Psyc 121: Visual Processing and the Human Eye

What is the visible spectrum range for humans?

400nm - 700nm

Which animals can see ultraviolet light?

Bees, birds, and other animals.

What type of light can snakes and other reptiles see?

Infrared (700-900nm).

How does the color vision of dogs and cats compare to humans?

Dogs and cats see a similar range as humans but have fewer types of cones, resulting in fewer dimensions of color.

What are the main components of the human eye involved in focusing light?

The pupil, cornea, and lens.

What percentage of focusing is done by the cornea?

80%.

How does the lens of the eye adjust for focusing?

The lens can accommodate by contracting (getting thicker) or dilating (getting flatter).

What happens if the lens does not contract when focusing on a close object?

The object will appear blurry.

What is the role of the pupil in image formation?

The pupil allows light to enter the eye, but it is not a point, so light would disperse onto the retina.

What causes afterimages to reappear when blinking?

Blinking partially resets contrast detectors in the visual system, enhancing edge perception.

What is the significance of edges and contours in afterimages?

Afterimages depend on edges and contours, and increased contrast can bring them back.

What is the function of the cornea in the eye?

The cornea does most of the focusing but cannot adjust its focusing power for different distances.

What happens when light shines on an object?

The object reflects light in all possible directions, some of which enter the eye.

What is the effect of multiple objects on the retina?

They create overlapping projections, leading to blur.

What is the purpose of the blurry pencil demo?

To demonstrate how the lens adjusts focus when viewing an object at different distances.

What occurs when the lens contracts?

The object is focused correctly.

What is the blind spot in the context of vision?

The area in the visual field where no photoreceptors are present, leading to a lack of visual information.

What are the two types of photoreceptors in the retina?

Rods and cones.

What is the difference between foveal and peripheral vision?

Foveal vision is sharp and detailed, while peripheral vision is less detailed and more sensitive to motion.

What is the role of rods in vision?

Rods are responsible for vision in low light conditions.

What is the role of cones in vision?

Cones are responsible for color vision and function best in bright light.

What is the importance of the retina in the eye?

The retina contains photoreceptors that convert light into neural signals for vision.

What is the distance at which you can no longer focus on an object called?

The 'near point'.

What happens to the lens as we age, affecting our near point?

The lens becomes stiffer, causing the near point to get farther away, a condition known as presbyopia.

What visual aid is commonly needed after age 45 due to presbyopia?

Reading glasses.

What is myopia?

Myopia, or nearsightedness, is the inability to focus on far-away objects.

What type of glasses are used to correct myopia?

Concave glasses.

What type of glasses are used to correct presbyopia?

Convex glasses.

What is one method to focus light besides using lenses?

Shrinking the pupil.

What effect does pupil contraction have on light and image clarity?

It reduces dispersion (less blur) but allows less light to reach the eye, making objects appear dimmer.

How can you estimate visual angle using your thumb?

One thumb-width at arm's length is approximately 2 degrees.

What is the size-distance equation for visual angle?

Visual angle ≈ Object size / Distance.

What happens to light once it is focused on the retina?

It is absorbed by photoreceptors (rods and cones) and converted to neural signals.

What is the primary function of cones in the retina?

Cones are most useful for color vision and function best in bright light.

What is the primary function of rods in the retina?

Rods are sensitive to light vs. dark and are useful in dim light.

Where are cones most densely located in the retina?

In the fovea.

Where are rods most densely located in the retina?

In the periphery of the retina.

How many rods and cones are typically found in the human retina?

Approximately 120 million rods and 6 million cones.

What is a 'blind spot' in the context of the retina?

A region in the retina that has no rods or cones.

What is the role of photoreceptors in the process of transduction?

They absorb light and convert it into neural signals that are relayed to the brain.

How does the lens change to focus on near objects?

The lens contracts to its maximum thickness.

What is the effect of aging on the lens's ability to focus?

The lens becomes less flexible, making it harder to focus on near objects.

What is the relationship between pupil size and image clarity?

A contracted pupil reduces blur but also decreases light intake, affecting brightness.

What type of photoreceptors are more numerous in the retina?

Rods, with approximately 120 million compared to about 6 million cones.

What is the composition of the fovea in terms of photoreceptors?

The fovea contains only cones.

What is the blind spot in the retina?

The region where ganglion cells exit the eye via the optic nerve, with no rods or cones present.

How far is the blind spot from the fovea in terms of visual angle?

About 12-15 degrees of visual angle.

What is the approximate size of the blind spot on the retina?

About 5 x 7 degrees.

What do people usually perceive in their blind spot?

Nothing, whiteness, darkness, or the surrounding pattern.

Why are we usually unaware of our blind spots?

1. The two blind spots do not overlap. 2. We are usually not paying attention to our periphery. 3. The brain 'fills in' missing information.

How many rods and cones send signals to ganglion cells in the retina?

About 90 million rods and 5 million cones send signals to approximately 1 million ganglion cells.

What is the function of ganglion cells in the retina?

They send signals to the brain.

What activity can help you find your blind spot?

Draw a cross and a circle on paper, close one eye, and adjust the distance until the circle disappears.

What is the average number of photoreceptors that each ganglion cell receives inputs from?

About 95 photoreceptors.

What is the convergence ratio for rods compared to cones?

The convergence ratio for rods is approximately 100:1, while for cones it is about 2.5:1.

What is the convergence ratio for cones in the fovea?

In the fovea, the convergence ratio for cones is approximately 1:1.

How does the convergence ratio affect foveal ganglion cells?

Foveal ganglion cells are much more sensitive to detail due to the lower convergence ratio.

What is the approximate number of rods that connect to one ganglion cell in peripheral vision?

Approximately 100 rods connect to one ganglion cell.

What is the approximate number of cones that connect to one ganglion cell in peripheral vision?

About 2 cones connect to one ganglion cell.

What is the total number of ganglion cells that leave the eye through the optic nerve?

Approximately 1 million ganglion cells leave the eye through the optic nerve.

How is the information represented by ganglion cells divided between foveal and peripheral vision?

About 0.5 million ganglion cells represent peripheral information, and about 0.5 million represent foveal information.

What must occur to discriminate equally across fovea and periphery?

Peripheral items need to be greatly magnified.

What is required to see detail in an item of interest?

We need to foveate to the item of interest.

What visual illusion is mentioned in the notes?

The Hermann grid.

What is the focus of the course regarding sensory modalities?

Understanding how different sensory modalities interact with each other.

What phenomenon is associated with the Hermann grid?

Disappearing gray spots.

What is the face inversion effect?

faces are harder to recognize upside down