26 - vision - BIOLOGY 325H Sensory systems: vision March...

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BIOLOGY 325H Sensory systems: vision March 26, 2008 Humans and other primates have a very highly developed visual system, and rely heavily on their sense of vision. Our vision is quite acute, i.e. we can see minute objects and detect small movements. In addition, humans, apes, and Old World monkeys are the only mammals with species-wide trichromatic (‘three color’) vision. But some aspects of our vision are not as sensitive as other species. For example, we have much poorer night vision than nocturnal mammals such as cats. And some species have more discriminating color vision: birds have tetrachromatic (‘four color’) vision, while some of the brightly colored fish that live in coral reef habitats have color vision that is pentachromatic (‘five color’). And some invertebrates have more than a dozen visual pigments with distinct color sensitivity. And then there are species that can see wavelengths of light to which we are completely blind. Today we will focus primarily on the role of the retina in the detection of light intensity and color. But it is important to realize that it is the brain – starting with the visual cortex – which transforms this retinal information into visual perception, and allows us to perform complex visual tasks like recognizing patterns or objects even when they are largely obscured by something else. Learning goals 1. Know that visible light is a subset of electromagnetic radiation defined by wavelength. What is monochromatic light? What is an absorption spectrum? What is peak absorp- tion? What three colors correspond to the wavelengths of peak absorption for human cones, and what is the relative order (short-to-long) of their wavelengths? How does your brain use the sensory information from cones to perceive color? 2. You should understand that most mammals are ‘color blind’ by human standards,
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26 - vision - BIOLOGY 325H Sensory systems: vision March...

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