Aerospace medicine and biology. A continuing bibliography (supplement 231)

This bibliography lists 284 reports, articles, and other documents introduced into the NASA scientific and technical information system in March 1982

Evaluation and neurocomputational modelling of visual adaptation to optically induced distortions

Spatial geometrical distortions are major artefacts in vision aid optical spectacles. Progressive additional lenses (PALs) are among such spectacles incurring inherent distortions. Distortions alter perceived features of the natural environment and are one of the causes for visual discomforts, such as apparent motion perception and spatial disorientation, experienced by novice spectacle wearers. Thus, fast and efficient visual adaptation to the distortions is a necessity to increase the users’ comfort and consequently overcome the related problems, e.g. risk of fall in the elderly when using PALs. Inspired by this necessity, the work is targeted to investigate the visual mechanisms underlying adaptation to distortions, in particular in PALs. Psychophysical procedures are employed to probe the characteristics of the neural mechanisms underlying the adaptation process in natural viewing conditions. With psychophysical approaches, three main properties of distortion adaptation are revealed; its cortical origin, the reference frame in which it is achieved and its long-term temporal dynamics. In order to discern how the functional organization of neurons enables the visual system to carry out a robust distortion adaptation in a natural environment, biologically plausible recurrent neural network models are utilized. Prediction performance of model variants with different neural network complexity and temporal dynamics of operation were assessed. From the model simulations, major functional roles of recurrent bottom-up and top-down cortical interactions in neural response tuning and in mediating adaptation at different time scales were depicted. The outcomes would further contribute to suggest a solution for facilitating adaptation. The relevance of the research within these aforementioned studies is not restricted to PALs but extends to distortions in other daily used optical utilities, such as virtual reality (VR) displays. Optical distortions are also artefacts in artificial sensory systems, like lens distortions in cameras used in machine vision. Understanding the neural correlates of distortion adaptation in human vision will thereby elicit characteristic features of robust and flexible neural systems to be implemented in brain inspired artificial vision

Measuring Compensatory Eye Movements to Assess Sensory and Learning Properties

This thesis deals with measuring compensatory eye movements to assess sensory and learning properties of humans and mice. We have used this method to determine the visual performance of humans and of mouse models of aging and congenital nystagmus and to measure the effect of direct stimulat

Optimization and improvement of a robotics gaze control system using LSTM networks

Producción CientíficaGaze control represents an important issue in the interaction between a robot and humans. Specifically, deciding who to pay attention to in a multi-party conversation is one way to improve the naturalness of a robot in human-robot interaction. This control can be carried out by means of two different models that receive the stimuli produced by the participants in an interaction, either an on-center off-surround competitive network or a recurrent neural network. A system based on a competitive neural network is able to decide who to look at with a smooth transition in the focus of attention when significant changes in stimuli occur. An important aspect in this process is the configuration of the different parameters of such neural network. The weights of the different stimuli have to be computed to achieve human-like behavior. This article explains how these weights can be obtained by solving an optimization problem. In addition, a new model using a recurrent neural network with LSTM layers is presented. This model uses the same set of stimuli but does not require its weighting. This new model is easier to train, avoiding manual configurations, and offers promising results in robot gaze control. The experiments carried out and some results are also presented.Ministerio de Ciencia, Innovación y Universidades (project TI2018-096652-B-I00)Junta de Castilla y León - Fondo Europeo de Desarrollo Regional (grant VA233P18

