Lecture 4

Question 1

Describe E2 of dark adaptation

Answer 1

Participant fixates directly on test light

• This stimulates (and thus isolates the
effect of) only cones, because that is the
only kind of receptor in the fovea

• Results show that sensitivity increases for
three to four minutes and then levels off
• The first stage of the dark adaptation
curve can be attributed to this

• only cones

Question 2

Describe E3 of dark adaptation

Answer 2

Accomplished by using a rod
monochromat participant (to isolate
the effect on rods)

• Results show that sensitivity increases
for about 25 minutes and then levels
off

• The second stage of the dark
adaptation curve can be attributed to
this

Question 3

Describe visual pigment regeneration

Answer 3

Process needed for transduction:
• Retinal molecule changes shape
• Opsin molecule separates
• The retina shows visual pigment
bleaching
• Retinal and opsin must then
recombine in a process called
regeneration, in order to be
capable of responding to light again

Question 4

Describe spectral sensitivity

Answer 4

the
sensitivity of rods and cones to different
parts of the visible spectrum

Question 5

Describe the difference between threshold and sensitivity

Answer 5

Threshold and sensitivity mean
something similar but are essentially
reciprocal concepts (1/threshold =
sensitivity)

Question 6

How do rods and cones differ in terms of their spectral sensitivity?

Answer 6

Rods are more sensitive to short-wavelength light (most sensitivity at 500 nm)

• Cones are most sensitive at 560 nm (on average, though see the next slide…)

Question 7

What is a Purkinje shift.

Answer 7

enhanced sensitivity to short wavelengths during dark
adaptation when the shift from cone to rod vision occurs

Question 8

How do rods and cones send signals vertically?

Answer 8

through:
• Bipolar cells
• Ganglion cells

Question 9

How are signals sent horizontally?

Answer 9

Between receptors by horizontal cells
• Between bipolar and between ganglion
cells by amacrine cells

Question 10

Describe the three traits of rods compared to cones in terms of neural convergence

Answer 10

• Are more sensitive to light
• Take less light to respond
• Have greater convergence

Question 11

Describe convergence for cones

Answer 11

• All-cone foveal vision results in high visual acuity
• This relates to the difference in convergence, in which fewer cones are
connected to any one ganglion cell (i.e. have less convergence)
• This kind of wiring allows cones to better discriminate detail (as compared
to rods)

Question 12

What are visual receptive fields?

Answer 12

the retinal region over which a given cell in the
visual system can be influenced (excited or inhibited) by light

Question 13

What are single cell responses?

Answer 13

stimulus is
presented to retina and response
of cell is measured by an electrode

Question 14

What are the 2 types of visual receptive fields?

Answer 14

Excitatory-centre-inhibitory surround
• Inhibitory-centre-excitatory surround

Question 15

What is centre surround antagonism?

Answer 15

Intermediate responses when both areas are
stimulated (centre-surround antagonism)

Question 16

Describe the visual pathway from the retina to the brain

Answer 16

• Signals from the retina exit the eye through
the optic nerve and then…

• Arrive first at the lateral geniculate
nucleus (LGN)

• Are then sent along to the primary visual
receiving area in the occipital lobe (the
striate cortex, beginning with area V1)

• Are then sent through two pathways to the
temporal lobe and the parietal lobe (the
dorsal and ventral streams)

• And finally arrive at the frontal lobe

Question 17

Describe the superior colliculus

Answer 17

receives some signals form the eye and and is
important for controlling eye-movements
• Accounts for ~10% nerve fibres leaving the eye

Question 18

Describe LGN

Answer 18

The LGN accounts for ~ 90% nerve fibres leaving the eye

• LGN cells have centre-surround receptive fields (like in the retina)

• More ‘information’ (a larger signal) is sent from the eye to the LGN,
as compared to what is passed along from the LGN to V1
(suggesting the LGN may regulate, or filter, what information is
passed along to V1)

• The LGN also receives more information from the cortex than it
sends to the cortex, suggesting a backward flow of information
that may constitute a feedback mechanism