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 in the acoustic stapedius reflex mechanism.

Abstract: Temporal summation in the acoustic stapedius reflex mechanism was studied by monitoring acoustic impedance changes at the ear-drum. The results show that the duration of short acoustic stimuli (“white noise” and 1/1 octave bands of noise) has a pronounced effect on the stapedius reflex response. For a ten-fold increase of stimulus duration the intensity level had to be lowered by about 22 dB in order to elicit the criterion response (50% of maximal obtainable impedance change). For stimulus durations shorter than 5&80 ms, the relationship between sound intensity and stimulus duration was about the same for all types of stimuli, indicating that for such short stimuli temporal summation in the acoustic stapedius reflex is independent of the type of stimulus. For longer durations, several time constants of summation were found. The time constants were largely dependent on the type of stimulus. Possible explanations of these findings are discussed.

Retinal inhomogeneity. II. Spatial summation

Abstract: Effects of spatial probability summation were measured with concentric cosine patterns forming a set of contiguous annular zones having mean eccentricities of 0°, 2.8°, and 6.1°. To detect these small effects reliably we measured contrast thresholds for all eccentricities at one spatial frequency in each experimental session by an interleaved-staircase method. Sharp edges were eliminated by truncating each zone at a zero crossing of the pattern, and fixation was controlled by stabilizing the retinal image. Under these conditions, each local region of the retina contributes to the sensitivity of larger regions by a standard, fourth-power summation rule, regardless of the number or contiguity of the component regions involved. This was experimentally confirmed with three nested zones for spatial frequencies from 0.5 to 5 cycles/degree. Together with the results of Part I of this series [ D. H. Kelly , J. Opt. Soc. Am. A1, 107 ( 1984)], the summation rule predicts that, over a large range, target size should have no effect on contrast sensitivity at high spatial frequencies, and this was also confirmed. Similar predictions were extrapolated to other contrast-sensitivity data for which empirical tests are not available.

Optimisation of perimetric stimuli for mapping changes in spatial summation in glaucoma.

Abstract: Despite being considered the current reference standard for perimetric testing in glaucoma, standard automated perimetry has several cardinal limitations, including an unacceptably high test-retest variability, which increases with increasing depth of defect, and a limited useable dynamic range, with test-retest variability spanning almost the entire instrument range in advanced glaucomatous damage. Prior studies have shown that spatial summation, the mechanism by which the visual system integrates light energy across the area of a stimulus, differs in disease, with an enlarged Ricco’s area (the limit of complete spatial summation) found in individuals with glaucoma. The aim of this work was to investigate whether a perimetric stimulus designed to exploit these changes in spatial summation would enable a greater signal/noise ratio (SNR) than that of the current standard stimulus, by directly measuring the displacement of the spatial summation function in glaucoma. Three stimulus forms were developed; one varying in area alone, one varying in both area and contrast simultaneously, and one varying in contrast alone, all operating within the local Ricco’s area. These novel stimuli were compared with the standard Goldmann III stimulus, in terms of disease signal, noise, and SNR. The experiments presented in this thesis indicate that a stimulus modulating in area alone may offer greater benefits for measuring glaucomatous changes in spatial summation in a clinical setting, in the form of a greater disease signal, more uniform response variability with depth of defect, and greater SNR, when compared with the standard Goldmann III stimulus. Additionally, there is some indication that this stimulus is more robust to the effects of intraocular straylight than the Goldmann III stimulus, although test-retest variability and robustness to optical defocus are largely similar. As this work represents the early investigations of this stimulus, further work is required to examine its translation into a clinical environment.

Frequency Selectivity and Temporal Processing in Friedreich's Ataxia: Clinical Aspects in Two Patients

Abstract: We performed psychoacoustical tuning curves and measured temporal summation in two patients with Friedreich's ataxia to study aspects of frequency selectivity and temporal processing in the auditory system. In the majority of frequencies tested, normal psychoacoustical tuning curves and unimpaired temporal summation functions were obtained. These findings suggest that the processing mechanism responsible for these phenomena is intact.