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Lecture 7

Psychology 2220A/B Lecture Notes - Lecture 7: Cochlea, Sound Localization, Cranial Nerves

Course Code
Scott Mac Dougall- Shackleton

of 8
• 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
A band 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 Primate Auditory 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
• 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 of Auditory 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
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 the Auditory 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
– Partial cochlear damage results in loss of hearing at particular frequencies
Auditory Scene Analysis
• 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
• The area of the body innervated by the left and right dorsal roots of a given segment of spinal
• 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
Cortical Areas 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
• 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