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Psych 1000 - Chapter 5 Notes.docx

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Western University
Psychology 1000
Terry Biggs

Sensory and Perceptual Processes - Synthesia (mixing of the senses) – a condition is which sensations are mixed (suggested that we are all synaesthetic at birth) - Sensation – The process by which our sense organs respond to translate stimuli into nerve impulses sent by the brain - Perception – Organizing the stimulus input and giving it meaning. The same sensory input may be perceived in different ways at different times - Stages of sensation and perception o Stimuli activate sensory receptors o Sensory receptors translate information into nerve impulses o Specialized neurons analyze stimuli features o Stimulus pieces are reconstructed and compared to stimuli in memory o Perception is then consciously experienced - Transduction – the process of sensory receptors translation stimulus information into nerve impulses - Feature detectors – specialized neurons that break down and analyze the specific features of the stimuli - The Binding Problem – How to bind all our perceptions into one complete whole while keeping its sensory elements separate - Psychophysics – sensitivity to stimuli; studies the relations between the physical characteristics of stimuli and sensory capabilities o Absolute limits of sensitivity – dimmest light in which we can see objects, softest sound we can hear, etc. o Recognizing differences between stimuli – smallest differences in brightness detectable, recognizing differences between tones - Stimulus Detection o The Absolute Threshold  The lowest intensity at which a stimulus can be detected 50% of the time  The lower the absolute threshold, the greater the sensitivity  However the environment contains a background level of stimulation for each sense and this level (the adaptation level) must be overcome if a stimuli is to be detected - Signal Detection Theory o Decision Criterion: A personal standard of certainty before a person will say they detect a stimulus (changes due to personal risk or uncertainty)  Affected by  Conservativeness or boldness (bold subjects show high hits and high false alarms)  Increasing rewards for hits or costs for misses (conservative subjects show high misses and high correct rejections)  Possible responses are hit, miss, false alarm, and correct rejection o Criterions may be manipulated by changing the payoff for each cell of the matrix o The shows that perception is to some extent a decision - The Difference Threshold o The smallest difference between two stimuli that people can perceive 50% of the time o The amount of energy required to overcome the adaptation level o Also called the jnd (just noticeable difference) o Weber’s Law: The JND is directly proportional to the magnitude of the stimulus with which the comparison is made  The smaller the Weber Fraction the less change is necessary to produce a JND o Locke’s experiment – one hand in cold water, one hand in hot water for 3 minutes, and then place it in tepid water. Both hands will then be in the same water but the sensations differ due to the prior adaptation - Sensory Adaptation o Sensory adaptation – the diminishing sensitivity to an unchanging stimulus as neurons are engineered to respond to a constant stimulus by decreasing their activity o There is a certain amount of adaptation that occurs in all sensory modalities - Subliminal Perception – A subliminal stimulus cannot be perceive consciously but do register in the nervous system o Subliminal advertising during a movie o Stimuli above threshold influence behavior much more than subliminal stimuli o Effects may be due to placebo effects Vision - Your eyes detect electromagnetic radiation (the normal stimulus for vision) not light o Electromagnetic radiation (light waves) are measured in nanometres o Technology helps us see the wavelengths not visible to the naked eye - Light waves enter the eye through the cornea, the transparent protective structure at the front of the eye o Behind the cornea is the pupil, an adjustable opening that can dilate or constrict to control the amount of light that enters the eye o The pupil’s size is controlled by muscles in the coloured iris that surrounds the pupil  Low levels of illumination cause the pupil to dilate, letting more light in to improve optical clarity, bright light triggers constriction of the pupil o Behind the pupil is the lens, an elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects o The lens focuses the visual image on the light-sensitive retain, a multi-layered tissue at the read of the fluid-filled eyeball o The ability to see clearly depends on the lens’s ability to focus the image directly onto the retina  Myopia (nearsightedness) – the lens focuses the visual image in front of the retina (too near the lens) resulting in a blurred image for faraway objects  Hyperopia (farsightedness) – the lens does not thicken enough and the image is focused behind the retina (too far from the lens) - Photoreceptors o The retina contains two types of specialized sensory neurons, which are light- sensitive receptor cells called rods and cones o Rods, which function best in dim light, are primarily black-and-white brightness receptors  They are about 500 times more sensitive to light than are cones, but they do not give rise to colour sensations  Nocturnal vision is due to the organism having more rods than cones o Cones, which are color receptors, function best in bright illumination o In humans, rods are found throughout the retina except in the fovea, a small area in the centre of the retina that contains only cones. Cones decrease in concentration as one moves way from the centre of the retina, and the periphery of the retina contains mainly rods o Rods and cones send their messages to the brain via two additional layers of cells  Bipolar cells have synaptic connections with the rods and cones, the bipolar cells