Figures and data
Expected changes in cortical contrast sensitivity in typically sighted controls for two different spatial frequencies (low spatial frequency, 0.3 cycles per degree (cpd), and high spatial frequency, 3.0 cpd), A: as a function of eccentricity and B: visual field quadrants. With reference to eccentricity, we expect higher sensitivity of V1 neuronal populations to 1) lower spatial frequencies in the periphery, and 2) higher spatial frequencies in the center of the visual field. By comparison, we expect both high and low spatial frequency stimulation to evoke greatest sensitivity in V1 neuronal populations encoding the left and right visual quadrants, less in the lower, and least in the upper quadrant.
Estimation of cortical contrast sensitivity across the visual field. Participants performed two fMRI tasks in the scanner: a contrast sensitivity task and a pRF mapping task. For each individual and tested spatial frequency, the contribution of each stimulus contrast level to the BOLD signal in the contrast sensitivity task was estimated using a GLM approach. Resulting β-coefficients for each contrast level were then projected onto the individual’s cortical surface. For each vertex in V1, a square root function (R(C) = a ∗ √C) was then fitted to these data, taking the estimated slope a as measure of cortical contrast sensitivity. V1 slopes were finally averaged across vertices based on their eccentricity and polar angle preference as estimated with pRF mapping, and across participants. Mean slopes were then projected back into the visual space, producing a heatmap projection of V1 contrast sensitivity across eccentricities and along visual field quadrants.
Spatial frequency preference V1 across the visual field. For each participant, five eccentricity bins were defined using subject-specific pRF estimates: 0.5°-2.5°, 2.5°-4.5°, 4.5°-9.5°, 9.5°-15°, and 15°-20°. A: Average β-values versus stimulus contrasts for low (0.3cpd; blue) and high (3cpd; red) spatial frequencies across eccentricity bins. Error bars are the 95% confidence intervals. Thick lines represent the group-level model fit, thin lines are the individual fits. B: Slopes projected into visual space for low (0.3 cpd) and high (3 cpd) spatial frequencies. The color scale corresponds to slope estimates, with higher values indicating higher cortical contrast sensitivities. C: Heat plots for each participant (C1-C7).
Anisotropies in V1 across visual field quadrants for low (0.3cpd; top row) and high (3cpd; bottom row) spatial frequencies. pRF estimates were used to link brain responses to visual field positions. Visual quadrants are ±45° around the cardinal meridians, with slope values for eccentricities between 0.5°-20°. Horizontal quadrants are left and right; vertical quadrants are upper and lower. A: Average β-values versus contrast levels for each anisotropy (horizontal vs. vertical, upper vs. lower, left vs. right). Error bars are 95% confidence intervals. Thick lines correspond to average model fit, which thin lines are individual fits. B: Slope values projected onto visual field quadrants. The color scale represents slope estimates, with higher values indicating greater V1 contrast sensitivity. C: Heat plots for each participant (C1-C7).
Reliability of V1 slopes across sessions, in 4 of the 7 controls. A: V1 contrast sensitivity (i.e., slopes) plotted in visual field space (using pRF estimates), showing a consistent session-independent increase in cortical sensitivity toward peripheral locations for the 0.3cpd condition. Higher slopes (warmer colors) indicate higher V1 sensitivity. B: Slopes for the 0.3cpd condition across two visits. C: Slopes for the 0.3cpd and 3cpd conditions collected within the same session.
V1 sensitivity (i.e., slope) to 3cpd condition, in the region of the artificial scotoma (3-8°). A: Masked region between 3-8°, representing the artificial scotoma. B: Averaged β-values between 0.5°-20° eccentricities in V1, under normal and masked conditions. 20 eccentricity bins of 1° were selected based on pRF estimates. The color scale indicates the presented contrast levels, and the black dotted lines mark the boundaries of the artificial scotoma. C: Average β-values versus contrast levels in V1 neurons encoding the region of artificial scotoma (3°-8°), under normal (blue) and masked (red) conditions. Lines correspond to the model fitted to the data. D: Slopes projected back onto the visual field under normal and masked conditions. pRF estimates were used to relate brain responses to visual field locations and to create the 1° eccentricity bins. The boundaries of the simulated scotoma region are represented by dotted lines. The color scale indicates slope estimates, with higher values (warmer colors) corresponding to higher V1 contrast sensitivity. E: Slopes plotted back into the visual space using the calibrated Benson template instead of pRF estimates.
