Sensation and Perception Week Two

Knowledge Check- Beginning of the Perceptual Processes

Path of light entering the eye

Cornea → Pupil (surrounded by Iris) → Lens → Retina (photoreceptors).

What is the function of the Cornea?

The clear outer protective layer at the front of the eye that does most of the initial focusing/refraction of light.

What is the function of the Pupil and Iris?

The Iris is the colored muscle ring that expands/contracts to adjust the size of the Pupil, controlling the amount of light entering the eye.

What is the function of the Lens?

Changes shape to adjust sharpness and accurately focus light rays onto the retina, forming an inverted image.

Where is the Retina located and what is its role?

Located at the back inner lining of the eye; contains photoreceptors (rods and cones) that absorb light and convert it into neural signals.

What is the Fovea and where is it located?

The central point of the retina containing only cones; responsible for high-acuity, detailed central vision.

What is the Peripheral Retina and what photoreceptors dominate it?

The outer areas surrounding the fovea, populated mostly by rods; responsible for peripheral and low-light vision.

What is the Optic Nerve?

A bundle of nerve fibers that carries visual neural signals from the retina to the brain.

What is the Blind Spot (Optic Disc) and why does it exist?

The blind spot is where the are no photoreceptors. We don’t know how we are still able to see without those blind spots in our vision.

What is the Blind Spot (Optic Disc) and why does it exist?

The location on the retina where the optic nerve exits to the brain. It contains zero photoreceptors, so no light can be detected there.

How many Cones are in the human eye and where are they concentrated?

~6 million cells; concentrated mostly in the center of the retina (fovea).

What type of vision do Cones provide?

Photopic vision (daylight/bright light vision, high detail/acuity, and color perception).

How many Rods are in the human eye and where are they located?

~120 million cells; located mainly in the peripheral regions of the retina.

What type of vision do Rods provide?

Scotopic vision (dim light/night vision, high sensitivity to movement/light, low detail, no color perception).

What is Sensory Transduction in vision?

The process of converting physical light energy (photons) into electrical/neural impulses that the brain can process.

What are the two components of a visual pigment molecule?

Opsin (a large protein) and Retinal (a small light-sensitive molecule attached to opsin).

What is Isomerization?

The change in shape of the retinal molecule when it absorbs a photon of light, triggering visual transduction.

What is the Dark Adaptation Curve?

A graph showing how visual sensitivity increases over time in the dark. It has two phases: rapid initial adaptation by cones, followed by slower but much higher sensitivity adaptation by rods.

What is the Rod-Cone Break in the dark adaptation curv

The point (around 7–10 minutes in the dark) where rod sensitivity overtakes cone sensitivity, causing a sudden increase in visual sensitivity

What is the Purkinje Shift?

The shift in color perception sensitivity as lighting transitions from bright (photopic) to dim (scotopic).

How does the Purkinje Shift affect how colors look in bright daylight vs. twilight/low light?

In daylight, long-wavelength colors like red appear brightest; in low light, sensitivity shifts toward shorter wavelengths, making blue and green objects appear brighter than red ones.

How many types of Cones exist in the human eye, and what are they?

3 types: S-cones (Short wavelength / Blue), M-cones (Medium wavelength / Green), and L-cones (Long wavelength / Red).

What is Spectral Sensitivity?

An eye's or photoreceptor's relative sensitivity to light at different wavelengths across the visible spectrum.

What part of the light spectrum are Rods most sensitive to?

Medium-short wavelengths (~500 nm, corresponding to green-blue light).

Why does the brain invert the image formed on the retina?

The convex lens naturally flips and inverts the incoming image onto the curved retina; the brain processes and flips the signal upright so we perceive the world correctly.