Same same but different: plasticity of a 'conserved' reflex

Transformation of sensory percepts into motor output form a core element of how any animal interacts with their environment. While some such sensorimotor transformations can be very elaborate and depend on the lifestyle of a species, others serve basic functions and are ubiquitous across vertebrates. Among the latter ones are gaze-stabilizing reflexes, which serve to maintain stable vision during head motion through compensatory eye movements. Despite this conservation throughout evolution, these reflexive behaviors must remain plastic depending on context or past experience to maintain functionality after e.g. impairments of motor or sensory systems through compensation, or to changes in the environment through adaptation. In this thesis, I employ tadpoles of the frog Xenopus laevis to investigate how neuronal circuits contribute to either adaptive or compensatory plasticity on otherwise conserved gaze-stabilizing reflexes. My first study centers on the role of bilateral visual pathways in the development of the optokinetic reflex (OKR). In early embryos, I unilaterally remove the precursor of the eye, the optic vesicle. Tadpoles that develop under such monocular conditions display pathfinding errors of retinal ganglion cells at the optic chiasm. Tadpoles with near normal contralateral projections functionally compensate for the loss of one eye and show consistent responses to both leftward and rightward moving stimuli. In animals with an induced aberrant ipsilateral projection, compensation is increasingly impaired with more pathfinding errors. Combined, this study shows that binocular eyes are required for appropriate visual circuit formation, and that resulting anatomical aberrations impose limitations on compensatory plasticity. In my second study I focus on the role of the cerebellum in plasticity. Combinations of prolonged, repetitive stimulation with lesions of the cerebellum revealed adaptive plasticity of the OKR, where initially very variable OKR responses converge towards a homeostatic motor output by selective increase and decrease of response magnitude. The cerebellum is specifically associated only with response increases, and only starts to exert this influence well after initial OKR onset. This study therefore shows that multiple brain areas differentially contribute to plasticity of eye movements, leading to heterogenous appearance of different modes of plasticity throughout development. Combined, these studies contribute to the understanding of development and purpose of plasticity in Xenopus OKR. Multiple brain areas are involved with plasticity, and their formation depends on canonical, bilateral visual input. Once functional, plasticity mechanisms serve to maintain homeostasis of the OKR response in response to both adaptation and compensation

Autistic adults show preserved normalisation of sensory responses in gaze processing

Progress in our understanding of autism spectrum disorder (ASD) has recently been sought by characterising how systematic differences in canonical neural computations employed across the sensory cortex might contribute to clinical symptoms in diverse sensory, cognitive, and social domains. A key proposal is that ASD is characterised by reduced divisive normalisation of sensory responses. This provides a bridge between genetic and molecular evidence for an increased ratio of cortical excitation to inhibition in ASD and the functional characteristics of sensory coding that are relevant for understanding perception and behaviour. Here we tested this hypothesis in the context of gaze processing (i.e., the perception of other people's direction of gaze), a domain with direct relevance to the core diagnostic features of ASD. We show that reduced divisive normalisation in gaze processing is associated with specific predictions regarding the psychophysical effects of sensory adaptation to gaze direction, and test these predictions in adults with ASD. We report compelling evidence that both divisive normalisation and sensory adaptation occur robustly in adults with ASD in the context of gaze processing. These results have important theoretical implications for defining the types of divisive computations that are likely to be intact or compromised in this condition (e.g., relating to local vs distal control of cortical gain). These results are also a strong testament to the typical sensory coding of gaze direction in ASD, despite the atypical responses to others' gaze that are a hallmark feature of this diagnosis.This research was supported by a Wellcome Trust Senior Clinical Research Fellowship (100227) awarded to GR and Australian Research Council Discovery Project (DP160102239) awarded to CC. This work was enabled partly by a study visit grant to CP from the Experimental Psychology Society. We thank all the participants who gave up their time to take part in this research

Homeostatic plasticity of eye movement performance in Xenopus tadpoles following prolonged visual image motion stimulation

