scispace - formally typeset
Search or ask a question
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.


Papers
More filters
Journal ArticleDOI
01 Mar 2021-Pain
TL;DR: The current experiment showed that spatial summation of pain behaves similarly for electrocutaneous and mechanical stimuli.
Abstract: Spatial acuity measured by 2-point discrimination (2PD) threshold and spatial summation of pain (SSp) are useful paradigms to probe the pain system in humans. Whether the results of these paradigms are influenced by different stimulus modalities and intensities is unclear. The aim of this study was to test 2PD controlling the stimulus modality and the intensity and to investigate the effect of modality on SSp. Thirty-seven healthy volunteers were tested for 2PDs with 2 stimulus modalities (electrocutaneous and mechanical) and intensity (noxious and innocuous). For each condition, participants received stimuli to either 1 or 2 points on their lower back with different distances (2-14 cm, steps of 2 cm). It was found that 2PDs were significantly smaller for noxious stimuli for both modalities. By contrast, between-modality comparison reproduced previous reports of impaired acuity for noxious stimulation. Higher pain intensities were reported when a larger area was stimulated (SSp), independent of the modality. Furthermore, reported pain intensities were higher when the distance between 2 stimulated areas was increased from 2 to 6 cm (P < 0.001), 8 cm (P < 0.01), and 14 cm (P < 0.01). 2PDs determined by mechanical and electrocutaneous stimuli were significantly correlated within both stimulus intensities, ie, innocuous (r = 0.34, P < 0.05) and noxious (r = 0.35, P < 0.05). The current results show 3 novel findings: (1) the precision of the pain system might be higher than in the innocuous (tactile) system when mechanical and electrocutaneous modalities are used, (2) the pattern of distance-based and area-based SSp seems to be comparable irrespective of the modality applied (mechanical and electrocutaneous), and (3) both modalities are moderately correlated.

6 citations

Journal ArticleDOI
TL;DR: Values indicate the upper limit of temporal summation for chromatic stimuli in the human early visual cortex.
Abstract: The temporal-summation characteristics of the human visual cortex were investigated by recording the magnetic responses to isoluminant red-green gratings. In one condition, exposure duration (ED) of a single-pulse stimulus was varied between 16.7 ms and 200 ms, and in the other, stimulus-onset-asynchrony (SOA) of a double-pulse (presented for 16.7 ms each) stimulus was varied between 16.7 ms and 200 ms. The magnetic responses showed an initial peak at a latency of around 100 ms, the origin of which was estimated to be in the vicinity of the striate cortex. The peak amplitude increased with increasing ED and decreased with increasing SOA, showing a clear sign of temporal summation. The critical ED and SOA estimated from the peak amplitude vs. ED/SOA functions were about 50 ms. These values indicate the upper limit of temporal summation for chromatic stimuli in the human early visual cortex.

6 citations

Journal ArticleDOI
TL;DR: The results showed that the chromatic mechanisms appear to organize their spatial integration with the adapting level, and there was no spatial summation for high-enough variations in the cone input.
Abstract: The effect of spatial summation on chromatic detection at suprathreshold levels for the red-green and yellow-blue chromatic opponent mechanisms has been studied using simple reaction time (RT) as a measurement of the response. We varied the target size in the experiments from 8 min of arc in diameter to 10 deg, and the hue-substitution paradigm was adopted to generate only chromatic changes in the cone input. Equiluminant stimuli were distributed along three tritan and three red-green confusion lines. Three reference stimuli were chosen as both reference and adapting stimuli, in this case to determine whether the chromatic adaptation affected the spatial summation. The results showed that the mean value of RT at a constant cone-input variation, either of the L #x2212; 2M channel or of the S #x2212; (L #x002B; M) channel, against the target size decreased until a stimulus size was reached, the RT being constant for greater sizes. The spatial summation was fulfilled for a maximum target size which was less for the L #x2212; 2M channel than for the S #x2212; (L #x002B; M) channel, this size decreasing as the cone-input variation rose. Furthermore, there was no spatial summation for high-enough variations in the cone input. In addition, the chromatic mechanisms appear to organize their spatial integration with the adapting level.

6 citations

Journal ArticleDOI
TL;DR: The detection threshold for a foveally presented Gabor stimulus (Gaussian‐windowed sinusoidal grating) is reduced in the presence of two suprathreshold flanking Gabors and such facilitation is orientation and configuration dependent, with maximal threshold reductions occurring with collinear flanking elements.
Abstract: Background: It has been shown that the detection threshold for a foveally presented Gabor stimulus (Gaussian-windowed sinusoidal grating) is reduced in the presence of two suprathreshold flanking Gabors and that such facilitation is orientation and configuration dependent, with maximal threshold reductions occurring with collinear flanking elements. Methods: We assessed the effect of varying relative orientation on detection thresholds for chains of three Gabors, with 0.96d centre-to-centre spacing, presented at 4.8d in the periphery. The central Gabor element in each chain was either collinear with its flanking elements or oriented orthogonally to them. Results: Thresholds for the configuration as a whole were found to be lower using the collinear configuration compared with the orthogonal configuration, consistent with the proposal that orientation-specific long-range intracortical interactions are involved. However, this configuration-dependent threshold difference disappeared when the spatial frequency of the Gabors was doubled from 3.33 cpd to 6.66 cpd. Conclusions: Configurational dependencies may disappear at higher spatial frequencies because, despite increased spatial summation at detection threshold contrast levels, the intrinsically smaller receptive field sizes of neurons tuned to high spatial frequencies render them incapable of encapsulating more than one of the spatially separated Gabors within their individual receptive fields.

6 citations


Network Information
Related Topics (5)
Visual cortex
18.8K papers, 1.2M citations
82% related
Stimulation
40.1K papers, 1.4M citations
76% related
NMDA receptor
24.2K papers, 1.3M citations
75% related
Prefrontal cortex
24K papers, 1.9M citations
74% related
Neuron
22.5K papers, 1.3M citations
74% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202323
202234
202118
20204
201911
201812