synapse with a layer of about one million ganglion cells, whose axons are collected in a bundle to form the optic nerve o The rods and cones not only form the rear layer of the retina, but their light- sensitive ends actually point away from the direction of the entering light so that they receive only a fraction of the light entering o The manner in which rods and cones are connected to the bipolar cells accounts for both the greater importance of rods in dim light and our greater ability to see fine detail bright illumination, when the cones are most active o Typically many rods are connected to the same bipolar cell, but in the fovea, the densely packed cones each have their own private line to a single bipolar cell o Visual acuity – our ability to see fine detail which is the greatest when the visual image projects directly onto the fovea, this results in the firing of a large number of cones and their private bipolar cells o The optic nerve exits through the back of the eye not far from the fovea, producing a blind spot where there are no photoreceptors - Visual Transduction o Transduction – the process whereby the characteristics of a stimulus are converted into nerve impulses o Rods and cons translate light wavers into nerve impulses through the action of protein molecules called photopigments o The absorption of light by these molecules produces a chemical reaction that changes the rate of neurotransmitter release at the receptor’s synapse with the bipolar cells - Brightness Vision and Darkness Adaptation o Rods have greater brightness sensitivity than cones throughout the colour spectrum except at the red end o Cones are most sensitive to low illumination in the greenish-yellow range of the spectrum o Dark adaptation – the progressive improvement in brightness that occurs over time under conditions of low illumination o After absorbing light, a photoreceptor is depleted of its pigment molecules for a period of time. If the eye has been exposed to conditions of high illumination, such as bright sunlight, a substantial amount of photopigment will be depleted. o During the process of dark adaptation, the photopigment molecules are regenerated, and the receptor’s sensitivity increases greatly - Historically, two different theories of colour vision have tried to explain how we are able to distinguished between tiny differences between light wavelengths in order to see color - Young – Helmholtz trichromatic theory o Individual cones are most sensitive to three different wavelengths: red, blue, and green (additive colour mixture) o Any colour in the visible spectrum can be produced by some combination of the wavelengths that correspond to these colours o There are three types of colour receptors in the retina o Although all cones can be stimulated by most wavelengths to varying degrees, individual cones are most sensitive to wavelengths that correspond to either blue, green, or red. Each of these receptor classes sends messages to the brain based on the extent to which they are activated by the light energy’s wavelength and the visual system combines the signals to recreate the original hue o According to this theory when we see colour we’re seeing patterns through differentially sensitive receptors o If all three cones are equally active, a pure white colour is perceived o Insufficient to cover all phenomena that occur, for example, according to the theory, yellow is produced by activity of the red and green receptors but certain people with red-green color-blindness are able to see yellow. Also this theory doesn’t explain afterimage - Opponent Process Theory – Three cone types respond to two different wavelengths o One type responds to green or red which are opposable colors (because people are red-green colorblind but not one or the other) because they are circuited together o Another type responds to blue or yellow and the last to black or white o This theory says that afterimage is a rebound reaction using the opponent process/color - Dual-process theory combines the trichromatic and opponent-process theories to account for the colour transduction process o The cones do contain one of three different protein photopigments that are most sensitive to wavelengths roughly corresponding to the colours red, blue, and green and different ratios of activity in these cones can produce a pattern of neural activity that corresponds to any hue in he spectrum o The opponent processes don’t occur at the level of the cones but rather, some neurons in the visual relay stations respond in an opponent-process fashion by altering their rate of firing (red will fire more and green less when you see red) - Colour-Blindness o Trichromat – people with normal vision that are sensitive to all 3 systems o Dichromat – blind in red-green or yellow-blue systems o Monochromat – sensitive only the black-white system o This deficiency is caused by an absence of the hue-sensitive photopigment in certain cone types - The optic nerve sends nerve impulses to a visual relay station in the thalamus and from there, 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 tiny8 regions of the retina and groups of neurons in the visual cortex - Groups of neurons within the primary visual cortex are organized to receive and integrate sensory nerve impulses originating in specific regions of the retina, these cells are known as feature detectors. - Parallel processing – overlapping modules of the brain simultaneously analyzing colour, shape, size, distance, and movement and constructing a unified image of its properties - Finally, the information analyzed and recombined by the primary visual cortex is routed to other cortical regions known as the visual association cortex where more complex features of the visual scene are combined and interpreted in light of our memories and knowledge - Also neurons in the brain respond selectively not only to basic stimulus characteristics but also to co
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