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Chapter 5

Chapter 5

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Western University
Psychology 1000
Terry Biggs

Psychology 1000 Chapter 5 Notes Chapter 5 Notes Sensation and Perception Synaesthesia a condition in which stimuli are experienced not only in the normal sensory modality, but in others as well (2 or more sense are coupled) 5 stages of sensory processing and perception of information o Stimulus (light, sounds waves, chemical module or pressure) translate into nerve impulses o Neurons break down and analyze specific features of the stimuli o Stimulus piece constructed into neural representation that is then compared with previously stored information o Allows us to recognize the stimulus and give it meaning (perception) o Received, translate, detect, reconstructed, compared, results Sensation 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; active process of organizing this stimulus input and giving it meaning Sensory Processes 5 senses: vision, audition (hearing), touch, gustation (taste) and olfaction (smell) Receptors in the brain monitor the chemical composition of our blood Psychophysics studies relations between the physical characteristics of stimuli and sensory capabilities; concerned with two kinds of sensitivity o Absolute limits of sensitivity (i.e. whats the weakest sound a human can detect? o Difference between stimuli (i.e. whats the smallest difference in light we can detect?) Stimulus Detection: The Absolute Threshold 1 Psychology 1000 Chapter 5 Notes Absolute threshold the lowest intensity at which a stimulus can be detected correctly 50% of the time Lower the absolute threshold, the greater the sensitivity Psychologists concluded that there concept of a fixed absolute threshold is inaccurate because theres no single point on the intensity scale that separates non-detection from detection of a stimulus o Instead theres a range of uncertainty and people set their own decision criterion o Decision criterion standard of how certain they must be that a stimulus is present before they will say they detect it o Signal detection theory concerned with the factors that influence sensory judgements o Participants can be influenced to become bolder or more conservative by manipulating the rewards and costs for giving correct and incorrect responses o Signal detection research shows us that perception is, in part, a decision The Neuroscience of Subliminal Perception and Prosopagnosia Subliminal Stimulus one that is so weak or brief that, although its received by the senses, it cannot be perceived consciously; the stimulus is well below the absolute threshold Jon Krosnick did a study that involved showing people nine slides of a particular person and measured their attitude towards that person o For half the participants, an unpleasant picture was shown right after, which was shown subliminally o The remaining were shown pleasant pictures o People who were shown the unpleasant picture expressed somewhat negative attitudes towards the original picture of the person o Shows a process of subconscious attitude conditioning Prosopagnosia unable to recognize familiar faces 2 Psychology 1000 Chapter 5 Notes o Have cortical damage in areas involving object perception o D.F. Study; 3 points to note High order facial recognition is a complex process involving several brain regions including the lateral occipital area and fusiform facial area and primary visual cortex Research emphasizes the importance of the case study to investigate psychological phenomena Highlights the subtle manner in which subliminal stimuli may have an effect Phillip Merikle and his colleagues argued that subliminal cues and bias what we perceive at a conscious level and may alter our conscious experience of those stimuli The Difference Threshold Difference Threshold smallest difference between two stimuli that people can perceive 50% of the time (sometimes called just noticeable difference jnd) Webers Law states that the difference threshold is directly proportional to the magnitude of the stimulus with which the comparison is being made and can be expressed as a Weber fraction o The smaller the fraction, the greater the sensitivity to differences Sensory Adaptation Sensory Adaptation the diminishing sensitivity to an unchanging stimulus; sensory neurons are engineered to respond to constant stimulus by decreasing their activity (habituation) If it wasnt for involuntary eye movements that keeps images moving about the retina, dormant objects would fade from eyesight if we stared at them The Human Eye 3 Psychology 1000 Chapter 5 Notes 1. Light waves enter through cornea transparent protective structure at the front of the eye 2. Behind cornea is the pupil adjustable opening that can dilate or constrict to control the amount of light that enters the eye; pupils size is controlled by muscles in the iris; low levels of illumination cause the pupil to dilate, letting more light into the eye to improve optical clarity; bright light triggers constriction of the pupil 3. Behind the pupil is the lens an elastic structure that becomes thinner to focus on distant objects and thicker to focus on nearby objects 4. Lens of the eye focuses the image on the retina a multi-layered tissue at the rear of the fluid filled eyeball; lens reverses the image from right to left and top to bottom when its projected on the retina but the brain reconstructs the visual input into the image that we perceive o Myopia (near sightedness) good vision for nearby objects and difficulty seeing far away; lens focuses the visual image in front of the retina; eyeball is longer (front to back) o Hyperopia (farsightedness) - good distance vision but difficulty seeing close up objects; lens doesnt thicken enough and the image is focused behind the retina Photoreceptors: The Rods and Cones Retina contains two types of receptor cells, rods and cones Rods function best in dim light and primarily black and white brightness receptors Cones colour receptors ; function best in bright illumination Fovea -small area in center of retina that contains only cones Rods and cones send their messages to the brain by two additional layers of cells: o Bipolar cells synaptic connections with the rods and cones o Also synapse with a layer of about 1 million ganglion cells whose axons are collected into a bundle to form the optic nerve 4
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