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Chapter 5

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Department
Psychology
Course
Psychology 1000
Professor
Dr.Mike
Semester
Winter

Description
SENSATION AND PERCEPTION Synesthesia: the “mixing of the senses” when people may experience sounds as colours, or tastes as touch sensations that have different shape. SENSATION PERCEPTION Stimulus (ex. Sound) receptors translate feature detectors stimulus features neural repre- matching process Activates specialized  stimulus properties  break down and  are reconstructed  sentation is  results in recognition Sensory receptors into the language of analyze stimulus into neural repre- compared with and interpretation Nerve impulses features sentation previous info of stimuli In the brain Sensation: the stimulus-detection process by which our sense organs respond to and translate environmental stimuli into nerve impulses that are sent to the brain Perception: making “sense” of what our senses tell us- is the active process of organizing this stimulus input and giving it meaning. SENSORY PROCESSES 5 classical senses: 1) Vision 2) audition (hearing) 3) touch 4) gestation (taste) 5) olfaction (smell) *other senses: -touch can be divided into separate senses of pressure pain and temperature -receptors in the brain sense chemical composition of our blood -immune system has sensory functions which allow it to detect foreign invaders and receive stimulation from the brain STIMULUS DETECTION: THE ABSOLUTE THRESHOLD -researchers answer “how intense must a stimulus be for us to detect it” by stimulating a patient and asking them if they felt it, but to answer “whether we actually sensed very faint stimuli” researchers designate… Absolute threshold: the lowest intensity at which a stimulus can be detected correctly 50 percent of the time  The lower the absolute threshold, the greater the sensitivity SIGNAL DETECTION THEORY: -people’s apparent sensitivity can fluctuate quite a bit -concluded that the concept of fixed absolute threshold is inaccurate because there is no single point on the intensity scale that separates non-detection from detection - there is a range of uncertainty and people set their own decision criterion -decision criterion -a standard of how certain they are that a stimulus is present before they will say they detect it -can also change based on factors such as fatigue, expectation, and potential significance of stimuli Signal detection Theory is concerned with the factors that influence sensory judgments Experiment: typical experiment is having a light turn on and tell participants that there may or not be a quiet tone, they must say whether they hear that tone or not Possible Results: tone is present: “yes” (a hit), “no” (a miss) Tone is absent: “yes” (a false alarm), “no” (a correct rejection) Outcome: -bold patients who frequently say “yes” have more hits, but also more false alarms than conservative participants -increasing rewards for hits and costs for misses results in lower detection threshold (more “yes”) -ex. Physicians become more conservative in their “yes” response since cost for fake alarms are increased *At low stimulus intensities, both the participant’s and situation’s characteristics influence the decision criterion *RESEARCH SHOWS THAT PERCEPTION IS, IN PART, A DECISION RESEARCH FOUNDATIONS: Subliminal Stimuli: Can they affect Behaviour? BACKGROUND: Subliminal stimulus: one that is so weak or brief that, although it is received by the senses, it cannot be perceived consciously –the stimulus is well below the absolute threshold. -persuasive stimuli above the absolute threshold are far more influential than subliminal attempts to sneak into our subconscious mind, perhaps because we are more certain to “get the message” METHOD: -Anthony Greenwald and his co-workers used commercially produced tapes purporting either self-esteem or improve memory -participants lacking either of two areas would take an original test, then be given either of the two tapes, and could be told that they were receiving the actual tape or were actually receiving one but told they were the other RESULTS: -people who thought they were listening to either self-esteem tapes but were actually given memory tapes showed a larger increases in self esteem than the participants who actually listened to it, but were told they were listening to memory CONCLUSION: -the effect was stronger when they merely expected the subliminal messaged as compared to the actual content of the tape. -therefore, subliminal messages may have an effect, but their influence is much more subtle than once perceived. THE DIFFERENCE THRESHOLD (distinguishing between stimuli) Difference threshold: the smallest difference between two stimuli that people can perceive 50 percent of the time (also called the just noticeable difference – jnd) Ernest Webber: discovered that there is some degree of lawfulness in the range of sensitivities in our sensory system.  