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  • 1
    Electronic Resource
    Electronic Resource
    Distributed parallel processing in the vertical vestibulo-ocular reflex: Learning networks compared to tensor theory (1990)
    Springer
    Biological cybernetics 63 (1990), S. 161-167 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The vestibulo-ocular reflex (VOR) is capable of producing compensatory eye movements in three dimensions. It utilizes the head rotational velocity signals from the semicircular canals to control the contractions of the extraocular muscles. Since canal and muscle coordinate frames are not orthogonal and differ from one another, a sensorimotor transformation must be produced by the VOR neural network. Tensor theory has been used to construct a linear transformation that can model the three-dimensional behavior of the VOR. But tensor theory does not take the distributed, redundant nature of the VOR neural network into account. It suggests that the neurons subserving the VOR, such as vestibular nucleus neurons, should have specific sensitivity-vectors. Actual data, however, are not in accord. Data from the cat show that the sensitivity-vectors of vestibular nucleus neurons, rather than aligning with any specific vectors, are dispersed widely. As an alternative to tensor theory, we modeled the vertical VOR as a three-layered neural network programmed using the back-propagation learning algorithm. Units in mature networks had divergent sensitivity-vectors which resembled those of actual vestibular nucleus neurons in the cat. This similarity suggests that the VOR sensorimotor transformation may be represented redundantly rather than uniquely. The results demonstrate how vestibular nucleus neurons can encode the VOR sensorimotor transformation in a distributed manner.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195854
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  • 2
    Electronic Resource
    Electronic Resource
    The distributed representation of vestibulo-oculomotor signals by brain-stem neurons (1989)
    Springer
    Biological cybernetics 61 (1989), S. 79-88 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The vestibuloocular reflex and other oculomotor functions are subserved by populations of neurons operating in parallel. This distributed aspect of the system's organization has been largely ignored in previous block diagram models. Neurons that transmit oculomotor signals, such as those in the vestibular nucleus (VN), actually combine the different types of signals in a diverse, seemingly random way that could not be predicted from a block diagram. We used the backpropagation learning algorithm to program distributed neural-network models of the vestibulo-oculomotor system. Networks were trained to combine vestibular, pursuit and saccadic eye velocity command signals. The model neurons in these neural networks have diverse combinations of vestibulo-oculomotor signals that are qualitatively similar to those reported for actual VN neurons in the monkey. This similarity implicates a learning mechanism as an organizing influence on the vestibulo-oculomotor system and demonstrates how VN neurons can encode vestibulo-oculomotor signals in a diverse, distributed manner.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00204592
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  • 3
    Electronic Resource
    Electronic Resource
    The use of matrices in analyzing the three-dimensional behavior of the vestibulo-ocular reflex (1982)
    Springer
    Biological cybernetics 46 (1982), S. 53-66 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The vestibulo-ocular reflex rotates the eye about the axis of a head rotation at the same speed but in the opposite direction to make the visual axes in space independent of head motion. This reflex works in all three degrees of freedom: roll, pitch, and yaw. The rotations may be described by vectors and the reflex by a transformation in the form of a matrix. The reflex consists of three parts: sensory, central, and motor. The transduction of head rotation into three neural signals, which may also be described by a vector, is described by a canal matrix. The neural, motorcommand vector is transformed to an eye rotation by a muscle matrix. Since these two matrices are known, one can solve for the central matrix which gives the strength of the connections between all the vestibular neurons and all the eye-muscle motoneurons. The role of the metric tensor in these transformations is described. This method of analysis is used in three applications. A lesion may be simulated by altering the elements in any or all of the three component matrices. By matrix multiplication, the resulting abnormal behavior of the reflex can be described quantitatively in all degrees of freedom. The method is also used to directly compare the differences in brain-stem connections between humans and rabbits that accommodate the altered actions of the muscles of the two species. Finally the method allows a quantitative assessment of the changes that take place in the brainstem connections when plastic changes are induced by artificially dissociating head movements from apparent motion of the visual environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335351
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  • 4
    Electronic Resource
    Electronic Resource
    Ambivalence in modelling oblique saccades (1988)
    Springer
    Biological cybernetics 58 (1988), S. 13-18 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Human oblique saccades might be made by synchronized but independent vertical and horizontal pulse generators; we call this the Cartesian theory. Another hypothesis is that the oblique amplitude and angle are coded centrally and trigonometricallyderived signals are sent to the horizontal and vertical muscles (the polar coordinate theory). We took a Cartesian model and cross-coupled the two generators to produce saccades identical to those of a polar coordinate model. This is disproof by counterexample: the experimental evidence claimed to support the polar coordinate model does not necessarily do so. Moreover, the behavior reported for oblique saccades is so variable, contradictory, idiosyncratic, and species-dependent that any model of the central organization of oblique saccades is probably premature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00363952
