On the basis of prior literature, binocular integration is predominantly a low-level visual phenomenon and thus is more likely to affect the encoding process of the visual sensory information. Consequently, we hypothesized that binocular viewing would most likely affect the sensory noise parameter and not the participant's prior probability of inferring a common cause. In line with our hypothesis, first, we observed no effect of stimulus condition (F(1,14) = 1.69,
P = 0.214, η
2p = 0.108), viewing condition (F(1,14) = 0.55,
P = 0.470, η
2p = 0.038) and stimulus-viewing interaction (F(1,14) = 1.33,
P = 0.268, η
2p = 0.087) on the participant's prior probability of inferring a common cause, p
C=1 (
Fig. 7). Conversely, sensory noise (σ) was affected by both stimulus condition (F(1,14) = 5.68,
P = 0.032, η
2p = 0.288) and viewing condition (F(1,14) = 17.39,
P = 9.43 × 10
−4, η
2p = 0.554) but not their interaction (F(1,14) = 0.65,
P = 0.433, η
2p = 0.045). Moreover, in accordance with our behavioral findings, we expected the difference in sensory noise across the viewing conditions to occur for the flash-beep stimulus condition but not for the speech stimulus condition. Therefore we conducted paired
t-tests with Bonferroni correction between the binocular and monocular sensory noise values for the flash-beep condition and speech condition separately. Although there was a statistically significant reduction in sensory noise during binocular viewing for the flash-beep condition (t(14) = −4.0,
P = 0.001, d = −1.032, Bonferroni-adjusted α = 0.025), the binocular difference in sensory noise for the speech condition was not statistically significant (t(14) = −1.78,
P = 0.097, d = −0.46, Bonferroni-adjusted α = 0.025). These findings indicate that the effect of binocular viewing on audiovisual temporal perception observed for the flash-beep stimuli may stem from enhanced low-level unisensory mechanisms in the form of a reduction in sensory noise affecting the measurement of physical asynchrony during audiovisual temporal perception.