Different rules for binocular combination of luminance flicker in cortical and subcortical pathways

Abstract

How does the brain combine information across the eyes? In primary visual cortex, spatial patterns are subject to "ocularity invariance", where monocular and binocular responses are rendered equal by mutual suppression between the eyes. Here we asked whether this invariance holds for pure changes in luminance. We collected steady-state EEG and pupillometry data simultaneously, and find strong deviations from ocularity invariance both in the cortex and also in the subcortical pathway that determines pupil diameter. In cortex, we find strong binocular facilitation, and negligible interocular suppression from cortical sources, whereas measurements of pupil diameter showed weaker facilitation and stronger suppression. This was not purely a consequence of the temporal stimulus parameters; pronounced binocular facilitation was also observed at faster flicker rates. Near-linear binocular combination was also found for the same stimuli using a perceptual matching task. A hierarchical Bayesian implementation of a standard binocular combination model confirms that interocular suppression was substantially weaker for our EEG and matching data compared with the pupillometry results. These findings illustrate that ocularity invariance is not a ubiquitous feature of visual processing, and that the brain can repurpose a generic algorithm for different functions by adjusting parameters such as the weight of suppression between pathways.

Binocular combination in the autonomic nervous system

“…The pupillometry data were analysed using the same method we used in our previous study (5). The data were converted from mp4 videos to a csv text file using the Pupil Player software (45), which estimated pupil diameter for each eye on each frame using a 3D model of the eyeball.…”

“…The prior for the ω parameter was Gaussian, with a mean of 1 and standard deviation of 0.5. Priors for the other free parameters were also Gaussian, with mean values based on previous work (5). We calculated over 10 6 posterior samples, and retained 10% for plotting.…”

“…To describe our data, we used the same model described in our previous study (5). The model has the same general form as the first stage of the contrast gain control model proposed by (33), but omits the second stage.…”

“…The anatomical segregation of the subcortical pathway from the rest of the brain means that this binocular combination of signals must occur independently of the cortical processes of binocular integration required for visual perception. Our recent work (5) has shown that the algorithm underlying binocular combination of light in the pupil pathway differs from that in the cortex. Here we extend this paradigm to compare binocular combination in different photoreceptor pathways that feed into the autonomic nervous system.…”

Different rules for binocular combination of luminance flicker in cortical and subcortical pathways

“…EEG data were converted from the ANT-EEProbe format to a compressed csv text file using a custom Matlab script (available at: https://github.com/bakerdh/PupillometryEEG/ copy archived at Baker, 2023 ; Segala et al, 2023 ) and components of the EEGlab toolbox ( Delorme and Makeig, 2004 ). The data for each participant were then loaded into R for analysis, where a 10 s waveform for each trial at each electrode was extracted (omitting the first 2 s).…”