An introduction to presentation

An Introduction To PresentationMACCS

10/16/07 C:\Christopher - MEG\An Introduction To Presentation.odp page 2

Outline

Experiment structureTabsSDL and PCLScript structure:

Settings and setup in your scriptEventsPCL, logic and loops


Experiment StructureAn overall 'Experiment' file

Composed of one or a number of 'Scenario' files

Scenario files are played in order one after another


Experiment StructureScenario files may be separate SDL and PCL files – more on this later

Experiment

Scenario 1 (SDL)

Scenario 2 (SDL)

PCL 1

PCL 2


Experiment StructureOr both SDL and PCL can be encompassed in the one scenario file

Experiment

Scenario 1 (SDL/ PCL)

Scenario 2 (SDL/ PCL)


Experiment Structure

Depends on personal preference/ styleHaving SDL and PCL scripts in the same file makes it easier for me to editEasier to open all you need if all in one fileI tend not to use SDL only as very limited, therefore will not be covered here


Tabs

The Experiment file contains tabs to cover all of the needed components and settings:


Tabs

The Main tab shows the name of the experiment and location to place log files, both of which can be edited in this tab:


Tabs - ScenariosThe Scenarios tab allows you to add stimulus directory and scenarios:


Tabs – Settings (General)Check 'Wait for return to start scenario':


Tabs – Settings (Response)Best to add buttons to 'default', then 'test':


Tabs – Settings (Video)Your PC will probably only have one video card available. This is fine for testing

When you get to either the ERP or MEG lab this will need to be changed to the 'Radeon' driver

'Current setting' should be fine for most experiments


Tabs – Settings (Audio)'Primary Sound Driver' is the typical setting


Tabs – Settings (Port)Port codes in the ERP and MEG labs are sent by parallel port

Your PC probably won't have a parallel port so you will need to change these settings in the lab

ask for help

To test and run your script on your own PC, click 'Add'

Select an available port, usually 'COM1'


Tabs – Settings (Logfiles)You can typically leave most of these settings alone

A very useful function is the prompt for Subject IDWhen you run the experiment you will see a window in which to type the subject's ID, and press 'enter'

It's not necessary to adjust any settings in the 'Advanced' tab


Tabs - Summary

Save your experiment nameAdd LOG and STIM foldersAdd scenarios'Wait for return to start scenario'Add buttonsAdd an output portSelect 'Prompt' for Subject ID


SDL and PCLTwo language styles implemented in Presentation script

SDL is most useful for:Implementing initial settings

Loading and preparing stimuli

Creating 'Events'

PCL is most useful for:Logic functions

Loops

Output files

'Doing the work'


SDL and PCL

SDL = WHAT

PCL = HOW


Script Structure - SDL

Settings

Load Stimuli

Arrange Stimuli

Define Events


Script Structure – SDL - exampleSettings example:

ISIRGB

Sends port codes

Note comments marked with a “#”


Settings and SetupPort code pulse width:

Onset

Pulse width


Settings and SetupYou can define your own parameters.

Easy to find

Make changes in only one location

Here is the same example with parameter substitutions:



Settings

Load Stimuli

Arrange Stimuli

Define Events


Load StimuliA visual stimulus example:

Your own shortcutCan be '.bmp' or '.jpg'


Load StimuliAn auditory stimulus example:

Must be '.wav' file;

up to 8 channels;

8, 16 or 24 bit



Settings

Load Stimuli

Arrange Stimuli

Define Events


Arrange StimuliBack to our visual stimulus example...

