Visually-induced Visually-induced auditory spatial adaptation auditory spatial adaptation

in monkeys and humansin monkeys and humans

Norbert Kopčo

Center for Cognitive Neuroscience, Duke UniversityHearing Research Center, Boston University

Technical University of Košice, Slovakia

(Frequent flier # OK10509496)

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IntroductionVisual stimuli can affect the perception of sound location

e.g. the Ventriloquism Effect

Way to go

Red Sox! Way to go

Red Sox!

But does effect persist?

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IntroductionVisual stimuli can affect the perception of sound location

e.g. the Ventriloquist Effect

Way to go

Red Sox!But does effect persist?

- barn owls: prism adaptation (Knudsen et al.)- monkeys: “ventriloquism aftereffect” (Woods and Recanzone, Curr. Biol. 2004)

Why does the effect persist?Calibration of auditory perception(on different time scales):- to new environments (rooms)- to anatomical changes (head size)

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GOALS

1. Ventriloquism “aftereffect” in saccade task, in monkeys and humans?- well-defined sensory-motor paradigm- bridge to barn owl prism adaptation studies (on different time

scale)

2. Reference frame of plasticity?- Visual, auditory, or oculomotor reference frame?

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Methods

Basic idea:

1. Pre-adaptation baseline: Measure auditory saccade accuracy

2. Adaptation phase: Present combined visual-auditory stimuli, with visual location shifted

3. Compare auditory saccade accuracy pre- and post-adaptation

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Methods

Initial experiment: Does it work?

Design:MonkeyPre-adaptation baseline – ~100 Auditory-only trialsAdaptation phase –

80% V-A stimuli, visual stimulus shifted 6 deg. Left or Right

20% Auditory-onlyCompare Auditory-only trials from adaptation phase to pre-

adaptation phase

Sounds: Loudspeakers

Visual stimuli: LEDs

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RESULTS

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RESULTS

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RESULTS

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RESULTS

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QUESTION

How does vision calibrate sound perception in primates?

- monkeys and humans

Unlike barn owls, monkeys and humans make eye movements. With every eye movement, the relationship between visual space and auditory space changes.

Visual and auditory spatial information are different!

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Visual and auditory spatial information are different!

VISION:Retina provides “map” of object locations

Locations shift when eyes move

Frame of reference is “eye-centered”

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Visual and auditory spatial information are different!

AUDITORY:Sound location calculated from interaural timing and level differences

Cue values do NOT shift when eyes move

Frame of reference is “head-centered”

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Goals

Eye-centered?

Head (ear) -centered?

Oculomotor?

?

?

Perform behavioral experiments to answer the following questions:

Does visual calibration of auditory space occur in eye-centered, head-centered, or a hybrid coordinate system?

Are humans and monkeys similar?

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Experimental Setup

Audiovisual display as viewed by the subject

Horizontal location (degrees)

Ver

tical

loca

tion

(deg

rees

)

9 speakers in front of listener (~1 m distance), separated by 7.5° (humans) or 6° (monkeys)

Light-emitting diodes (LEDs)at three center speakers:- aligned with speakers, or- displaced to the left or to the right (by 5°-humans, 6°-monkeys)

2 LEDs below speaker array used as fixation points (FP)

Stimuli:Auditory stimulus:300-ms broadband noise burstAudio-Visual stimulus:Same noise with synchronously

lid LED.

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Method

Audiovisual display Expected behavior

Stimulus Location (°)

Mag

nitu

de (°

)

Induce shift: - in only one region of space- from a single fixation point

Test to see if shift generalizes to the same sub-region in:- head-centered space- eye-centered space

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Experiment: Procedure

Audiovisual display as viewed by the subject

Horizontal location (degrees)

Ver

tical

loca

tion

(deg

rees

)

One trial consists of:

1. Fixation point (FP) appears.

2. Subject fixates FP.

3. Target stimulus is presented (Audio-Visual or Auditory-only).

4. Subject saccades to perceived location of stimulus (humans instructed to always saccade to sound).

5. Monkeys only: Reward for responding within a criterion window (+- 10° from speaker).

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Experiment: ProcedureExperiment divided into 1-hour blocks.AV stimulus type kept constant within a block (left, right, or no displacement).12 blocks for humans, 16 for monkeys.Subjects: 7 humans, 2 monkeys.

Within a block three types of trials, randomly interleaved:

AV FP on left and right. In presentation collapsed to right.

AV stimuli50 % of trials

FPLEDs

Speakers

A-only stimuli trained FP: 25% of trials A-only stimuli

shifted FP: 25% of trials

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Results: HumansAudiovisual display

Expected Responses

FPLEDs

Speakers

Stimulus Location (°)

Indu

ced

Shi

ft M

agni

tude

(M+S

E °

)

or

Trained FP A-onlyresponses:- Shift induced in trained sub-region- Generalization to untrained regions (asymmetrical)

Shifted FP A-onlyresponses:- Shift reduced in center region

Head-centered representation,modulated by eye position

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Results: MonkeysAudiovisual display

Expected Responses

FPLEDs

Speakers

Stimulus Location (°)

Mag

nitu

de o

f Ind

uced

Shi

ft (°

)

or

Trained FP A-onlyresponses:- Shift in trained sub- region weaker- Generalization to untrained regions stronger (asymmetry oppo- site to humans)

Shifted FP A-onlyresponses:- Shift decreases on the right- Shift increases on the leftHumans:

Representationmore mixedthan in humans

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SummaryThe main results are consistent across species:

Locally induced ventriloquist effect results in short-term adaptation, causing 30-to-50% shifts in responses to A-only stimuli from trained sub-region.

The induced shift generalizes outside the trained sub-region, with gradually decreasing strength (However, the pattern of generalization differs across the species)

The pattern of induced shift changes as the eyes move. But, overall, it appears to be in a representation frame that is more head-centered than eye-centered.

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Discussion (almost done)Posterior ParietalCortexNeural adaptation could have been

induced at several stages along thepathway (IC, MGB, AC, PPX, MC,SC).

In humans, multiple effects observed at different temporalscales likely adaptation atmultiple stages

Future workExamine temporal and spatialfactors influencing the eye-centered modulation.Look at other trained sub-regions.

Midbrain

Pons

Cerebrum

Thalamus

Midbrain

Pons

Thalamus

(Kandel, Schwartz, Jessel) and (Purves)

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Humans: temporal profile

In humans, multiple effects observed at different temporal scales likely adaptation at

multiple stages

FPLEDs

Speakers

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Humans: ipsilateral shift

FPLEDs

Speakers

Eye-centered modulation does not occur. Possible explanation: the modulation is specific to the eye-centered hemisphere in which the audiovisual shift is induced (I-Fan currently testing)

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Monkeys: central vs. ipsi shift

FPLEDs

Speakers

FPLEDs

Speakers

Are the monkeys really adapting in an eye-centered co-ordinate frame?

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SummaryThe main results are consistent across species (when shift induced

in CENTER):Shift induced in the center

Shift generalizes to non-trained sub-regions

Shift changes with eye movement

The consistency across species is less obvious when the trained sub-region shifts to IPSI:

Humans: The relatively small eye modulation disappears

Monkeys: Eye movement induces shift that is almost purely eye-centric

Jennifer Groh

Center for Cognitive Neuroscience, Duke University

I-Fan Lin

Barbara Shinn-Cunningham

Hearing Research Center, Boston University

Support

NIH grants to Barb and Jenni

Slovak Science Grant Agency

Collaborators