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Summation

About: Summation is a research topic. Over the lifetime, 954 publications have been published within this topic receiving 45593 citations. The topic is also known as: summation & sum of a sequence.


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Journal ArticleDOI
TL;DR: Age-related changes in the visual system, although leading to a reduction in contrast sensitivity, are not accompanied by a change in temporal summation for a detection task with an achromatic 0.48° diameter spot stimulus.
Abstract: Purpose: To examine the temporal summation of a Goldmann III–sized stimulus under the conditions of standard automated perimetry in healthy participants of varying age. Methods: Twenty-seven healthy individuals of varying age (24–80 years) were tested. Achromatic contrast thresholds were measured for seven 0.48° diameter (near Goldmann III) spot stimuli of varying presentation duration (1–24 frames, 1.8–191.9 ms) at 8.8° eccentricity in the visual field along the 45°, 135°, 225°, and 315° meridians. All stimuli were displayed on a CRT display with a background set to 10 cd/m2. Iterative two-phase regression analysis was used to estimate the critical duration from each localized temporal summation function. Results: A significant decrease in contrast sensitivity for all stimulus durations examined in this study was observed with increasing age in both the superior and inferior hemifield (P < 0.001). Despite this, no significant change in the critical duration was observed as a function of age in either the superior (r2 = 9.1 × 10−9, P = 0.99) or inferior hemifield (r2 = 2.4 × 10−5, P = 0.98). Conclusions: Age-related changes in the visual system, although leading to a reduction in contrast sensitivity, are not accompanied by a change in temporal summation for a detection task with an achromatic 0.48° diameter spot stimulus. This is important to know when proceeding to examine temporal summation changes in diseases like glaucoma.

10 citations

Journal Article
TL;DR: The JASTAP computer model simulates functional features of a real neuron with chemical transmission of information through the simulation of the selected integrative neuronal functions directly influencing the animation of a neuronal network.
Abstract: The JASTAP computer model simulates functional features of a real neuron with chemical transmission of information; it is focused on the simulation of the selected integrative neuronal functions directly influencing the animation of a neuronal network : a) Type and time-course of the synaptic potential (excitatory, excitatory with afterpotential, inhibitory). b) Latency, threshold, absolute refractory period, phasic and tonic spiking activity, synaptic weight, input-output function. c) Spatial and temporal summation. d) Heterosynaptic interactions of the synapses at the presynaptic site (facilitation, inhibition). e) Activity induced changes of the synaptic transmission (habituation, sensitization, fatigue, frequency potentiation, posttetanic depression, posttetanic potentiation, Hebbian learning). This program is written in C++ language for IBM PC compatible computers with 640 kB RAM, VGA graphics card and hard disk (mathematical coprocessor is not required but can significantly speed up computation). The program can define neural network by simple command language and simulate its activity in discrete time intervals on 0.5 ms steps. The results can be displayed in time slices (visualization in the form of the intracellular recording with a microelectrode) or saved to disk files. Ambition of the JASTAP model is to simulate some of the biologically realistic functions of the neuronal networks assembled of several dozens of model neurons

10 citations

Journal ArticleDOI
TL;DR: The results suggest that the earliest visual responses in V1 follow a linear summation rule when attention is not involved and that attention can affect the earliest interactions between multiple objects.
Abstract: In natural scenes, multiple objects are usually presented simultaneously. How do specific areas of the brain respond to multiple objects based on their responses to each individual object? Previous functional magnetic resonance imaging (fMRI) studies have shown that the activity induced by a multiobject stimulus in the primary visual cortex (V1) can be predicted by the linear or nonlinear sum of the activities induced by its component objects. However, there has been little evidence from electroencephelogram (EEG) studies so far. Here we explored how V1 responded to multiple objects by comparing the EEG signals evoked by a three-grating stimulus with those evoked by its two components (the central grating and 2 flanking gratings). We focused on the earliest visual component C1 (onset latency of ∼50 ms) because it has been shown to reflect the feedforward responses of neurons in V1. We found that when the stimulus was unattended, the amplitude of the C1 evoked by the three-grating stimulus roughly equaled the sum of the amplitudes of the C1s evoked by its two components, regardless of the distances between these gratings. When the stimulus was attended, this linear spatial summation existed only when the three gratings were far apart from each other. When the three gratings were close to each other, the spatial summation became compressed. These results suggest that the earliest visual responses in V1 follow a linear summation rule when attention is not involved and that attention can affect the earliest interactions between multiple objects.

10 citations

Journal ArticleDOI
TL;DR: A simple form of the auditory running‐average hypothesis is presented, and is applied to two phenomena: the temporal summation of loudness and the delayed perception of the offset of brief stimuli.
Abstract: A simple form of the auditory running‐average hypothesis is presented, and is applied to two phenomena: the temporal summation of loudness and the delayed perception of the offset of brief stimuli. For both phenomena, the predictions of the hypothesis describe the data well.

10 citations

Journal ArticleDOI
TL;DR: There is a nonlinear interaction between these excitatory and inhibitory synaptic currents that is not due to hyperpolarization itself, but probably is a result of their own synaptic conductance changes, i.e., shunting.
Abstract: The interaction of excitatory and inhibitory inputs to the accessory optic system was studied with whole cell recordings in the turtle basal optic nucleus. Previous studies have shown that visual p...

10 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202323
202234
202118
20204
201911
201812