Lecture 23: Speech and Language

Language Areas

Linguistic abilities depend on the integrity of several specialized areas

→ located primarily in the association cortices of the left temporal, parietal, and frontal lobes

Broca’s area

Language/speech production

(frontal cortex)

Wernicke’s area

Understanding of written and spoken language

Broca’s aphasia (Expressive Aphasia)

Slow, laborious, non-fluent speech

• Patients “know what they want to say, they just cannot get it out”

• Motor planning deficits → Lesions in left posterior frontal lobe

Wernicke's aphasia (Sensory/Receptive aphasia)

Impairment of language comprehension (written and spoken)

• Speech is phonetically and grammatically normal, but meaningless

• Inability to convert thoughts into words

• Often accompanied by denial of deficit

Lesions in the left posterior temporal lobe (pretty sure)

→ Also auditory association cortex

Conduction Aphasia

Meaningful, fluent speech → relatively good comprehension, but very poor repetition

Short-term memory/rehearsal of words and speech is disrupted.

Arcuate fasciculus conveys info about sounds, but not meaning.

Lateralization of language

Split-brain patients:

• Right hand or right visual field (left hemisphere) → Able to name object

• Left hand or left visual field (right hemisphere) → Problem naming object

Stereognosis

The ability to perceive and recognize the form of an object in the absence of visual information

Wada Test

Short-acting anesthetic injected into the left carotid artery

→Transiently ‘anesthetizes’ the left hemisphere & tests its functional capabilities

If the left hemisphere is dominant for language, the patient transiently becomes aphasic while carrying out an ongoing verbal task, like counting

→ Shows that ~97% of humans, including the majority of left-handers, have verbal language functions represented in the left hemisphere

planum temporale

Part of Wernicke’s area

→ Larger on the left (dominant) side

Sign Language

• Left hemisphere lesions → deficits in sign production and comprehension

• Right hemisphere lesions → impaired visuospatial processing and emotional processing

Critical Period

• Becoming fluent requires linguistic experience relatively early in life

• Decline in fluency of nonnative speakers as a function of age

Bird Vocal Communication

• Some birds use songs to define their territory and attract mates

• Early sensory exposure and practice are key determinants of subsequent perceptual and behavioral abilities

• The developmental period for learning these vocal behaviors is restricted to early life

Sensory acquisition stage

Juvenile bird listens to and memorizes the song of an adult male ‘tutor’ of its own species

Sensory-motor learning stage

Practice! The young bird matches its song to the memorized tutor model by auditory feedback

Crystallized song stage

The bird’s songs become acoustically stable

Ape Language

Apes can learn to sign and are able to communicate with humans.

However, it is disputed as to whether they can form syntax to manipulate such signs.

Early Intensive Behavioral Intervention (EIBI)

• Early: before 3-4 years of age • Intense: 20+ hours/week

• Long term: 1-2 years

• Increase in IQ scores of 17 points (> 1 SD) and significant gains in language and adaptive behavior

• Shorter latencies and increased cortical activation following 2 years of EIBI, which was associated with improved social behavior

Dysarthria

Difficulty moving the muscles to speak

Motor deficit rather than motor planning deficit