Weber’s Law: the jnd is directly proportional to the magnitude of the stimulus with which the comparison is being made, and can be expressed as the Weber fraction Ex) Weber fraction of weights is 1/50 – this means that if you lift something of 50 grams, a comparison weight must be at least 51 grams to tell the difference. -the smaller the fraction, the greater the sensitivity to differences -Weber’s law breaks down at extremely high and low intensities of stimulation (cant tell the difference) SENSORY ADAPTATION Sensory adaptation: the diminishing sensitivity to an unchanging stimulus with the passage of time as sensory neurons habituates to stimulation -occurs in all sensory modalities Ex) Vision:  tiny involuntary movements in the eye keeps images moving about the retina so that stationary objects do not fade from sight if we stare at them -reduces our overall sensitivity, but it’s adaptive because it allows our senses to pick up environmental changes SENSORY SYSTEMS VISION: -the normal stimulus for vision is electromagnetic energy (light energy) and measured in nanometers -human visual system is sensitive to wavelengths extended from 700nm (red) to 400nm (blue-violet) THE HUMAN EYE: Cornea: a transparent protective structure at the front of the eye where light waves enter Pupil: an adjustable opening behind the cornea that can dilate or constrict to control the amount of light that enters the eye *Low levels of illumination cause the pupil to dilate to let more of the light in Iris: Have muscles which control the pupil size; coloured and surrounds pupil Lens: an elastic structure behind the pupil which becomes thinner to focus on distant objects, and thicker to focus on nearby objects Retina: where the lens focuses the visual image on (like the film of a camera); a light sensitive, multi-layer tissue at the back on the eyeball *the lens inverts the image from right to left and top to bottom when projected on retina, the brain reconstructs the image to what we perceive.  Myopia (nearsightedness): good vision for nearby objects, but have difficulty seeing objects far away -lens focuses the image in front of the retina -occurs when the eyeball is longer (front to back)  Hyperopia (farsightedness): good distance vision, but have difficulty seeing close up objects -occurs when the lens does not thicken enough -image is focused on a point behind the retina (too far from lens) -usually occurs with people who are aging PHOTORECEPTORS: The retina contains two types of light sensitive receptor cells: 1) RODS: -function best in dim light, and are primarily black and white brightness receptors (night)...Ex) owls -around 120 million in the human eye -500 times more sensitive to light than cones, but they do not give rise to colour sensations -found throughout the retina except in the fovea; at the greatest concentration in the periphery which contains mainly rods -many rods are connected to the same bipolar cell, therefore their electrical messages are additive in the bipolar cell and can therefore fire it  The reasons why it is easier to detect a faint star when you look slightly to the side because you are using the periphery of the retina where there is a high concentration of rods 2) CONES: -colour receptors which function best in bright illumination(day)…ex pigeons/chipmunks only have cones -around 6 million in the human eye -cones are found in greatest concentration in the fovea (small area in centre of retina that contains only cones), and their concentration decreases as you move away from the centre of the retina -in the periphery, cones share bipolar cells like rods -in the fovea, each cone has their own “private line” to a single bipolar cell  visual acuity (ability to see fine detail) is greatest when the visual image projects directly on the fovea since this focusing results in the firing of a large number of cones and their private line bipolar cells (ex. Birds of prey) Rods and cones send messages to the brain via two layers of cells… Bipolar cells: have synaptic connections with both rods and cones, and then synapse with a layer of 1 million ganglion cells whose axons form the optic nerve  Optic nerve exits through the back of the eye (not far from fovea), producing a blind spot (no photoreceptors) *** both rods and cones form the rear layer of the retina and their light sensitive ends point away from where the light is entering, therefore they receive only a fraction of the light energy that enters the eye VISUAL TRANSDUCTION: Transduction: the process whereby the characteristics of a stimulus are converted into nerve impulses -rods and cones translate light waves into nerve impulses by protein molecules called photopigments  Photopigments