Background
• Neural organization of speech perception difficult to
characterize
• 1st hypothesis: based on auditory cortex (auditory
language comprehension disorders, left STG lesions)
• Challenged by 2 discoveries
– Deficits in speech sound perception contribute minimally to
auditory comprehension in Wernicke’s aphasia
– Destruction of left STG leads to deficits in speech production
(not auditory comprehension)
• Deficits in syllable discrimination from frontoparietal
damage
• Syllable discrimination and word comprehension doubly
dissociated (can have one without the other)
Paradox and Article Goal
• First imaging studies:
– Passive listening highlights ST regions bilaterally
– Syllable discrimination activates left STG and left IF lobe
• Paradox remains
• Damage to left regions causes mainly deficits in speech
production (not auditory comprehension issues)
• In this article we will:
– Describe and extend a dual-stream model of speech processing
that resolves paradox
– Outline central components
– Discuss model assumptions and relevant evidence
Task Dependence and Definitions
• Neural organization of speech processing is task
dependent => must define task of interest
• Speech perception and speech recognition doubly
dissociate (can have one without the other)
• Speech processing = any task involving aurally presented
speech
• Speech perception = sublexical tasks (e.g. syllable
discrimination)
• Speech recognition = mapping of acoustic signals to
mental lexicon
• Not necessarily a single route to recognition
• Perception tasks involve executive control and working
memory
Dual-stream model
Ventral stream: sound to meaning
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[Dorsal stream: sound to action]
Parallel computations and bilateral organization
Multi-time resolution processing
STS crucial to phonological-level processing
Lexical, semantic and grammatical linkages
Parallel routes
Lexical phonological networks in STS
Dorsal stream: sound to action
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Less agreement on role of auditory dorsal stream
Spatial hearing, “where” function
Interface with motor system
Need for auditory-motor integration
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Learning to speak is a motor task
Neural mechanism for mapping sounds to speech gestures
Generation of sensory representation of new words
Continues to function in adults
• Evidence for a sensorimotor dorsal stream
– Left lesions (conduction aphasia: phonemic errors but
comprehends)
– Functional imaging (next figure)
Auditory-motor task for speech
Summary and future perspectives
• Acoustic speech network must interface with
– Conceptual systems
– Motor-articulatory systems
• Above basic concept accounts for an array of
fundamental observations
• It also fits with similar proposals in the visual and
somatosensory domains
• Might be a reflection of a more general principle of
sensory systems organization
• Future work
– Specify within-stream details
– Empirical work to test hypotheses
– How neural models map to linguistic and psycholiguistic models
Operculum