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.

Area summation in human vision at and above detection threshold

Abstract: The initial image-processing stages of visual cortex are well suited to a local (patchwise) analysis of the viewed scene. But the world’s structures extend over space as textures and surfaces, suggesting the need for spatial integration. Most models of contrast vision fall shy of this process because (i) the weak area summation at detection threshold is attributed to probability summation (PS) and (ii) there is little or no advantage of area well above threshold. Both of these views are challenged here. First, it is shown that results at threshold are consistent with linear summation of contrast following retinal inhomogeneity, spatial filtering, nonlinear contrast transduction and multiple sources of additive Gaussian noise. We suggest that the suprathreshold loss of the area advantage in previous studies is due to a concomitant increase in suppression from the pedestal. To overcome this confound, a novel stimulus class is designed where: (i) the observer operates on a constant retinal area, (ii) the target area is controlled within this summation field, and (iii) the pedestal is fixed in size. Using this arrangement, substantial summation is found along the entire masking function, including the region of facilitation. Our analysis shows that PS and uncertainty cannot account for the results, and that suprathreshold summation of contrast extends over at least seven target cycles of grating.

Sensory function and gating of histaminergic neuron C2 in Aplysia

Abstract: This paper explores the possible sensory function of the identified histaminergic neuron C2 Mechanical stimulation of a narrow region around the mouth of the animal (perioral zone) elicits brief depolarizing potentials in C2 Extracellular recordings from the peripheral axons of C2 indicate that the depolarizing potentials are due to action potentials that are conveyed from the periphery but do not invade the cell body, since they fail at a region with a low safety factor within the cerebral ganglion These blocked axonal spikes (A- spikes) function as if they were excitatory synaptic inputs to C2, since the synaptic output of C2 does not occur unless the A-spikes succeed in evoking full action potentials in the soma (or an electrically close initial segment) of C2 Furthermore, like synaptic potentials, the A-spikes exhibit temporal and spatial summation, and facilitation C2 receives both tonic and phasic inhibitory synaptic potentials, which can decrease the summation of A-spikes and thereby alter the frequency-filtering properties of C2 or block its synaptic output Thus, C2 appears to be an unusual proprioceptive afferent that has a high degree of integrative function and may provide critical gating that is dependent on a variety of external and internal conditions

Non-linearities of Temporal Summation in Neurones in Area 17 of the Cat*

Abstract: Sinusoidal temporal modulation of the contrast of sinusoidal gratings has been used to provide one description of the temporal properties of neurones in area 17 of the cat's visual cortex. Concurrently, the waveforms of the neurones' responses to 2 s flashes of identical gratings were examined. In most neurones, the response to the long flash was much more transient than would be expected from the shape of the temporal-frequency tuning curve. Temporal summation in cortical neurones is non-linear.