BioPsych Chapter 6

True or False: Shapes are more easily identified with peripheral vision than foveal vision.

False

The optic nerve is composed of axons from which of the following cells?

Ganglion

How do the retinas of predatory birds, such as hawks, differ from the retinas of prey species, such as rats?

Hawks have greater density of receptors on the top half of their retinas than do rats.

Why are men more likely to experience color vision deficiency than women?

It is a sex-linked genetic disorder.

Describe the functional and anatomic differences between rods and cones.

Rods and cones are photoreceptor cells of the retina. They contain photopigments (chemicals that release energy when struck by light). Photopigments consist of 11-cis-retinal bound to proteins called opsins. Rods are sensitive to light of low intensity. They detect brightness and are abundant in the periphery of the eye where they respond to faint light (120 million per retina). They connect to magnocellular neurons which are distributed evenly throughout the retina. They have larger cell bodies and visual fields and are highly sensitive to large overall pattern and moving stimuli. Cones are maximally sensitive to one of three different wavelengths of light that encodes color vision. Cones are most abundant in and around the fovea (6 million per retina). They are essential for color vision and are more useful in bright light and allow for the best visual acuity. Though cones are outnumbered, they provide about 90% of the brain's input. Humans have three different types of cones, each sensitive to a different set of wavelengths. We discriminate among wavelengths by the ratio of activity across the three types of cones: short (blue), medium (green), and long-wavelength (red) cones. Cones mostly connect to parvocellular neurons located in or near the fovea. They have smaller cell bodies and small receptive fields and are highly sensitive to detect color and visual detail

Describe why humans have a blind spot.

The ganglion cell axons form the optic nerve (or optic tract), exits through the back of the eye. The point at which it leaves (which is also where the blood vessels enter and leave) is the blind spot, because it has no receptors.

True or False: Faces excite the fusiform gyrus more than any other visual stimulus.

True

True or False: The optic nerve is composed of axons from ganglion cells.

True

Which theory emphasizes the idea that color vision depends on the relative responses of three kinds of cones?

Young-Helmholtz theory

What is strabismus?

a failure of the two eyes to focus on the same thing at the same time

Damage to the magnocellular pathway would most likely lead to the loss of:

motion perception.

If a kitten is reared with one eye shut, cells in its visual cortex become sensitive to:

only the eye that has been active.

In depth perception, different views are received by each eye, depending on the distance of the object being viewed. What is this called?

retinal disparity

In the visual system, the ____ and ____ constantly feed information back and forth.

thalamus; cortex

What is blindsight? how does it work? provide examples in your answer

Blindsight is when someone can respond to a visual stimuli without being able to perceive or see what they are responding to. Blindsight is often due to damage to the primary visual cortex (V1). So a person can move out of the way of an object but say that they cannot see anything.

Describe the key functions of the major pathways in the visual cortex.

Ganglion cells from the retina travel via the axons from each eye cross to the opposite side of the brain. Most of the ganglion cell axons go to the lateral geniculate nucleus (LGN) of the thalamus. Axons from the LGN synapse with the visual areas of the cerebral cortex. The primary visual cortex (V1) receives information from the LGN and sends information to the secondary visual cortex (V2). V1 is also known as the striate cortex located in the occipital cortex. This area of the cortex is responsible for the first stage of visual processing. People with damage to this area report no conscious vision or visual imagery, even in their dreams. The phenomenon of blindsight occurs with damage to V1. The secondary visual cortex or V2 processes visual information further and then transmits it to additional areas. The connections between V1 and V2 are reciprocal. V2 cell responds to a pattern of light in a particular orientation and most strongly to a moving stimulus. Information traveling from V1/V2 travels in two pathways. The dorsal pathway passes through the parietal cortex and helps motor system locate objects. Thus the dorsal stream processes location and orientation of objects in space and is known as the "where" pathway. The ventral pathway is the path that goes through the temporal lobe and processes object recognition. The ventral stream is known as the "what" pathway. V4 is important for the ability to perceive the color of an object despite changes in the lighting. This is called color constancy. Areas in V5 that process motion includes MT (middle temporal cortex), and an adjacent region, area MST (medial superior temporal cortex). MT and MST receive input mostly from the magnocellular path, which detects overall patterns, including movement over large areas of the visual field.

Describe the difference between parvocellular and magnocellular neurons and pathways.

Parvocellular neurons have small receptive fields and respond best to visual details and color. These cells synapse only onto cells of the LGN, which then sends information via the ventral stream Magnocellular neurons have larger receptive fields and respond best to moving stimuli. Most of these cells synapse onto cells of the LGN, but a few connect to other areas of the thalamus, sends information via the dorsal stream.

____ are chemicals that release energy when struck by light.

Photopigments

Why does the fovea provide the clearest, most detailed visual information?

Receptors are tightly packed there.

Describe the trichromatic, opponent-process, and retinex theories of color vision.

Tri-Chromatic theory of Young and Helmholtz states that color perception occurs through the relative rates of response by three kinds of cones: Short wavelength (blue), medium-wavelength (green), long-wavelength (red). According to this theory of color vision, we discriminate among wavelengths by the ratio of activity across the three types of cones. Individuals differ in regards to where the short, medium, and long-wavelength cones are distributed in the retina. Opponent-processes theory of Suggests that we perceive color in terms of paired opposites such as white-black, red-green, and yellow-blue due to excitation or inhibition of bipolar cells, each a member of a pair of complementary colors (yellow-blue, red-green, white-black Each pair has a center that responds to a particular wavelength that is maximally stimulated when hit by that wavelength of light and a surround that is inhibited. Opponent-process theory states that negative afterimages result from fatiguing a response by opponent-process cells (e.g., a cell that responds to green light becomes fatigued after prolonged stimulation, which results in a red afterimage when the green light is removed). Retinex theory states that cortex compares information from various parts of the retina to determine the brightness and color for each area to explains color and brightness constancy

A cell that responds best to a bar of light throughout a large area of its receptive field, without a strong inhibitory area at one end is most likely a:

complex cell

The law of specific nerve energies states that:

every stimulation of the optic nerve is perceived as light.

Human newborns come into the world predisposed to pay more attention to _____ than any other stationary displays.

faces

A(n) ____ cell has a strong inhibitory area at one end of its bar-shaped receptive field.

hypercomplex

Chemicals that release energy when struck by light are called:

photopigments.

Color constancy is the ability to:

recognize the color of an object despite changes in lighting.

A person with visual agnosia is unable to:

recognize visual objects.

Light from the left half of the world strikes what part of the retina?

the right half

According to the Young-Helmholtz theory, what is the basis for color vision?

three kinds of cones