Human white matter structural properties correlate with individual difference in stereoacuity

Abstract

Humans have substantial individual differences in the performance to identify binocular disparity (stereoacuity; Hess et al, 2016), but its neuroanatomical basis remains unknown. Given that both dorsal and ventral visual cortices process binocular disparity (Parker, 2007; Murphy et al., 2016), one candidate is a white matter tract connecting dorsal and ventral visual areas (Vertical Occipital Fasciculus, VOF; Yeatman et al., 2014; Takemura et al., 2016). Here we tested how the structural property of the VOF is related to the individual difference in stereoacuity by combining structural MRI and psychophysics. We collected diffusion-weighted MRI (dMRI; 2 mm isotropic, 64 directions) and quantitative MRI data (1 mm isotropic) from 19 participants with normal or corrected-to-normal vision (age 20-37, mean: 25.1 years old). After we identified the VOF in each subject using probabilistic tractography (Yeatman et al., 2014), we evaluated its structural properties using Fractional Anisotropy (FA) and Macromolecular Tissue Volume (MTV) measurements that quantify neural tissue density (Mezer et al., 2013). In psychophysics, we presented random-dot stereogram composed of central disk (disparity was varied from±0.002 deg to±0.128 deg) and surrounding annulus (zero disparity). Subjects are asked to judge whether the center disk was nearer or farther than the surrounding annulus. Based on the results of the psychophysical experiment, we classified subjects into higher (N=10) or lower (N=9) stereoacuity groups. We found that higher stereoacuity group showed significantly higher FA values, along the dorsal segment of the right VOF (d'=1.0). We also observed an inter-group difference in MTV along the whole right VOF (d'=0.88). We did not observe a significant difference in other tracts in visual cortex (e.g. optic radiation, forceps major). This result suggests that structural properties of white matter tract involved in dorsal-ventral communications are related to individual difference in stereoacuity.

Meeting abstract presented at VSS 2017