VISION

Chapter 1: Introduction: Optical Illusions

Optical illusions exploit the disconnect between sensation and perception
Afterimages are ghost effects that take advantage of glitches in human vision
Vision is a complex sense that involves sensory receptors in the eyes and the cerebral cortex

Eyebrows, eyelashes, eyelids, and tear-producing lacrimal apparatus protect the eyes
The eyeball is irregularly spherical and contains fluids to maintain its shape
The eye is tethered by extrinsic eye muscles and located in the bony orbit of the skull

The eye's wall consists of the fibrous, vascular, and inner layers
The fibrous layer includes the sclera and the transparent cornea
The vascular layer contains the posterior choroid and the iris
The iris is made up of smooth muscle tissue and controls the size of the pupil
Light enters through the cornea and pupil and is focused by the lens onto the retina

The retina has an outer pigmented layer and an inner neural layer
Photoreceptors, bipolar neurons, and ganglion neurons are present in the inner neural layer
Bipolar neurons connect photoreceptors and ganglion neurons
Ganglion neurons form the optic nerve, which carries impulses to the brain's visual cortex

Cones detect fine detail and color, while rods register grayscale
Cones are located near the center of the retina, while rods are found in the periphery
Rods and cones are wired to the retina differently
Rods provide information about general shape and light/dark, while cones allow for detailed color vision

Staring at a flag and then looking at an empty white space creates a phantom flag of different colors
Photoreceptors can make us see afterimages
- Some stimuli, like brilliant colors or bright lights, continue firing action potentials even after we close our eyes or look away
Cones can get tired and stop responding
- Staring at a brightly colored image for too long can tire the cones
The flag illusion:
- Looked at an image with bright turquoise stripes
- Blue and green cones got tired, leaving only red cones to fire
- Looked at a white screen that included all colors and wavelengths of visible light
- Only the red cones were able to respond, resulting in the stripes appearing red
- Rods registered black and white, so the afterimage of the stars and stripes turned white

Explored the inner layer of the eye, which consists of the retina and its three kinds of neurons: photoreceptors, bipolar cells, and ganglion neurons
Learned about distinguishing rods from cones
Dissected how the weird flag illusion works