V1 responses to gray patches with gratings in the surround. a) Extracellular recordings across V1 layers in awake head-fixed mice on a running disk. b) Example session of current source density analysis to identify cortical layers. c) Sparse noise protocol (top) for RF (receptive field) mapping. Example RF for MUA (multi-unit activity). d) Illustration of main stimulus conditions: In the classical condition (Gr), grating stimuli of different sizes were presented, either drifting (Dr) or stationary (St). In the gray-center/grating-surround condition (GcGr), a gray patch was centered on the neuronal RF and had the same luminance as the background during the inter-trial interval. Hence, at stimulus onset, only the surround stimulus changes. Shown here is a grating (top) or gray center patch (bottom) of 70°. The dashed circle represents an RF of 20° diameter. e) Average firing rates of single units, normalized to baseline, shown in logarithmic scale. The left panel corresponds to the early (0.04 s to 0.15 s) and the right panel to the late stimulus period (0.2 s to 1 s after stimulus onset) (number of neurons n=335, 6 animals). f) Statistical analysis for all conditions from e). Sizes are separated into small < 45° and large ≥ 45° (*p-values < 0.01 comparing drifting vs. stationary per size, Wilcoxon signed-rank test). g) Average spike density normalized to baseline in logarithmic scale. Solid lines represent drifting conditions and dashed lines represent stationary conditions. The black line on top of each subplot represents the stimulus period. h) Histogram of rise times of neural responses for Gr (black) or GcGr (red) (sizes ≥ 45°), PDF is the probability density function. Solid lines are a Kernel smoothing function of the histogram. Difference between drifting and stationary gratings: *p-value < 0.01. i) Each point represents the peak response time of the average spike density function as a function of response magnitude.

LGN responses to gray patches with a grating in the surround. a) Stimuli, as in Figure 1. b) Representative scheme of extracellular recordings in LGN. c) Average firing rates normalized to baseline (30 single units, 2 animals).

Neural responses to rectangular gray patches with orthogonal grating stimuli in the surround. a) Spatially continuous gratings (C) and a gray rectangular patch covering the gratings (GcC). The stimulus could be presented as either drifting or stationary. b) Non-continuous gratings in the surround (NC), which was covered by the gray patch in a subset of trials (GcNC). c) Population size tuning shown as the logarithm of firing rates normalized to baseline during early (0.04 s to .15 s) and late (0.2 s to 1 s) stimulus periods. “Dr” and “St” refer to drifting and stationary conditions. d) Statistical analysis of data in (d). Sizes were divided in small (< 45°) and large (≥ 45°) *p-values < 0.01 Wilcoxon signed-rank test. e) Average spike density function for different sizes of the rectangular gray patch. Solid line represents the stimulus period. f) Histogram of response latencies (rise time) for Gr (black) and GcGr (red) conditions. Latency was computed for sizes of ≥ 45°. The black and red lines are (kernel) smoothing estimates. Drifting and stationary conditions are pooled together. PDF corresponds to the probability density function (Wilcoxon signed-rank test, *p-value < 0.01). g) Scatter plot of rise time for the Gr vs. GcGr condition (sizes ≥ 45°, r-Pearson correlation value).

Neural responses to gray patch with pink noise background in the surround. a) Illustration of stimuli for 70° gray patch: Pink noise patch with a gray background (PN), or a gray patch with a pink noise background (GcPN). The black line is the PSTH for the PN condition. b) Average normalized firing rates (relative to baseline; logarithmic scale) for different sizes of the gray patch in the gray-center/noise-surround (GcPN) condition. For comparison, we include the pink noise condition at the size of 0 (PN; black dot). c) Average (normalized to baseline) spike density function for different sizes of the gray patch. d) Probability density function (PDF) of the rise time of the response. The line highlighted shows the Kernel smoothing function estimate from the PDF (Wilcoxon signed-rank test, *p-value < 0.01). e) Scatter plot of the rise time for the PN or GcPN conditions (sizes ≥ 45°, r-Pearson correlation value).