Visual image motion-driven ocular motor behaviors such as the optokinetic reflex (OKR) provide sensory feedback for optimizing gaze stability during head/body motion. The performance of this visuo-motor reflex is subject to plastic alterations depending on requirements imposed by specific eco-physiological or developmental circumstances. While visuo-motor plasticity can be experimentally induced by various combinations of motion-related stimuli, the extent to which such evoked behavioral alterations contribute to the behavioral demands of an environment remains often obscure. Here, we used isolated preparations of Xenopus laevis tadpoles to assess the extent and ontogenetic dependency of visuo-motor plasticity during prolonged visual image motion. While a reliable attenuation of large OKR amplitudes can be induced already in young larvae, a robust response magnitude-dependent bidirectional plasticity is present only at older developmental stages. The possibility of older larvae to faithfully enhance small OKR amplitudes coincides with the developmental maturation of inferior olivary-Purkinje cell signal integration. This conclusion was supported by the loss of behavioral plasticity following transection of the climbing fiber pathway and by the immunohistochemical demonstration of a considerable volumetric extension of the Purkinje cell dendritic area between the two tested stages. The bidirectional behavioral alterations with different developmental onsets might functionally serve to standardize the motor output, comparable to the known differential adaptability of vestibulo-ocular reflexes in these animals. This homeostatic plasticity potentially equilibrates the working range of ocular motor behaviors during altered visuo-vestibular conditions or prolonged head/body motion to fine-tune resultant eye movements

Attentional Facilitation for Faces in Dynamic Spatial Cueing Tasks

This thesis explored whether faces produce inhibition of return (IOR) in dynamic displays. As previous literature exclusively used static displays, it is not possible to discern whether the IOR observed is attributable directly to the face or simply reflects location-based IOR. Whether faces produce object-based IOR is suggested as a way to distinguish two contemporary theories of IOR: the habituation hypothesis and detection cost theory. In the habituation hypothesis, IOR reflects a weaker response to previously attended objects due to habituation, whereas detection cost theory proposes IOR as an attentional cost incurred when there is a similarity between the cue and target. As highly salient objects may not be habituated to, the habituation hypothesis would predict that certain objects would not show IOR, whereas detection cost theory would predict IOR for all objects provided the relationship between cue and target remains the same. Thus, whether faces produce object-based IOR may distinguish between these accounts. Nine experiments were conducted comparing face stimuli to other objects in spatial cueing tasks. In the eight experiments that used dynamic displays, faces did not produce object-based IOR. In fact, cueing effects for faces were consistently in the direction of facilitation, rather than inhibition. This was the case for schematic and photographic faces and for both manual and saccadic responses. A secondary finding was that other schematic objects also did not produce object-based IOR, while shapes and photographic objects did produce object-based IOR. The present data are most consistent with the habituation hypothesis, although this only specifically explains the lack of IOR for faces rather than the presence of facilitation. This cueing effect may be explained by the maintenance of attention at cued faces and/or the interaction of different perceptual representations and their subsequent attentional effects

A Learning-Style Theory for Understanding Autistic Behaviors

Understanding autism's ever-expanding array of behaviors, from sensation to cognition, is a major challenge. We posit that autistic and typically developing brains implement different algorithms that are better suited to learn, represent, and process different tasks; consequently, they develop different interests and behaviors. Computationally, a continuum of algorithms exists, from lookup table (LUT) learning, which aims to store experiences precisely, to interpolation (INT) learning, which focuses on extracting underlying statistical structure (regularities) from experiences. We hypothesize that autistic and typical brains, respectively, are biased toward LUT and INT learning, in low- and high-dimensional feature spaces, possibly because of their narrow and broad tuning functions. The LUT style is good at learning relationships that are local, precise, rigid, and contain little regularity for generalization (e.g., the name–number association in a phonebook). However, it is poor at learning relationships that are context dependent, noisy, flexible, and do contain regularities for generalization (e.g., associations between gaze direction and intention, language and meaning, sensory input and interpretation, motor-control signal and movement, and social situation and proper response). The LUT style poorly compresses information, resulting in inefficiency, sensory overload (overwhelm), restricted interests, and resistance to change. It also leads to poor prediction and anticipation, frequent surprises and over-reaction (hyper-sensitivity), impaired attentional selection and switching, concreteness, strong local focus, weak adaptation, and superior and inferior performances on simple and complex tasks. The spectrum nature of autism can be explained by different degrees of LUT learning among different individuals, and in different systems of the same individual. Our theory suggests that therapy should focus on training autistic LUT algorithm to learn regularities