Showing papers by "Dalhousie University published in 1977"

Seasonal growth in Laminaria longicruris: Relations with dissolved inorganic nutrients and internal reserves of nitrogen

Abstract: Observations have been made on seasonal fluctuations in dissolved inorganic nutrients, internal reserves of nitrogen and growth rates in Laminaria longicruris. The onset of winter growth in shallow-water stations (6 and 9 m) correlated well with improved dissolved nitrate conditions in the sea. During the winter, reserves of NO 3 - were accumulated by the plants and reached maximum values of 150 μmoles per g fresh weight in March. This represents a concentration factor of approximately 28,000 over the ambient levels, or an internal nitrogen reserve of 2.1% of the dry weight of the tissue. Depletion of this nitrogen pool followed the disappearance of the external NO 3 - with a lag period of up to 2 months. Rapid kelp growth was measured during this period. Reserves of organic nitrogen also reached maximum values in March and declined slowly throughout the summer into autumn. It is suggested that the combined inorganic and organic nitrogen reserves sustain the rapid growth rates into July and at reduced rate through the late summer. Fertilization of an experimental perimental kelp bed with NaNO3 increased the internal plant reserves of NO 3 - and produced a much improved summer growth rate. The enriched plants developed very small reserves of carbohydrate during the rapid summer growth phase.

Physiological identification and analysis of dentate granule cell responses to stimulation of the medial and lateral perforant pathways in the rat

Abstract: Stimulation of the dorsomedial or ventrolateral perforant pathways resulted in quantitatively different extracellularly recorded EPSPs in the fascia dentata of the rat. The two potential differed in latency to peak and in width at half amplitude in a manner consistent with the different locus of termination of the two pathways on the granule cell dendrites. Both potentials were able to follow brief stimulus trains of 100 Hz, which suggests that they are monosynaptic. Medially elicited responses had their peak negativity approximately 100 to 180 μm deeper in the molecular layer than laterally elicited responses. Stimulation at short intervals along a dorsomedial to ventrolateral track in the angular bundle yielded a step function rather than a continuum of EPSP peak latency and half-width, in agreement with Hjorth-Simonsen's ('72) evidence for the separateness of the two pathways. Both pathways were able to induce granule cell discharge. Laterally elicited spikes, however, were delayed. Stimulation at intermediate locations frequently elicited double spikes from granule cell population. Population spikes elicited by either pathway were inhibited for as long as 100 msec after a single discharge. Both pathways showed facilitation with double stimuli at short intervals, and both showed post-tetanic potentiation lasting at least 30 minutes. Under conditins where it could be shown that the two pathways at least partially converged onto the same granule cells, the response of one pathway did not increase when long lasting potentiation was induced on the other.

Right-Hemisphere Language Processing in Normal Right-Handers.

Abstract: Three experiments were conducted to investigate the verbal performance of the right cerebral hemisphere in right-handed individuals with normal intact brains. A manual reaction time (RT) measure was used to assess the relative efficiency of lateral stimulus-response pathways (e.g., left visual field-right hemisphere-left hand) in processing linguistic information. Experiment 1 showed that the right and left hemispheres were equally efficient at recognizing concrete object nouns in a lexical decision task. The RT data also suggested that abstract nouns may be recognized only by the left hemisphere. Experiments 2 and 3 demonstrated the right hemisphere's ability to detect semantic relationships between concrete nouns and their superordinate categories. The findings were discussed in terms of their consistency with data from split-brain research and their implications for models of the functional organization of language skills in the normal brain. It was proposed that the right hemisphere in the intact brain can play a functional role in processing language.

Visual acuity and contrast sensitivity in multiple sclerosis--hidden visual loss: an auxiliary diagnostic test.

Abstract: In 48 patients with multiple sclerosis sine-wave gratings were used to test visual sensitivity for coarse, medium, and fine detail rather than measuring visual acuity for fine detail only, as in conventional clinical tests. In 20/48 patients the test revealed a visual defect of neural origin, qualitatively different from that caused by refractive error. In 11 of these 20 patients, visual sensitivity to detail of medium coarseness was markedly degraded, even though sensitivity to both coarse and fine detail was unimpaired. In 3 of these 20 patients visual sensitivity to coarse detail was selectively degraded. These visual defects could not be detected by the Snellen test, yet the patient might experience visual problems in everyday life and also experience distorted visual perception. Possible neural bases for these visual impairments are discussed. Since 8 of the 14 patients with selective loss showed no clinical evidence of visual involvement, the test can aid the earlier diagnosis of multiple sclerosis.

