Abstract
Optical refraction causes light to bend at interfaces between optical media. This phenomenon can significantly distort visual stimuli presented to aquatic animals in water, yet refraction has often been ignored in the design and interpretation of visual neuroscience experiments. Here we provide a computational tool that transforms between projected and received stimuli in order to detect and control these distortions. The tool considers the most commonly encountered interface geometry, and we show that this and other common configurations produce stereotyped distortions. By correcting these distortions, we reduced discrepancies in the literature concerning stimuli that evoke escape behavior, and we expect this tool will help reconcile other confusing aspects of the literature. This tool also aids experimental design, and we illustrate the dangers that uncorrected stimuli pose to receptive field mapping experiments.
Highlights
Behavior[13,14], and we expect this tool will help reconcile other confusing aspects of the literature
When light traveling from the screen reaches the air-water interface, it is refracted according to Snell’s law[15] (Fig. 1a, bottom)
Snell’s law implies that distant stimuli appear to the fish at the asymptotic value of θ(θ′) (~48.6°). This implies that the entire horizon is compressed into a 97.2° “Snell window” whose size does not depend on the distances between the fish and the interface or the screen and the interface, but the distance ratio da/dw determines the abruptness of the θ(θ′) transformation
Summary
Behavior[13,14], and we expect this tool will help reconcile other confusing aspects of the literature. When light traveling from the screen reaches the air-water interface, it is refracted according to Snell’s law[15] (Fig. 1a, bottom). By solving Snell’s equations for this arena configuration (Appendix 1), we determined the apparent position of a point on the screen, θ, as a function of its true position, θ′ (Fig. 1b).
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