Exam 2 Chapter 5

In the cerebral cortex, where does speech perception begin? Where does it continue? Where does it terminate?

With spectrotemporal processing on the dorsal plane of the temporal lobe; it continues with phonetic processing in dorsal and lateral parts of the STG; it terminates w/ word form recognition in the mid-posterior STS.

What does the flow of neural activity (in relation to hierarchical organization) reflect?

The progressive extraction of increasingly complex linguistic representations, from phonetic features to phonemic sequences syllables and whole words.

What drives hierarchical organization?

The incoming speech stream influenced by prior knowledge & expectations as well.

Although speech perception appears hierarchical, further complexities have been found like…

The division of the lateral STG into separate zones that are differentially sensitive to the onsets and sustained parts of utterances.

What do many neuroimaging and neuropsychological studies tell us about what hemispheres are involved the early stages of cortical speech perception?

Present in both hemispheres with a mild-moderate left sided bias.

According the Asymmetric Sampling in Time (AST) hypothesis, what is the left hemisphere dominant for detecting?

Rapidly changing signals in the 20-80 ms range (artic cues)

According the Asymmetric Sampling in Time (AST) hypothesis, what is the right hemisphere dominant for detecting?

Longer signals in the 150-300 ms range (syllabic cues)

After the early cortical stages of speech processing have occurred, what is the next step?

A fork in the river! There are separate streams for the “what” and the “how”.

What does the ventral stream do in terms of speech perception?

Comprehension

What does the dorsal stream do in terms of speech perception?

Maps auditory representations of speech onto matching motor representations.

Where did the initial evidence for the dual-stream model come from?

Brain damaged patients. They displayed double dissociations between the ability to comprehend utterances and the ability to repeat them, or closely monitor their phonological makeup.

The ventral stream allows listeners to understand the ———— ———- of utterances.

Conceptual content

What is the “what” stream?

Ventral

What are the two components of the ventral stream?

1. The Lexical Interface

2. The Combinational Network

The Lexical Interface (Ventral Stream)

• Contains lemmas

• During speech perception, the lexical interface maps the sound structures of words onto the appropriate meanings of syntactic features

• It is hard to localize in brain, appears to be in the pMTG bilaterally but with mild-mod left sided bias

Lemmas

Abstract word units that tie together the phonological, semantic, and grammatical properties of words.

The Combinatorial Network (Ventral Stream)

• Uses input from the lexical interface to derive the composite meanings of phrases and sentences

• It might integrate both semantic and syntactic properties of the words in phrases and sentences

• Recent research suggests it is primarily involved in semantic combinatorial processing

• Resides in the aMTG and adjacent parts of the ATL, predominantly in the left hemisphere

What is the “how” stream?

Dorsal stream

What are the functions of the dorsal stream?

• Allows listeners to overtly repeat utterances

• Essential for verbal STM

• Facilitates speech perception

  • Partly through automatic motor stimulation

What are the two components of the dorsal stream?

1. Sensorimotor interface

2. Articulatory network

Sensorimotor Interface (Dorsal Stream)

• Relay structure

• Maps sound structures of works onto the corresponding motor representations and vice versa

• Resides in area SPT (deep in posterior end of sylvian fissure)

Articulatory Network (Dorsal Stream)

• Underlies speech production

• Depends on several regions in the left frontal lobe