Destruction of kelp-beds by sea-urchins: A cyclical phenomenon or irreversible degradation?

Abstract: A stable kelp bed ecosystem in St. Margaret's Bay, Nova Scotia (Canada), had as its main producersLaminaria longicruris andL. digita. Most algal production was exported as detritus, but there was a moderate population of herbivores, mainly the sea urchinsStrongylocentrotus droebachiensis. These were eaten by crabs,Cancer irroratus and by lobsters,Homarus americanus. Lobsters also preyed on crabs. Beginning in 1968, sea urchins became locally abundant and overgrazed the kelp beds, converting large areas to urchindominated barren grounds. Almost all kelp beds in St. Margaret's Bay (140 km2) have now been destroyed. During the same period, lobster biomass decreased, and the hypothesis was put forward that reduction in lobster predation led to increased urchin abundance and kelp bed destruction. Evidence is presented for the hypothesis that urchin-dominated barren grounds are a new, stable configuration of the ecosystem, and that a long-term decrease in primary and secondary productivity of these coastal waters can be expected.

An annual carbon budget for the kelp Laminaria longicruris

Abstract: Oxygen evolution and uptake by whole thalli of the large marine alga Laminaria longicruris de la Pylaie were measured for 24 h, once every 2 weeks for a year, using large chambers to incubate the plants on the sea bed Diel rates of photosynthesis and respiration were calculated from these measurements and continuous light measurements were used to extrapolate the data between observation dates The resulting estimates were combined with measurements of growth and carbon content to give an annual carbon budget for a typical mature plant Annual net assimilation was 68 mgC per cm2 of frond surface (71 cal cm-2) Approximately 45% of this appeared in the production of new frond tissue, and a further 12% was accounted for by storage of carbon in mature frond tissue About 8% was needed for stipe growth, and the remaining 35% was assumed to be lost as dissolved organic carbon Diel net photosynthetic rates reached a maximum in June and July and were negative only in November, indicating an ability to produce a photosynthetic surplus throughout winter In early winter the plants drew on stored reserves to supplement photosynthesis in providing carbon for growth, but from January onwards photosynthesis provided more than enough carbon for growth

Circadian rhythm of synaptic excitability in rat and monkey central nervous system

Abstract: Synaptic responses in hippocampal granule cells to stimulation of their afferent fibers from the entorhinal cortex fluctuate with a 24-hour period. The phase of this cycle for rats and monkeys depends on whether the animal is naturally nocturnal or diurnal. In a rat blinded by enucleation, the rhythm persists but drifts out of phase with the rhythm of sighted controls.

The inferior olivary nucleus of the rat: a light and electron microscopic study.

Abstract: This study provides basic data on the normal structure of the inferior olivary nucleus of the rat at both the light and electron microscopic level. The cytoarchitecture of the nucleus was mapped in serial sections cut in the transverse plane and stained with cresyl violet. The bulk of the inferior olive is composed of the princpal olive and the dorsal and medial accessory olives. The dorsal cap, nucleus β, ventrolateral outgrowth and dorsomedial cell column are minor subgroups of cells which are clearly represented in the nucleus. Golgi preparations revesled two types of dendritic pattern both of which are found in the principal olive and in the accessory olives. Portions of the dendritic tree are varicose in appearance and bulbous expansions, often bearing spines, are pendage may be observed; namely, simple spines, pedunculatd club-shaped spines, and racemose appendages. Appendages are most numerous in association with distal portions of th dendritic tree. Analysis of the principal olive of the principal olive and of the accessory olives with the electron microscope revealed the following characteristics: Round vesicle terminals which are the predominat type found in the nucleus range in size from 0.3 μm. to 4.0 μm. Pleomorphic vesicle terminals range in size from 0.5 μm to 3.5 μm. Both types of terminal are ubiquitous in their distribution with regard to the dendritic tree of olivery neurons but are more numerous in relation to dendritic elements measuring less than 2 μm in diameter. Axosomatic synapses and synapses on proximal dendrites are few in number and are made by both types of terminal. A third type of terminal which contains up to 25% dense core vesicles is found infrequently in all three major subnuclei. Much of the surface of the soma of olivary neurons is covered with glial cell processes or by dendritic elements. No membrane specialization is found between these apposed surfaces. Dendritic spines, some of which contain a well marked spine apparatus, are commonly seen and appear to correspond to the pendunculated club-shaped spines seen in the Golgi preparations. Other large dendritic profiles which are packed with mitochondria are considered to possibly correspond to the varicose dilations of the dendrites or to “bleb-like” protrusions of dendritic shafts seen in Golgi preparations Glomerulus-like structures are seen in the neuropil and have been shown to possess a core of small dendritic elements which are contacted at their pertially surrounded by glial cell processes and has been termed a synaptic cluster. Such axo-dendritic complexes are largest and most numerous in the principal olive and rostral half of the medial accessory olive. In some planes of section, it is possible to trace the dendritic core of the synaptic cluster back to a larger dendritic shaft. It is suggested that such dendritic cores correspond to the racemose appendages which are seen in Golgi preparations. Gap junctions and attachment plaques are frequently seen between dendritic elements in synaptic clusters and also between dendritic elements which are not part of synaptic clusters, in all three major subnuclei. In the medial accessory olive, several examples of two gap junctions arranged in series between three small dendritic elements have been observed.

