Lecture 7: The Visual System i. ii. iii. iv. v. vi. vii. Transduction a. In sensation, transformation of stimulus energy into neural impulses b. Phototransduction: conversion of light energy into neural impulses Light Characteristics a. Wavelength: the distance from the peak of one wave to the peak of the next i. Short wavelength= high frequency (bluish color, high pitched sounds) ii. Long wavelength= low frequency (reddish color, low pitched sounds) b. Related to perceived hue (color) Intensity (Brightness/Lightness) a. Intensity- amount of energy in a wave (amplitude) i. Great amplitude (bright colors, loud sounds) ii. Small amplitude (dull colors, soft sounds) b. Related to perceived brightness The Lens a. Accommodation i. The eye’s lens changes shape to help focus objects on the retina b. Nearsightedness: i. Image focused in front c. Farsightedness: i. Image focused behind retina Theories of Color Vision a. Trichromatic theory (Young-Helmholtz) i. Retina contains three receptors maximally sensitive to red, blue and green wavelengths Color Blindness a. Most people are trichromats b. If red cones filled with green photopigment (or vice versa): dichromats i. More common in males (approx. 10%) Opponent Process Theory a. We process four primary colors opposed in pairs of red-green, blue-yellow, and black white (Hering) i. Competition between colors ii. Can explain afterimages