Measuring temporal summation in visual detection with a single-photon source

Abstract

Temporal summation is an important feature of the visual system which combines visual signals that arrive at different times. Previous research estimated complete summation to last for 100ms for stimuli judged "just detectable." We measured the full range of temporal summation for much weaker stimuli using a new paradigm and a novel light source, developed in the field of quantum optics for generating small numbers of photons with precise timing characteristics and reduced variance in photon number. Dark-adapted participants judged whether a light was presented to the left or right of their fixation in each trial. In Experiment 1, stimuli contained a stream of photons delivered at a constant rate while the duration was systematically varied. Accuracy should increase with duration as long as the later photons can be integrated with the proceeding ones into a single signal. The temporal integration window was estimated as the point that performance no longer improved, and was found to be 650ms on average. In Experiment 2, the duration of the visual stimuli was kept short (100ms or <30ms) while the number of photons was varied to explore the efficiency of summation over the integration window compared to Experiment 1. There was some indication that temporal summation remains efficient over the integration window, although there is variation between individuals. The relatively long integration window measured in this study may be relevant to studies of the absolute visual threshold, i.e., tests of single-photon vision, where "single" photons should be separated by greater than the integration window to avoid summation.

Dyslexic Readers Improve without Training When Using a Computer-Guided Reading Strategy

“…In Experiment 1 the presentation time was limited to 500 ms, because temporal summation is effective up to this fixation time [ 73 ]. The results of Experiment 1 and earlier studies on temporal summation [ 37 , 38 , 39 , 73 , 74 , 75 , 76 , 77 , 78 , 79 ] support the hypothesis that improvement of word recognition requires prolongation instead of shortening [ 32 , 86 , 87 , 88 ] of the fixation time. The finding that readers improve when they extend their fixation times demonstrates that attention does not decrease during fixation, and that the readers can maintain their attention for the required fixation time.…”

The extraordinary AFD thermosensor of C. elegans

“…Such sensitivity is specific to the thermoreceptor currents, since voltage-activated currents in AFD have a Q 10 of less than 3 [67]. This extraordinary thermosensitivity reflects the action of a nonlinear amplification cascade (see below) akin to the one that mediates phototransduction and enables vertebrates, including humans, to detect single photons of visible light [28,82,31].…”

Analytical Resolution of the Dark Night Sky (Olbers') Paradox

“…In addition to the spatial constraint that applies to the primary image that is projected upon the celestial sphere, there is a secondary temporal constraint (applicable to both a presumed large‐scale homogeneous universe with an infinite number of stars and galaxies, and a Galactic scale inhomogeneous star field) that limits the observed cumulative brightness of the night sky as recorded on the detector surface (retina) of the imaging device. The temporal constraint is manifested as a high‐pass power (apparent brightness) filter, that is a result of the finite temporal summation window of the imaging device, which in the case of the fully dark‐adapted unaided human eye is approximately 650 ms (Holmes et al ), making the fully dark‐adapted human eye incapable of registering as vision any luminous astronomical object that projects an apparent brightness that is fainter than G mag 8.…”

“…The above implies that the human eye can only sum photons over a sliding temporal window of approximately 650 ms (Holmes et al ), and it can only register as “visible” those luminous objects that produce a photon flux that arrives at a rate (per second) that exceeds a certain minimum threshold that cannot be increased beyond the biological limits allowed by dark adaptation. As such, all photons that arrive on a specific retinal rod, but do not arrive at a rate high enough to contribute to a sum that is above the threshold during the sliding summation window of 650 ms, will be dissipated internally without registering as a sensation of vision.…”

“…In Equation (3), the surface area a d corresponds to the surface area of the pupil through which the photons pass before being absorbed by the retinal rods. For the human eye, in scotopic vision, the temporal summation window is in the order of 650 ms for a dark‐adapted pupil diameter of 6.6 mm (Holmes et al ). Therefore, the minimum photon flux (photons s −1 ) that is required for the unaided human eye to see a star can be computed from a knowledge of the luminosity and the distance of stars that are known to be barely visible under the best of seeing conditions.…”