Diel variations in the photosynthetic parameters of coastal marine phytoplankton

Abstract: The diel variations in the assimilation number, PmB, of natural assemblages of coastal marine phytoplankton were examined and a working model proposed to characterize the apparent diel rhythm No rhythm could be distinguished for the initial slope of the light saturation curve, α, although α and PmB were highly correlated and the daily and hourly variations in α were as great as those in PmB Diel variations in the derived parameter Ik(≡PmB/α) were described by a model similar to that proposed for PmB The rhythm PmB was found to have a significant effect on the estimation of daily productivity Correlations with environmental covariates support the hypothesis that the photosynthetic rhythms observed in the field result both from intrinsic oscillations within the phytoplankton cells and from varying environmental factors

The tonic hypothesis and the patterning of behavior

Abstract: One useful way to think about problems of behavioral organization is in terms of the question of pattern formation. A pattern in this sense is defined as the separation of behavior into component activities on the one hand and the examination of linkages between these components on the other. We can think here in terms of an analogy to a musical performance, where the performance must be defined both in terms of individual notes and pauses and in terms of the simultaneous and sequential articulation of these individual notes and pauses. The question for analysis in terms of behavioral mechanisms is the extent to which definable underlying processes are circumscribed in terms of their “temporal” and “lateral” aspects, This problem is often summarized in terms of the issue of control specificity.S* It is quite clear that certain causal processes in behavior may extend over longer time periods than the individual activities that they influence. For example, seasonal changes in hormonal state in a stickleback fish can produce long-term consequences, as measured by the relative probabilities of various activity patterns such as fighting and courtship.13 When viewed from a long time scale perspective, the hormonal shifts that occur during the onset of breeding season in sticklebacks can increase the probability both of fighting and of courtship behavior, as shown in FIGURE 1. Short-term interactions between fighting and courtship are often negative rather than positive, however. This means that the occurrence of fighting behavior reduces the likelihood that courtship activities will be observed in close proximity on the one hand, and that occurrences of courtship behavior decrease the likelihood that fighting will be observed within the next short time frame, on the other. Clearly, one of the major tasks of the behavioral scientist is to come to grips with the relations between causal processes that operate over quite disparate time scales. We can, for convenience, call the relatively long-term processes “tonic.” The fact that processes exist that extend beyond the articulation of any individual form of behavioral expression carries with it the logical conclusion that these processes exist during the performance of several different classes of activity. A question that follows, therefore, is whether certain classes of causal factors may influence several different classes of overt behavioral expression.

Serum 5alpha-androstane-3alpha,17beta-diol, androsterone, and testosterone concentrations in the male rat. Influence of age and gonadotropin stimulation.

Abstract: Serum concentrations of testosterone plus dihydrotestosterone (T-DHT), 5α-androstane- 3α, 17β-diol (Diol) and androsterone were measured during sexual maturation in male rats. Diol concentrations of 1 to 2.25 ng/ml were found in animals 10–90 days of age with no significant changes. Diol was the major androgen (5.75-8 times T-DHT) from age 20–40 days. Androsterone rose to 1.25 ng/ml at 25 days of age and declined to values of <0.5 ng/ml from age 30–90 days. Testosterone-DHT levels were 1 ng/ml or less from 10–40 days of age, and then rose to a peak at 60 days. The ratio of Diol to T-DHT was significantly elevated from age 20–35 days, indicating that Diol is the major androgen in circulation at this time. Acute treatment of 33 day old rats with LH, but not with FSH, resulted in a dose-dependent increase in serum T-DHT, Diol, and androsterone. The dose-response and time course of response for the three steroids were nearly identical. Changes in testes capacity to secrete androgens were assessed at 25, 33, 4...

