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 Taste

Thermal Temperature

Electromagnetic Vision (Electroreception) (Infrared detection)

Pain receptors may fall into any of the first three categories

Stimulus energy

mV

Time

mV

Time

Receptor potential

Action potentials

TRANSDUCTION

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)

Auditory Receptor (Hair Cell)

To Brain

Transmission Neuron (Spiral Ganglion Cell)

To Spinal Cord

Touch Receptor (Dorsal Root Ganglion Cell)

Receptor portion

Transmission portion

Comparison patch

Difficult Problems for Perceptual Systems

Context problemObjects often appear in a complex and varying context of other objects, making recognition of objects difficult.

Category complexity problemThe specific things that define a category are often quite different, making categorization difficult.

Missing dimensions problemVision: 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.

objective

subjective

identification

estimation

description

Behavioral Approaches

feedback

no feedback

A B C

2AFC Task

Descriptive models

Normative (optimal) models

Information processing models

Physiological models

Computational/Mathematical Approaches

Convolve withpoint spread

Multiply by transmittance

Sum over each receptor aperture

Multiply by absorption spectrum and sum

A Physiological Model of Receptor Responses

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.

Recurrent Themes