Lesson 2: Begining of the Perceptual Process

Question 1

How does a tree become a perception of a tree?

Answer 1

Information about the tree (distal stimulus) is carried in light reflected from the tree and into the eye. When this light reaches the receptors in the retina, creating the proximal stimulus, it becomes transformed into electrical signals that contain information about the tree, which are transmitted to the brain, where eventually these electrical signals become transformed into a perception of the tree

Question 2

The energy within the electromagnetic spectrum that humans can perceive

Answer 2

visible light

Question 3

where does the light reflected from objects first enter the eye?

Answer 3

the pupil

Question 4

where is an image focused in the eye?

Answer 4

the cornea and the lens

Question 5

Where is a sharp image formed in the eye?

Answer 5

the retina, the network of neurons that covers the back of the eye and that contains the receptors for vision

Question 6

what are the two types of visual receptors?

Answer 6

cones and rods

Question 7

Where are the visual pigments located and what do they do?

Answer 7

located on the outer-segments of rods and cones. They are light-sensitive chemicals that react to light and trigger electrical signals.

Question 8

cones and rods are different in (3)

Answer 8

1. number
2. shape
3. distribution across the retina

Question 9

what is the fovea? and contains which receptors?

Answer 9

The point of central focus. Contains only cones

Question 10

when we look directly at an object, where does the image fall in the eye?

Answer 10

the fovea

Question 11

what is the peripheral retina? Which receptors does it have?

Answer 11

all of the retina outside the fovea. Contains both rods and cones. contains more rods than cones.

Question 12

how many cones and rods are there in the retina?

Answer 12

6 million cones
120 million rods

Question 13

What happens when functioning receptors are missing from one area of the retina?

Answer 13

Macular degeneration is a condition in which the cone-rich fovea and a small area that surrounds it are destroyed. Most common in older people. Creates blind region in central vision.

Question 14

why do we have a blind spot at 20 degrees in the eye? (2)

Answer 14

• Because there are no receptors since it is the area where the ganglion cells leave the eye to form the optic nerve.
• Brain “fills in” the place where the image disappears with a perception that matches its surrounding patterns.

Question 15

retinitis pigmentosa

Answer 15

genetic disease in which the retina breaks down. Attacks the peripheral rod receptors and results in poor vision in the peripheral visual field. Eventually, in severe cases, the foveal cone receptors are also attacked, resulting in complete
blindness

Question 16

forms and functions of the optical system?

Answer 16

lens: 20% of focusing, can change its shape to
adjust the eye’s focus for objects located at different distances.
This change in shape = ciliary muscles, which increase the focusing power of the lens (its ability to
bend light) by increasing its curvature

cornea: 80% of the eye’s focusing power, fixed in place so it
cannot adjust its focus.

Question 17

Accommodation

Answer 17

change in the lens’s shape that occurs when the ciliary muscles at the front of the eye tighten and increase the curvature of the lens so that it gets thicker

Question 18

presbyopia

Answer 18

loss of the ability to accommodate. lens hardening, weakening of ciliary muscles

Question 19

myopia/nearsightedness

Answer 19

inability to see distant objects clearly
solution = corrective lens
point of focus for parallel rays of light = in front of the retina

Question 20

Types of myopia and why?

Answer 20

1. Refractive Myopia = cornea and/or the lens bends the light too much
2. Axial Myopia = eyeball is too long

Question 21

hyperopia/farsightedness

Answer 21

point of focus for the parallel rays of light = behind the retina,
because the eyeball is too short.
solution= for young ppl- accomodation, for old ppl= corrective lenses

Question 22

Two parts of the visual pigments?

Answer 22

1. opsin
2. retinal

Question 23

isomerization

Answer 23

change in the shape of the retinal from bent to straight. Causes a chain reaction that activates thousands of
charged molecules to create electrical signals in receptors.

Question 24

Dark adaptation

Answer 24

Process of increasing sensitivity in the dark

Question 25

Rod monochromats

Answer 25

no cones due to a rare genetic defect

Question 26

visual pigment regeneration

Answer 26

process of reforming the visual pigment molecule by the retinal returning to its bent shape and becoming reattached to the opsin.

Question 27

visual pigment bleaching

Answer 27

molecule becomes lighter in color due to the change in shape and separation of the retinal from the opsin

Question 28

perception and physiology

Answer 28

1. Our sensitivity to light depends on the concentration of a
   chemical—the visual pigment
2. The speed at which our sensitivity increases in the dark
   depends on a chemical reaction—the regeneration of the
   visual pigment.

Question 29

Detached retina

Answer 29

The retina becomes detached from the pigment epithelium, a layer that contains enzymes necessary for pigment regeneration

Question 30

Monochromatic light

Answer 30

light of a single wavelenght

Question 31

How do we measure cone spectral sensitivity?