Complexity as a system property

Abstract: Complexity is generally viewed as an intrinsic property of certain kinds of systems, or at least, as a property of a specific description of such systems. The view towards complexity taken in the present note is different; namely, that complexity reflects the necessity for many distinct modes of description of a system. This in turn depends upon the number of ways we can effectively interact with a system, and ultimately on the number of distinct subsystems which available observational techniques make accessible to us. A number of important implications of this point of view, bearing particularly on system analysis in biology, and on reductionism as a general analytic strategy, are pointed out. The relation between the concepts of complexity, error and emergence is briefly explored.

Direct detection of depolarisation-induced release of ATP from a synaptosomal preparation.

Abstract: SEVERAL groups have shown that ATP is released from neural tissues during depolarisation, where it or its metabolites might function as neurotransmitters or neuromodulators1. They measured radiolabelled adenosine derivatives in perfusates following depolarisation of their preparations. Recently, Israel et al.2 described a method for continuously and directly detecting the release of ATP from the electric organ of Torpedo marmorata after stimulation of its motor nerve. I have used a modification of this technique to study the depolarisation-induced release of ATP from a purified synaptosomal fraction prepared from rat brain. I report here that depolarisation of synaptosomes elicits a release of ATP which can be directly and continuously detected by this technique.

Epithelial influences on skeletogenesis in the mandible of the embryonic chick

Abstract: Intact mandibular processes and the enzymatically separated mesenchymal and epithelial components of the mandible from embryonic chicks of 2.5- to 5-day incubation (Hamburger and Hamilton, '51: stages 16-25) were grown individually, either in organ culture or as grafts to the chorioallantoic membranes of host embryos. The differentiation of cultured and grafted intact mandibular processes was histologically normal, but the time of histodifferentiation differed from that in vivo. The histodifferentiation of cultured and grafted mandibular mesenchyme grown isolated from its epithelium depended upon the age of the embryo from which the mesenchyme had been obtained. Intramembranous ossification producing membrane bones of the mandible occurred in mesenchyme isolated from 4.5- to 5-day embryos (HH 24–25), but did not occur in mesenchyme isolated from younger embryos. Cartilage (Meckel's) and subperichondrial bone in the articular process of Meckel's cartilage differentiated in mesenchyme isolated from embryos of all age groups tested (HH 16–25). Mandibular mesenchyme, therefore, requires the presence of epithelium until 4.5 days of incubation if the membrane bones of the mandible are to differentiate; if epithelial influences are required for Meckel's cartilage and subperichondrial bone formation, they are not required beyond 2.5 days of incubation. Mandibular epithelium isolated from its mesenchyme became layers of squamous cells in culture; but when grafted onto the chorioallantoic membrane, the epithelium became underlain by host fibroblasts and differentiated into a stratified squamous epithelium. Mandibular epithelium, therefore, is capable of differentiation in the presence of foreign fibroblasts derived from the chorioallantoic membrane.

Geochemistry and origin of volcanic rocks of the Andes (26° 28°S)

Abstract: Mesozoic to Recent volcanic rocks from a transect of the Central Andes between latitudes 26 ° and 28 ° South in northern Chile and Argentina show chemical and temporal zonation with respect to the Peru-Chile trench. Jurassic to Eocene lavas occur closer to the trench and are comparable to calc-alkaline rocks of island arcs. Eastwards they are followed by Miocene to Quaternary sequences of typical continental margin calc-alkaline rocks which have higher contents of K, Rb, Sr, Ba, Zr, and REE and also higher K/Na and La/Yb ratios. The rocks occurring farthest from the trench have shoshonitic affinities. The distribution of major and trace elements is consistent with a model in which magmas were derived by anatexis of an upper mantle source already enriched in LILE and located above the descending oceanic slab. It is suggested that the chemical variations across the volcanic belt reflect systematic changes in the composition of the magmas due to a decreasing degree of partial melting with increasing depth, and probably also due to the heterogeneity of the source materials.

