Topic
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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TL;DR: Temporal summation was measured for tones within, above, and below a narrow-band noise centered at 1000 cps as a function of the time interval between the onset of the noise and onset of tones as discussed by the authors.
Abstract: Temporal summation was measured for tones within, above, and below a narrow‐band noise centered at 1000 cps as a function of the time interval between the onset of the noise and the onset of the tones. The results show that the theory of temporal auditory summation is sufficient to predict the threshold of audibility for tones in a steady‐state condition where there exists a threshold shift not caused by the physical presence of a masking stimulus. Variation of the time interval between the onset of the narrow‐band noise and the tones did not produce results different from those found in the steady state.
28 citations
TL;DR: The formation of neuronal networks in vitro is controlled by cellular mechanisms that favor inhibitory connections in general and specifically enhance the formation of reciprocal connections between pairs of excitatory and inhibitory neurons.
Abstract: Muller, Thomas H., D. Swandulla, and H. U. Zeilhofer. Synaptic connectivity in cultured hypothalamic neuronal networks. J. Neurophysiol. 77: 3218–3225, 1997. We have developed a novel approach to a...
27 citations
TL;DR: Temporal summation obtained by repeated stimulations of subthreshold intensity appears to represent a new tool for investigating nociceptive pathophysiologic processes in horses.
Abstract: Objective—To investigate whether facilitation of the nociceptive withdrawal reflex (NWR) can be evoked and quantified as a measure of temporal summation from the distal aspect of the left forelimb and hind limb in standing nonsedated horses via repeated stimulations of various subthreshold intensities and frequencies. Animals—10 adult horses. Procedure—Surface electromyographic activity evoked by stimulation of the digital palmar and plantar nerves was recorded from the common digital extensor and cranial tibial muscles. For each horse, the NWR threshold intensity to a single stimulus was determined for the forelimb and hind limb. Repeated stimulations were performed at subthreshold intensities and at frequencies of 2, 5, and 10 Hz. The reflex amplitude was quantified, and the behavioral responses accompanying the stimulations were scored. Results—Repeated stimulations at subthreshold intensities were able to summate and facilitate the NWR in conscious horses. The reflex facilitation was significantly rel...
27 citations
TL;DR: The concept that transmitter-induced p.p.s.ps may trigger voltage-sensitive conductances other than those initiating action potentials, and that in the present case this could produce a true post-e.p.) hyperpolarization is introduced.
Abstract: We have postulated that an excitatory postsynaptic potential (e.p.s.p.) may open voltage-sensitive K+ (‘M’) channels1, in an appropriate depolarizing range, and that this could alter the e.p.s.p. waveform. Consequently, the fast e.p.s.p. in neurones of sympathetic ganglia, elicited by a nicotinic action of acetylcholine (ACh)2, could be followed by a hyperpolarization, produced by the opening of M channels during the depolarizing e.p.s.p. and their subsequent slow closure (time constant∼150 ms)1. This introduces the concept that transmitter-induced p.s.ps may trigger voltage-sensitive conductances other than those initiating action potentials, and that in the present case this could produce a true post-e.p.s.p. hyperpolarization. (Some hyperpolarizations other than inhibitory postsynaptic potentials (i.p.s.ps) have been reported to follow e.p.s.ps3,4.) We show here that this is so.
26 citations
TL;DR: This model has three stages of summation: short-range summation within linear receptive fields, medium-range integration to compute contrast energy for multiple patches of the image, and long-range pooling of the contrast integrators by probability summation.
Abstract: Classical studies of area summation measure contrast detection thresholds as a function of grating diameter. Unfortunately, (i) this approach is compromised by retinal inhomogeneity and (ii) it potentially confounds summation of signal with summation of internal noise. The Swiss cheese stimulus of T. S. Meese and R. J. Summers (2007) and the closely related Battenberg stimulus of T. S. Meese (2010) were designed to avoid these problems by keeping target diameter constant and modulating interdigitated checks of first-order carrier contrast within the stimulus region. This approach has revealed a contrast integration process with greater potency than the classical model of spatial probability summation. Here, we used Swiss cheese stimuli to investigate the spatial limits of contrast integration over a range of carrier frequencies (1–16 c/deg) and raised plaid modulator frequencies (0.25–32 cycles/check). Subthreshold summation for interdigitated carrier pairs remained strong (~4 to 6 dB) up to 4 to 8 cycles/check. Our computational analysis of these results implied linear signal combination (following square-law transduction) over either (i) 12 carrier cycles or more or (ii) 1.27 deg or more. Our model has three stages of summation: short-range summation within linear receptive fields, medium-range integration to compute contrast energy for multiple patches of the image, and long-range pooling of the contrast integrators by probability summation. Our analysis legitimizes the inclusion of widespread integration of signal (and noise) within hierarchical image processing models. It also confirms the individual differences in the spatial extent of integration that emerge from our approach.
26 citations