Precise visuotopic organization of the blind spot representation in primate V1.

The optic disk is a region of the retina consisting mainly of ganglion cell axons and blood vessels, which generates a visual scotoma known as the blind spot (BS). Information present in the surroundings of the BS can be used to complete the missing information. However, the neuronal mechanisms underlying these perceptual phenomena are poorly understood. We investigate the topography of the BS representation (BSR) in cortical area V1 of the capuchin monkey, using single and multiple electrodes. Receptive fields (RFs) of neurons inside the BSR were investigated using two distinct automatic bias-free mapping methods. The first method (local mapping) consisted of randomly flashing small white squares. For the second mapping method (global mapping), we used a single long bar that moved in one of eight directions. The latter stimulus was capable of eliciting neuronal activity inside the BSR, possibly attributable to long-range surround activity taking place outside the borders of the BSR. Importantly, we found that the neuronal activity inside the BSR is organized topographically in a manner similar to that found in other portions of V1. On average, the RFs inside the BS were larger than those outside. However, no differences in orientation or direction tuning were found between the two regions. We propose that area V1 exhibits a continuous functional topographic map, which is not interrupted in the BSR, as expected by the distribution of photoreceptors in the retina. Thus V1 topography is better described as "visuotopic" rather than as a discontinuous "retinotopic" map.

Preenchimento perceptivo da mancha cega não distorce a percepção do tamanho linear / Filling-in of the blind spot does not distort linear size perception

Ao se olhar o mundo monocularmente, não se percebe que há uma mancha cega no campo visual correspondente ao disco óptico, região da retina em que não há fotorreceptores. Ao contrário, bordas e padrões de superfícies são percebidos como se fossem detectados por fotorreceptores, fenômeno denominado preenchimento perceptivo. Para investigar se o preenchimento perceptivo distorce o espaço percebido, trinta adultos tiveram suas manchas cegas do olho direito mapeadas e fizeram as comparações de tamanho de pares de barras horizontais em condição monocular direita. Os resultados apontam uma assimetria lateral no campo visual central do olho direito nas comparações de tamanho e que o preenchimento perceptivo na mancha cega não distorce o espaço visual percebido.

When looking at the world monocularly, we do not perceive that there is a blind spot in the visual field corresponding to the optic disc, the region of the retina where there are no photoreceptors. In contrast, we perceive edges and patterns of surfaces as if were detected by photoreceptors. This phenomenon is called filling-in. To investigate whether the filling-in distorts space perception, thirty adults had their right eye blind spots mapped and they compared the length of two horizontal bars under right monocular viewing condition. The results point out a lateral asymmetry in the central visual field of the right eye in length comparisons and that the filling-in effect at the blind spot does not distort visual space perception.

Preenchimento perceptivo da mancha cega não distorce a percepção do tamanho linear / Filling-in of the blind spot does not distort linear size perception

Ao se olhar o mundo monocularmente, não se percebe que há uma mancha cega no campo visual correspondente ao disco óptico, região da retina em que não há fotorreceptores. Ao contrário, bordas e padrões de superfícies são percebidos como se fossem detectados por fotorreceptores, fenômeno denominado preenchimento perceptivo. Para investigar se o preenchimento perceptivo distorce o espaço percebido, trinta adultos tiveram suas manchas cegas do olho direito mapeadas e fizeram as comparações de tamanho de pares de barras horizontais em condição monocular direita. Os resultados apontam uma assimetria lateral no campo visual central do olho direito nas comparações de tamanho e que o preenchimento perceptivo na mancha cega não distorce o espaço visual percebido.(AU)

When looking at the world monocularly, we do not perceive that there is a blind spot in the visual field corresponding to the optic disc, the region of the retina where there are no photoreceptors. In contrast, we perceive edges and patterns of surfaces as if were detected by photoreceptors. This phenomenon is called filling-in. To investigate whether the filling-in distorts space perception, thirty adults had their right eye blind spots mapped and they compared the length of two horizontal bars under right monocular viewing condition. The results point out a lateral asymmetry in the central visual field of the right eye in length comparisons and that the filling-in effect at the blind spot does not distort visual space perception.(AU)