What Factors Affect Binocular Summation?

Abstract

Binocular vision may serve as a good model for research on awareness. Binocular summation (BS) can be defined as the superiority of binocular over monocular visual performance. Early studies of BS found an improvement of a factor of about 1.4 (empirically), leading to models suggesting a quadratic summation of the two monocular inputs (√2). Neural interaction modulates a target's visibility within the same eye or between eyes (facilitation or suppression). Recent results indicated that at a closely flanked stimulus, BS is characterized by instability; it relies on the specific order in which the stimulus condition is displayed. Otherwise, BS is stable. These results were revealed in experiments where the tested eye was open, whereas the other eye was occluded (mono-optic glasses, blocked presentation); thus, the participants were aware of the tested eye. Therefore, in this study, we repeated the same experiments but utilized stereoscopic glasses (intermixed at random presentation) to control the monocular and binocular vision, thus potentially eliminating awareness of the tested condition. The stimuli consisted of a central vertically oriented Gabor target and high-contrast Gabor flankers positioned in two configurations (orthogonal or collinear) with target-flanker separations of either two or three wavelengths (λ), presented at four different presentation times (40, 80, 120, and 200 ms). The results indicate that when utilizing stereoscopic glasses and mixing the testing conditions, the BS is normal, raising the possibility that awareness may be involved.

Keywords: awareness; binocular advantage; binocular summation; binocular vision; collinear facilitation; inter-ocular suppression; lateral masking; presentation time; spatial interactions; stereo glasses.

Figure 5

Binocular summation factor (monocular/binocular contrast detection threshold ratio) according to presentation times of 200, 120, 80, and 40 (ms) using the LM paradigm. The single target (ST), collinear configuration (COLL), orthogonal configuration (ORTHO) with target_flanker separations of 2 and 3λ for each configuration. (A) 200 (ms). (B) 120 (ms). (C) 80 (ms). (D) 40 (ms). N = 5, Error bars represent the standard error of the mean (SEM). Each dot represents an individual participant. The 1.4 dashed line represents the expected binocular summation (BS), whereas the 1 dashed line represents the absence of a BS effect.

Figure 6

The violin plot shows the ratio of the monocular to binocular contrast detection threshold for 5 different participants averaged from experiment 1.A (mixed between eyes) for isolated stimuli vs. stimuli with context at 4 different presentation times (N = 5). We averaged all conditions as a mean value of the BS ratio for the different presentation times under each stimulus condition. We found that the binocular advantage was significantly greater for isolated (single target) than for closely flanked stimuli, collinear 2λ (p = 0.00 ***, using Tukey’s post hoc analysis after 2-way ANOVA). Each dot represents an individual participant. The 1.4 dashed line represents the expected binocular summation (BS), whereas the 1 solid line represents the absence of a BS effect.

Figure 7

The order of the stimulation across trials was blocked for the eye presentation. (A) Collinear Interactions as a function of the presentation time (200, 120, 80, and 40 ms). Monocular (MON.), binocular (BIN.), collinear configuration (COLL) with target_flanker separations of 2 and 3λ. Facilitation is indicated by values below zero, and suppression by values above zero. N = 5. Error bars represent the standard error of the mean (SEM). The blue arrow points to the left from longer to shorter presentation times, which describes the testing order of the stimulus condition. The solid purple lines represent the collinear interactions at 2λ, denoted by open and filled circles for monocular and binocular presentations, respectively, whereas the dashed dark red lines represent the collinear interactions at 3λ, denoted by open and filled squares for monocular and binocular presentations, respectively. (B) The line plot represents the distribution of the binocular summation factor (the monocular/binocular contrast detection threshold ratio) as a function of the presentation time (200, 120, 80, and 40 ms) utilizing the LM paradigm for 5 different participants (each different shape represents an individual participant). Single target (ST), collinear configuration with target_flanker separations of 2λ (COLL2). N = 5, error bars represent the standard error of the mean (SEM). The 1.4 dashed line represents the expected binocular summation (BS), whereas the 1 solid line represents the absence of a BS effect.

Figure 8

The violin plot shows the ratio of the monocular to binocular contrast detection threshold for 5 different participants averaged from experiment 1.B (non-mixed between eyes) for isolated stimuli vs. stimuli with context at 4 different presentation times (N = 5). We averaged all conditions as a mean value of the BS ratio for all the presentation times under each stimulus condition. We found that the binocular advantage was significantly greater for isolated (single target) than for closely flanked stimuli, collinear 2λ (p = 0.00 ***, using Tukey’s post hoc analysis after 2-way ANOVA). Each dot represents an individual participant. The 1.4 dashed line represents the expected binocular summation (BS), whereas the 1 solid line represents the absence of a BS effect.

