Perception

Question 1

Action Potential

Answer 1

Communication within neurons is done via electrical signals.
• Neurotransmitters affect the post-synaptic neuron by changing ion
distributions and resulting electrical potentials.
• If the post-synaptic cell reaches threshold, an action potential is fired and
propagates down the axon, releasing neurotransmitter that affects the next
neuron.

Question 2

Receptive Field

Answer 2

• In single-cell recording, a neuron’s firing rate, or frequency of action
potentials, is recorded as various kinds of visual stimuli are presented
to the subject.
• Using these methods, researchers map out the receptive field – the
kinds of stimuli to which the neuron best responds – for various cells
of the visual system.

Question 3

Center-Surround Organization

Answer 3

• The receptive fields of the bipolar cells, ganglion cells,
and cells in the lateral geniculate nucleus have a
center-surround organization.

Question 4

feature detection (detectors)

Answer 4

Bottom-up (or data-driven) processing
• Perceptual information triggers a response in feature detectors.
• Feature detectors in turn excite and inhibit complex-pattern detectors.
• Top-down (or concept-driven) processing
• Broader patterns of knowledge and expectation trigger responses in complex
pattern detectors.
• Complex pattern detectors in turn excite and inhibit feature detectors.

Question 5

Neural Circuits

Answer 5

• Receptors:
• Cell bodies:
• Excitatory synapses:
• Inhibitory synapses:

One unit of light
produces one unit of response
•A ganglion needs 10 response
units
• The ganglion has to fire in order
to perceive the light

Top: Linear
• No convergence
• Bottom:
• Convergent
• All excitatory

One unit of light
produces one unit of response
•A ganglion needs 10 response
units
• The ganglion has to fire in order
to perceive the light

Convergent circuit
• Receptors 3, 4, and 5 are excitatory on B
• Receptors 1, 2 (A) and 6, 7 (C) are inhibitory on B

Question 6

Simple Cells

Answer 6

Like retinal and LGN cells
have excitatory and
inhibitory fields
• Not center
-surround
• Arranged side
-by
-side
• Responds best to bars of
light in particular
orientations

Question 7

Complex Cells

Answer 7

• Also respond best to bars
of light in a particular
orientation
• However, bar has to move
across entire receptive
field

Question 8

What and where systems

Answer 8

Processing of several aspects of the stimulus
simultaneously is called parallel processing. The
brain divides a visual scene into subdivisions such
as color, depth, form, movement, etc.

These secondary visual areas lead to two major
processing streams, the what system and the where
system
• Entire visual system from beginning to end is
engineered in two distinct pathways

The what system:
• Is concerned with the identification of objects
• Involves an occipital-temporal pathway
• Damage to this system can result in visual agnosia
• The where system:
• Is concerned with determining the locations of objects
and guiding our actions in response
• Involves an occipital-parietal pathway
• Damage to this system can result in problems with
reaching for seen objects