Correspondence between visual field perimetry map and V1 sensitivity map, in a patient with Leber Hereditary Optic Neuropathy. A: Left eye. B: Right eye. Top row: Gray scale visual field map obtained with the Compass fundus perimeter (CenterVue, Padova, Italy), using Standard Perimetry display convention. Sensitivity is represented with symbols and related dB intervals, with larger values describing better sensitivity. Red circle indicates the area of the visual space stimulated in the fMRI contrast sensitivity task. Middle row: Heatmap of V1 sensitivity (i.e., slopes) across the visual field. Here, we divided the space between the upper-left, upper-right, lower-left and lower-right quadrants (as opposed to the left, right, upper and lower quadrants used in previous sections), to match the layout of visual field perimetry maps. Slope values were averaged for each visual quadrant and 1° eccentricity bin and projected back into the visual space, using the subject-specific pRF map. Color scale corresponds to the steepness of the slope estimate. For better visualization of sensitivity differences across quadrants, we also averaged the slopes between 0.5-20° eccentricities in each quadrant, generating a single slope value for each visual quadrant (inset heat plots). The range of slope values were reduced on the color scale for these inset plots. Bottom: Heatmap of V1 sensitivity (i.e., slopes) across the visual field, using the Benson retinotopic template map instead of the pRF data.
Schematic of Large-Field Set-Up. A: The participant lies on the scanner bed in the 64-channel coil without top to reduce obstruction and views the 40° screen via a mirror above their face (1). Stimuli are displayed using back-projection from a projector (2) outside the room, onto a screen (3) positioned behind the participant’s head. The top of the screen follows the scanner bore curvature to maximise field of view. Monocular eye-tracking is achieved by mounting the illuminator and camera of the eye-tracker (4) vertically on a support (5) at the back of the scanner bore. An image of the eye is obtained via a dual-mirror set-up, including a small mirror inside an aperture cut on the side of the screen (6) and the participant mirror (1). If the right eye is being tracked, the eye-tracker is placed on the left side of the scanner bore, and the eye-tracker mirror (6) is placed in the right screen aperture. B: Schematic of the large-field screen, with the area of stimulus presentation shown in cyan and the mirror used for eye-tracking in magenta. The mirror is positioned within one of the two rectangular apertures cut on either side of the screen.
Results from the multilevel modelling approach in each individual participant. pRF mapping was used to link brain responses to visual field locations.
Post-Hoc test on ANOVA visual quadrant position effect (PolarLocation) at the individual level. pRF mapping was used to relate brain responses to visual field locations.
V1 contrast sensitivity (i.e., slopes) across 5 eccentricity bins (0.5°-2.5°, 2.5°-4.5°, 4.5°-9.5°, 9.5°-15°, and 15-20°), defined using the calibrated Benson atlas. A: β-values versus contrast levels for each eccentricity bin. Blue and red lines represent the contrast sensitivity model fits for the 0.3cpd and 3cpd conditions, respectively. Thinner lines correspond to individual fits. B: V1 contrast sensitivity index (i.e., slope) projected back into the visual space using the calibrated Benson atlas, for each eccentricity bin and spatial frequency condition. The color scale indicates slope estimates, with higher values representing higher V1 contrast sensitivity.
V1 contrast sensitivity (i.e., slopes) across visual field quadrants using the calibrated Benson atlas, for the 0.3cpd and 3cpd conditions. Visual quadrants were defined as ±45° regions around the cardinal meridians and slope values were selected for eccentricities between 0.5-20°. Horizontal quadrants are left and right, whilst upper and lower quadrants define the vertical quadrants. A: β-values versus contrast levels for each anisotropy effects: horizontal versus vertical, upper versus lower, and left versus right. Group-level model fits are in thick lines, whilst thinner lines correspond to individual fits. Error bars represent the 95% confidence intervals. B: V1 contrast sensitivity index (i.e., slope) projected back into the upper, lower, left and right visual field quadrants for the 0.3cpd and 3cpd conditions. The color scale represents slope estimates, with higher values indicating higher V1 contrast sensitivity.
V1 contrast sensitivity (i.e., slope) to the 0.3cpd condition plotted back into visual space under fixation (A) and controlled eye-motion (B) conditions, in participant C6. pRF estimates were used to relate brain responses to visual field positions.
Group-Level ANOVA analysis on slope estimates, as function of spatial frequency, eccentricities, and visual quadrant positions. The Benson template retinotopic map was used to relate brain responses to visual field locations.