Neural activity for a gray patch with a black or white surround. a) White stimuli: white patches with a gray surround (WcGs) or a gray patch with a white surround (GcWs). b) Black stimuli: black center with a gray surround (BcGs) or a gray patch with a black surround (GcBs). c) Average firing rates normalized to baseline and in logarithmic scale for early (0.04 s to 0.15 s) and late (0.2 s to 1 s) stimulus period. d) Same as (c) for black stimuli shown in (b). e) Mean and SEM of neural responses for small and large patch sizes, separately for early and late stimulus periods. (*p-values < 0.01). f) Average spike density for different stimulus sizes. Spike densities are normalized to baseline and shown in a logarithmic scale. g) Histogram of response latencies across neurons (response rise time). The line highlighted shows the estimated probability density (kernel smoothing). Response latencies were computed for patch sizes of 45° and larger. PDF corresponds to the probability density function. h) Scatter plot of the rise time for the classical and gray patch condition per unit (n=247, 6 animals, r-Pearson correlation value).

Population analyses to investigate stimulus specificity. a) Dissimilarity matrices of firing rate vectors across trials. The distance between firing rate vectors was computed using Euclidean distances. For visualization purposes, the diagonal shows the maximum value. StGr: Stationary grating (classical condition). DrGr: Drifting grating (classical condition). StGcGr indicates a gray-center/gratings surround with a stationary grating (i.e. patch condition). b) Mean distances between protocols based on dissimilarity matrices. Black lines show the (i.e., SEM), where n is the number of samples (i.e., distances). St-GcSt indicates the distance between stationary grating (classical) and gray-center/stationary-grating (patch) conditions. For gratings with a circular gray patch during early periods, only (St-GcSt, St-GcDr) were not distinguishable (p-val equals 0.396). For late periods, all the distances were statistically distinguishable. For Gratings with rectangular patch during early periods, (St-GcSt, Dr-GcSt), (St-GcSt, Dr-GcDr), and (Dr-GcSt, Dr-GcDr) were not significant distinguishable (p-values equal to 0.4585, 0.9402, 0.9478, respectively). For late periods, all the comparison yielded significance. Finally, for B&W, all the comparisons were statistically significant except for the distances between (BcGs-GcWs, GcBs-GcWs) (p-val = 0.0247) for early periods. For late periods, the comparisons (BcGs-GcBs, BcGs-WcGs) and (GcBs-GcWs, GcBs-WcGs) were not significantly distinct (p-values 0.0338 and 0.0308, respectively). c) 2D t-SNE embedding based on dissimilarity matrices shown in a). d) Support Vector Classifier (SVC) based on matrices in a). Classification score across 20 repetitions. 40% of trials were used for training and 60% for testing.

Firing rate across V1 Layers to gratings in the far surround a) Stimuli presented as in Figure 1). Drifting and stationary gratings and gratings covered with a gray patch. b) CSD analysis from the first 200 ms in response to 45° gratings (left) and gratings covered by a 45° gray patch (right). c) Population size tuning per layer. Firing rate during the early and late period of stimulation, every unit is normalized to baseline (Superficial units n = 22, L4 units n = 213 and deep layer units n = 208, Wilcoxon signed ranked test p < 0.01). d) Probability density function of the rise time per unit separated into layers for drifting and stationary gratings. From top to bottom superficial units, layer 4 units, and deep units (*p-values < 0.01 Wilcoxon signed ranked test p < 0.01). e) Scatter plot of the rise time for Gr or GcGr separated by layers (sizes ≥ 45°, r-Pearson correlation value).

Firing rates to 90° gratings vs different sizes of the patches covering gratings. a) Scatter plots comparing 90° Gr (we define it as full-field) to different sizes of the gray patch for the drifting condition (r-Pearson correlation coeffcient). b) Same as in a for stationary conditions. c) Full-field gratings (90°) compared to different sizes of the gray patch covering gratings during the early stimulus presentation from 0.04 s to 0.15 s (Mean and the SEM. * p-values < 0.01 units per size 5° and 10°, n = 117 neurons, for sizes > 10°, n = 335 neurons, 6 animals). d) Same as c) but for the late stimulus period 0.2 s to 1 s.

Comparison of firing rate during the late period for larger sizes for all protocols. a-d) Stimuli on the top, plots represent the average of the population firing rate during the late period from 0.2 s to 1 s, each unit is normalized to baseline, for sizes ≥ 45°. Each protocol includes different units and is normalized to the baseline for each block (*p-values < 0.01, Wilcoxon signed-rank test, each group is compared within the same protocol).