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Chapter 5 Lecture Notes PSYA01

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University of Toronto Scarborough
Steve Joordens

CHAPTER 5 SENSATION PSYA01y Vision evolved to provide distal sensory control of the movements that the animal makes In order to survive and reproduce in that world Milner and Goodale 1996p11 y Our auditory sense has more time to process signalsy Because they are attuned to different aspects of our world the senses contribute to the richness of experiencey Given the role that speech plays in human culture audition is extremely important for social behavior With vision it provides information about distant events as does the sense of smell which can tell us about sources of aromatic molecules far upwind y Body senses are closely tied to our own movements Information from specialized organs in the inner ear and from receptors in the muscles and joints is actually produced by our own movements This information helps us maintain our balance as we engage in our everyday activities SENSORY PROCESSING y Sensation detection of simpleelementary properties of stimuli such as brightness color warmth and sweetness y Perception detection of the more complex properties of a stimulus including its location and nature involves learning detection of objects both animate and inanimate their locations their movements and their backgrounds y Eg Sensation seeing the color redPerception seeing a red apple y Psychologists used to believe that perceptions depended heavily on learning whereas pure sensations involved innate prewired physiological mechanisms y Research has shown that experience is essential to the development of some of the most elementary features of sensory systems Transduction y The only sense receptors that the brain possesses detect such things as temperature and salt concentration of the blood and these receptors cannot inform it about what is going on outside y Useful actions require information about the external world which is gathered by the sense organs located outside the brain y Sense organs detect stimuli provided by light sound odor taste or mechanical contact with the environment Information about these stimuli is transmitted to the brain through neural impulsesaction potentials carried by the axons in sensory nerves y The task of sense organs is to transmit signals to the brain that are coded in such a way as to represent faithfully the events that have occurred in the environment The task of the brain is to analyze this information and reconstruct what has occurred y Transduction literally leading across the process by which sense organs convert energy from environmental events into neural activity conversion of physical stimuli into changes in the activity of receptor cells of sensory organsEach sense organ responds to a particular form of energy given off by an environmental stimulus and translates that energy into neural firing to which the brain can respond y Receptor cells neurons that directly respond to a physical stimulus such as light vibrations or aromatic molecules They release chemical transmitter substances that stimulate other neurons thus altering the rate of firing of their axonsy In somatosenses body senses dendrites of neurons respond directly to physical stimuli without the intervention of specialized receptor cells However some of these neurons do have specialized endings that enable them to respond to particular kinds of sensory information Sensory Coding y Nerves are bundles of axons which can do no more than transmit action potentials Action potentials are fixed in size and duration cannot be altered Chapter 4 y Therefore different stimuli cannot be translated into different types of action potentials y Code a system of symbols or signals representing information2 general forms a Anatomical coding a means by which the nervous system represents information wherein different features are coded by the activity of different neurons used by the brain to interpret the location and type of sensory stimulus according to which incoming nerve fibers are activeOptic nerves nerves that connect the eyes with the brainSensory coding for the body surface is anatomical ie the primary somatosensory cortex contains a neural map of the skin and receptors in the skin in different parts of the body send information to different parts of the primary somatosensory cortex Similarly the primary visual cortex maintains a map of the visual field b Temporal coding a means by which the nervous system represents information wherein different features are coded by the pattern of activity of neurons coding of information in terms of timeRate simplest form of temporal code By firing at a faster or slower rate according to the intensity of a stimulus an axon can communicate quantitative information to the brainEg a light touch to the skin can be encoded by a low rate of firing More forceful touch high rate of firing
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