Lecture 9 Study Guide

Question 1

the way neural convergence patterns form basic center-surround receptive fields in the retina.

Answer 1

Visual field mapping of receptive field.

–>

Pattern of activation on retina.

–>

Ganglion cell action potentials.

Question 2

the relationship of visual fields for each eye to the path retinal ganglion cell
axons take to layers of lateral geniculate nucleus (LGN)

Answer 2

Approximately 1 million
ganglion cells send axons out of each retina. These axons form the optic nerve.

• Approximately 10% of these go to the superior colliculus, to 
aid with orienting and 
multisensory responses. 90% 
go to the lateral geniculate 
nucleus (LGN) of the thalamus. 

• About 900,000 ganglion axons go to each LGN; about 360,000 LGN axons (40%) go to visual cortex.

Question 3

the basic organization

and function of LGN (e.g. What information is kept separated and how?).

Answer 3

Each LGN has six layers

Each LGN receives signals from both eyes, but the signals from each eye are
sent to different layers.

each (half) eye sends
signals to both LGNs, but the
information from each eye is kept segregated.

LGN regulates (processes) neural information from the retina and cortex before passing it to the primary visual 
cortex (V1). (More signal comes from the cortex than the eyes. This is top-down process information.)

Question 4

the concept of retinotopic mapping and where it exists.

Answer 4

each place on the retina corresponds to a place on the LGN

The receptive field on the retina influences neurons throughout the visual system.

LGN, V1

Retinotopic maps retained in
the visual cortex.

The information stays spatially segregated and organized.

Question 5

the receptive field properties of neurons in retina, LGN, and V1.

Answer 5

Responses properties of LGN cells are similar to those of
the retinal ganglion cells. Both have center surround
receptive fields.

Question 6

the role hierarchical neural convergence plays in producing the functions of feature detectors (i.e. simple, complex and end-stopped cells) in V1.

Answer 6

cells in the cortex respond
differently than cells in retina and LGN!

receptive fields –> center-surround cells –> simple cells –> complex cell –> end stopped cells (moving, bars of light, certain length and detecting corners)

Question 7

describe the process of selective adaptation in a feature detector and how this is used experimentally.

Answer 7

Fatigue or adaptation to stimulus results in two main effects:

– The neural firing rate will decrease.

– The same neurons will fire less when a similar stimulus
is immediately presented again.

experiment:

• Measure sensitivity to range of one stimulus characteristic (i.e. contrast of vertical bars).
• Adapt to that characteristic by extended exposure (1-2 min.)
• Re-measure the sensitivity to range of the stimulus characteristic (how much more contrast needed for detection?)
• Psychophysical curve should show selective adaptation for specific orientation if neurons are tuned to this characteristic.

This psychophysics experiment (Marr’s computational level 1) shows that perception matches the cellular firing patterns seen in single-cell recordings
(Marr’s implementation level 3)

Question 8

how cortical magnification affects acuity in a specific area of the retina.

Answer 8

Using functional magnetic 
resonance imaging (fMRI), it has 
been found that the fovea has 
greater representation in the 
striate cortex (V1) than 
proportionally anticipated. 

Fovea accounts for .01% of retina
– Signals from fovea account for 8% to 10% of the visual cortex
– This provides additional
processing for high-acuity tasks.

Items in the center of foveal
vision will have greater
representation in V1.

• This facilitates greater
acuity for detail and feature
processing.

• More cortical processing for
areas of greater functional
importance.

Question 9

Visual Field organization

Answer 9

Items in the left visual field go the right side of both retinas.

• Signals from the right side of both retinas go to the right lateral geniculate nucleus (LGN).

Question 10

How are end-stopped cells formed?

Answer 10

Made by converging signals from complex cells within striate cortex (V1).

Question 11

experience dependent plasticity

Answer 11

Animals are reared in environments that contain only certain types of stimuli.

behavioral and neural responses
showed the development of neurons specific to the environmental stimuli
(and absence of cells responded to opposite orientation).