NEUR 2600 Lecture Notes - Lecture 9: Retinal Ganglion Cell, Occipital Lobe, Magnocellular Cell
CHAPTER 9: HOW DO WE SENSE, PERCEIVE, AND SEE THE WORLD?
● Nature of sensation and perception
○ The only input our brain receives from the “real” world is a series of action
potentials passed along the neurons of our various sensory pathways
■ How nerves can turn energy, such as light waves, into nerve impulses is
understood
■ The pathways those nerve impulses take to reach the brain are also
known
○ Less well understood is how we perceive one set of nerve impulses as a
representation of the world
○ Sensory receptors
■ Specialized cells that transduce (convert) sensory energy (e.g., light) into
neural activity
■ Each sensory system’s receptors are designed to respond only to a
narrow band of energy
● Vision: light energy produces chemical energy
● Auditory: air pressure produces mechanical energy
● Somatosensory: mechanical energy
● Taste and olfaction: chemical molecules
■ Receptive field
● Specific part of the world to which a sensory receptor organ
responds
○ Sample sensory information and help locate sensory
events in space
● Optic flow
○ Stream of visual stimuli that accompanies an observer’s
forward movement through space
● Auditory flow
○ Change in sound heard as a person and a sound source
pass each other
● Each photoreceptor neuron has a unique receptive field that
partially overlaps adjacent fields
■ Receptor density and sensitivity
● Density is important for determining the sensitivity of a sensory
system
○ Example: more tactile receptors on the fingers than on the
arm
● Differences in receptor density determine the special abilities of
many animals
○ Example: olfactory ability of dogs
■ Neural relays
● All receptors connect to the cortex through a sequence of three or
four intervening neurons
○ Information can be modified at various stages in the relay,
allowing the sensory system to mediate different
responses
● There is no straight-through, point-to-point correspondence
between one neural relay and the next
○ A recording of activity in each successive relay
○ Sensory neural relays are central to the hierarchy of motor
responses in the brain
○ Sensory coding representation
■ Sensory information is encoded by action potentials that travel along
peripheral nerves to the CNS
● How do action potentials encode the different kinds of sensations
(e.g., vision and touch)
● How do they encode the features of particular sensations (e.g.,
purple and blue)
■ Presence of a stimulus can be encoded by an increase or decrease in
discharge rate
● Increase or decrease can encode stimulus intensity
■ How do action potentials encode various kinds of sensations (e.g., vision
and touch)
■ The answer to this is more complex
● Different sensations are processed in different areas of the cortex
● We learn to distinguish the senses through experience
● Each system has distinct wiring set up at all levels of neural
organization
■ The neocortex represents the sensory field of each modality- vision,
hearing, touch, smell, and taste- as a spatially organized neural
representation of the external world
● Topographic map is a neural-spatial representation of the body or
of the areas of the sensory world perceived by a sensory organ
● In mammals, each sensory system has at least one primary
cortical area
● These may project to secondary areas
○ Perception
■ Sensation
● Registration of physical stimuli from the environment by the
sensory organs
■ Perception
● Subjective interpretation of sensations by the brain
● Our visual experience is not an objective reproduction of what is
out there; rather it is a subjective construction of reality that is
manufactured by the brain
● The visual system’s functional anatomy
○ Vision is our primary sensory experience
○ Far more of the human brain is dedicated to vision than to any other sense
○ Understanding the visual system’s organization is therefore key to understanding
human brain function
○ Visible light and the structure of the eye
■ Light is electromagnetic energy that we see
■ Range of electromagnetic energy visible to humans
● About 400 nanometers (violet) to 700 nanometers (red)
● Nanometer (nm): one-billionth of a meter
Document Summary
The only input our brain receives from the real world is a series of action potentials passed along the neurons of our various sensory pathways. How nerves can turn energy, such as light waves, into nerve impulses is understood. The pathways those nerve impulses take to reach the brain are also known. Less well understood is how we perceive one set of nerve impulses as a representation of the world. Specialized cells that transduce (convert) sensory energy (e. g. , light) into neural activity. Each sensory system"s receptors are designed to respond only to a narrow band of energy. Specific part of the world to which a sensory receptor organ responds. Sample sensory information and help locate sensory events in space. Stream of visual stimuli that accompanies an observer"s forward movement through space. Change in sound heard as a person and a sound source pass each other. Each photoreceptor neuron has a unique receptive field that partially overlaps adjacent fields.
