Sensation And Perception Ch. 2 Study Questions

Front 1

Describe the two ways used to conceptualize light.

Back 1

One way to conceptualize light is to think of it as a wave. Another way is to think of it as a stream of photons, tiny particles, each consisting of one quantum of energy.

Front 2

Describe the difference between light that is reflected and light that is transmitted.

Back 2

Reflected light occurs when a ray of light strikes a light-colored surface and then bounces back to its point of origin. Transmitted light occurs when light is neither reflected nor absorbed by a surface. It occurs when the surface is transparent, such as in the case of a window. In this case, light is passed through the surface.

Front 3

What is the purpose of the cornea?

Back 3

The cornea is a transparent surface on the exterior of the eye. It protects the eye from the outside world. Being transparent, it allows the light to be transmitted through it and into the eye.

Front 4

What is the purpose of the retina?

Back 4

The retina is a light-sensitive membrane in the back of the eye that contains rods and cones, which receive an image from the lens and send it to the brain through the optic nerve.

Front 5

How does the process of accommodation take place in the eye?

Back 5

Accommodation takes place in the lens of the eye. The lens changes its refractive power by changing its shape. This causes the eye to be able to focus on a given object.

Front 6

What is astigmatism and how can it be fixed?

Back 6

Astigmatism is a visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye, usually the cornea. It can be fixed by wearing lens that have two focal points (that provide different amounts of focusing power in the horizontal and vertical planes).

Front 7

Why are photoreceptors important in the process of seeing?

Back 7

Photoreceptors are the cells that make up the backmost layer of the retina. They are sensitive to light, and as soon as they sense it, they can cause neurons in the intermediate layers to fire action potentials. Photoreceptors are important in the process of seeing because by causing neurons to react to light they help continue the process of seeing.

Front 8

What are rods and cones?

Back 8

Rods and cones are photoreceptors present in the retina. Rods are specialized for night vision, while cones are specialized for daylight vision, fine visual acuity and color.

Front 9

Explain what happens in the process of hyperpolarizaion.

Back 9

Hyperpolarization is an increase in membrane potential where the inner membrane surface becomes more negative than the outer membrane surface. This process is one in a sequence of events that occur once light is sensed by the photoreceptors.

Front 10

Why can't rods signal differences in color?

Back 10

Rods cannot signal differences in color because they only have one type of photopigment. Cones, on the other hand have three types of photopigments, which help them differentiate between colors.

Front 11

What is the role of the horizontal cells?

Back 11

Horizontal cells are specialized retinal cells that contact both retinal and bipolar cells. They help in the process of lateral inhibition, which allows the signals that reach retinal ganglion cells to be based on differences on activations between nearby photoreceptors.

Front 12

What is visual acuity?

Back 12

Visual acuity is a measure of the finest detail that one can resolve.

Front 13

What is the difference between an "ON" midget bipolar cell and an "Off" midget bipolar cell?

Back 13

An "ON" midget bipolar cell is a small cone bipolar cell that depolarizes in response to an increase in light intensity. An "OFF" midget bipolar cell is a small cone bipolar cell that depolarizes in response to a decrease in light intensity. These two cells have opposite reactions to light.

Front 14

What is the receptive field?

Back 14

The receptive field is the region in space in which stimuli will activate a neuron. Receptive fields vary in size.

Front 15

Why is the center-surround organization of the visual system important?

Back 15

The center-surround organization of the visual system is important because it allows for a sensitivity in contrast to be perceived. For instance, ganglion cells are most sensitive to differences in the intensity of light in the center and in the surround, and they are relatively unaffected by the average intensity of light. This is useful because the average intensity of light falling on the retina will vary a lot, depending on whether the observer is indoors, outdoors, etc.

Front 16

What is a filter and how is it important in vision?

Back 16

A filter is an acoustic, electrical, electronic, biological, or optical device, instrument, or computer program that allows the passage of some frequencies or digital elements and blocks others. Filter is important in vision because it allows the transformation of the raw image into a representation by the brain. The filter highlights certain important visual information while it eliminates other unimportant information.

Front 17

What are some consequences of the differing sizes of parasol and midget receptive fields?

Back 17

Midget cells have smaller receptive fields than parasol cells have at all eccentricities. This allows the parasol cells to respond to a larger portion of the visual field. In addition, they are much more sensitive to visual stimuli under low lighting conditions than midget cells. Midget cells, on the other hand, provide finer resolution (greater acuity) than parasol cells can, as long as there is enough light for them to operate.

Front 18

Explain how the pupil adapts to dark and light conditions.

Back 18

The pupil has the ability to dilate and constrict, depending on the amount of light in the area. For instance, under well-lit conditions, the pupil tends to constrict. Under dark conditions, the pupil dilates, to allow more light into the eye.

Front 19

Explain why it is that we are generally not bothered by variations in overall light levels

Back 19

We are generally not bothered by variations in overall light levels because we have several mechanisms for regulating how much light enters the eye. One mechanism is the pupil size. Another is the photopigment regeneration rates. Yet another is the rod/cone dichotomy. Finally, the neural circuitry of the retina itself helps stabilize external light variations.

Front 20

Describe the family of diseases known as retinitis pigmentosa.

Back 20

Retinitis pigmentosa is a family of hereditary diseases that involve the progressive death of photoreceptors and degeneration of the pigment epithelium. The rods are usually affected before the cones. Therefore people suffering from this disease first notice vision problems in their peripheral vision and under low light conditions (where the rods play the dominant role in collecting light).

Front 21

Describe what happens to the visual field of a patient with retinitis pigmentosa

Back 21

20.Patients suffering from retinitis pigmentosa typically exhibit an overall shrinkage of their visual fields, as well as "ring scotomas," bands of blindness between the relatively normal central fields and the periphery.