent change of VOR gain over the three times scales of a run, a day and the 3-day experiment. 5. In B the same subjects underwent a similar pattern of vestibular stimulation, but during eight of the 2-min daily runs they attempted the reversed visual tracking task. VOR gain was measured during the 1st, 6th and last runs which were conducted in the dark for this purpose. Constancy of EOG gain was maintained by using red light throughout. 6. The results of B showed a substantial (approx. 25%) and highly significant (P « 0·001) reduction of VOR gain attributable solely to the 16 min of reversed visual tracking attempted during the 50 min daily experiment. In addition the pre-test control gain was lower on day 3 than on day 1 (approx. 10% attenuation, P < 0·01) indicating a small cumulative effect from beginning to end of the 3-day experiment. 7. It is concluded (A) that the repeated vestibular stimulus did not itself cause significant attenuation of VOR gain, but (B) that superposition of a reversed visual tracking task did induce retained VOR attenuation which was solely due to the antagonistic visual stimulus. 8. In conjunction with other experimental evidence it is inferred that this attenuation probably represents an adaptive change in the VOR induced at least in part by retinal image slip.

Partial molar volumes of organic compounds in water. III. Carbohydrates

Abstract: Partial molar volumes in water at 25°C have been determined for a number of carbohydrates, including mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, and polysaccharides and their derivatives The experimental values can be calculated from the van der Waals volumes of the molecules if account is taken of the shrinkage in volume caused by hydrogen-bonding of solvent molecules to the hydroxyl groups of the sugars

Interrelationships between bed morphology and bed‐material transport for a small, gravel‐bed channel*

Abstract: Bed conditions (micro-relief, textural associations and packing structural arrangements) in the gravel-bed channel of Seale's Brook are shown to be closely interrelated; various categories are identified and related to mode of bed material transport and deposition. Entrainment of bed material, commonly treated as a simple function of particle weight and channel hydraulics, is also shown to be strongly affected by varying and variable bed conditions. In particular, the classic concept of competence appears to be of restricted utility in such channels; resistance of bed material to fluid drag and to particle impact is augmented, over large parts of the channel bed, by its interlocking structure, made possible by the wide range in particle calibre, and by the characteristic disc and blade shapes of the slate debris. Particle mobility, as indicated by distance of travel of labelled bed material, is only partly a function of particle weight; indeed, although particle mobility decreases from small pebbles to large cobbles, it also decreases for the finest bed material (very small pebbles). This appears to be explicable, partly in terms of the ease of entrainment (and duration of travel), and, partly in relation to the ease of transport of material over an uneven channel bed surface. Particle mobility is greatest for material in open and infilled structures and smallest for sediment in tight structural arrangements. Local bed slope also exerts an influence on the probability of particle entrainment and on particle mobility. The findings emphasize the need for combining sedimentological and engineering approaches to bed material transport in coarse-bedded channels, and, at the same time, illustrate some of the reasons for the existence of indeterminacy in the modelling of bed-material transporting processes.

Assessment of a cognitive training program for hyperactive children.

Abstract: Modeling, self-verbalization, and self-reinforcement techniques were used to train hyperactive children in more effective and less impulsive strategies for approaching cognitive tasks, academic problems, and social situations. Eighteen hyperactive children took part in the training program. The control group, which received no training, consisted of 11 children, matched with the experimental group on age, IQ, and measures of hyperactivity and impulsivity. Several tests and measures, some of which have been shown to differentiate between hyperactive and normal children, were administered prior to training, at the end of the 3- month training period, and after a further 3- month period in which no training took place. The trained group showed significantly greater improvement on several of the measures, both at the time of posttesting and on the follow-up evaluation.

Darwin's finches: population variation and natural selection

Abstract: Van Valen's model, which relates morphological variation to ecological variation in an adaptive scheme, was investigated with individually marked and measured Darwin's finches on two adjacent Galapagos islands, Santa Cruz and Daphne Major. Results show that environmental heterogeneity is correlated with large continuous, morphological variation: variation in bill dimensions of Geospiza fortis is greater on Santa Cruz than on Daphne, as is environmental heterogeneity. Within populations of this species, different phenotypes distribute themselves in different habitat patches, select foods of different sizes and hardness, and exploit them with efficiencies that are phenotype- (bill size) dependent. These data constitute indirect evidence that natural selection has a controlling influence over the level of phenotypic variation exhibited by a population. Further evidence is that phenotypes did not survive equally well during the study period; on Daphne island G. fortis was apparently subjected to directional selection on bill tip length and G. scandens to normalizing selection on body weight and bill depth. Other factors which may have contributed to the establishment of a difference in variation between Santa Cruz and Daphne populations are the founder effect, genetic drift, and assortative mating. Annual climatic unpredictability is considered a source of environmental heterogeneity which, through its effect upon food supply, favors large morphological variation. It is predicted that species of large individual size are more influenced by this than are small species, and consequently exhibit greater size-corrected variation. The prediction is tested with data from six Geospiza species, and found to be correct.

