Module 18-20

lens

Changes shape to help focus images on the retina

Cornea

Protects the eye and bends light to provide focus

In order to focus near and far objects on the retina, the lens changes its shape though a process called

Accommodation

Why do we see an afterimage when we look away at a white piece of paper after staring at a yellow and green flag, as in Figure 18.12?

- According to Hering's opponent-process theory staring at yellow triggers neural firing in the yellow portion of the cone, but when we look away, the blue, repressed neural impulses being to fire. Green produces a red afterimage and black produces a white afterimage.

How does vision in the fovea relate to placement and quantity of rods and cones? How might the experience of nocturnal animals be different from humans in regard to their visual system's physiology?

- Cones are concentrated near the center of the retina and objects that fall on that portion of the retina are seen more clearly. Rods, which line the perimeter in greater numbers aid in peripheral vision - Nocturnal animals have a greater number of rods and it is easier for them to see things in minimal lighting

Discuss how the Young-Helmholtz trichromatic theory explains how we see and perceive color. Then discuss how it explains color blindness.

- Cones are set to receive three different wavelengths, making them receptive to what we call red, blue, or green. When we stimulate combinations of these cones, we see other colors - Colorblind is actually an incorrect term - certain cones may not function correctly.

Where are feature detectors located, and what is their function? How do feature detectors work together to portray a "whole' image?

- Feature detectors are specialized neurons in the occipital lobe's visual cortex and they receive information from the indivuals ganglion cells in the retina. They detect specific features - lines, edges, angles, and movement - of an object and pass this neural information along to other cortical areas where it is combined for form a larger picture

What are the two physical characteristics of light and how do they determine our awareness of hue and intensity?

- Frequency or wavelength determines hue (or color) - Amplitude or wave height determines intensity (or brightness)

Explain how Hering's opponent-process theory adds to the explanation of how we see and perceive color

- Hering's opponent-process theory states that we have three sets of cones, similar to the Young Helmholtz theory, but these cones see pairs of colors - red/green, blue/yellow or black/white. In the retina, some neurons are turned "on" by red and "off" by green, and vice-versa. The cones "see" either one or the other of the pairs

How might parallel processing be related to blindsight (described in Module 13)?

- People are able to "guess" whether sticks are horizontal or vertical even if they can't actually "see" the sticks - the parallel processing in our mind, or dual processing, sees what the conscious mind cannot.

How does parallel processing help us analyze a visual scene? How would the four subdimensions mentioned in the text allow you to see and perceive a person walking toward you on the street?

- The brain divides the scene into sub dimensions - motion, form, depth, color - and works on all aspects simultaneously. Then these perceptions are integrated by different visual teams.

Light waves with lower frequencies around 700 nanometer will produce which colors?

- They will produce reddish hues

Using fMRI scans, how are we able to tell if a person is looking at a "shoe, chair, or face?"

- This brain activity is so specific that we are able to tell what a person is looking at

what percentage of people are impacted?

1 in 50, or 2%

bipolar cells

Active ganglion cells

How large is the portion of light visible to humans related to the spectrum of electromagnetic energy?

A relatively small portion of the electromagnetic spectrum is actually visible to humans. The wavelengths from about 400 to 700 nanometers make up what we can the visible spectrum.

iris

A ring of muscle tissue that controls the size of the pupil opening

Name three ways in which rods and cones differ.

A. Rods detect black, white, and gray, while cones give rise to color sensations B. Cones do not necessarily respond to the dark while rods do (twilight vision). C. Cones can detect fine detail, while rods cannot.

Why are cones, rather than rods better able to detect fine detail?

Cones have a direct connection to bipolar cells, whereas rods share bipolar cells with other rods.

The Young-Helmholtz theory suggests that human perceive color through

Cones on the retina that contain three different color receptors

retina

Light sensitive inner surface of the eye, containing the rods and cones that begin the processing of visual information

rods

Retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision

cones

Retinal receptors that function in well-lit conditions. Detect fine detail and give it rise to color sensations

Why does human vision have a blind spot?

The "blind spot" is a section of the retina that does not contain receptor cells (rods and cones) because that is where the optic nerve exits the back of the eye

pupil

The center of the eye through which light enters

fovea

The central focal point in the retina, around which the eye's cones cluster

optic nerve

The point at which the optic nerve leaves the eye, creating a "blind spot" because no receptors nerves are located there

interposition

an object partially covered by another is seen as farther away

relative motion

as we move, objects at different distances appear to move at different rates

monocular cues

depth cues, such as interposition and linear perspective, available to either eye alone

relative size

if two objects are presumed to be the same size, the one that casts a smaller retinal image is perceived as farther away

linear perspective

parallel lines appear to converge with distance

what subgroup of human is most impacted?

males

what is the most common deficiency?

red/green color deficiency

depth perception

the ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance

ganglion cells

the strands that form the optic nerve

2. Frequency is to amplitude as ___________ is to ______________________.

wavelength, wave height

relative height

we perceive objects higher in our field of vision as farther away