Multivalued convexity and optimization: A unified approach to inequality and equality constraints

Abstract: Multivalued functions satisfying a general convexity condition are examined in the first section. The second section establishes a general transposition theorem for such functions and develops an abstract multiplier principle for them. In particular both convex inequality and linear equality constraints are seen to satisfy the same generalized constraint qualification. The final section examines quasi-convex programmes.

A Behavioural Technique for the Rapid Assessment of the Visual Capabilities of Kittens

Abstract: A behavioural method is described for the measurement of various visual spatial acuities in kittens as young as thirty days of age. Expamples are given of applications of the technique to measurement of the visual acuity for gratings in normal kittens as well as to studies of the time course of behavioural recovery from the effects of early monocular visual deprivation.

Recovery from the effects of monocular deprivation in kittens

Abstract: Significant recovery from the effects of early unilateral eye closure has been found following a period of reversed deprivation involving forced usage of the deprived eye. A simple period of binocular vision, however, has been reported to be ineffective. We have compared these two recovery conditions (reversed deprivation and binocular vision) in kittens initially deprived to the age of 45 or 60 days, and given seven to eight weeks of recovery. We estimated behavioral recovery by measuring visual acuity through the deprived eye. Kittens deprived to day 45 attained nearly normal grating resolution in their deprived eyes (5–6 cycles/degree), while those deprived to day 60 showed enduring partial acuity deficits (4–5 cycles/degree). Surprisingly, the deprived eye's acuity in kittens given binocular vision during recovery was nearly the same as that possessed by the deprived eyes of reverse-deprived kittens. We estimated physiological recovery from the visual response properties and eye dominance of 359 cortical neurons; all kittens showed shifts in eye dominance from the situation that obtains after a period of deprivation. Reverse-deprived kittens, in agreement with previous reports, showed more pronounced shifts of cortical eye dominance than did binocularly recovered kittens. Nevertheless, significant recovery of both the deprived eye's influence and of the selectivity of its receptive fields was seen in kittens given binocular vision. In no case was there significant recovery of cortical binocular interaction: most neurons were monocularly driven, and were aggregated into ocular dominance columns strongly dominated by one eye or the other. Since both behavioral and electrophysiological measurements suggest considerable recovery of function even in cases where kittens were merely given binocular vision during recovery, we conclude that the two eyes'effectiveness is not solely determined by competitive interaction – significant changes can occur when neither eye has a competitive advantage over the other.

Rapid effects of veratridine, tetrodotoxin, gramicidin D, valinomycin and NaCN on the Na+, K+ and ATP contents of synaptosomes.

Abstract: — The effects of brief exposures of a number of depolarizing agents on 24Na+ influx and on the Na+, K+ and ATP contents of synaptosomes were studied using a Millipore filtration technique to terminate the reaction. When synaptosomes were incubated in normal medium, there was a rapid influx of 24Na+ and a gain in Na’contents; neither the 24Na+ influx nor the Na+ gain were blocked by tetrodotoxin suggesting that this Na+ entry did not involve Na+-channels. Veratridine markedly increased the rate of 24Na+ influx into synaptosomes and also increased the Na+ content and decreased the K+ content of synaptosomes within the first 10s of exposure. The normal ion contents were reversed by 1 min. The effects of veratridine on Na+ influx and on synaptosomal ion contents were prevented by tetrodotoxin and required Na+ in the medium. The ionophores gramicidin D and valinomycin also rapidly reversed the Na+ and K+ contents of synaptosomes, but these effects could not be blocked by tetrodotoxin. The reducing effect of gramicidin D on synaptosomal K+ content required Na’in the medium, whereas valinomycin caused a fall in the K+ content of synaptosomes in a Na+-free medium. Veratridine and gramicidin D, at concentrations known to reverse the synaptosomal ion contents, did not affect synaptosomal ATP levels. In contrast, valinomycin and NaCN caused an abrupt fall in synaptosomal ATP levels. The above findings suggest that veratridine quickly alters synaptosomal Na+ and K+ contents by opening Na +-channels in the presynaptic membrane, and provide direct evidence for the existence of Na+-channels in synaptosomes. In contrast, gramicidin D and valinomycin appear to act independently of Na +-channels, possibly by their ionophoric effects and, in the case of valinomycin, by diminishing synaptosomal ATP contents and hence diminishing Na+-pump activity. The rapid reversals of Na+ and K+ contents by these drugs could affect the resting membrane potentials, Na+-Ca2+ exchange across the synaptosomal membrane, and the release, synthesis and uptake of neurotransmitters by synaptosomes.

