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Chapter 5

Chapter notes Chapter 5 Notes

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Psychology 1000
Terry Biggs

Chapter 5 Sensory and Perception Synaesthesia- mixing of senses, sounds a colours or tastes as touch sensations o Provide glimpses into different aspects of how we sense and understand our world Sensory and perceptual process o Begin when specific types of stimuli activate specialized sensory motor receptors o Whether the stimulus is light, sound waves, a chemical molecule or pressure, your sensory receptors must translate this info into the language of nerve impulses o Once this translation occurs, specialized neurons break down and analyze the specific features of the stimuli o These numerous stimulus pieces are reconstructed into a neural representation that is then compared with previously stored info, such as our knowledge of what particular objects look, smell or feel like o This matching of a new stimulus with our internal storehouse knowledge allows us to recognize the stimulus and give it meaning o We then consciously experience a perception Sensation- environmental stimuli into nerve impulses that are sent to the brain Perception- making sense of what are senses tell us is the active process of organizing this stimulus input and giving it meaning Perception is an active an d creative process, the same sensory input may be perceived in different ways at different times o Your interpretation, or perception, is influenced by contex SENSORY PROCESSES 5 classical senses o Vision o Audition- hearing o Touch pressure pain temperature o Gustation- taste o Olfaction- smell Immune system also has sensory functions that allow it to detect foreign invaders and to receive stimulation from the brain Human sensory systems are designed to extract from the environment the information that we need to function and survive Psychophysics- studies relations between physical characteristics of stimuli and sensory capabilities, is concerned with 2 types of sensitivity o Absolute limits of sensitivity Softest sound or weakest salt solution humans can detect o Differences between stimuli Smallest difference in brightness that we can detect, how much difference must there be in two tones before we can tell that they are not identical? Stimulus Detection: The Absolute Threshold We are often unsure of whether we have actually sensed very faint stimuli, researchers designate the absolute threshold as the lowest intensity at which a stimulus can be detected correctly 50% of the time o Therefore the lower the absolute threshold the greater the sensitivity Signal Detection Theory Decision criterion- a standard of how certain for must be that a stimulus is present before they will say they detect it o can change from time to time, depending on factors such as fatigue, expectation, and the potential significance of the stimulus Signal detection theory- is concerned with the factors that influence sensory judgement At low stimulus intensities, both the participants and the situations characteristics influence then decision criterion Subliminal stimulus- one that is so weak or brief that although it is received by the senses it cannot be received consciously o The stimulus is well below the absolute threshold STUDY, pg 173: Prosopagnosia- unable to recognize familiar faces 3 points to take away from this study o It would appear that the higher-order facial recognition is a complex process involving several brain regions including the LOA( lateral occipital area) and the FFA( fusi-form facial area), in addition to the primary visual cortex. Nonetheless, a person with severe damage can still pick up certain information about the visual stimuli by using heuristic rules to identity faces- oval, skin tone o This research emphasizes the importance of the case study to investigate psychological phenomena, fMRI imaging allows the researchers to precisely identify the regions and deficits involved with this disorder o The study highlights the subtle manner in which subliminal stimuli may have an effect, it is argued that effect is one of biasing perceptionsubliminal cues can bias what we perceive at a conscious level and may alter our conscious experience of those stimuli The Difference Threshold Distinguishing between stimuli can sometimes be as important as detecting stimuli o Ex. a slight variation in taste might signal that the food is tainted or spoiled o Professional wine tasters and piano tuners make a living by being able to make very slight discriminations between stimuli o Difference threshold- the smallest difference between two stimuli that people can perceive 50% of the time Sometimes called the just noticeable difference (jnd) o Ernst Weber (Veh-Ber) 1830- some degree of lawfulness in the range of sensitivities within our sensory system 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. Ex. the difference threshold for weights is a Weber fraction of approx. 1/50 meaning that if you lift 50 grams a comparison weight must weigh at least 51 grams in order to be able to judge it is heavier. If the first weight is 500g the other one must be 510g (ie. 1/50=10-500) The smaller the fraction(1/333) the greater the sensitivity to the difference Sensory Adaptation Because of changes in our environment sensory systems are finely attuned to changes in stimulation Sensory neurons are engineered to respond to a constant stimulus by decreasing their activity and the diminishing sensitivity to an unchanging stimulus called sensory adaption Adaption (sometimes called habituation) is part of everyday experience o After a while monotonous background sounds are largely unheard o Feel of a watch on your arm goes unnoticed Adaption occurs in all sensory modalities, including vision Sensory adaption may reduce our overall sensitivity, but it is adaptive because it frees our senses from the constant and the mundane to pick up informative changes in the environment o May turn out to be important changes for our well-being or survival
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