Perceptual processes ch 2

Light: A Physical Perspective

• Light is a narrow band of the electromagnetic spectrum, it can be a wave or a stream of photons.
• A wave is a disturbance in a medium travelling from one point to another without permanent displacement.
• Photons are a quantum of electromagnetic radiation exhibiting both particle and wave properties.

Light and the Visible Spectrum

• The visible spectrum is a small portion of the full electromagnetic spectrum.
• The spectrum's length has been compressed for easier visualization in a log scale.

Light Interactions

• Light can be absorbed, scattered, reflected, transmitted, or refracted.
• Absorption is when light energy is taken up and not transmitted.
• Scattering describes the irregular dispersal of light.
• Reflection is the redirection of light when it hits a surface.
• Transmission is the passage of light through a surface.
• Refraction is the bending of light as it passes into a different medium.

The Eye as a Camera Analogy

• Aperture (iris/pupil): regulates the amount of light entering the eye.
• Focus (lens): changes shape to adjust focus.
• Film (retina): records an image.
• While there are similarities, the eye is not a perfect camera analogue. The retina adapts to changing light settings and the lens physically molds to refocus light. A camera's lens moves, not the eye's.

Eye Anatomy and Function

• Cornea: transparent protective outer layer (responsible for 80% of light refraction.)
• Aqueous humor: watery fluid filling the anterior chamber providing nutrients and removing waste.
• Crystalline lens: ovoid structure bending light to focus on the retina.
• Vitreous humor: transparent gel-like substance filling most of the eye

Eye Conditions

• Angle-closure glaucoma: a disease resulting in optic nerve damage caused by excess aqueous humor buildup in the eye.

The Iris & Pupil

• Iris: muscular diaphragm regulating light entry through pupil dilation/constriction.
• Pupil: A circular opening in the center of the iris. It's response to light conditions helps the visual system adapt to ambient light levels.

Retina Structure and Function

• Retina: the light-sensitive membrane at the back of the eye.
• Photoreceptors: Rods and cones located at the back of the retina responsible for the initial transducing of light into neural energy.
• Rods: specialized for night vision and low-light conditions, not color-sensitive.
• Cones: specialized for daytime vision, color vision, and sharp details; high light conditions.
• Optic Disc: the area where the optic nerve leaves the eye, known as the blind spot.
• Fovea: The point of highest visual acuity located near the center of the macula.
• Macula: pigmented region near the center of the retina
• Retinal Pigmented Epithelium: opaque cells needed for rods and cones to function.

Retinal Topography

• Retinal Geography: the distribution of rods and cones (cones are concentrated for sharper vision).

Visual Angle

• Vision scientists use visual angle for determining size estimations of objects and stimuli.

Light Detection and Adaptation

• Photoreceptors have 3 parts: outer and inner segments, and synaptic terminal.
• Photoreceptors sense light in 6 steps: light absorption, isomerization, deactivation, phototransduction, electrical transmission, visual perception.
• Adaptation is the system's changing responsiveness to differing light conditions.
• Two key adaptation mechanisms: Pupil dilation and photoreceptor adaptation (bleaching, desensitizing or regenerating)
• Retinal ganglion cells are responsible for the processing of light and sending signals to the brain. P- and M-type cells are responsible for different parts of our visual experience for object recognition and motion.

Receptive Fields

• Receptive fields are the regions of the retina that affect the firing rate of a neuron.
• Ganglion cells contain ON-center and OFF-center receptive fields (excitable when the center area is triggered, and inhibited by the surrounding areas).

Persistent Hyperplastic Primary Vitreous, Glaucoma and other conditions

• It's a congenital disease of the eye
• Certain conditions increase the risk of glaucoma, cataracts, retinal detachment and interocular hemorrhage (which can lead to some forms of blindness (loss of vision).