Answer 31

by having a subject look directly at a test light so that it stimulates only the cones in the fovea

Question 32

How do we measure rod spectral sensitivity?

Answer 32

measuring sensitivity after the eye is dark-adapted (so
the rods control vision because they are the most sensitive receptors) and presenting test flashes in the peripheral retina, off to the side of the fixation point

Question 33

which receptors are faster at adapting to the dark? which one is more sensitive to the dark?

Answer 33

cones = faster. maxed out at 3 to 5 minutes
rods= catches up to cones at 7 min and goes further = more sensitive. maxed out at 20-30 min.
why? because visual regeneration occurs faster in cones

Question 34

spectral sensitivity

Answer 34

eye’s sensitivity to light as a function of the light’s wavelength

Question 35

which receptors are more sensitive to short-wavelength light?

Answer 35

rods

Question 36

What is the Purkinje shift?

Answer 36

enhanced perception of short wavelengths during dark adaptation, that is the tendency for eyes to shift towards the blue and green colors of the visible spectrum

Question 37

Absorption spectrum

Answer 37

a plot of the amount of light absorbed versus the
the wavelength of the light

Question 38

How many receptors does each eye have ? and how many ganglion cells?

Answer 38

126 million R, 1 million G…. each ganglion cell
receives signals from 126 receptors

Question 39

What are the group of neurons that receive signals from the optic nerve - 2

Answer 39

1. lateral geniculate nucleus
2. visual receiving area
   both in the cortex

Question 40

electrical signals are recorded from where? and how?

Answer 40

axons, using a small electrode

Question 41

-70mV

Answer 41

resting potential, when the inside of the axon is 70mV more negative than the outside

Question 42

What do we mean by an action potential being propagated response?

Answer 42

once the response is triggered, it travels all the way down the axon without decreasing in size

Question 43

changing the stimulus intensity affects what

Answer 43

rate of firing. 500 to 800 impulses/second

Question 44

refractory period

Answer 44

the interval between the time one nerve impulse
occurs and the next one can be generated in the axon. approx 1ms

Question 45

spontaneous activity

Answer 45

Action potentials that occur in the absence of stimuli from the environment

Question 46

What does the opening of sodium channels represent?

Answer 46

An increase in the membrane’s permeability
to sodium

Question 47

What happens during the rising phase of the action potential?

Answer 47

Sodium enters the axon through channels. This increases the positive charge inside from -70mV to +40mV.

Question 48

The falling phase of the action potential?

Answer 48

sodium channels close. potassium channels open, and potassium leaves the axon. This returns the charge from +40mV to -70mv.

Question 49

The falling phase of the action potential?

Answer 49

sodium channels close. potassium channels open, and potassium leaves the axon. This returns the charge from +40mV to -70mv.

Question 50

excitatory response (depolarization)

Answer 50

occurs when the inside of the neuron becomes more positive. Increases firing rate

Question 51

inhibitory response (hyperpolarization)

Answer 51

occurs when the inside of the neuron becomes more negative. decreases firing rate

Question 52

neural circuits

Answer 52

interconnected groups of neurons within the retina

Question 53

Where do signals generated in the receptors travel to? (2)

Answer 53

1. Bipolar cells (B)
2. Ganglion cells (G)

Question 54

neurons that connect neurons across
the retina (2)

Answer 54

1. horizontal cells
2. amacrine cells

Question 55

neural convergence

Answer 55

occurs when a number of neurons synapse onto a single neuron

Question 56

what does convergence entail for rods and cones?

Answer 56

(1) the rods = more sensitive because more convergence
(2) the cones = better visual acuity because of less convergence and receptors in the fovea are packed closely together

Question 57

why is it easier to see stars if we look to its side and not straight on?

Answer 57

1. Because the star’s image falls on the rod-rich peripheral
   retina.
2. The rods have greater convergence than the cones
3. takes less light to generate a response from an
   individual rod receptor than from an individual cone receptor

Question 58

Preferential looking (PL) technique - infant visual acuity

Answer 58

Two stimuli are presented. The experimenter looks at children’s eyes to see which one they look at more. This is to determine if infants see a difference between two stimuli.

Question 59

visual evoked potential (VEP) - infant visual acuity

Answer 59

The electrical signal is recorded by disc electrodes placed on the infant’s head over the visual cortex. For this technique, researchers alternate a gray field with a grating or checkerboard pattern. If the stripes or checks are large enough to be detected by the visual system, the visual cortex generates an electrical response called the visual evoked potential

Question 60

why do infants have poor acuity? (2)

Answer 60

1. infant’s cones are spaced far apart
2. visual area of the brain is poorly developed at birth,
   with fewer neurons and synapses than in the adult cortex