Retina Retina covered with light sensitive receptors –RODS Primarily for night vision and movement Sensitive to broad spectrum of light Poor color discrimination Sense intensity or shades of gray –CONES Used to sense color

Retina Center of retina has the most cones –Allows for high acuity for objects focused at the center of the retina Edge of retina dominated by rods

Distribution of photopigments Not distributed evenly –Mainly reds (64%) – few blues (4%) Insensitivity to long wavelengths (cyan to deep blue) High sensitivity short wavelengths (yellow & orange) –Center of retina (high acuity) has no blue cones Small blue objects will disappear if you fixate on them

Color sensitivity and image detection Most sensitive to the center of the spectrum –Blues and reds must be brighter than greens and yellows Brightness mainly determined by reds & greens – expressed on a scale of luminance –Light energy corrected for wavelength sensitivity

Color sensitivity and image detection Shapes detected by finding edges –Combine brightness and color differences for sharpness –Hard to deal with blue edges and shapes As we age, lenses yellow –Sensitivity to blue reduced Fluid between lens and retina absorbs more light –Perceive a lower level of brightness

Focus Different wavelengths focus at different distances behind eyes lens –Some color combinations require the eye to constantly re-focus causing fatigue Red objects appear closer than blue objects Highly saturated colors more difficult to focus than less-saturated.