absorb the light which produces a chemical reaction that changes the rate of neurotransmitter release at the receptors synapse with bipolar cells -the greater the change in transmitter release, the stronger the signal passed on -if the nerve responses are triggered at the three levels (rod/cone, bipolar, ganglion), the message goes to the visual relay station in the thalamus and then the visual cortex BRIGHTNESS VISION AND DARK ADAPTATION: Brightness sensitivity of both rods and cones depends in part on the wavelengths of light  Rods have much greater brightness sensitivity than cones throughout the colour spectrum except at the red end (rods are relatively insensitive to red light)  Cones are most sensitive to low illumination in the greenish yellow range of the spectrum ex) fire engines have changed from the red light to a greenish-yellow light which both rods and cones are sensitive to in dim lighting ex) airport landing lights are blue since rods are sensitive to blue at night when cones are not active Dark Adaptation: the progressive improvement in brightness sensitivity that occurs overtime under conditions of low illumination (dark). -after absorbing light (being in the bright), a photoreceptor is depleted of its pigment molecules for a period of time; during process of dark adaptation, the photopigment molecules are being regenerated and the receptors sensitivity will increase greatly.  Cones gradually become more sensitive to fainter lights as time passes, but after 5-10 minutes, their sensitivity has reached their maximum  Rods regenerate their photopigments slower than cones, but after ½ an hour, they have reached their maximum which is greater than the maximum of cones Ex) at night, fighter pilots sit in rooms that are red so that the rods are insensitive and are therefore in the dark and going through dark adaptation earlier so they will be ready as soon as needed COLOUR VISION: Two different theories of colour vision: 1) The Trichromatic Theory: -1800 Young and Helmholtz -additive colour mixture: any colour in the visible spectrum can be produced by the combination of blue, green and red wavelengths -there are three types of colour receptors in the retina (one for red, blue or green); each of the receptors classes send messages to the brain based on the ratio by which they were activated by the light energy’s wavelength -the visual system then combines the signals to recreate its original hue -all three = equally activated = pure white colour produced Problem: -yellow is produced by activity of red and green photoreceptors, yet people with red-green colour blindness can still see yellow -colour afterimage in which an image will appear in a different colour after a certain colour stimulus has been viewed and then withdrawn. 2) Opponent Process Theory: -1870 Ewald Hering -assumed that there are three types of cones, each of which can respond to two different wavelengths (red- green, blue-yellow, white-black) -depending on the stimuli, the cone can respond with one chemical reaction for red, and another reaction for green -explains colour afterimage TODAY WE ACCEPT… The Dual-Process Theory: -combines both theories to account for the colour transduction process -cones do indeed contain one of three different protein photopigments which are most sensitive to blue, red, or green wavelengths (Trichromatic theory) -opponent processes do not occur at the level of cones -certain ganglion cells and some neurons in the visual relay station or visual cortex respond in an opponent-process fashion by altering the rate of firing (ex. A cell will respond to red light with a high rate of firing, and respond to green light with a low rate of firing) -Red-green opponent processes are triggered by the input of red-green sensitive cones -blue is triggered by blue sensitive cones while yellow is triggered by simultaneous red-green sensitive cones Trichromats: sensitive to all three systems (red-green, blue-yellow, black-white) Dichromats: the absence of a hue sensitive photopigment of a certain type Monochromats: sensitive only to the black-white system and is totally colour blind **most colour deficient people are dichromats and have their deficiency in the red-green system ANALYSIS AND RECONSTRUCTION OF VISUAL SCENES -the process of combining the messages received from the photoreceptors into the perception of a visual scene -the optic nerve sends nerve impulses to a visual relay station in the thalamus, then the input is routed to various parts of the cortex (particularly the primary visual cortex in the occipital lobe) -there is a point-to-point correspondence between tiny regions of the retina and groups of neurons in the visual cortex -the fovea: produces high visual acuity and is represented by a large area on the visual cortex -Feature detectors: -sensory neurons that respond to