A ratio model of perceived speed in the human visual system

The perceived speed of moving images changes over time. Prolonged viewing of a pattern (adaptation) leads to an exponential decrease in its perceived speed. Similarly, responses of neurones tuned to motion reduce exponentially over time. It is tempting to link these phenomena. However, under certain conditions, perceived speed increases after adaptation and the time course of these perceptual effects varies widely. We propose a model that comprises two temporally tuned mechanisms whose sensitivities reduce exponentially over time. Perceived speed is taken as the ratio of these filters' outputs. The model captures increases and decreases in perceived speed following adaptation and describes our data well with just four free parameters. Whilst the model captures perceptual time courses that vary widely, parameter estimates for the time constants of the underlying filters are in good agreement with estimates of the time course of adaptation of direction selective neurones in the mammalian visual system.     

A model of the peripheral auditory system

Summary Recent electrophysiological data obtained from auditory nerve fibers of cats have made possible the formulation of a model of the peripheral auditory system that relates the all-or-none activity of these fibers to acoustic stimulation. The components of the model are intended to represent the major functional components of the peripheral system. These components are: (i) a linear mechanical system intended to represent the outer, middle, and mechanical parts of the inner ear; (ii) a transducer intended to represent the action of the sensory cells; and (iii) a model neuron whose properties are intended to represent the nerve excitation process. A general-purpose digital computer has been used to determine the response of the model to a variety of acoustic stimuli. These results have been compared with data obtained from auditory nerve fibers.This work was supported in part by the Joint Services Electronics Program (Contract DA 36-039-AMC-03200(E); and in part by the National Science Foundation (Grant GP-2495), the National Institutes of Health (Grant MH-04737-05), the National Aeronautics and Space Administration (Grant NsG-496); and by Research Grant NB-01344, National Institute of Neurological Diseases and Blindness of the National Institutes of Health, Public Health Service.     

Emotional facial expression detection in the peripheral visual field

Background

In everyday life, signals of danger, such as aversive facial expressions, usually appear in the peripheral visual field. Although facial expression processing in central vision has been extensively studied, this processing in peripheral vision has been poorly studied.

Methodology/Principal Findings

Using behavioral measures, we explored the human ability to detect fear and disgust vs. neutral expressions and compared it to the ability to discriminate between genders at eccentricities up to 40°. Responses were faster for the detection of emotion compared to gender. Emotion was detected from fearful faces up to 40° of eccentricity.

Conclusions

Our results demonstrate the human ability to detect facial expressions presented in the far periphery up to 40° of eccentricity. The increasing advantage of emotion compared to gender processing with increasing eccentricity might reflect a major implication of the magnocellular visual pathway in facial expression processing. This advantage may suggest that emotion detection, relative to gender identification, is less impacted by visual acuity and within-face crowding in the periphery. These results are consistent with specific and automatic processing of danger-related information, which may drive attention to those messages and allow for a fast behavioral reaction.     

Intermittent hypoxic loading: a model system to study the early stages of myocardial lesions

Authors applied the model system of intermittent hypoxic loading to study the development of early myocardial alterations. It was found that a primary role is played by the deficiency of high-energy phosphate synthesis and by the disturbance of energetic and transport processes. The change of Ca2+-control, activation of anaerobic glycolysis and intracellular acidosis were found to be instrumental in decreasing contractility, impairing membranes and finally in a diffuse destruction of myofilaments.     

A recurrent system incorporating characteristics of the visual system: a model for the function of backward neural connections in the visual system

A recurrent system is constructed in order to investigate the role of the backward neural connections found in the primate visual system. The system incorporates a layer to perform localized spatial frequency analysis of input images, a function which has been assumed to take place in the primary visual cortex. The function of the system is examined by simulation. The results show that the system can separate an object pattern from its background, irrespective of its precise position. The acceptable displacement range for input images is determined from the width of the window function used to calculate the local Fourier transform. A multilayer version of the above recurrent system is also constructed.     

Fusion and scission of membranes: Ubiquitous topological transformations in cells

The 2016 Nobel Prizes were awarded to Yoshinori Ohsumi for autophagy and to David Thouless, Duncan Haldane and Michael Kosterlitz for topological transitions. Both of these phenomena are intrinsically related when it comes to membranes. Here, we give a brief account on topological transformations of lipid membranes, commonly known as membrane fusion and membrane scission, and introduce the underlying topological invariant, the genus. The genus of a shape is a useful concept to distinguish unambiguously the processes of membrane fusion/scission and offers a simple method to describe complex, cellular membrane structures, such as fenestrated cristae. We distinguish and highlight the connection between topological transformations of lipid membranes and the recent awards, and point out the extraordinarily large number of topological changes during autophagy.      

A model for processing of movement in the visual system

Processing of spatio-temporal information in the human visual system has been investigated thoroughly during the past decade, but is still far from being properly understood. Moreover, the theory of separation of information by means of sustained and transient channels already at the retinal level is not satisfactory, as experimental results indicate that these two types of channels span a continuum of temporal characteristics. It is however obvious, that the process of pattern recognition and velocity perception calls for their separation at some level of the hierarchy. In this communication, we extend our model of three-dimensional spatio-temporal frequency expansion in the visual system (Gafni and Zeevi, 1977) to show how velocity-information extraction channels, sensitive to direction and velocity exclusively, can be formed by simple summation of signals from well-defined sets of channels representing points in the frequency space. Correspondence of these channels to characteristics of the cortical neurons is discussed.     

