Binocular and monocular detection of Gabor patches in binocular two-dimensional noise

Dynamic properties of internal noise probed by modulating binocular rivalry

Neural systems are inherently noisy, and this noise can affect our perception from moment to moment. This is particularly apparent in binocular rivalry, where perception of competing stimuli shown to the left and right eyes alternates over time. We modulated rivalling stimuli using dynamic sequences of external noise of various rates and amplitudes. We repeated each external noise sequence twice, and assessed the consistency of percepts across repetitions. External noise modulations of sufficiently high contrast increased consistency scores above baseline, and were most effective at 1/8Hz. A computational model of rivalry in which internal noise has a 1/f (pink) temporal amplitude spectrum, and a standard deviation of 16% contrast, provided the best account of our data. Our novel technique provides detailed estimates of the dynamic properties of internal noise during binocular rivalry, and by extension the stochastic processes that drive our perception and other types of spontaneous brain activity.

Although our perception of the world appears constant, sensory representations are variable because of the ‘noisy’ nature of biological neurons. Here we used a binocular rivalry paradigm, in which conflicting images are shown to the two eyes, to probe the properties of this internal variability. Using a novel paradigm in which the contrasts of rivalling stimuli are modulated by two independent external noise streams, we infer the amplitude and character of this internal noise. The temporal amplitude spectrum of the noise has a 1/f spectrum, similar to that of natural visual input, and consistent with the idea that the visual system evolved to match its environment.

Binocular summation revisited: Beyond √2

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. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Binocular integration and disparity selectivity in mouse primary visual cortex

Signals from the two eyes are first integrated in primary visual cortex (V1). In many mammals, this binocular integration is an important first step in the development of stereopsis, the perception of depth from disparity. Neurons in the binocular zone of mouse V1 receive inputs from both eyes, but it is unclear how that binocular information is integrated and whether this integration has a function similar to that found in other mammals. Using extracellular recordings, we demonstrate that mouse V1 neurons are tuned for binocular disparities, or spatial differences, between the inputs from each eye, thus extracting signals potentially useful for estimating depth. The disparities encoded by mouse V1 are significantly larger than those encoded by cat and primate. Interestingly, these larger disparities correspond to distances that are likely to be ecologically relevant in natural viewing, given the stereo-geometry of the mouse visual system. Across mammalian species, it appears that binocular integration is a common cortical computation used to extract information relevant for estimating depth. As such, it is a prime example of how the integration of multiple sensory signals is used to generate accurate estimates of properties in our environment.

Senescent effects on binocular summation for contrast sensitivity and spatial interval acuity

PURPOSE

Age effects on binocular summation, a cortically mediated visual function, were compared for resolution acuity, contrast sensitivity (CS), and spatial interval (SI) hyperacuity.

METHOD

The binocular and monocular thresholds of healthy, optimally-corrected healthy young (mean age 21.3 years) and old (mean age 69.9 years) observers were determined for acuity, SI discrimination, and CS at 1.0, 2.0, 4.0, 8.0 and 18.0 c/deg.

RESULTS

No age effects were observed on monocular or binocular SI discrimination. The binocular summation ratios (BSRs) did not exceed the expected probability gain for resolution acuity or SI discrimination in either age group. Older observers showed a binocular inhibition effect on the SI task. On the CS task, the BSRs of the young significantly exceeded those of the old only at 18.0 c/deg.

CONCLUSIONS

1.) Binocular summation of high spatial frequency contrast information, which may be less robust in the senescent visual system, did not appear to be related to interocular CS differences, 2.) SI discrimination of high contrast, well-separated targets appears to be unaffected by aging, and 3.) Binocular neural summation on SI discrimination may be more likely to be seen with targets that are narrowly separated or low in contrast.

Two eyes: square root 2 better than one?

Classical data on the detection of simple patterns show that two eyes are more sensitive than one eye. The degree of binocular summation is important for inferences about the underlying combination mechanism. In a signal detection theory framework, sensitivity is limited by internal noise. If noise is added centrally after binocular combination, binocular sensitivity is expected to be twice as good as monocular. If the noise is added peripherally at each eye prior to combination, binocular sensitivity will be sqrt[2] higher than monocular. In a large sample of observers (51), we measured contrast sensitivity for detection of gratings at several spatial frequencies using left, right, or both eyes. Estimates of binocular summation using both binocular summation ratios and Minkowski coefficients show a summation ratio with means in the range of 1.5-1.6. The 95% confidence interval overlaps with the value of sqrt[2] predicted by the peripheral noise model and does not overlap with the value of 2 predicted by the central noise model.

Colour-luminance interactions in binocular summation

Using a noise-masking paradigm we test the notion of binocular detection mechanisms that combine luminance and colour contrast. Binocular summation was measured for achromatic and red-green isoluminant Gabor stimuli over a range of temporal frequencies and was compared with and without the presence of a two-dimensional, dynamic, luminance noise mask (correlated). While we found that luminance noise reduced binocular luminance summation at all temporal frequencies, binocular red-green summation was reduced only at frequencies of 8 Hz and above. Our results suggest the existence of binocular colour-luminance interactions restricted to high temporal frequencies.

Effects of quantum noise and binocular summation on dose requirements in stereoradiography

In the case of a quantum-noise limited detector, signal detection theory suggests that stereoradiographic images can be acquired with one half of the per-image dose needed for a standard radiographic projection, as information from the two stereo images can be combined. Previously, film-screen stereoradiography has been performed using the same per-image dose as in projection radiography, i.e., doubling the total dose. In this paper, the assumption of a possible decrease in dose for stereoradiography was tested by a series of contrast-detail experiments, using phantom images acquired over a range of exposures. The number of visible details, the effective reduction of the dose, and the effective decrease in the threshold signal-to-noise ratio were determined using human observers under several display and viewing conditions. These results were averaged over five observers and compared with multiple readings by a single observer and with the results of an additional observer with limited stereoscopic acuity. Experimental results show that the total dose needed to produce a stereoradiographic image pair is approximately 1.1 times the dose needed for a single projection in standard radiography, indicating that under these conditions the human visual system demonstrates almost ideal binocular summation.