AUDITORY CORTEX 4SEPT 21, 2015 – DAY 12

Brain & Language

LING 4110-4890-5110-7960

NSCI 4110-4891-6110

Fall 2015

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Course organization• http://www.tulane.edu/~howard/BrLg/• Fun with https://www.facebook.com/BrLg15/• I am still working on grading.

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AUDITORY CORTEX 3The quiz was the review

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Summary

LH

• stops & liquids/glides/fricatives

• lexical stress• CONvert ~ conVERT• tone languages

• phrasal stress• noun compounding• stress retraction

• clausal stress• contrastive stress

RH

• vowels (?)• emotional prosody• sentence type

• declarative, interrogative, imperative

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Size of temporal integration windows

• Primary auditory cortex builds high-fidelity representations of the signal and surrounding non-primary areas differentially ‘elaborate’ this signal by analyzing it on different time scales (Poeppel et al., 2008)• LH (non-primary) temporal cortex houses neuronal ensembles

with somewhat shorter integration constants (say, 20-50 ms) and therefore LH cortical fields preferentially reflect [fast] temporal properties of acoustic signals

• RH (non-primary) temporal cortex houses neuronal ensembles a large proportion of which have longer (150-300 ms) integration windows, and therefore are better suited to analyze [slower] spectral change

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AUDITORY CORTEX 4

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FREQUENCY IN THE VISUAL DOMAINSpatial frequency

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High- vs. low-frequency spatial information

What is this?

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Salvador Dali “Gala Contemplating the Mediterranean Sea, which at 30 meters becomes the portrait of Abraham Lincoln (Homage to Rothko)”, 1976

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"Lincoln illusion” Harmon & Jules (1973)

• Blurring acts as a low-pass filter, reducing the high masking frequencies

• http://www.michaelbach.de/ot/fcs_mosaic/index.html

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Spatial frequencyHigh spatial frequency

(two cycles per degree)

Low spatial frequency

(one cycle per degree)

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Spatial frequency:LHD ~ stimulus ~ RHD

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Lateralization of frequency• RH allows the low frequencies of a stimulus to pass through, ignoring the higher ones (low-pass filter).

• LH allows the high frequencies of a stimulus to pass through, ignoring the lower ones (a high-pass filter).

• Duration becomes a measure of frequency in the temporal domain:• a brief signal has a high temporal frequency; • a prolonged signal has a low temporal frequency,• and at least two other domains are recognized, the

spectral and the spatial (but we ignore spatial frequency for now).

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FINE VS. COARSE CODING

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Categorical vs. graded or coordinate spatial relations

Is the black dot

above or below the bar?

Is the black dot

near or far from the bar?

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Categorical > LH Graded > RH

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Fine vs. coarse coding

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Fine coding:small receptive fieldwith no overlap

Coarse coding:large receptive field

with overlap

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A conversion to resolutionLeft hemisphere, fine coding:

9 neurons index 9 regions of space

Right hemisphere, coarse coding:

4 neurons index 12+ regions of space

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Summary of lateralization of phonologyLH

fine grained, small window of temporal integration

• high temporal frequency:• rapid cues, like stops

• high spectral frequency: • formants

• categorical distinctions: • lexical, phrasal, clausal

stress;• lexical tone in Thai/Chinese

RHcoarse grained,

large window of temporal integration

• low temporal frequency: • slow cues, like vowels

• low spectral frequency: • fundamental

• graded/coordinate distinctions:• emotional intonation,• sentence type?

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CATEGORICAL PERCEPTIONof voice-onset time

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'BP' for [bi] vs. [pʰi]

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Voice-onset time (VOT)

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Is VOT perceived as a continuum?

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What is this?(ignore the fact that it is crooked)

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If VOT is gradually lengthened from 0

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Altmanna (2014) Categorical speech perception during active discrimination of consonants and vowels

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This bar graph depicts the mean (n=15) response amplitudes from 430 to 500 ms after S2 onset within the left temporal cortex cluster as a region-of-interest.

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By the way …

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Chinchillas do this too!

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Conclusion• Categorical perception

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NEXT TIMEDo we have class on Wednesday?

Mid-posterior STS, Wernicke’s area

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