particular features of stimuli such as shape, angle, or colour -found that certain neurons fired most frequently when lines of certain orientations were presented -within the cortex, all the information is integrated and analyzed by successively more complex feature detector systems to produce our perception of objects -parallel processing: all the different components of an image are processed simultaneously and then constructed into a unified image of its properties -Visual Association Cortex: -more complex features of the visual scene are combined and interpreted in light of our memories and knowledge ends with us “recognizing” the image for what it “is” AUDITION -sense of hearing is sound waves, a form of mechanical energy -hearing is actually pressure waves in a conducting medium Sound waves have two characteristics 1) Frequency: -the number of sound waves (cycles) per second; measured in Hertz (Hz) -frequency is related to pitch (the higher the frequency, the higher the pitch) -common sounds are at lower frequencies 2) Amplitude -the vertical size of sound waves; the amount of compression and expansion of the molecules in conducting medium -the amplitude is related to loudness -Differences in amplitudes are measured in decibels (db)- a measure of physical pressures at the eardrum -absolute threshold for hearing in 0db; and increases of 10 db represents a tenfold increase in loudness AUDITORY TRANSDUCTION -sound waves travel into the auditory canal leading to the eardrum (a movable membrane that vibrates in response to the sound waves -middle ear: behind the eardrum; a cavity housing three tiny bones; the hammer, anvil, and stirrup  The vibrating of these bones amplifies the sound waves more than 30 times -hammer is attached firmly to the eardrum -stirrup is attached to another membrane, the oval window (forms the boundary between the middle and inner ear) -inner ear:  The cochlea: a coiled, snail shaped tube, filled with fluid that contains the basilar membrane ( a sheet of tissue that runs in its length)  Organ of Corti: rests on the basilar membrane; contains thousands of hair cells that are actual sound receptors -tips of hair cells are attached to another membrane that overhangs the basilar membrane -hair cells synapse with the neurons of the auditory nerve which sends nerve impulses to the auditory relay station in the thalamus and then the auditory cortex in the temporal lobe How does it happen? 1) Sound waves strike eardrum and pressure created in oval window by hammer, anvil, and stirrup of middle ear 2) Sets the fluid inside the cochlea into motion 3) Fluid waves vibrate the basilar membrane and the membrane above it, causing a bending of the hair cells in the organ of corti 4) This triggers a release of neurotransmitter substance into the synaptic space between the hair cells and neurons of auditory nerve 5) Nerve impulses are sent to the brain **within the auditory cortex, there are feature detector neurons which respond to specific kinds of auditory input CODING OF PITCH AND LOUDNESS Loudness:  Rate of firing: high amplitude sound waves cause the hair cells to bend more and release more neurotransmitter substance at the point where they synapse with the auditory nerve cells  Which hair cells are sending messages: certain receptor neurons have higher thresholds than others, so that they will fire only when considerable bending of the hair cells occurs (intense sound) Pitch: -Two competing theories accounting for pitch perception 1) Frequency Theory: -nerve impulses sent to the brain match the frequency of the sound wave -Problem since neurons are limited in their rate of firing (refractory period) and therefore cannot produce high enough frequencies of firing to match the high frequencies of the sound waves 2) Place Theory: -Georg con Bekesy cut tiny holes in the cochleas of guinea pigs and human cadavers to observe what happened in the fluid filled cochlea when stimulated with different frequencies -found that: high frequency sounds produced an abrupt wave that peaked close to the oval window, whereas low-frequency sounds produced a slower wave that peaked farther down the cochlear canal -Therefore: the specific point in the cochlea where the fluid wake peaks and most strongly bends the hair cells serves as the frequency coding cue **At low frequencies, the frequency theory holds true; At high frequencies, the place theory holds true SOUND LOCALIZATION: Sound localization: when the nervous system uses information concerning the time and intensity differences of sounds arriving at the two ears to locate the source of sound in space -the sound will arrive first, and loudest at the ear closer to the sound; if the intensity and time is the same for both ears, then the sound is directly in front Ex) Barn Owl: the right ear
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