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Lecture 7

Psych 2220A Lecture 7

8 Pages
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Department
Psychology
Course Code
Psychology 2220A/B
Professor
Scott Mac Dougall- Shackleton

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Psych 2220A Lecture 7 Hearing • The auditory system (7.2) • Auditory perception and stream segregation (not in text in detail) Auditory Cortex • Auditory cortex is located in the temporal lobe • Core region: includes primary cortex • Belt surrounds the core region –Aband of secondary cortex • Secondary cortex outside the belt – Referred to as parabelt areas • About ten separate areas of secondary auditory cortex in primates Organization of PrimateAuditory Cortex • Functional columns (cells of a column respond to the same frequency) • Tonotopic organization • Secondary areas do not respond well to pure tones, likely important for more complex features of sounds Stimuli • Still much to learn about dimensions of sounds processed in different parts of auditory cortex • Challenge of using simple sound stimuli (tones) – easy to manipulate, but lack complex features that the cortex may be designed to process – many cortical cells respond to vocalization sounds Two Streams ofAuditory Cortex • Auditory signals are conducted to two areas of association cortex – Prefrontal cortex – Posterior parietal cortex • Anterior auditory pathway may be more involved in identifying sounds (what) • Posterior auditory pathway may be more involved in locating sounds (where) Auditory-Visual Interactions • There is evidence for interactions between the auditory and visual systems – e.g. some posterior parietal neurons with both visual and auditory receptive fields • Interaction in primary sensory cortices indicate that sensory system interaction is an early and integral part of sensory processing McGurk effect • Phonemes often vary continuously, but are perceived categorically • Visual and auditory input of two phonemes can give rise to perception of intermediate phoneme! • http://www.youtube.com/watch?v=G-lN8vWm3m0 Psych 2220A Lecture 7 Where Does the Perception of Pitch Occur? • Most auditory neurons respond to changes in frequency rather than pitch • One small area just anterior to primary auditory cortex has neurons that respond to pitch rather than frequency – May be where frequencies of sound are converted to perception of pitch Effects of Damage to theAuditory System • Lesions of auditory cortex in rats results in few permanent hearing deficits • Lesions in monkeys and humans hinder sound localization and pitch discrimination • Deafness in humans – Total deafness is rare, due to multiple pathways – Two kinds: conductive deafness (damage to ossicles) and nerve deafness (damage to cochlea) – Partial cochlear damage results in loss of hearing at particular frequencies Auditory SceneAnalysis • Cocktail party phenomenon – Pop-out of salient stimuli • Stream segregation – Complex auditory stream partitioned into individual auditory objects • Completion of partial stimuli – Specialized perception of phonemes and speech Stream segregation •Auditory streams segregate based on pitch similarities and timing Completion of Partial Stimuli • Picket fence effect * Somatosensory System Text Section 7.3 * Somatosensory Homunculus • Homunculus = “little man” • Shows the relative size of the somatosensory representation devoted to various body parts • Do you notice a relationship between the size of the representation and the sensitivity (e.g., two-point touch threshold)? Somatosensory System: Touch and Pain • Somatosensory system is three separate and interacting systems: • Exteroceptive – external stimuli • Proprioceptive – body position • Interoceptive – body conditions (e.g., temperature and blood pressure) Psych 2220A Lecture 7 Cutaneous Receptors • Free nerve endings – Temperature and pain • Pacinian corpuscles –Adapt rapidly, large and deep; onion-like – Respond to sudden displacements of the skin • Merkel’s disks – gradual skin indentation • Ruffini endings – gradual skin stretch Dermatome • The area of the body innervated by the left and right dorsal roots of a given segment of spinal cord • Considerable overlap between adjacent dermatomes Two Major Somatosensory Pathways • Dorsal-column medial-lemniscus system – Mainly touch and proprioception – First synapse in the dorsal column nuclei of the medulla •Anterolateral system – Mainly pain and temperature – Synapse upon entering the spinal cord – Three tracts – spinothalamic, spinoreticular, spinotectal • Lots of overlap in function of these two pathways Spinal Injury • Transection of both paths leads to complete lack of sensation below the level of the cut CorticalAreas of Somatosensation • Primary somatosensory cortex (SI) – Postcentral gyrus – Somatotopic organization (somatosensory homunculus) – more sensitive, more cortex – Input largely contralateral • SII – mainly input from SI – Somatotopic; input from both sides of the • Much of the output from SI and SII goes to association cortex in posterior parietal lobe Platypunculus? • Platypus homunculus (platypunculus?) – Platypus has tactile and electrosensory receptors – bill = 75% of S1 Receptive Fields of S1 Neurons • Similar to V1, many neuron’s receptive fields have antagonistic excitatory and inhibitory areas • Columnar organization: in a column receptive fields are for same part of the body Psych 2220A Lecture 7 Effects of Damage to the Primary Somatosensory Cortex • Effects of damage to the primary somatosensory cortex are often mild – Likely due to numerous parallel pathways Somatosensory System andAssociation Cortex • Highest level of sensory hierarchy are areas of association cortex in prefrontal and posterior parietal cortex • Posterior parietal cortex contains bimodal neurons – Neurons that respond to activation of two different sensory systems –Allow integration of visual and somatosensory input SomatosensoryAgnosias • Astereognosia – inability to recognize objects by touch – Pure cases are rare – other sensory deficits are usually present • Asomatognosia – the failure to recognize parts of one’s own body Perception of Pain • Despite its unpleasantness, pain is adaptive and needed • No obvious cortical representation of pain (although the anterior cingulate gyrus appears involved in the emotional component of pain) • Descending pain control – pain can be suppressed by cognitive and emotional factors Descending Pain Control • Circuitry identified by the following studies: • Electrical stimulation of the periaqueductal gray (PAG) has analgesic effects • PAG and other brain areas have opiate receptors • Existence of endogenous opiates (natural analgesics) – endorphins Neuropathic Pain • Severe chronic pain in the absence of a recognizable pain stimulus • Likely from pathology of nervous system linked to an injury • Some evidence for aberrant glial cell signals triggering neural pain pathways Chemical Senses: Smell and Taste • Olfaction (smell) – Detects airborne chemicals • Gustation (taste)
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