Article Figures & Data
Figures
- Figure 1.
Spatiotemporal response of VSD signal evoked by black/white stimuli. Population responses to black and white square stimuli from one example imaging session. A, Following fixation on a uniform gray screen, a 2 × 2° square appeared. In the current example, the stimuli were centered at 1.75° left of the fixation point (red dot) and 3.0° below. The squares had either negative contrast (“Black,” −64%) or positive contrast (“White,” +64%) with respect to the background luminance. B, Average VSD activation maps evoked by a 300 ms presentation of black stimulus (Bi) and white stimulus (Bii); n = 12 trials. Big blood vessels are colored in gray (here and in all other figures). Numbers correspond to milliseconds after stimulus onset. The arrows (map at t = 120) point to the spatial modulation in the upper and right edges. The three green arrows point to the evoked neural response at the corners and the two cyan arrows point to the evoked response at the edge middles of the square stimulus. A, anterior; P, posterior; M, medial; L, lateral. C, Time courses of the evoked population response for the black (Ci) and white (Cii) stimulus. Time courses are computed for ROIs (depicted in B, on the map at t = 80, red and green circles) located at the center and at the edge of the evoked pattern. Trace width denotes ±1 SEM over trials. Stimulus duration is denoted by a black bar below the x-axis. D, Same as in C but grouped by center ROI (Di) and edge ROI (Dii) for comparison between the black and the white responses.
- Figure 2.
Response time courses—grand averages. Responses to black and white square stimuli averaged over n = 9 sessions from both monkeys. A, Time courses of the evoked population response for the black (Ai) and white (Aii) stimulus. Time course are computed for ROIs located at the center and at the edges of the evoked pattern (red and blue ROIs in Fig. 3Ci, left). Trace width denotes ±1 SEM over sessions. B, Same as in A but time courses grouped by center ROI (Bi) and edge ROI (Bii) for comparison between the black and the white responses. In each session, the time courses were normalized to the response amplitude of the black, edge condition at t = 170 ms. Dashed rectangles in A and B mark the time frames of averaging for spatial analysis and model evaluation (60–100 ms).
- Figure 3.
Spatial differences between black and white neural responses. Population responses to black and white stimuli. A, B, Same data as in Figure 1. A, Maps of population response (averaged over 60–100 ms post-stimulus onset) from one example session, evoked by black (left) and white (right) squares. Bi–Bv Spatial profiles of the black and white population responses (see Materials and Methods). The location of the spatial profiles on the maps is shown on the top insets. Black and gray curves depict the responses to the black and white stimuli, respectively. C, Grand average of response ratios averaged >9 imaging sessions. Ci, Edges versus center. Left, Location of ROIs on the example map from A. Blue ROIs correspond to the square edges and the red ROI to the center. Middle, Black/white ratios for the edges (blue) and center (red) ROIs. Error bars are ±1 SEM over sessions, asterisks across bars indicate significance of differences between ratios. Asterisks over individual bars indicate significance of difference from a ratio of 1 (*p < 0.05, **p < 0.01, ***p < 0.001). Right, The edges/center ratio for the black and white responses. Cii, Corners versus edges middles. Same as Ci, only for the corners (marked in green) and the middles of the edges (cyan) ROIs.
- Figure 4.
Different contributions of contrast responses and surface responses. A, VSD activation pattern evoked by a 2 × 2° square contour stimulus (inset, red dot marks the fixation point), presented 1.5 left of the fixation point and 2.5° below for 300 ms, averaged 60–100 ms (n = 11 trials, large blood vessels are colored gray). Blue and red regions (area 0.46 mm2) depict the ROIs used to measure edge and center activation, respectively. B, Average activation evoked by the stimulus in A at the edges (blue) and center (red) ROIs, and at the center region of the response evoked by a large surface stimulus (orange), centered at the same location as A (size 8 × 8°, n = 21 trials). Significance of >0 activation measured by Wilcoxon signed rank test (***p < 0.001). C, VSD pattern evoked by a 2 × 2° square surface stimulus (inset) presented at (−1.5 and −2.5°) for 300 ms, averaged 60–100 ms (n = 20 trials, large blood vessels are colored gray). Red region depicts ROI used to measure center activation, same one as in A. D, Comparison of spatial profiles of the responses shown in A (cyan curve) and C (blue curve, shading marks ±1 SEM). Paths spanned the top-left corner, center, and bottom-right corner of both responses (1.2 × 13.6 mm). Curves smoothed with a Gaussian (σ = 0.17 mm) for visualization purposes. Center activation in response to the filled square is clearly present and much higher than that evoked by the square contour.
