Effect of cone spectral topography on chromatic detection sensitivity.

The spatial and spectral topography of the cone mosaic set the limits for detection and discrimination of chromatic sinewave gratings. Here, we sought to compare the spatial characteristics of mechanisms mediating hue perception against those mediating chromatic detection in individuals with known spectral topography and with optical aberrations removed with adaptive optics. Chromatic detection sensitivity in general exceeded previous measurements and decreased monotonically for increasingly skewed cone spectral compositions. The spatial grain of hue perception was significantly coarser than chromatic detection, consistent with separate neural mechanisms for color vision operating at different spatial scales.

Retinal spatiotemporal dynamics on emergence of visual persistence and afterimages.

Visual persistence (stimulus perception that prolongs for a few milliseconds after the physical disappearance of the stimulus) and afterimages (an illusory percept that lingers after the physical disappearance of the stimulus at the retinotopic location of the preceding stimulus) are classic perceptual phenomena reflecting temporal characteristics of the visual system. These phenomena are modulated by some common stimulus aspects: A longer stimulus generates shorter persistence and a longer afterimage and a lower spatial-frequency stimulus generates shorter persistence and a stronger afterimage. The current study proposes that these spatiotemporal characteristics of visual persistence and afterimages can be explained by a generic retinal processing architecture. Wilson (1997) developed a neural network model of retinal circuitry and demonstrated that afterimages emerge due to a retinal light-adaptive gain control mechanism. In this study, we provide an overview of the retinal physiology to assess the feasibility of his retinal model, and simulate psychophysical experiments on persistence and afterimages in the same model to provide systematic explanations to the stimulus duration and spatial frequency effects. Our results suggest that these characteristics emerge from the spatiotemporal characteristics of each cell (response gain and time course, receptive-field structure) that comprises a part of the feedforward-feedback laminar network in the retina. The retinal circuitry performs short- and long-term adaptive operations as the signal transmission is recurrently regulated by various feedback mechanisms and consequently engenders complicated spatiotemporal dynamics in the ganglion cell responses that match the patterns of the perceptual phenomena. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Retinal Lateral Inhibition Provides the Biological Basis of Long-Range Spatial Induction.

Retinal lateral inhibition is one of the conventional efficient coding mechanisms in the visual system that is produced by interneurons that pool signals over a neighborhood of presynaptic feedforward cells and send inhibitory signals back to them. Thus, the receptive-field (RF) of a retinal ganglion cell has a center-surround receptive-field (RF) profile that is classically represented as a difference-of-Gaussian (DOG) adequate for efficient spatial contrast coding. The DOG RF profile has been attributed to produce the psychophysical phenomena of brightness induction, in which the perceived brightness of an object is affected by that of its vicinity, either shifting away from it (brightness contrast) or becoming more similar to it (brightness assimilation) depending on the size of the surfaces surrounding the object. While brightness contrast can be modeled using a DOG with a narrow surround, brightness assimilation requires a wide suppressive surround. Early retinal studies determined that the suppressive surround of a retinal ganglion cell is narrow (< 100-300 µm; 'classic RF'), which led researchers to postulate that brightness assimilation must originate at some post-retinal, possibly cortical, stage where long-range interactions are feasible. However, more recent studies have reported that the retinal interneurons also exhibit a spatially wide component (> 500-1000 µm). In the current study, we examine the effect of this wide interneuron RF component in two biophysical retinal models and show that for both of the retinal models it explains the long-range effect evidenced in simultaneous brightness induction phenomena and that the spatial extent of this long-range effect of the retinal model responses matches that of perceptual data. These results suggest that the retinal lateral inhibition mechanism alone can regulate local as well as long-range spatial induction through the narrow and wide RF components of retinal interneurons, arguing against the existing view that spatial induction is operated by two separate local vs. long-range mechanisms.