The Visual Process

1. The Visual Process Mr. Koch AP Psychology Forest Lake High School

2. The Visual Process • Transduction • the process by which our sensory systems convert stimulus energy into neural messages • Wavelength • The distance from one wave peak to the next • Hue • The color we experience (determined by wavelength) • Amplitude • Height of the wave peak • Intensity • Amount of energy in light waves, influences brightness (determined by amplitude)

3. Fovea (point of central focus) Retina Lens Iris Cornea Pupil Optic Nerve Iris – a colored muscle that surrounds and dilates or constricts the pupil (regulates amount of light entering) Lens – focuses the incoming rays by changing its curvature (called accommodation) Retina – the light-sensitive surface on which the rays focus – the multilayered tissue that lines the inside of the back of the eyeball Blind Spot Pupil - small opening which allows light to enter. *Note: the retina has many receptor cells which convert the inverted image (light energy) into neural impulses. When sent to the brain, these neural impulses are reassembled to create a perceived, upright-seeming image.

5. The Retina • Light travels through outer cells to buried receptor cells called rods and cones. • The rods and cones generate neural signals to alert the next layer of cells called the bipolar cells. • The bipolar cells activate the ganglion cells, whose axons converge like strands of rope to form an optic nerve that carries information to the brain. • Where the optic nerve leaves the eye there are no receptor cells, creating a blind spot. • The fovea is where the cones are clustered, the retina’s area of central focus (no rods).

6. Rods vs. Cones Rods Cones Many have their own bipolar cells – aids in precise info and detection of fine detail. Color vision Do not respond in dim light (can’t see colors in dim light) 6 million Center of retina Low sensitivity in dim light • Do not have their own bipolar cells, they share with other rods. • No color. • Remain sensitive in dim light, takes about 20 minutes to adjust • 120 million • Periphery of retina • High sensitivity in dim light – help see in the dark.

7. Visual Information Processing • Feature Detectors • Certain cortical neurons which receive visual info and respond to only certain features of a scene • Parallel Processing • The brain’s capability to process visual components simultaneously (i.e. a face as opposed to an eye, a nose, etc.) – it breaks vision down into sub-dimensions such as color, depth, movement, and form

8. Color Vision • We can discriminate 7 million different shades! • 1 in 50 people are “color-deficient” (esp. males – genetic) • Young-HemholzTrichromatic Theory • The retina has 3 types of color receptors – each sensitive to red, green, or blue. When we combine these, wegetalltheothercolors • Herring: afterimages – Opponent Process Theory • After leaving the receptor cells, visual information is analyzed in terms of opponent colors • Red/Green; Blue/Yellow; Black/White • White contains all colors in spectrum

9. Color Vision • Summary • The retina’s red, green, and blue cones respond in varying degrees to different stimuli; their signals are then processed by the nervous system’s opponent-process cells en route from the thalamus to the visual cortex • Color Constancy • Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the objects • Perception of color is influenced by the context