Transcript 2_Vision
Vision Eyes, Optic Nerves, Ganglion Cells, Occipital Lobe… Its got it all! Anatomy Key Elements: Pupil, Lens, Retina, Fovea, Photoreceptors- Rods and Cones, Optic Nerve, Occipital Lobe Visual Transduction • Begins when light waves enter the eye • Photoreceptors (rods and cones) on the retina interpret the waves – Rods work in the dark and are found all over the retina (nearly 18X more rods than cones) – Cones measure color and are found only on the fovea (area of most focus on the retina) • Bipolar cells take info from rods and cones to the GANGLION CELLS (sense/afferent neurons) – GC AXONS ARE the Optic Nerve. – So… TRANSDUCTION occurs in the retina.! Brightness Explained • How much light reaches the retina? –Controlled by the PUPIL • Dilated Pupil=DARK • Contracted Pupil=LIGHT –Pupil Dilates in the Dark to expose more light waves to the photoreceptors »Many drugs can interfere with this by acting as agonists (replicating the neurotransmitters) involved in determining Pupil dilation and Contraction! (Primarily Dopamine and Endorphin) How does the Visual System Create Color? • Color does not exist in the world, only in the mind---WHOA! – color is a sensation created when light waves are transduced (I have no idea if this is the correct past tense of transduction) and then processed in our visual cortex –Only CONES (visual receptor cells) can detect color. These are only found in the FOVEA The Nature of Light • Electromagnetic spectrum- range of electromagnetic energy – Visible spectrum- part of the electromagnetic field that our brain can interpret in color • To interpret energy outside of the visible spectrum, we employ devices- radio’s, TVs, etc –Long waves- red –Medium waves- yellows/greens –Short waves- blues Electromagnetic Spectrum 2 Theories for How we Sense Colors 1. Trichomatic Theory: explains the initial stages of color vision- 3 types of cones sense the visible light- red, green, and blue 2. Opponent-Process Theory: explains vision from the bipolar cells on- upon the sensation of 1 color, your brain will inhibit its compliment- red/green; yellow/blue, etc • This explains the negative afterimage on p 121 Color Blindness • Color weakness- shades and pale colors are difficult to distinguish • Color blindness- cannot see specific colors –Most red/green –Rarely blue/yellow –Only 500 ever have reported complete color blindness