Figure 9

Collinear Interactions as a function of the presentation time (200, 120, 80, and 40 ms). Monocular (MON.), binocular (BIN.), collinear configuration (COLL) with target_flanker separations of 2 and 3λ. Facilitation is indicated by values below zero, and suppression by values above zero. N = 5. Error bars represent the standard error of the mean (SEM). The blue arrow, which points to the left from longer to shorter presentation times, describes the testing order of the stimulus condition. The solid purple lines represent the collinear interactions at 2λ, denoted by open and filled circles for monocular and binocular presentations, respectively, whereas the dashed dark red lines represent the collinear interactions at 3λ denoted by open and filled squares for monocular and binocular presentations, respectively. (A). The current study utilizes stereo glasses to control the monocular and binocular presentations. (B). Taken from our previous study (https://doi.org/10.1038/s41598-023-48380-2 (accessed on 5 December 2023)) utilizing mono-optic glasses to control the monocular and binocular presentations.

Figure 1

Details of the experimental design. The testing order of the stimulus condition for blocks and sessions are presented in the diagram. The BIN binocular, RE right eye, LE left eye, single target, collinear, and orthogonal configurations at target_flanker separations of 2 and 3λ for each configuration. The stimuli were displayed at 4 different presentation times: 200, 120, 80, and 40 ms following a gradual order from the longest to the shortest. All the conditions were displayed for one presentation time first, and then displayed for the next presentation time. The two-temporal alternative forced-choice paradigm (2TAFC) and the staircase procedure were utilized to measure the target contrast detection threshold. Stereoscopic glasses were utilized to control the monocular and binocular presentations. Each data point was repeated 3 times (A). Experiment 1.A (mixed between eyes): We used 5 files; each file included a different stimulus condition namely single target, collinear 3λ, orthogonal 3λ, collinear 2λ, and orthogonal 2λ. Each file included three blocks: the first block for the binocular condition (BIN), the second block for the right eye (RE), and the third block for the left eye (LE); Across trials, the eyes (right, left, and binocular) were displayed randomly, and by mixed trials. (B). Experiment 1.B (non-mixed between eyes): We used 3 files; the first file included one block for the single target condition, the second file included two blocks for collinear and orthogonal 3λ conditions, and the third file included two blocks for collinear and orthogonal 2λ conditions. For each stimulus condition we tested the binocular, right, and left eye, respectively. Across trials, the eyes (right, left, and binocular) were displayed separately, and by non-mixed trials.

Figure 2

The lateral masking paradigm (LM). Stimuli that were utilized in the research. (A) Gabor target example was utilized in the experiments: single target condition. (B) The LM paradigm. (C) Spatial configurations that were utilized in the research: collinear (left) and orthogonal (right). To measure the target contrast detection threshold, the two-temporal alternative forced-choice paradigm (2TAFC) and a 3:1 staircase procedure, known to converge to a 79% correct response, were utilized. Participants were required to determine in which interval (the first or second) the central Gabor target has been presented as illustrated in panel (B).

Figure 3

The mean monocular and binocular contrast detection thresholds according to the presentation times of 200, 120, 80, and 40 (ms) using the LM paradigm. The single target (ST), collinear configuration (COLL), and orthogonal configuration (ORTHO) with target_flanker separations of 2 and 3λ for each configuration. (A) 200 ms. (B) 120 ms. (C) 80 ms. (D) 40 ms. N = 5, Error bars represent the standard error of the mean (SEM). Each dot represents an individual participant.

Figure 4

The order of the stimulation across trials was intermixed at random for the eye presentation. Collinear interactions as a function of the presentation time (200, 120, 80, and 40 ms). Monocular (MON.), binocular (BIN.), collinear configuration (COLL) with target_flanker separations of 2 and 3λ. Facilitation is indicated by values below zero, and suppression by values above zero. N = 5. Error bars represent the standard error of the mean (SEM). The blue arrow points to the left from longer to shorter presentation times that indicate the testing order of the stimulus condition. The solid purple lines represent the collinear interactions at 2λ, denoted by open and filled circles for monocular and binocular presentations, respectively, whereas the dashed dark red lines represent the collinear interactions at 3λ, denoted by open and filled squares for monocular and binocular presentations, respectively. [threshold elevation = log (masked target contrast detection threshold/single target contrast detection threshold)]. Next, we compared the threshold elevation between the monocular and binocular presentations for collinear configurations at 2 and 3λ at 4 different presentation times.