Transcript NS_intro_sensory

Major Sensory and Perceptual Systems
Sense
Source of information
Seeing
Light
Hearing
Sound
Balance
Gravity and acceleration
Touch
Pressure
Temperature
Temperature
Pose
Joint position and muscle stress
Smell & Taste
Chemical structure
Overarching Principle
Sensory and perceptual systems (including their associated
mechanisms for learning and plasticity) evolve in the service
of obtaining information about the environment that is
relevant for the tasks the organism must perform in order to
survive and reproduce.
Corollary: The design of the sensory and perceptual
systems is determined by the tasks it performs, by the
physical/statistical properties of the environment, and by
various biological factors/constraints.
Sensory and Perceptual Processing Starts with Transduction
Transduction = the transformation of physical energy
into a neural code (changes in membrane potential,
generation of action potentials)
Transduction is the responsibility of specialized
neurons called “receptors”
A receptor is specialized to respond best to one
particular type of stimulus energy
There Are 4 Basic Types of Receptor Cells
Mechanoreceptive
Somatosensory (touch)
Proprioceptive (muscle and joint receptors)
Vestibular
Auditory
(Lateral line)
Chemical
Olfaction
Pain receptors
Taste
may fall into any
Thermal
of the first three
Temperature
categories
Electromagnetic
Vision
(Electroreception)
(Infrared detection)
Stimulus energy
TRANSDUCTION
Receptor potential
mV
Time
Action potentials
mV
Time
Stimulus triggers a receptor potential in the receptor; receptor potential triggers
action potentials in the transmission neuron (or its own axon if it has one); the
CNS only sees the action potentials
Receptors can have axons which transmit signals to the
central nervous system (e.g., somatosensory, olfaction), or
they can make a synapse on a second, separate
“transmission neuron”, which relays the signal to the
central nervous system (e.g., audition, vision)
Receptor portion
Touch Receptor
(Dorsal Root
Ganglion Cell)
Transmission
portion
Auditory Receptor (Hair Cell)
Transmission Neuron (Spiral Ganglion
Cell)
To Brain
To Spinal Cord
Comparison patch
Difficult Problems for Perceptual Systems
Context problem
Objects often appear in a complex and varying context of other
objects, making recognition of objects difficult.
Category complexity problem
The specific things that define a category are often quite different,
making categorization difficult.
Missing dimensions problem
Vision: The images in the eyes have two-dimensions in space and
one dimension in time. The third dimension in space (depth) is lost
and must be reconstructed.
Audition, Olfaction: The signals reaching the ears and nose have one
dimension in time. Any other dimensions must be reconstructed.
Approaches to Understanding Sensory Systems
Natural tasks
Natural scene statistics
Anatomy
Responses of and within individual neurons
Responses of neural populations
Perceptual/behavioral performance
Mathematical and computational modeling
Approaches to Understanding Sensory Systems
Natural tasks
Natural scene statistics
Anatomy
Responses of and within individual neurons
Responses of neural populations
Perceptual/behavioral performance
Mathematical and computational modeling
Natural reflectance spectra
Regan et al. (2001)
Approaches to Understanding Sensory Systems
Natural tasks
Natural scene statistics
Anatomy
Responses of and within individual neurons
Responses of neural populations
Perceptual/behavioral performance
Mathematical and computational modeling
Microscopy, Imaging, Assays
Single and multi-unit recording
Optical, Calcium, Functional-MR imaging
Event related potentials (ERPs)
Lesion, Knockouts, etc.
Behavioral Approaches
A
B
C
description
feedback
objective
identification
no feedback
subjective
estimation
2AFC Task
Computational/Mathematical Approaches
Descriptive models
Normative (optimal) models
Information processing models
Physiological models
A Physiological Model of Receptor Responses
Convolve with
point spread
Multiply by
transmittance
Sum over each
receptor aperture
Multiply by absorption
spectrum and sum
Recurrent Themes
Perception is a very complex process.
Perception generally involves the integration of many
sources of information most of which are not very
reliable.
There are many approaches to the study of perceptual
systems and each has made important contributions to
our understanding.