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Chapter 5-9

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Steve Joordens

PLEASE DO NOT COPYCHAPTER 5 SensationEverything we learn is detected by sense organs and transmitted to our brains by sensory nervesSense organs and sensory nerves provide us with useful information about the outside worldBut how specific that information is depends on things like the specific modality of the information the characteristics of the information the state of the brain at the time it receives itinformation from different sources in the environment are processed differently by sensory systems Ex there is a clear difference between vision and auditionVision we see different things every second but we have a sense that our visual world is stablethe visual system must provide that stabilitySound it is not so variablethe intensity of sound changes depending on how far we are from the source but these changes are more gradual than those faced by the visual systemalso sounds can go around obstacles unlike lightour auditory sense has more time to process signals So our senses are attuned to different aspects of our world and they combine together to give us a rich experience of the worldAudition is important for social behavior vision for information about distant events sense of smell can tell us about sources of aromatic molecules far upwindTaste and touch deal with events occurring immediately nearby Sensory ProcessingExperience is traditionally studied by distinguishing between sensation and perceptionSensation the detection of the elementary properties of a stimulus ex seeing the colour red seeing a movementPerception the detection of the more complex properties of a stimulus including its location and nature involves learning ex seeing a red apple seeing a soccer ball coming and realizing you need to move to block itDetecting a sound is not the same as identifying what the source of the sound meansLong ago they thought that perceptions depended on learning and sensations involved innate prewired physiological mechanismsBut until now there has been no clear boundary between simple sensations and complex perceptionsResearch experience is essential to the development of some of the most elementary features of sensory systems We will look at our sensory mechanisms the visual auditory gustatory olfactory somatosensory systemsTradition5 senses but we actually have several moreEx the somatosensory system can be separated into various components for touch warmth coolness vibration physical damage head tilt etcit just depends if you want to use the term sense for them TransductionThe brain is separated from the outside world and the only receptors it has looks at temperature and salt concentration of the bloodno receptors for the outside worldUseful actions require information from the external world so this information is gathered by the sense organs located outside of the brainthNotes by Mary Lee Notes from Psychology the Science of Behavior 4 Ed CarlsonHeth PLEASE DO NOT COPY Sense organs detect stimuli from light sound odor taste mechanical contact from the environmenttransported to brain through neural impulsesit is the task of the sense organs to transmit signals to the brain that are coded to represent events in the environmentthe brain analyzes this information and reconstructs what just happened Transduction the conversion of physical stimuli into changes in the activity of receptor cells of sensory organsenergy from environmental eventsneural activityeach sense organ responds to a particular form of energy and translates it into neural firingThe means of transduction for most cases is specialized neurons called receptor cells receptor cell a neuron that directly responds to a physical stimulus such as light vibrations or aromatic moleculesthey release chemical transmitter substances that stimulate other neurons thus altering the rate of firing of their axonsFor the somatosensory systems dendrites of neurons respond directly to physical stimuli without the intervention of specialized receptor cellsbut there may still be a bit of specialization some of these neurons have specialized endings that let them respond to particular kinds of sensory information The Types of Transduction Accomplished by the Sense Organs Location of Sense Organ Environmental Stimuli Energy Transduced Eye Light Radiant energy Ear Sound Mechanical energy Vestibular system Tilt and rotation of head Mechanical energy Tongue Taste Recognition of molecular shape Nose Odour Recognition of molecular shape Skin internal organs Touch Mechanical energy Temperature Thermal energy Vibration Mechanical energy Muscle Pain Chemical reaction Stretch mechanical energySensory CodingSensory information is translated into firing of action potentials but there arent different types of action potentialsBut we can still detect a lot of different stimuli with each of our sense organs ex we can discriminate among 75 million different colours we can recognize up to 10 000 odorsdiscriminate the degree of pressure involved sharpness or bluntness softness or hardness and temperature of the object were touchingYou may ask if action potentials cant be altered how do the sensory organs tell the brain a red apple or a yellow lemon that you see for exthe information must be coded somehow in the activity of the axons and it is in two general forms anatomical coding and temporal coding Anatomical CodingRecall Mullers doctrine of specific nerve energiesthe brain learns what is happening through the activity of specific sets of neuronssensory organs are in different places and send their information to the brain through different sets of nervesThe brain uses anatomical coding to interpret the location and type of sensory stimulus according to which incoming nerve fibres are active anatomical coding a means by which the nervous system represents information different features are coded by the activity of different neurons thNotes by Mary Lee Notes from Psychology the Science of Behavior 4 Ed CarlsonHeth PLEASE DO NOT COPY Ex rub your eyeslightsensitive receptors are there and they are mechanically stimulatedaction potentials are produced in the optic nervesbrain acts as if the neural activity in the optic nerves was produced by lightyou see stars and flashesThis can be seen in the other senses tooartificially stimulate the nerves that convey tastesensation of tasteelectrical stimulation of the auditory nervesensation of a buzzing noise Temporal CodingTemporal coding a means by which the nervous system represents information different features are coded by the pattern of activity of neuronsit is in terms of timeThe simplest form of temporal code is rate by firing at a fasterslower rate according to the intensity of a stimulus an axon can communicate quantitative information to the brainEx light touchencoded by a low rate of firing more forceful touchby a high rate of firing Anatomical coding The firing of particular set of neurons tells where the body is being touchedTemporal coding the rate at which these neurons fire tells how intense that touch is PsychophysicsPsychophysics a branch of psychology that measures the quantitative relation between physical stimuli and perceptual experiencephysics of the mindScientists have to find ways to measure peoples sensations and there are two methods the justnoticeable difference and the procedures of signal detection theory The Principle of the JustNoticeable DifferenceWeber looked at the ability of humans to discriminate between various stimuli he measured the justnoticeable difference jndjustnoticeable difference jnd the smallest difference between two similar stimuli that can be distinguished also called difference threshold The jnd is directly related to the magnitude of that stimulusGive people two metal objects and ask if they were different in weightparticipants said they were the same unless they differed by a factor of 1 in 40 they could barely distinguish 40 g and 41 g 80 g and 82 g etcthe difference in weight between 40 and 41 g and 80 and 82 g is the jndDifferent senses had different ratios ex ratio for differences in brightness of white light is 1 in 60Weber fraction the ratio between a jnd and the magnitude of a stimulus reasonably constant over the middle range of most stimulus intensities Fechner used Webers concept of the jnd to measure peoples sensationsassumption the jnd was the basic unit of a sensory experiencehe measured the absolute magnitude of a sensation in jndsExperiment put participant in dark room and have two bulbs one is sample one is comparisonsample is turned off comparison is brightened until they notice a differencethe value is one jndset sample to one jnd comparison is brightened until they notice a differencethe value is two jndscontinue this until the lights become uncomfortably bright thNotes by Mary Lee Notes from Psychology the Science of Behavior 4 Ed CarlsonHeth
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