psychophysics in the magnet sean marrett functional mri facility, nimh/nih/dhhs, bethesda, md, usa

Psychophysics in the Magnet

Sean MarrettFunctional MRI Facility, NIMH/NIH/DHHS, Bethesda, MD, USA

Imagine you are starting up your own FMRI lab

• Goal is to maximize the range of possible fMRI experiments and ease with which they can be set up.

• Exercise in this seminar is to consider range of essential equipment and pros and cons of different configurations

• Bare bones and build up from there

What is needed• Experiment control and stimulus generation software (sometimes

the same, sometimes very different)• Interface with scanner to allow synchronization• Visual display • Device to allow subject feedback• Auditory stimulus delivery• Physiological monitoring setup with scanner synchronization• Method for recording eye-movement• Force measurement• Pain stimulation• Digression on head motion

– Prospective head movement correction

Hostile magnet• Strong static magnetic field can disrupt operation of many devices • Projectors Projectiles• RF emitted by coil(s) can interfere with operation and damage some

equipment and can also cause heating in devices / objects that can make them a hazard

• Rapidly changing magnetic field (gradient) can induce current in devices which can interfere or damage electronic devices

• Gradients also responsible for high levels of acoustic noise which make MR very loud (up to 120dB) which can damage hearing and also make it hard to communicate with subjects. Significant ear protection required

• Cables bringing electronic signals in and out of magnet room can bring in small signals that cause artifacts, especially because RF signals detected in FMRI are so tiny tat very low levels of spurious signals brought in from outside can produce prominent or subtle artifacts in reconstructed images.

fORP FIU932

Interface box for button pressesConnects to user’s laptop via USBConnects to trigger box via BNCConnects to button box via proprietary 12-pin fiber connector.Compatible with legacy button boxes.

Current Designs FIU932 System

Synchronization Devices

Stimulus presentation software (Experimental control)

• What is needed • Commercial packages

– E-prime– Presentation

• Open source alternatives– PsychoPy– VisionEgg– Psychophysics Toolbox (+ Matlab($$))– Pygame

Visual stimulus

• Simplest setup includes external projector • Wave guide/ Long throw lens • Good mirror system & screen (DaLite)

Visual stimulus (cont)

• Projector sited inside magnet room• (Faraday cage)• Projector <> Projectile• Some video signals are right around NMR

resonance frequencies• Optical mux/demux

Hyperion Projector (3T-D / NMRF 3T)

Visual stimulus (cont)

• Integrated goggle systems (Resonance technologies, Nordic Neuro)

• Image guides (Avotec)• LCD Panels

Examples: integrated goggle systems

Video system practicalities

• Rear projection vs front projection (Easy set-up and more uniform field of view for diverse body types)

• Optics and long-throw lens (Buhl/Navitar is your friend)• Some modern DLP projectors very hard to modify• Inside magnet / Faraday cage• Outside magnet / wave guide / operation (turning it on

and off)• Timing and synchronization / video memory buffer• E.g. unreliable timing can make backward masking

problematic!

Delivering auditory stimulus in the magnet

• Very loud ambient noise• Headphones with transducers outside magnet• Headphones with electrostatics inside magnet

– Confon system• Opto-acoustic systems• Noise cancellation features• Gradients also responsible for high levels of acoustic noise

which make MR very loud (up to 120dB) which can damage hearing and also make it hard to communicate with subjects.

• Significant ear protection required• Close fitting head coils complicate ear protection and audio

delivery

Example audio delivery systems

Recording subject feedback/response (basic)

• Classic button box• Must be synchronized with scanner• Best if well-integrated with experimental

control software• Several vendors including CurrentDesign,

Psychology Software Tools, Cedrus• Range from classic button box to foot

response, VAS etc• Examples

Basic button boxes

Recording subject response• MRI compatible joystick / mouse• MRI compatible keyboard• Accelerometer/force measurement

Recording subject behavior

• Hand position/orientation • Video feed of subject face/limbs• Eye recording and tracking (next slide)

Eye movement system diagram

Eye movement recording systems

Recording subject behavior more advanced

• Musical instruments• Virtual reality

Subject/patient physiology

• Respiration• Pulse• Electrodermal activity• Integrated with scanner – easy to turn off/on• External system (Biopac or equivalent)

Biopac data acquisition system

Biopac Display

The 1st trace is from the respiration sensor / belt.The 2nd trace shows data from the pulse oximeter.The 3rd trace is the scanner’s TR trigger.The 4th trace is the filtered respiration data (similar to #1).The 5th trace is the filtered pulse oximeter data (similar to #2).

Touch, taste

• Ingeholm touch simulator• Taste – gustatory• Other specialized devices (shout out to

George Dold and Section on Instrumentation)

John E. Ingeholm , George R. Dold , Lawerence E. Pfeffer , David Ide , Seth R. Goldstein , Kenneth O. Johnson , Ro...

The Helix: A multi-modal tactile stimulator for human functional neuroimaging

Gustatory stimulus deliveryJohn Ingeholm and George Dold and Tom Talbot and others

Other essential devices from Section on Instrumentation

Pain

• Medoc stimulator

Recording vocal responses (and communicating with subject)

• Noise cancelling microphones

Starting your own lab – FMRI device budget

• Scanner sync interface + basic button box ~ $2K and up

• Projector/visual display system - $4K and up (including mirror fabrication)

• Audio system - $5K and up• Eye tracking - $10K and up• External physiological monitor $5K and up