Binocular summation revisited: Beyond √2.

Abstract

Our ability to detect faint images is better with two eyes than with one, but how great is this improvement? A meta-analysis of 65 studies published across more than 5 decades shows definitively that psychophysical binocular summation (the ratio of binocular to monocular contrast sensitivity) is significantly greater than the canonical value of √2. Several methodological factors were also found to affect summation estimates. Binocular summation was significantly affected by both the spatial and temporal frequency of the stimulus, and stimulus speed (the ratio of temporal to spatial frequency) systematically predicts summation levels, with slow speeds (high spatial and low temporal frequencies) producing the strongest summation. We furthermore show that empirical summation estimates are affected by the ratio of monocular sensitivities, which varies across individuals, and is abnormal in visual disorders such as amblyopia. A simple modeling framework is presented to interpret the results of summation experiments. In combination with the empirical results, this model suggests that there is no single value for binocular summation, but instead that summation ratios depend on methodological factors that influence the strength of a nonlinearity occurring early in the visual pathway, before binocular combination of signals. Best practice methodological guidelines are proposed for obtaining accurate estimates of neural summation in future studies, including those involving patient groups with impaired binocular vision.

Binocular facilitation in light‐mediated melatonin suppression?

“…In a study on the dazzle reflex, that is the aversive response to bright light, the authors note that “the light intensity to produce extreme dazzle under monocular conditions has to be an order of magnitude greater than under binocular conditions”, corroborating earlier reports of binocular facilitation in discomfort to light . In vision, binocular summation has been investigated thoroughly for detecting faint lights . For stimuli that are easily detectable, an otherwise unarticulated field when viewed with both eyes appears twice as bright as a field seen by one eye .…”

Interocular difference thresholds are mediated by binocular differencing, not summing, channels

“…The involvement of BÀ channels in binocular vision is evident from studies of contrast detection (Cohn et al, 1981), motion perception (May, Zhaoping, & Hibbard, 2012; see also Kingdom, 2012), orientation perception (May & Zhaoping, 2016), stereopsis (Goncalves & Welchman, 2017;Kingdom, Yared, Hibbard, & May, in press), binocular rivalry (Said & Heeger, 2013), visual-evoked potentials (Katyal, Vergeer, He, He, & Engel, 2018), and interocular difference detection (Kingdom et al, 2018). Involvement of Bþ channels has also emerged from many of these studies, but its main support comes from the plethora of studies demonstrating substantial improvements in thresholds for detecting stimuli when viewed by both eyes compared to one (see recent review and metanalysis by Baker, Lygo, Meese, & Georgeson, 2018), as well as from studies modeling the appearance of dichoptic mixtures of stimuli differing in luminance or color contrast (Hovis, 1989;Baker, Wallis, Georgeson, & Meese, 2012;Kingdom & Libenson, 2015).…”

Monocular and Binocular Temporal Visual Perception of Infantile Nystagmus

“…In contrast sensitivity, binocular summation refers to the equation of CSbin = sqrt (CSright 2 + CSleft 2 ). At high spatial frequencies, the summation is higher 16 . In addition, the longer the presentation time, the higher the summation will be.…”

“…Studies on normally sighted populations with normal development agree that binocular summation occurs when no difference exists between the eyes' performance. Thus, the most accepted theory of binocular summation suggests that binocular summation is absent or minor in cases of abnormal binocular development such as amblyopia, and that it decreases as the magnitude of the difference between the eyes increases [16][17][18][19][20][21] . However, some studies found evidence of binocular summation in cases of amblyopia 22,23 .…”

“…Early studies of binocular summation found an empirical improvement of a factor of about 1.4, leading to models assuming a quadratic summation of the two monocular inputs (√2) 16,[67][68][69][70][71][72][73] . A recent review by Baker et al (2018) showed that different amounts of binocular summation exist in a range from √2 to 2 values 17 because the amount of binocular summation is affected by the spatiotemporal parameters of the stimulus. Ding and Sperling (2005), in their study on binocular summation, suggested a gain control theory based on studies by Cogan (1987) and Wilson (2003).…”