A model of the human visual system in its response to certain classes of moving stimuli

The purpose of this study is to construct a functional model of the human visual system in its response to certain classes of moving stimuli.Experimental data are presented describing the interdependence of the input variables, temporal frequency, spatial period, etc., for two constant response states, viz. threshold motion response and threshold flicker response. On the basis of these data, two basic units are isolated, a vertical (V) unit and a horizontal (H) unit. The H-unit is identified with the Reichardt multiplier (Reichardt and Varju, 1959), and the V-unit with the de Lange filter (de Lange, 1954).A definition of the general motion response of the H-units is obtained, and this is then reduced to an expression which may be applied directly to the observed motion response data. By this method, Thorson's simplification of the Reichardt scheme (Thorson, 1966) is adopted for the H-unit and total and relative (population) weighting factors, associated with the H-unit output, are defined.In order to reconcile the theoretical square-wave threshold motion response with the experimental data, Thorson's simplification is modified with the introduction of a low-pass filter on the output. The amended scheme is shown to predict a (temporal) frequency-dependent phase-sensitivity. This prediction is tested experimentally, and its validity indicated.     

Learning invariant object recognition in the visual system with continuous transformations

The cerebral cortex utilizes spatiotemporal continuity in the world to help build invariant representations. In vision, these might be representations of objects. The temporal continuity typical of objects has been used in an associative learning rule with a short-term memory trace to help build invariant object representations. In this paper, we show that spatial continuity can also provide a basis for helping a system to self-organize invariant representations. We introduce a new learning paradigm “continuous transformation learning” which operates by mapping spatially similar input patterns to the same postsynaptic neurons in a competitive learning system. As the inputs move through the space of possible continuous transforms (e.g. translation, rotation, etc.), the active synapses are modified onto the set of postsynaptic neurons. Because other transforms of the same stimulus overlap with previously learned exemplars, a common set of postsynaptic neurons is activated by the new transforms, and learning of the new active inputs onto the same postsynaptic neurons is facilitated. We demonstrate that a hierarchical model of cortical processing in the ventral visual system can be trained with continuous transform learning, and highlight differences in the learning of invariant representations to those achieved by trace learning.     

The magnetic field sensitivity of the human visual system shows resonance and compass characteristic

Orientation in the geomagnetic field is essential for many animal species. As yet, the interaction mechanisms of this weak field with the organisms are understood only incompletely. One mechanism in question is the interaction with the photochemical reaction in the retina. We show that the visual sensitivity of man is influenced by periodic sinusoidal inversion of the vertical component of the geomagnetic field. This effect indicates visual fixation in north-south direction and shows a pronounced resonance at a period duration of 110 s. These findings should be helpful in identifying in detail the mechanisms which are influenced by the geomagnetic field.     

A model of pulse generation in the peripheral nervous system

A model of pulse generation in the peripheral nervous system is discussed in this paper. The model uses no nonlinear circuit analogues of cellular membrane but rather a direct piecewise linear characterization of the membrane permeability changes and related ionic transport which accompany pulse generation. The relative simplicity of the model notwithstanding, predictions of pulse frequency versus generator potential amplitude relationship and pulse frequency versus pulse amplitude relationship as well as the threshold property of the process are correctly furnished by straight-forward calculations.The research reported here was performed while the author was a visiting faculty member at the California Institute of Technology.     

Analytical model of readaptation of the human visual system after light exposure

The process of readaptation of the human visual system is considered as the behavior of a follow-up system, with the brightness of the background being the control signal. The times of recovery of visual acuity calculated by the model are compared with the experimental data.     

A biologically plausible model of early visual motion processing I: Theory and implementation

A model of local image encoding is described which explicitly incorporates quantitative data about the number density, bandwidth and receptive field organisation of neurons involved in motion detection. The model solves the problem of extracting local velocity on the basis of inputs tuned to spatiotemporal frequency and sensitive to contrast. The spatiotemporally tuned, opponent motion filters are followed by a compressive non-linearity and comprise a first stage. The inter-stage signals are interpreted as those from single neurons and the second stage is modelled as a neural-network layer. The second stage uses semilinear units and models the effect of lateral, on-centre off-surround, intralayer connections. Characterisation of the first stage leads to a clarification of the concept of the psychophysical channel and its relation to physiological data. The quantitative parametrisation of the model allows the simulation of several psychophysical phenomena which are reported in a companion paper.     

A model of a human heart via graph nano topological spaces

In this paper,new forms of nano topological spaces through a neighborhood system of vertices for a digraph will be presented and studied.We apply the connection between digraph theory and nano topological spaces in the human heart as an example in real life.We have a blood flow system in the human heart with respect to oxygenated and deoxygenated blood circulation.Our study will be definitely helpful to develop a tool in solving the blood flow system in the human heart.Finally,we have succeeded in improving Proposition 1.6 in [7] and Proposition 4.4.1 in [11].