13 research outputs found

    The Fourier analysis of saccadic eye movements

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    This thesis examines saccadic eye movements in the frequency domain and develops sensitive tools for characterising their dynamics. It tests a variety of saccade models and provides the first strong empirical evidence that saccades are time-optimal. By enabling inferences on the neural command, it also allows for better clinical differentiation of abnormalities and the evaluation of putative mechanisms for the development of congenital nystagmus. Chapters 3 and 4 show how Fourier transforms reveal sharp minima in saccade frequency spectra, which are robust to instrument noise. The minima allow models based purely on the output trajectory, purely on the neural input, or both, to be directly compared and distinguished. The standard, most commonly accepted model based on bang-bang control theory is discounted. Chapter 5 provides the first empirical evidence that saccades are time-optimal by demonstrating that saccade bandwidths overlap across amplitude onto a single slope at high frequencies. In Chapter 6, the overlap also allows optimal (Wiener) filtering in the frequency domain without a priori assumptions. Deconvolution of the aggregate neural driving signal is then possible for current models of the oculomotor plant. The final two chapters apply these Fourier techniques to the quick phases of physiological (optokinetic) nystagmus and of pathological (congenital) nystagmus. These quick phases are commonly assumed to be saccadic in origin. This assumption is thoroughly tested and found to hold, but with subtle differences implying that the smooth pursuit system interacts with the saccade system during the movement. This interaction is taken into account in Chapter 8 in the assessment of congenital nystagmus quick phases, which are found to be essentially normal. Congenital nystagmus models based on saccadic abnormalities are appraised

    Cerebellar control of eye movements: from cerebellar cortex to cerebellar nuclei

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    Arguably visual information is the most important source of sensory information for us human beings, allowing us to perceive the world. Almost a quarter of our brain is devoted to visual processing. To achieve a precise projection of objects of interest onto the retinal fovea, the region offering the highest spatial resolution and other advantages for the analysis of visual objects, two major types of eye movements, saccades and smooth pursuit are deployed. Saccades shift the image of an object of interest into the fovea. In case the object should be moving, smooth pursuit eye movements (SPEM) try to keep the image of the object within the confines of the fovea in order to ensure sufficient time for its analysis. It has been known that the oculomotor vermis (OMV) of the cerebellar cortex is dedicated to the control of both saccades and SPEM. However, it has remained unclear if the same oculomotor vermal neurons contribute to controlling these two different types of movements, a scenario that does not look very likely considering their dramatically different kinematics. To address this question, we recorded the activity of OMV Purkinje cells (PCs), the only type of output neuron of cerebellar cortex, in monkeys, and the most suitable animal model for studies of the cerebellar control of eye movements made by humans. During recordings the monkeys were performing saccades and smooth pursuit eye movement (SPEM). Subjecting the recorded saccade and SPEM related PC simple spike responses to a multiple regression analysis, we found that, for saccades, the neural firing pattern is mainly determined by eye position. In contrast, in the case of SPEM, eye velocity plays the most important role in defining the firing pattern. These results indicate that the cerebellar computations for saccades and SPEM are different, even at the level of individual PCs. Both saccades and SPEM can be adaptively changed by the experience of insufficiencies, compromising the precision of saccades or the minimization of object image slip in the case of SPEM. As both forms of adaptation rely on the cerebellar oculomotor vermis (OMV), most probably deploying a shared neuronal machinery, one might expect that the adaptation of one type of eye movement should affect the kinematics of the other. In order to test this expectation, we subjected 2 monkeys to a standard saccadic adaption paradigm with SPEM test trials at the end and, alternatively, the same 2 monkeys plus a 3rd one to a random saccadic adaptation paradigm with interleaved trials of SPEM. In contrast to our expectation we observed at best marginal transfer which, moreover was little consistent across experiments and subjects. The lack of consistent transfer of saccadic adaptation decisively constrains models of the implementation of oculomotor learning in the OMV, suggesting an extensive separation of saccade and SPEM-related synapses on P-cell dendritic trees. The OMV projects ipsilaterally to the caudal fastigial nuclei (cFN) (Yamada & Noda, 1987), which is also called the fastigial oculomotor region. Not surprisingly, in view of the established role of the OMV in the control of saccades and SPEM, also the cFN is known to contribute to both. Microsaccades are small saccades produced during fixation, whose amplitudes are <1 degree. The concept of a microsaccade-saccade continuum is supported by the fact that studies on the underpinnings of microsaccades have shown that those oculomotor structures explored contribute to saccades of all sizes. The OMV is one of these structures for which a microsaccade-macrosaccade continuum has been established. As shown in this second work package, this continuum is maintained at the level of the cFN, the recipient of saccade-related signals from the OMV. Furthermore, we demonstrate that the pre-microsaccadic baseline firing rate of cFN neurons has properties suitable to ensure precise fixation. In summary, our results demonstrate the participation of the cerebellum in the control of saccades and SPEM at the level of cerebellar cortex as well as at the level of the caudal fastigial nucleus. It establishes that, contrary to the still dominating view of a separation of the cerebellar machinery for saccades and SPEM, these two forms of goal-directed eye movements rely on largely overlapping, if not identical circuitry. Irrespective of this overlap, learning based adjustments maintain a stunning degree of independence. This is established by our behavioral work. It suggests that this specificity may be a consequence of delimiting distinct dendritic territories of OMV Purkinje cells for the two types of eye movements. Finally, this work supports the notion of a general micro- macrosaccade continuum by establishing that also cFN neurons care for both, micro- and macrosaccades

