Hardware compatibility¶
Video cards¶
We generally have good experiences with recent NVIDIA or ATI cards. OpenGL mode should work with all drivers that use an OpenGL specification >= 2.0. Drivers implementing an older OpenGL specification (>= 1.4) should work when the ‘GL_ARB_texture_non_power_of_two’ extension is present.
On some some integrated Intel cards syncing to the vertical retrace does not seem to work!
Working configurations¶
Here is a list of configurations we observed to work:
- Nvidia GTX 650 (Linux-x86; NVIDIA driver 310.14)
- Nvidia Quadro NVS 290 (Linux-x86; NVIDIA driver 295.40)
- Nvidia Quadro NVS 290 (Windows XP SP3; NVIDIA driver)
We recommend to always use the Expyriment test suite to check the performance of your specific configuration!
External devices¶
Besides standard serial and parallel port communication, there is special support for:
Event button box¶
An event button box is a simple device which sends out values (bytes) whenever a button is pressed (or released).
Event button boxes can be used by initializing an expyriment.io.EventButtonBox object:
bb = expyriment.io.EventButtonBox(expyriment.io.SerialPort("COM1"))
key, rt = bb.wait() # Wait for any value
Streaming button box¶
A streaming button box constantly sends out a certain baseline value (e.g. 0) in predefined intervals (e.g. each 1 ms). Button press (or release) events (if present) are added to the baseline.
Streaming button boxes can be used by initializing an expyriment.io.StreamingButtonBox object:
bb = expyriment.io.StreamingButtonBox(expyriment.io.SerialPort("COM1"),
baseline=128)
key, rt = bb.wait() # Wait for any value other than 128
This allows for instance for calculating the response timing without relying on the computers internal clock, but by “counting” the incoming bytes from the button box:
bb = expyriment.io.StreamingButtonBox(
expyriment.io.SerialPort("COM1"), baseline=128)
bb.clear()
exp.clock.wait(1000)
rt = bb.interface.read_input().index(129) # Get reaction time by counting
# input events since last clear
It is important to notice that operating systems only buffer a certain amount of bytes (usually 4096). To prevent an overflow of this buffer, the button box has to be checked regularly. Additionally, an input_history can be used on the expyriment.io.SerialPort object which is automatically updated whenever the serial port is polled or cleared. By setting the os_buffer_size correctly, a warning will be logged whenever the amount of bytes in the OS serial port buffer reaches maximum capacity. The important part now is to update the input_history regularly. To gain maximal control, this should be done manually at Sending to external deviceappropriate places in the code. However, Expyriment provides also the possibility to register a callback function which will be called regularly during all waiting methods in the library. By registering the check() method of the streaming button box, the input_history will be updated fairly regular, which should suffice for most use cases:
expyriment.control.register_wait_callback_function(bb.check)
bb.interface.input_history.check_value(129) # Check if 129 was
# received at any time
# RT by counting elements in input history
start = bb.interface.input_history.get_size() - 1
exp.clock.wait(1000)
rt = bb.interface.input_nput_history.check_value(129,
search_start_position=start) - start
Trigger input¶
Expyriment can wait for triggers from external devices, like for instance an MR scanner.
When updated regularly, Expyriment can also keep track of the amount of triggers that have been received. Importantly, this has to be done manually
Trigger inputs can be used by initializing an expyriment.io.TriggerInput object.
Basic usage
In most of the cases, a researcher knows when a trigger is to be expected and he can wait for it explicitly. Code execution will be blocked until the trigger is received:
trigger = exyriment.io.TriggerInput(expyriment.io.SerialPort("COM1"))
trigger.wait(1) # Wait for code 1
Advanced usage
In some cases, code blocking might not be a solution, since a trial has to continue while waiting for the trigger. For instance, in an fMRI study, a trial might consist of several components and span several TR. One way to solve this would be logging constantly all input events in a separate thread. However, this will introduce timing uncertainties, since the operating system is in charge of how and when threads communicate. We thus decided against an implementation with threads for the same reasons Expyriment does not implement a main event loop: Maximal control by the user. Nevertheless, input events can still be buffered without introducing timing uncertainties, given the following two conditions:
- Incoming events are streaming, either by sending some baseline in regular intervals (e.g. a 0 each millisecond), or by a regular incoming signal of interest (e.g. a constant TR from the MR scanner).
- The input device is polled regularly, such that the serial port OS buffer does not overflow. (Most implementations use an OS buffer of 4096 bytes).
If those two conditions are met, an input_history can be used on the expyriment.io.SerialPort object which is automatically updated whenever the serial port is polled or cleared. By setting the os_buffer_size correctly, a warning will be logged whenever the amount of bytes in the OS serial port buffer reaches maximum capacity. The important part now is to update the input_history regularly. To gain maximal control, this should be done manually at appropriate places in the code. However, Expyriment provides also the possibility to register a callback function which will be called regularly during all waiting methods in the library. By registering the get_trigger() method of the input trigger, the input_history will be updated fairly regular, which should suffice for most use cases:
trigger = exyriment.io.TriggerInput(expyriment.io.SerialPort(external"COM1",
input_history=True, os_buffer_size=3000))
expyriment.control.register_wait_callback_function(trigger.get_triggers)
print trigger.trigger_count
Marker output¶
Expyriment can send markers to external devices, like for instance EEG computers.
Marker outputs can be used by creating an expyriment.io.MarkerOutput object.
Basic usage
Sending out markers is straight forward. Some devices (e.g. EEG systems) expect a 0 to be send after the code. We can specify this by telling the output marker at what duration this 0 is supposed to be sent:
marker = expyriment.io.MarkerOutput(expyriment.io.SerialPort("COM1"), duration=20)
marker.send(1) # Send code 1
Cedrus response devices¶
Expyriment comes with a high-level wrapper for Cedrus response devices expyriment.io.extras.CedrusResponseDevice_, which allows you to easily use all Cedrus response devices.
To use these devices, however, the third-party Python package pyxid needs to be installed on the system.
Installing pyxid
