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Lecture 2

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Matthias Niemeier

Lecture 2 Example of a short answer question: Which kinds of psychophysical methods exist? Mention at least four. Describe one of them in more detail. Method of limits, method of constant stimuli, method of adjustment, cross-modality matching method, magnitude estimation, Method of cross modality matching would work in a way that one asks the perceived intensity or magnitude of a sound and ask to match that with a source of light in terms of brightness. It is sort of like comparing apples and oranges, but it is shown to be consistent and fairly systematic. A little light physics What is light? It is electromagnetic waves or some sort of tiny particle; can be considered both but depends on the situation or the type of metaphor that should be used; waves when talking about distances; particles (photons) when talking about light hitting a surface such as a photo receptor; light itself is a small range of electromagnetic waves in a continuum in what is possible, starting with gamma rays, x-rays, ultraviolet, etc.; What happens to light? Light can be absorbed, reflected, refracted, diffracted, transmitted, Absorbed means energy (in this case light) is taken up, and is not transmitted at all; e.g., dust, surfaces, filters; Diffracted: Bent, or having waves that are spread out, (e.g., waves of sound or light, as they encounter an obstacle, e.g., pass through a narrow aperture); whenever waves encounter some sort of an obstacle and thus bend; Reflected: Energy that is redirected when it strikes a surface Purkinje reflections, eye movements; four different surfaces as light passes through the eye- inner/outer surfaces of the cornea and lens; thus four surfaces that the light is somewhat reflected and it is called Purkinje reflections; Transmitted: Energy that is passed on through a surface (when it is neither reflected nor absorbed by the surface); energy encounters a surface and is transmitted in some form that is not called reflection or absorption and is transformed for example into electrical energy; in terms of vision that is relevant and photo receptors (solar panels are one example) Refracted: Energy that is altered in its course as it passes into another medium, (e.g., light entering water from the air) Depth of a swimming pool, rainbows, eye glasses; pencil in a glass of water looks like it is bending; the two different media have to have different densities and depending on the difference in densities, it will determine the degree to which refraction occurs; practical implications are that a swimming pool looks shallower than it actually is; it is absolutely necessary for vision, glasses do this and importantly the eyes do this as well (occurs in the lens as well as other places); The Human Eye Why is sensing light a good idea? dfdfdfd Provides information about nutrition, perceive possible dangers, circadian rhythm works based on light, social information, sense different seasons (extract sap from trees) Evolution of the eye; very primitive mechanisms of light sensing have to do with so called eye spots; some protein on a singular cell/ some organism that senses light and travels in that direction or the opposite if it is getting to dry; so just a single protein or cluster of proteins on the membrane on single cells that sends light; if you have multiple cells, you can have something like nerves and photo receptors being one type of neurons actually; To achieve more spatial vision, it is a good idea to have a depressed or folded area that allows limited directionality; light can only come from certain directions and not others, only hitting certain photoreceptors; it is restricting what the directions of lights can be stimulated different parts of this photo sensitive area; As a next step, it makes sense to have some sort of pinhole; light coming from some source of light will only hit a certain part of the retina where light will actually stimulate photoreceptors; it is more restrictive; the water based chamber is something that a weird fish or something would have; an obvious issue is that this cavity does not discriminate and it can allow organisms and such to enter which may cause infections, thus it is not very hygienic; If this cavity is closed and there is an inside fluid of some sort that is independent of any kind of bacteria that floats around outside there; the purpose of the transparent membrane in front (cornea) is that the liquid inside is always the same density, and this is important in order for the re
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