- Figure 5.
Computing the expected response using a model. A, Visual stimuli. Left, Black stimulus. Right, White stimulus (lower left quadrants). B, Relative luminance values of each stimulus from A. Each pixel with respect to the luminance value present at the same location before stimulus onset (see Materials and Methods and Eq. 1). C, Values from B diverged into three pathways of processing: positive LTLM, negative LTLM (both obtained by rectification, Eqs. 5 and 6), and contrast (Eqs. 7 and 8). All three pathways are calculated using a weighted sum of a circular PRF (Eqs. 2 and 3) with a size that increases linearly as a function of eccentricity (Eq. 4). D, The three pathways from C, operated on by a nonlinearity function (Naka—Rushton; Eq. 9). Half-saturation values (C50, L50+, and L50−) for the Naka–Rushton equation are calculated from response statistics in a surround field that is larger than the PRF, resulting in spatially specific divisive surround (Eqs. 10–12). E, The expected response obtained by linear summation of the three pathways from D (Eq. 13). F, The expected response after spatial transformation to cortical coordinates (V1) of the imaged eccentricities (see Materials and Methods for further details).
- Figure 6.
Model performance—observed versus predicted. Evaluation of model performance on the example session from Figure 1. A, Spatial maps of the observed VSD signal from one imaging session (maps averaged over 60–100 ms post-stimulus onset) and the predicted maps. Ai, Black stimulus. Aii, White stimulus. B, Spatial paths over the maps in A, showing three spatial profiles (marked over the left map in Ai) that pass through the center, corners, and edges of the black (Bi) and white (Bii) patterns. Solid curves show the observed response, and dashed curves show the predicted response (gaps in the curves correspond to blood vessels). Left y-axis is for the predicted response; right y-axis is for the observed response. Ordinate ranges are set between 0 and mean + 2 SD for each curve individually. C, Scatter plots of the expected versus the observed response of all the pixels in the three spatial profiles for black (Ci, left) and white (Cii, right), along with regression lines for each section and r values.
- Figure 7.
Model performance—average over all sessions. Quantification of model prediction performance for spatial and black/white ratios, averaged over all n = 9 sessions. A, Observed and predicted responses in the ROIs. Locations of ROIs are depicted in Ci and Cii for Ai, Bi, and Aii, Bii, respectively (see Materials and Methods). Ai, Left, Depicts the ratio between the edges and the center for black; right depicts the ratio between the corners and the edge middles for black. Error bars are ±1 SEM over sessions. Aii, Same as Ai but for the responses to the white square. B, The ratios between the black and white responses in all four ROI types: edges and center (Bi) and corners and edge middles (Bii). C, Illustration of ROIs on an example map and corresponding predicted map from session shown in Figure 1. Ci, ROIs corresponding to square edges (blue) and to the center (red), superposed on a response map. Cii, ROIs corresponding to square corners (green) and to the edge middles (cyan), superposed on the corresponding predicted map.
- Figure 8.
Contrast– response curves—observed versus predicted. A, Observed versus predicted responses in a rectangular spatial profile for different contrast levels. Negative contrasts represent the black squares (Ai) and positive contrasts represent the white squares (Aii). The path of the spatial profile is marked as a white rectangle over the map in the middle. Solid curves show the observed response, normalized to the maximal response across all curves. Dashed curves show the predicted response, normalized to the maximal predicted response across all curves. Correlation values (r) between the observed and predicted curves, computed before normalization, are marked on each graph. B, Contrast curves for the black (Bi, left) and white (Bii, right) stimuli compared between the observed and the predicted in two ROIs: The center of the square (red) and the mean over the square edges (blue), as depicted in the map. All activation values normalized to the activation at the edges for the 74% black condition for data and predictions separately, resulting in an activation value of 1 for the black/edge ROI for both the data and model.
