|Don't forget the BBTK v2 is a dedicated self-contained hardware device that is designed to record onsets, reaction times and TTL event mark physical events in the real world as they occur with sub-millisecond accuracy. It has been specifically developed to help researchers address timing issues related to their own paradigms running on their own hardware.
Shown below is a simple visual stimulus reaction time experiment where we are using a response pad together with a BBTK v2. It is intended to give you a flavour of how the BBTK v2 could work for you and how easy it is to use.
Remember the BBTK v2 could be wired to your own response device in order to trigger that. Plus you could choose to have more monitoring sensors (opto-detectors, mics, TTL inputs etc) and more outputs from the BBTK v2 (sounders, Robotic Key Actuator, TTL event markers etc).
When carrying out any experiment you should ask yourself:
- Are you always carrying out the experiments you assume you are?
- Are you aware of millisecond timing error in your own experiments?
- Are you confident you can replicate experiments using different hardware and software in another lab?
A simple visual stimulus is presented once every second with a blank interval of one second. A human participant's task is normally to press a response button as quickly as possible and then release it.
Questions we should ask
- Are visual stimuli presented for one second?
- Are interstimulus intervals (ISIs) accurate at one second?
- Are response times (RTs) recorded accurately from the first frame of the visual stimulus?
- Are response durations accurate?
How we test
An opto-detector, or photodiode, is hooked up to a monitor where a visual event marker will appear (black to white block transition). This will physically monitor for the onset, duration and offset of each visual stimulus.
Opto-detector placed on back/white block
B. Active Switch Closure
An Active Switch Closure lead is plugged into the BBTK USB response pads external button socket 1. This lead could actually trigger your own response device, or one of our Robotic Key Actuators could be used to press a key on a laptop of screen region on an iPad. This signal could also be a TTL output from the BBTK v2 if required.
C. Select target timings using wizard
Using a wizard enter the target response time and key down duration. In this case we are using the Digital Stimulus Capture And Response wizard. Target RT is 300mS and button down duration is 100mS. These are our benchmark figures.
Easily enter target timing specifications using a wizard
D. Start experiment
Start the experiment generator and click start on the BBTK v2 software. Let the BBTK respond to each stimulus presentation and step through your experiment as though it was a real human participant.
E. Analyze true real world timing data
Analyze collected timing data using our easy to use PC software. Either look up timings in the Line By Line spreadsheet view or use the moveable cursors to check on individual timings.
The BBTK v2 PC software in action (click to enlarge)
Easily read off timings such as opto-detector onset, offsets and durations in the spreadsheet view
Use the quick graph to chart any columns in the spreadsheet view
Analyse data in the 20 Channel Logic Analyser
Answers to our original questions
1. Visual stimuli
Visual stimuli are not presented accurately for one second as intended as they vary by upto two refreshes.
2. Interstimulus intervals
Interstimulus intervals (ISIs) are not one second as intended as they vary according to refresh inaccuracies in the monitor used.
3. Response times
By comparing the response times (RTs) recorded by the experiment generator against our target RTs we can see that the true RTs are radically different. This is because the experiment generator times responses from the time it requests the stimulus image be displayed and not when it actually appears in the real world. If you think about it, how can a piece of software know when a visual stimulus appears physically? Remember the target RTs were all 300mS.
Response time error that is due to the hardware alone
4. Response durations
Response durations are not 100mS as intended due to a combination of response times being measured from the wrong start point by the experiment generator, i.e. not the point where the stimulus image appeared in the real world, and because of error introduced by using a standard response device combined with the accuracy and precision issues within the experiment generator.
In this example visual stimuli were not presented as intended and RTs were not recorded correctly. You should note that the figures in this example have been kept deliberately simple. Remember that the variations and recorded are purely the result of equipment error as the BBTK v2 consistently fed in RTs of 300mS.
It is likely that your own paradigms will contain more error than in this simple example!