Population Response to Natural Images in the Primary Visual Cortex Encodes Local Stimulus Attributes and Perceptual Processing

Abstract

The primary visual cortex (V1) is extensively studied with a large repertoire of stimuli, yet little is known about its encoding of natural images. Using voltage-sensitive dye imaging in behaving monkeys, we measured neural population response evoked in V1 by natural images presented during a face/scramble discrimination task. The population response showed two distinct phases of activity: an early phase that was spread over most of the imaged area, and a late phase that was spatially confined. To study the detailed relation between the stimulus and the population response, we used a simple encoding model to compute a continuous map of the expected neural response based on local attributes of the stimulus (luminance and contrast), followed by an analytical retinotopic transformation. Then, we computed the spatial correlation between the maps of the expected and observed response. We found that the early response was highly correlated with the local luminance of the stimulus and was sufficient to effectively discriminate between stimuli at the single trial level. The late response, on the other hand, showed a much lower correlation to the local luminance, was confined to central parts of the face images, and was highly correlated with the animal's perceptual report. Our study reveals a continuous spatial encoding of low-and high-level features of natural images in V1. The low level is directly linked to the stimulus basic local attributes and the high level is correlated with the perceptual outcome of the stimulus processing.

Representation of Color Surfaces in V1: Edge Enhancement and Unfilled Holes

“…We showed that the latency to peak response at the center of achromatic surfaces increased with distance from the edges and that the responses seemed to propagate linearly from the edges to the center. The mean propagation speed of the population response was well within the range of previously reported horizontal connections' speed (Grinvald et al, 1994;Bringuier et al, 1999;Slovin et al, 2002). Our findings therefore support a horizontal-connection-mediated neuronal filling-in mechanism for achromatic surfaces (Spillmann and De Weerd, 2003;Huang and Paradiso, 2008).…”

“…The average speed was 0.088 Ϯ 0.0045 m/s. This speed is in the range of the previously reported horizontal connections speed (Grinvald et al, 1994;Bringuier et al, 1999;Slovin et al, 2002). The derived velocities were reproducible across different square sizes and spatial profiles (see Materials and Methods).…”

“…To verify the choice of our ROIs and spatial profiles (see Analysis of spatial profiles and ROIs above) we implemented a retinotopic 2D analytical model that maps the visual field onto the cortical surface and used the monopole version (Schira et al, 2010) with a polar compression factor as previously described in . The model's three free parameters (k, a, ␣) were determined for each imaged V1 hemisphere using a set of 7-11 control points obtained in an independent experiment (see Retinotopic mapping of V1 above; Ayzenshtat et al, 2012), and were a ϭ 0.74, k ϭ 2.95, and ␣ ϭ 1.54 for Monkey T, and a ϭ 3.8, k ϭ 1.2, and ␣ ϭ 0.59 for Monkey H. The model was implemented for few example sessions in which the results were reproduced.…”

Recent Progress in Voltage-Sensitive Dye Imaging for Neuroscience

“…Recently visual image encoding was studied using VSDi in behaving monkeys by recording the population response evoked in V1 by the presentation of the natural images during a face/scramble discrimination task. 96 Authors reported that the population response showed two phases: (1), that was spread over most of the area of the recording, and (2), which was spatially confined. 96 These experiment results present a spatial encoding of low-and high-level features of visual images in the V1: the low level is correlated to the image's basic local attributes and the high level is related with the perceptual outcome of the visual image processing.…”

“…96 Authors reported that the population response showed two phases: (1), that was spread over most of the area of the recording, and (2), which was spatially confined. 96 These experiment results present a spatial encoding of low-and high-level features of visual images in the V1: the low level is correlated to the image's basic local attributes and the high level is related with the perceptual outcome of the visual image processing. 96 Neural responses in response to collinear or orthogonal arrays of Gabor patches have been visualized by the VSDi imaging in the awake monkey.…”