Sexual arousal in women: a comparison of cognitive and physiological responses by continuous measurement.

Abstract: Six sexually normal women were exposed to a wide variety of erotic video tapes while vaginal, groin, and breast vasocongestion measures were taken. The women indicated their subjective level of sexual arousal while viewing the tapes by positioning a lever device along a calibrated scale. The results indicated highly significant positive correlations among the cognitive and physiological measures for five out of six individual subjects, although the pooled group data failed to show significance. The methodology described in this research shows promise as a diagnostic and research tool.

Predicting Changes in Tidal Regime: The Open Boundary Problem

Abstract: Attempts to predict the impact on a tidal regime of large engineering structures are generally based on the use of a numerical model which is calibrated to reproduce the natural tidal regime and then rerun with the structures in place. It is usually assumed that the “input” tide at the open boundary is unchanged by the structures, though this is clearly wrong in principle. We show how errors in this procedure can be corrected for, or at least estimated, using output from the numerical model and estimates of the impedance of the exterior ocean. The ocean impedance can be expressed as an infinite series in terms of the normal modes of the ocean, with some terms allowing for near-resonant enhancement of particular modes, and the infinite tail corresponding to a local source-like behavior which can be estimated independently. Application of the technique to the problem of predicting the impact of Fundy tidal power suggests that any predicted change may be uncertain to about ±25% of the change in mass...

Genetics of larvae and spat growth rate in the oyster Crassostrea virginica

Abstract: The heritability of oyster (Crassostrea virginica) larval growth rate was estimated to be in the range of 0.25 to 0.50 and a significant part of this genetic variation is of the additive type. Larval growth rate and spat growth rate were found to be highly correlated. These results suggest that a selection program for faster growing larvae and spat would be successful.

Photographic Atlas of the Mid-Atlantic Ridge Rift Valley

Abstract: Geologic Setting.- Photographic Techniques.- Submarine Volcanic Products.- Volcanic Vents.- Major Flow Units.- Individual Flow Units.- Bulbous Pillows.- Flattened Pillows.- Elongate Pillows.- Hollow Pillows.- Knobby Pillows.- Trapdoor Pillows.- Sheet Flows.- Flow Foot Rubble and Talus.- Features of Pillow Crust.- Faults and Related Tectonic Features.- Tensional Fissures.- Gjar.- Isolated Fault Block.- Small-scale Grabens.- Fault Scarps of Inner Floor.- Simple Fault Scarps.- Rotated and Tilted Blocks.- Slump Notches.- Patterns of Faulting.- Faulted Sedimentary Rock.- Rift Valley Walls.- References Cited.

Electromyographic Abnormalities in Chronic Environmental Arsenicalism

Abstract: In this study of 92 people using wells with arsenic concentrations of >0.05 ppm (and with 21 control subjects), 27 of them had clinical features possibly attributable to chronic arsenic poisoning. There was a positive relationship between frequency of clinical features, and well and hair arsenic concentrations. Although the relationship between toxicity and hair arsenic concentration was rather varied, 1 ppm appears to be satisfactory upper limit of acceptability. For drinking water, an acceptable limit of 0.01 ppm and a maximum permissible limit of 0.05 ppm of arsenic appear satisfactory, but leave little safety margin.

Attention and visual dominance: a chronometric analysis.

Abstract: Three chronometric experiments, each comparing vision and kinesthesis, were conducted to study visual dominance. The time required to switch attention from vision and from kinesthesis was equal, while switching to kinesthesis was faster than switching to vision (Experiment 1). Responses to a combined visual-kinesthetic stimulus were slower than responses to a kinesthetic stimulus alone when the subject was expecting the bimodal stimulus. The visual dominance effect was shown to depend on the subject knowing the modality of the stimulus in advance (Experiment 2). When subjects were instructed to attend one modality they had equal difficulty with conflicting visual and kinesthetic information (Experiment 3). These findings suggest that visual dominance results from a bias to attend vision when that modality seems adequate for the task. Te bias to attend vision may develop to overcome a deficiency in visual alerting. Language: en