Anchoring device between Sertoli cells and late spermatids in rat seminiferous tubules

Abstract: Near the end of spermiogensis, the late spermatids remain attached to the superficial layer of the seminiferous epithelium for an appreciable period of time (i.e., 3 to 4 days). Ths sickle-shaped heads of the spermatids are embedded in an apical process of Sertoli cell cytoplasm which is connected to the rest of the cell by a narrow stalk. In the concavity of the head several long (2-3 mum) and very narrow (50 nm) tubular projections of the spermatid's plasma membrane invaginate the Sertoli cell cytoplasm. These tubular processes terminate by a bulbous swelling which may measure up to 1 mum in diameter. Along the process the plasma membrane of the Sertoli cell is closely apposed to the spermatid's membrane, the intracellular space being only 6-8 nm wide. In the Sertoli cytoplasm immediately surrounding the tubular portion of the structure there is an accumulation of filamentous material, while next to the bulbous extremity there are, at a shrot distance, smooth surfaced cisternae of endoplasmic reticulum. The whole structure was referred to as a tubulobulbar complex. These complexes, of which there are up to 24 per spermatid, appear as these cells complete their migration toward the apex of the Sertoli cells. They disappear just before the release of the spermatids in the lumen of the seminiferous tubule as a result of the fragmentation of the spermatid's plasma membrane followed by a resorption of the Sertoli plasma membrane. Morphological evidence suggests that the Tubulobulbar complexes serve as anchoring devices that retain the spermatids at the surface of the seminiferous epithelium while their dissolution contributes in part to the process of spermiation. Similar tubulobulbar complexes were also formed by the plasma membranes of two adjacent Sertoli cells close to the Sertoli-Sertoli tight junctions near the tubular limiting membrane.

Antiserum to somatostatin prevents stress-induced inhibition of growth hormone secretion in the rat.

Abstract: Plasma growth hormone levels fall and remain low for several hours after stress in the rat. When antiserums to somatostatin are administered to rats prior to stress, growth hormone secretory pulses are partially restored. The results provide evidence that circulating somatostatin plays a prominent role in stress-induced inhibition of growth hormone secretion in the rat.

Spherical hypersurfaces in complex manifolds

Abstract: There has recently been a great deal of progress in the mapping or biholomorphic classication theory of domains with strongly pseudoconvex (s. ~. c.) boundaries in C"+l(n> 1). This is based on the combination of results of Chern-Moser [5] on the local differential geometry of real hypersurfaces in C" + 1, and C. Fefferman's marvelous extension theorem [6], which reduces the biholomorphic equivalence of s. ~k. c. domains to the CR equivalence of their boundaries. It is a simple consequence of this work that such domains have an infinite number of "moduli", i.e., there are smooth families of inequivalent such domains depending on arbitrarily many independent parameters (e.g., [3]). Given further restrictive assumptions on the local nature of the boundary, one expects to recover a finite-dimensional problem. In this paper, we make the most drastic assumption possible: we consider domains whose boundaries are everywhere locally CR equivalent to the unit sphere S 2n+l c[~n+l . Such hypersurfaces will be called spherical. The results are of two kinds. On the one hand, we classify the simply-connected spherical hypersurfaces M which are homogeneous under AutcR(M), the automorphism group of the CR structure on M. A consideration of compact space-forms associated to these homogeneous spaces shows the sphere and its quotients by roots of unity are the only compact, homogeneous spherical hypersurfaces. Together with a result of Webster, this completes the classification of compact homogeneous s.~O.c, hypersurfaces in [14]. On the other hand, it is not clear that any of the compact spherical hypersurfaces constructed in the course of the above bound domains in ~,+1, and we, at least, wondered whether S 2"+1 was the only example. In w we give a method for constructing large families of inequivalent such domains in ~"+ 1 Finally, we mention that some interesting global behavior of the chains of E. Cartan and Chern-Moser are observed in examples of w 6 and w 8. Rather more interesting and exotic behavior of chains has been found by Fefferman in [-7], in necessarily less symmetric boundaries than those considered here.

Pattern Recognition in Humans: Correlations Which Cannot be Perceived

Abstract: Random-dot Moire patterns are manipulated to destroy our ability to perceive the spatial correlations which remain present in the patterns.

The effects of reward and punishment on reaction times and autonomic activity in hyperactive and normal children.

Abstract: The performance of hyperactive and control children was compared on a delayed reaction time task under three reinforcement conditions: reward, punishment, and reward plus punishment. Hyperactives had slower and more variable reaction times, suggesting an attentional deficit. Although each of the three reinforcement conditons was successful in improving reaction times for both subject groups, reward led to a significant increase in impulsive responses in the hyperactive children. Autonomic data revealed that reward also increased arousal to a greater extent than punishment or reward plus punishment. Although resting skin conductance was not different in the two groups of subjects, hyperactives produced fewer specific autonomic responses to signal stimuli.