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.

Temporal summation and reaction time to double-light pulses at suprathreshold levels

Abstract: Temporal summation of the visual system was studied at suprathreshold levels by measuring reaction time (RT) to the double pulses that were equal in luminance (L) and duration. The RTs were determined as functions of L and the stimulus onset asynchrony (SOA) between the onsets of the two pulses. The relation between RT and L obtained for a given SOA was found to be a power function with the exponent 1/3. The function relating L to SOA was then derived for each of three criterion RTs. The L-SOA relationship indicated partial summation at SOAs shorter than about 20 msec. Inhibition was observed at SOAs longer than about 80 msec. These findings were consistent with the predictions from a temporal integration model.

Chapter 16 – Postsynaptic Potentials and Synaptic Integration

Abstract: Postsynaptic potentials (PSPs) can be divided into two broad classes on the basis of mechanisms. One class is based on the direct binding of a transmitter molecule(s) with a receptor-channel complex; these receptors are ionotropic. The other class of PSPs is based on the indirect effect of a transmitter molecule(s) binding with a G-protein-coupled receptor (GPCR), which affects the channel either directly or through additional steps in which the level of a second messenger is altered. Whether a neuron fires in response to synaptic input depends, at least in part, on how many action potentials are produced in any one presynaptic excitatory pathway and on how many individual convergent excitatory input pathways are activated. The final behavior of the cell is also due to the summation of inhibitory PSPs in time and space, as well as to the properties of the voltage-dependent currents in the soma and along the dendrites.

Temporal summation measurements with the Octopus 1-2-3 perimeter.

Abstract: Until recently, measurements of temporal summation required the construction of specialized instrumentation or the custom modification of an existing perimeter, which meant that such testing was unstandardized and relatively expensive. This precluded extensive use of this type of visual response testing, especially in a clinical setting. In an effort to change this situation, a personal computer (PC) program has been devised that makes use of a new interface for remote operation of the Octopus 1-2-3 automated perimeter. The program can be used to measure temporal summation at 1-5 locations in the visual field (0 degrees-30 degrees eccentricity) for 1-10 stimulus durations (5.6-999 ms) in the presence or absence of background illumination (10 cd/m2). Two auxiliary programs for analyzing the resulting data have been developed as well. Preliminary measurement trials were performed on four normal and two glaucomatous eyes at three test locations for ten stimulus durations in both the presence and the absence of background illumination. Ten examinations were carried out for each eye to reduce the effects of short-term fluctuations. The resulting temporal summation curves and the associated critical durations were similar to those found in the literature. No effect of disease on the critical duration was found (n = 2). With this program package, the effects of disease on temporal summation can now be tested using a commercially available instrument. To determine its clinical usefulness, though, investigations with larger populations will have to be made.