    3D Dynamic Modeling of the Head-Neck Complex for Fast Eye and Head Orientation Movements Research

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    A 3D dynamic computer model for the movement of the head-neck complex is presented. It incorporates anatomically correct information about the diverse elements forming the system. The skeleton is considered as a set of interconnected rigid 3D bodies following the Newton-Euler laws of movement. The muscles are modeled using Enderle's linear model, which shows equivalent dynamic characteristics to Loeb's virtual muscle model. The soft tissues, namely, the ligaments, intervertebral disks, and facet joints, are modeled considering their physiological roles and dynamics. In contrast with other head and neck models developed for safety research, the model is aimed to study the neural control of the complex during fast eye and head movements, such as saccades and gaze shifts. In particular, the time-optimal hypothesis and the feedback control ones are discussed

    Constructing the space of visual attention

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    Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Architecture, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Page 180 blank. Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 168-171).This thesis explores the nature of a human experience in space through a primary inquiry into vision. This inquiry begins by questioning the existing methods and instruments employed to capture and represent a human experience of space. While existing qualitative and quantitative methods and instruments -- from "subjective" interviews to "objective" photographic documentation -- may lead to insight in the study of a human experience in space, we argue that they are inherently limited with respect to physiological realities. As one moves about the world, one believes to see the world as continuous and fully resolved. However, this is not how human vision is currently understood to function on a physiological level. If we want to understand how humans visually construct a space, then we must examine patterns of visual attention on a physiological level. In order to inquire into patterns of visual attention in three dimensional space, we need to develop new instruments and new methods of representation. The instruments we require, directly address the physiological realities of vision, and the methods of representation seek to situate the human subject within a space of their own construction. In order to achieve this goal we have developed PUPIL, a custom set of hardware and software instruments, that capture the subject's eye movements. Using PUPIL, we have conducted a series of trials from proof of concept -- demonstrating the capabilities of our instruments -- to critical inquiry of the relationship between a human subject and a space. We have developed software to visualize this unique spatial experience, and have posed open questions based on the initial findings of our trials. This thesis aims to contribute to spatial design disciplines, by providing a new way to capture and represent a human experience of space.by Moritz Philipp Kassner [and] William Rhoades Patera.S.M

    Nineteenth Annual Conference on Manual Control

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    Intrinsic dimensionality in vision: Nonlinear filter design and applications

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    Biological vision and computer vision cannot be treated independently anymore. The digital revolution and the emergence of more and more sophisticated technical applications caused a symbiosis between the two communities. Competitive technical devices challenging the human performance rely increasingly on algorithms motivated by the human vision system. On the other hand, computational methods can be used to gain a richer understanding of neural behavior, e.g. the behavior of populations of multiple processing units. The relations between computational approaches and biological findings range from low level vision to cortical areas being responsible for higher cognitive abilities. In early stages of the visual cortex cells have been recorded which could not be explained by the standard approach of orientation- and frequency-selective linear filters anymore. These cells did not respond to straight lines or simple gratings but they fired whenever a more complicated stimulus, like a corner or an end-stopped line, was presented within the receptive field. Using the concept of intrinsic dimensionality, these cells can be classified as intrinsic-two-dimensional systems. The intrinsic dimensionality determines the number of degrees of freedom in the domain which is required to completely determine a signal. A constant image has dimension zero, straight lines and trigonometric functions in one direction have dimension one, and the remaining signals, which require the full number of degrees of freedom, have the dimension two. In this term the reported cells respond to two dimensional signals only. Motivated by the classical approach, which can be realized by orientation- and frequency-selective Gabor-filter functions, a generalized Gabor framework is developed in the context of second-order Volterra systems. The generalized Gabor approach is then used to design intrinsic two-dimensional systems which have the same selectivity properties like the reported cells in early visual cortex. Numerical cognition is commonly assumed to be a higher cognitive ability of humans. The estimation of the number of things from the environment requires a high degree of abstraction. Several studies showed that humans and other species have access to this abstract information. But it is still unclear how this information can be extracted by neural hardware. If one wants to deal with this issue, one has to think about the immense invariance property of number. One can apply a high number of operations to objects which do not change its number. In this work, this problem is considered from a topological perspective. Well known relations between differential geometry and topology are used to develop a computational model. Surprisingly, the resulting operators providing the features which are integrated in the system are intrinsic-two-dimensional operators. This model is used to conduct standard number estimation experiments. The results are then compared to reported human behavior. The last topic of this work is active object recognition. The ability to move the information gathering device, like humans can move their eyes, provides the opportunity to choose the next action. Studies of human saccade behavior suggest that this is not done in a random manner. In order to decrease the time an active object recognition system needs to reach a certain level of performance, several action selection strategies are investigated. The strategies considered within this work are based on information theoretical and probabilistic concepts. These strategies are finally compared to a strategy based on an intrinsic-two-dimensional operator. All three topics are investigated with respect to their relation to the concept of intrinsic dimensionality from a mathematical point of view

    Aerospace Medicine and Biology: A cumulative index to the 1982 issues

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    This publication is a cumulative index to the abstracts contained in the Supplements 229 through 240 of Aerospace Medicine and Biology: A continuing Bibliography. It includes three indexes: subject, personal author, and corporate source

    Aerospace Medicine and Biology: A Cumulative Index to the 1985 Issues

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    This publication is a cumulative index to the abstracts contained in the Supplements 268 through 279 of Aerospace Medicine and Biology: A Continuing Bibliography. It includes seven indexes - subject, personal author, corporate source, foreign technology, contract number, report number, and accession number
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