Deciphering the elemental building blocks of visual appearance

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Seeing is a product of a complex physical and physiological chain of events. While some isolated stages of the visual pathway are well understood, studying the direct link between the physical stimulus and perception remains one of the challenges in vision science. In humans, the activation of the retinal photoreceptor mosaic constitutes the cellular entry point of the visual signal. To isolate the single cell contribution to the overall percept is difficult, because in normal viewing, tens of thousands of photoreceptors are stimulated at any given moment. Moreover, precise experimental access is hindered by the optical imperfections and the constant movement of the eye. Recent advances in adaptive optics micro-stimulation, however, now make it possible to target single photoreceptor cells in the living retina for isolated function testing.Here, we ask in how far each individual photoreceptor contributes to the visual percept and if elemental cellular signals also instantiate perceptual elements. How does it look to see with only a single photoreceptor, and how do these elemental percepts combine and interact when stimuli are more complex? We will tackle these questions by direct mapping of highly controlled single (and multiple) cell stimulation and the subjective appearances they elicit. While the microscopic mapping between single cell stimulation and appearance is to-date entirely unknown, there is also a lack of understanding of the relation between stimulus and appearance on a macroscopic level, i.e. the more natural condition of spatially extended stimuli. One reason is that by far the largest part of vision research uses performance measures, like visual acuity or sensitivity, to study how well visual stimuli can be detected or discriminated, but not how they appear subjectively. To understand the underlying mechanisms of visual space perception, however, it is important to have a precise account of one of the central outputs of the system — visual appearance. Here, we will combine micro and macro captures of visual appearance, all the way from the single cone in the fovea to large arrays of cones in the periphery. To this end, we will develop novel procedures to accurately quantify subjective appearance and apply these methods in a number of paradigms that are known to alter stimulus appearance. By combining cutting-edge high-resolution optical stimulation techniques with novel appearance-based psychophysical methods in a large range of behavioral experiments, we aim to uncover the elemental building blocks of visual space perception.