SENSATION AND PERCEPTION CHAPTER 5 1 LEARNING OBJECTIVES Describe transduction, sensation, and perception for the following sensory systems: Vision Audition (hearing) Skin and body Touch Pain Chemical Olfaction (smell) Gustation (taste) 2 1
INTRODUCTION Sensation Awareness due to the stimulation of a sense organ Basic registration of a physical stimulus by a receptor Bottom-up processing Perception Organization, identification, and interpretation of a sensation in order to form a mental representation Top Down processing Can you have sensation without perception? Can you have sensation without perception? INTRODUCTION Transduction Conversion of physical stimuli in the world to electrical signals in the central nervous system (CNS) 4 2
INTRODUCTION Sensation and perception are essential for survival and reproduction of the species We need to know what is around us, interpret the data, and make decisions Sensation and perception are the basis for how we study psychological processes like consciousness, memory, emotion, and decision making In terms of consciousness, sensation and perception appear to be seamless events. But they are not. Receptors break complex information into parts, relay the information to the brain, which reassembles the information 5 OUTLINE Psychophysics Vision Audition (hearing) Skin and body Touch Pain Chemical Olfaction (smell) Gustation (taste) 6 3
PSYCHOPHYSICS Psychophysics Physical stimuli versus the experience Early introspection failed because of memories and emotions Gustav Fechner Gustav Fechner 7 SENSORY THRESHOLDS Absolute threshold: smallest quantity of physical energy that can be detected reliably (50% of time) by an observer. Difference threshold: smallest difference in stimulation that can be detected when 2 stimuli are presented 4
JUST NOTICEABLE DIFFERENCE/ WEBER S LAW A just noticeable difference in stimulation is a constant proportion of the original stimulus The greater the original stimulus, the more it must be increased or decreased for the difference to be noticeable. OUTLINE Psychophysics Vision Audition (hearing) Skin and body Touch Pain Chemical Olfaction (smell) Gustation (taste) 10 5
VISION - STIMULUS 11 VISION - RECEPTORS 12 6
VISION - TRANSDUCTION Photopigments cause chemical reaction Action Potential Convergence allows many receptors to use 1 neuron for afferent signaling 13 VISION - TRANSDUCTION Center-Surround receptive fields allow for more than 1 signal to be sent by 1 afferent neuron Either excitatory or inhibitory for each region This center-surround configuration is important in the detection of edges 14 7
VISION - CORTEX 15 BLINDSIGHT Weiskrantz et al., 1974 Patient D.B. had severe headaches Surgical removal of arteriovenous malformation in occipital lobe Produced scotoma: partial loss of vision in a part of the visual field 8
CONNECTIONS OF VISUAL SYSTEM BLINDSIGHT 18 9
VISION: PERCEPTION Top Down processing Bottom Up processing 19 VISION: PERCEPTION Write down: what are the 5 objects to the left? 10
VISION: PERCEPTION Again, write down the objects to the left. VISION: PERCEPTION How many did you get correct in your first list and your second list? If you had incorrect guesses explain why? How did your brain do this visual perception task? 11
OUTLINE Psychophysics Vision Audition (hearing) Skin and body Touch Pain Chemical Olfaction (smell) Gustation (taste) 23 AUDITION - STIMULUS Air pressure changes that unfold over time Three dimensions for the stimulus Frequency of the sound high versus a low sound Amplitude loudness of a sound Complexity how many frequencies are mixed together 400 Hz 1500 Hz 24 12
AUDITION - RECEPTORS 25 http://www.youtube.com/watch? NR=1&feature=endscreen&v=0jyxhozq89g http://www.youtube.com/watch? v=petrigtenoc&feature=related http://www.youtube.com/watch?v=dyenmlufauw 26 13
AUDITION - TRANSDUCTION The tectorial membrane bounces on the hair cells in rhythmic fashion to physically open ion channels and produce action potentials in the cochlear nerve Receptors in the cochlea are tuned to send action potential only for certain frequencies from high (outermost) to low (innermost). More receptors/ afferent signals for 500-5,000 Hz (human speech) 27 14
COCHLEAR IMPLANTS AUDITION - CORTEX There are specialized brain regions for complex sounds and language. (secondary auditory cortex = language & music) Pink = primary auditory cortex Green = language comprehension area Blue = language production area Yellow = Supramarginal gyrus 30 15
IN CLASS ACTIVITY You are a doctor/neurologist and a patient comes in complaining that he can t see. What might be the problem? How would you test to see if that was the case? 31 OUTLINE Psychophysics Vision Audition (hearing) Skin and body Touch Pain Chemical Olfaction (smell) Gustation (taste) 32 16
SKIN RECEPTORS Pacinian corpuscles touch, high frequency vibration Free-nerve endings - temperature, pain Meissner's corpuscles pressure, low frequency vibration Merkel's disks - pressure Ruffini's corpuscles stretch, vibration (not pressure) 33 TOUCH - TRANSDUCTION Mechanoreceptors (Meisners, Merkel, Ruffini, Pacinian, and Hair cells) physical movement opens ion channels to depolarize the neuron and send action potentials to the brain Bare or Free Nerve endings detect increases or decreases in temperature and chemicals released in response to tissue damage (like histamines) The nerve impulses make a primary synapse in the spinal cord before moving to the thalamus and then the CNS Allows for a modification of the signal Allows for a motor reflex 34 17
PAIN - GATE CONTROL THEORY Central control Large Input from Periphery Small Gate control system - + + SG T - + - Action system OUTLINE Psychophysics Vision Audition (hearing) Skin and body Touch Pain Chemical Olfaction (smell) Gustation (taste) 36 18
CHEMICAL SENSES OLFACTION Physical stimulus is aerosol chemicals that are inhaled 2 pathways Orthonasal (nose) Retronasal (throat) Transduction works like transmitter system (lock and key) 1000 different types and odorant often more than 1 receptor (pattern) 37 WHY DO SMELLS MAKE US REMEMBER? 19
CHEMICAL SENSES - OLFACTION Projections to the limbic system and frontal lobe closely link smell with memories and emotions Only sense that does not go through thalamus Evolutionary pressure to remember harmful stimuli strong long-term memory mechanism Olfaction is a powerful component to flavor linked with gustation (taste). As people age they report that food loses its taste. What they are experiencing is a loss of smell and not taste Black normal nose Grey pinched nose 39 OUTLINE Psychophysics Vision Audition (hearing) Skin and body Touch Pain Chemical Olfaction (smell) Gustation (taste) 40 20
CHEMICAL SENSES - GUSTATION Stimuli are chemicals that dissolve in saliva Receptors are taste buds found on the papillae of the tongue Transduction occurs when chemicals stimulate receptors Each taste sweet, salt, bitter, sour, umami has different mechanism 41 ARE YOU A SUPER TASTER? <15 less than average 15-35 average > 35 supertaster (25% population) 21
CHEMICAL SENSES - GUSTATION Projections to a number of areas Orbitofrontal flavor perception Amygdala cravings and aversions Somatosensory cortex tongue Hypothalamus hunger and satiety 43 IN CLASS ACTIVITY: VISION PROBLEMS Light not getting into eye or focusing (problem with cornea, pupil, iris, lens) Problem detecting light rays and transferring to action potentials (damaged rods and cones/retina/fovea, bipolar, ganglion cells) Problem transmitting that information to the brain (damaged optic nerve, damaged optic chiasm, damaged primary visual cortex [blindsight]) 22