1. Major Sensory and Perceptual Systems SenseSource of information SeeingLight HearingSound BalanceGravity and acceleration TouchPressureTemperature PoseJoint position and muscle stress Smell & TasteChemical structure

2. 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.

3. 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

4. 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

5. 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

6. 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

12. Comparison patch

13. 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.

14. 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

16. 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

17. Natural reflectance spectra Regan et al. (2001)

19. 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

20. Microscopy, Imaging, Assays Single and multi-unit recording Optical, Calcium, Functional-MR imaging Event related potentials (ERPs) Lesion, Knockouts, etc.

21. objective subjective identification estimation description Behavioral Approaches feedback no feedback A B C

22. 2AFC Task

24. Descriptive models Normative (optimal) models Information processing models Physiological models Computational/Mathematical Approaches

25. Convolve with point spread Multiply by transmittance Sum over each receptor aperture Multiply by absorption spectrum and sum A Physiological Model of Receptor Responses

26. 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