It can be very useful for easier later reference to arrange stimuli into arrays:

An array is just a type of LIST


Arrange StimuliInstead of having to call up the right filename, simply call the next item in the appropriate array

Can also call up an item based on it's reference number in the array

Especially useful for randomisation



Settings

Load Stimuli

Arrange Stimuli

Define Events


Define EventsExample including response dependent trials:

Picture within an event within a trial

“Some text”


Define EventsNote that you don't need a separate trial for each stimulus or stimulus type:

Duration may be left as default, be some other

fixed length, or depend on response

This trial includes response commands – only button 1 is

correct


Define EventsWe use a photodetector in the MEG lab for greater timing accuracy

It detects a white box presented in the corner of the screen

You should include a white box for any stimulus presentation that also has a port code

Just add this box command to

appropriate trials, as well as the “$VISTRIG...”

parameters to the top of the script. We will ensure it works correctly in

the lab


SDL - Summary

Provides settings, stimulus loading and arrangement, and events or trials

“#” can be used for comments, or to temporarily remove lines

Custom parameters can be used (“$ABC...”)

Useful to arrange stimuli into arrays

Stimulus commands are arranged within events, which are arranged within trials

You don't need a separate trial for each stimulus or even each stimulus group

Add 'box' command for MEG experiments


PCLIf you include PCL in the Scenario file, you must use the “begin_pcl” command

Open an output port in order to send port codes

Include a command to automatically name your logfile so it doesn't get lost

You can use “#” as a line break or box

If you keep your PCL separate, tell the scenario file about it in the header:


PCL, Logic and LoopsIn this example, we will present each image twice, in random order

A good way to accomplish this is to use an array, with index numbers representing categories

Note that in PCL, many commands are in the form “name.command(settings)” (“sequenceA” is a name, not a command)

We're filling an array with 8 ones and 8 twos. The remaining 8 will be zeros

“shuffle()” randomises the array


PCL, Logic and Loops

Start itemEnd item First number

Increment


A Word About Randomisation

When you use random functions, you don't always get what you expect – i.e. Clumping

You generally won't get all your items shown about the same number of times

You will therefore generally want to constrain the random!

Here we have arrays of ones, twos threes and fours serving as indexes for our stimulus arrays

We can now be sure all our images will be shown the same number of times each


PCL, Logic and LoopsWe're ready to commence the main task of presenting stimuli

The introduction screen and fixation cross are presented easily enough:

Trials are generally presented using loops:


PCL, Logic and LoopsA typical loop:

The index “i” is only valid inside the loop

You must increment the index manually

Has both pros and cons


PCL, Logic and LoopsNote that new lines and spacing are irrelevant in Presentation, so this is exactly the same loop:


PCL, Logic and LoopsWe will need more indexes to loop through the arrays for each category: faces, cars and butterflies

We set the picture to be one of the faces

“==” means “is equivalent to”

We give the logfile the description of that face from the beginning of the script

We tell the port we want “1” to be sent for facesWe present the face, increment the face index, and present a fixation cross

****


PCL, Logic and LoopsNote the use of “elseif” and “else” statements

Repeat the above procedure using the arrays and indexes for cars and for butterflies

Note that we want responses to be valid for butterflies, so we use the trial that includes a target button


PCL Output File

Stimulus manager

“||” = “logic or”“&&” = “logic and”


Testing and Debugging

'Analyze'

'Error Box'

'Run Scenario'


Run Your Experiment

'Run Experiment'


Experimental Design Considerations

Repetition Signal-to-noise-ratio

AT LEAST 60 trials per condition.

BreaksHappy and comfortable subjects

Tiring

Procedure length

Compromise between ideal number of trials and subject

fatigue

Performance of the conductive gel will decline with time

About two hours or less.

At MEG, maximum block length is 20 min


Experimental Design Considerations

Sufficient port codesAllocate different port codes to each category

Err on the side of excessive port codes

256 in ERP lab, about 16 in MEG lab

Visual offset and ISI

Visual ERP component

Do not overlap with epoch or pre-stimulus (baseline)

interval.

Assuming the allocation of a 200ms baseline interval, and

adding to this the 100ms offset component, you need an

ISI of at least 300ms. Add some more just to be sure!


Resources

Presentation help file is okay, but confusingNeurobehavioral Systems forum:

“www.neurobs.com/chatter_box/search”

ERP Lab Server Library:“\\Currawong\ERP\LIBRARY”

Education

An introduction to presentation