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.

Flicker-Defined Forms in the Ternus Display.

Abstract: Odic and Pratt (2008, Perception, 37, 1790-1804) proposed that the type of movement seen in the bistable Ternus display depends on the elements' temporal summation of contrast relative to the background. To test this theory, participants viewed a flicker-defined Ternus display where the elements had no temporal summation of contrast. Participants also viewed a luminance-defined control condition. Five interstimulus intervals (ISIs) (0, 20, 40, 60, and 80 ms) and two stimulus durations (SDs) (200 and 400 ms) were used in each condition. If temporal summation of contrast does not influence perceived group and end-to-end movement in flicker-defined forms, it was expected that the frequency of their reports would be equal to those in the luminance- defined control condition at the same ISIs and SDs. As predicted, the main effect of condition was not significant and participants reported both percepts at expected rates in both conditions, contrary to the predictions of Odic and Pratt (2008).

Resolution acuity and spatial summation of chromatic mechanisms in the peripheral retina.

Abstract: Green stimuli are more difficult to detect than red stimuli in the retinal periphery, as reported previously. We examined the spatial characteristics of chromatic mechanisms using stimuli, modulated from an achromatic background to each pole of the “red–green” cardinal axis in DKL space at 20 deg eccentricity. The “blue–yellow” cardinal axis was also studied for comparison. By measuring both grating discrimination at the resolution limit (resolution acuity) and spatial summation, assessed by the Michaelis–Menten function, we demonstrated a marked “red–green” asymmetry. The resolution acuity was worse and spatial summation more extended for “green” compared to “red” stimuli, while showing significant individual variations. Ricco’s area was also measured, but not determined for “green” spots because of the poor small stimuli detection. These results cannot be explained by differences in L- and M-cone numerosity and/or spatial arrangement, but rather have postreceptoral origin, probably at the cortical level.