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  • 5
    Electronic Resource
    Electronic Resource
    A learning network model of the neural integrator of the oculomotor system (1991)
    Springer
    Biological cybernetics 64 (1991), S. 447-454 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Certain premotor neurons of the oculomotor system fire at a rate proportional to desired eye velocity. Their output is integrated by a network of neurons to supply an eye positon command to the motoneurons of the extraocular muscles. This network, known as the neural integrator, is calibrated during infancy and then maintained through development and trauma with remarkable precision. We have modeled this system with a self-organizing neural network that learns to integrate vestibular velocity commands to generate appropriate eye movements. It learns by using current eye movement on any given trial to calculate the amount of retinal image slip and this is used as the error signal. The synaptic weights are then changed using a straightforward algorithm that is independent of the network configuration and does not necessitate backwards propagation of information. Minimization of the error in this fashion causes the network to develop multiple positive feedback loops that enable it to integrate a push-pull signal without integrating the background rate on which it rides. The network is also capable of recovering from various lesions and of generating more complicated signals to simulate induced postsaccadic drift and compensation for eye muscle mechanics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202608
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  • 6
    Electronic Resource
    Electronic Resource
    Climbing Fiber Intervention Blocks Plasticity of the Vestibuloocular Reflex (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 656 (1992), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1992.tb25226.x
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  • 7
    Electronic Resource
    Electronic Resource
    The Use of Control Systems Analysis in the Neurophysiology of Eye Movements (1981)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Neuroscience 4 (1981), S. 463-503 
    Details
    ISSN: 0147-006X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ne.04.030181.002335
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  • 8
    Electronic Resource
    Electronic Resource
    The impact of land use on the credibility of dispersive clay soils in central and southern Italy (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 14 (1998), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. Tracts of dispersive Plio-Pleistocene clays in central and southern Italy suffer from severe erosion, which has led to the creation of badlands characterized by ‘calanchi’(unvegetated knife-edge ridges) and ‘bian-cane’(cone-shaped hummocks). In recent decades, large areas of this eroded land have been reclaimed for arable cultivation by remodelling the landscape with heavy earth moving equipment. This exposes the clay to erosive rainfall. Wet aggregate strength was used to assess those physical and chemical properties that govern the erodibility of the clays. Regression analysis demonstrated that the most significant variables in predicting soil erodibility were the % organic matter and the exchangeable sodium percentage (ESP). Threshold values of 1–2% and 3–4% organic matter were obtained, dependent on the method of pre-wetting. Reclaimed land is on the borderline of these thresholds and therefore at risk of erosion. Nevertheless, the stability of reclaimed land is significantly higher than that of the badland parent material, ascribable to a lower ESP. Careful land management is required to avoid a recurrence of erosion and the reestablishment of badlands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.1998.tb00143.x
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  • 9
    Electronic Resource
    Electronic Resource
    The impact of cultivation practice and wheelings on runoff generation and soil erosion on the South Downs: some experimental results using simulated rainfall (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 8 (1992), S. 0 
    Details
    ISSN: 1475-2743
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract. The quantitative effects of different cultivation practices and wheelings on the generation of runoff and soil loss on the South Downs were assessed experimentally with a small drip-type rainfall simulator and rainfall intensities of 42.5 and 23.3 mm/h. Runoff volumes generated by different cultivation practices and between wheeled and non-wheeled areas were significantly different. Amounts of soil lost from different cultivation treatments and from wheelings were less consistent. Less runoff and erosion occurred from shallow cultivated land than from conventionally ploughed and cultivated land. Runoff is further increased by rolling ploughed land after drilling and along tramlines compressed by wheelings. Under high intensity rainfall, considerable runoff can be generated from stubble, especially from wheeled areas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1475-2743.1992.tb00913.x
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  • 10
    Electronic Resource
    Electronic Resource
    HIGH SPEED STIRRING TECHNIQUES IN SOLUBILITY STUDIES: A CRITICAL APPRAISAL AND APPLICATION TO HIPPURIC ACID ESTERS1 (1962)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 66 (1962), S. 897-899 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100811a033
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