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Chapter 7

Chapter 7 Mechanisms of Perception: Hearing, Touch, Smell, Taste, and Attention

14 Pages
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Department
Psychology
Course Code
PSYC 271
Professor
Monica Valsangkar- Smyth

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Chapter 7 Mechanisms of Perception: Hearing, Touch, Smell, Taste, and Attention - exteroceptive sensory systems interpret stimuli from outside the body 7.1 Principles of Sensory System Organization - primary sensory cortex secondary sensory cortex association cortex - interaction among these three types of sensory cortex and among other sensory structures are characterized by 3 major principles - hierarchical organization, functional segregation, and parallel processing - hierarchical organization - specific levels and ranks in relation to one another - moves through a sensory system from receptors, to thalamic nuclei, to primary sensory cortex, to secondary sensory cortex, to association cortex - neurons respond optimally to stimuli of greater and greater specificity - each level of a sensory hierarchy receives most of its input from lower levels and adds another layer of analysis before passing it on - the higher the damage, the more specific and complex the deficit - but leaves fundamental sensory abilities intact - sensation process of detecting stimuli - perception higher-order process of integrating, recognizing, and interpreting complete patterns of sensations - functional segregation - it was believed that the primary, secondary, and association acted together to perform the same function (homogeneous) - now we know that the three levels of the cerebral cortex contain functionally distinct areas that specialize in different kinds of analysis - parallel processing - used to be serial processing (linear flow) - now we know theres simultaneous analysis of a signal in different ways by the multiple parallel pathways of a neural network - two fundamentally different kinds of parallel streams of analysis in our sensory systems: one is capable of influencing our behaviour without our conscious awareness and one that influences our behaviour by engaging our conscious awareness - summary model of sensory organization - sensory systems characterized by a division of labour: multiple specialized areas, at multiple levels, are interconnected by multiple parallel pathways - binding problem combine individual sensory attribute to produce integrated perception - one possible solution a single area of the cortex at the top of the sensory hierarchy that receives signals from all other areas of the sensory system and puts them together to form perception - not found yet - perception must be the product of the combined activity of different interconnected cortical areas 7.2 Auditory System - perception of sound, or more accurately, the perception of objects and events through the sounds they make - sound is the vibration of air molecules that stimulate the auditory system - pure tones (sine waves) do not exist in real life - always complex (multiple component sine waves that add up) - Fourier analysis mathematical procedure for breaking down complex waves into their component sine waves - one theory of audition is that the auditory system performs a similar analysis in terms of their component sine waves - for any pure tone, there is a close relationship between the frequency of the tone and its perceived pitch; however the relationship between frequencies that make up natural sounds and their perceived pitch is complex - pitch of such sounds is related to their fundamental frequency - important characteristic of pitch perception is that the pitch of a complex sound may not be directly related to the frequency of any of the sounds component (always fundamental frequency) (ie. 200, 300, 400 100) - missing fundamental - the ear - pinnae ear canal tympanic membrane ossicles (malleus, incus, stapes) oval window cochlea round window - inside the cochlea theres the organ of Corti that contains basilar membrane and the tectorial membrane - tectorial membrane rests on the hair cells and pushes on the hair cells to stimulate action potentials in the auditory nerve (branch of the cranial nerve VIII) - humans can hear a difference in frequency of 0.2% - major principle of cochlear coding is that different frequencies produce maximal stimulation of hair cells at different points along the basilar membrane (higher frequencies producing greater activation closer to the windows (shorter wavelength) - tonotopic - despite everything firing, we still can sort out things - semicircular canals the receptive organs of the vestibular system - carries information about direction and intensity of head movements (maintain balance) - from the ear to the primary auditory cortex - axons of each auditory nerve synapse in the ipsilateral cochlear nuclei, from which many projections lead to the superior olives on both sides of the brain stem at the same level - axons of the olivary neurons project via the lateral lemniscus to the inferior colliculi, where they synapse on neurons that project to the primary auditory cortex - subcortical mechanisms of sound localization - mediated by the lateral and medial superior olives - medial superior olives respond to slight differences in timing - lateral superior olives respond to slight differences in the amplitude of sounds
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