Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Major Sensory and Perceptual SystemsSense Source of informationSeeing LightHearing SoundBalance Gravity and accelerationTouch PressureTemperature TemperaturePose Joint position and muscle stressSmell & Taste Chemical structureOverarching PrincipleSensory 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 TransductionTransduction = 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 energyThere 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 categoriesStimulus energymVTimemVTimeReceptor potentialAction potentialsTRANSDUCTIONStimulus 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 potentialsReceptors 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 BrainTransmission Neuron (Spiral Ganglion Cell)To Spinal CordTouch Receptor (Dorsal Root Ganglion Cell)Receptor portionTransmission portionComparison patchDifficult Problems for Perceptual SystemsContext 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 SystemsNatural tasksNatural scene statisticsAnatomyResponses of and within individual neuronsResponses of neural populationsPerceptual/behavioral performanceMathematical and computational modelingApproaches to Understanding Sensory SystemsNatural tasksNatural scene statisticsAnatomyResponses of and within individual neuronsResponses of neural populationsPerceptual/behavioral performanceMathematical and computational modelingNatural reflectance spectraRegan et al. (2001)Approaches to Understanding Sensory SystemsNatural tasksNatural scene statisticsAnatomyResponses of and within individual neuronsResponses of neural populationsPerceptual/behavioral performanceMathematical and computational modelingMicroscopy, Imaging, AssaysSingle and multi-unit recordingOptical, Calcium, Functional-MR imagingEvent related potentials (ERPs)Lesion, Knockouts, etc.objectivesubjectiveidentificationestimationdescriptionBehavioral Approachesfeedbackno feedbackABC2AFC TaskDescriptive modelsNormative (optimal) modelsInformation processing modelsPhysiological modelsComputational/Mathematical ApproachesConvolve withpoint spreadMultiply by transmittanceSum over each receptor apertureMultiply by absorption spectrum and sumA Physiological Model of Receptor ResponsesPerception 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