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Aug 31, 2015
… devices when running Python3.
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Python library for interfacing with Cedrus XID and StimTracker devices XID (eXperiment Interface Device) devices are used in software such as SuperLab, Presentation, and ePrime for receiving input as part of stimulus/response testing experiments. This handles all of the low level device handling for XID devices in python projects. The developer using this library must poll the attached device(s) for responses. Here's an example of how to do so: import pyxid # get a list of all attached XID devices devices = pyxid.get_xid_devices() dev = devices # get the first device to use if dev.is_response_device(): dev.reset_base_timer() dev.reset_rt_timer() while True: dev.poll_for_response() if dev.response_queue_size() > 0: response = dev.get_next_response() # do something with the response The response is a python dict with the following keys: pressed: True if the key was pressed, False if it was released key: Response pad key pressed by the subject port: Device port the response was from (typically 0) time: value of the Response Time timer when the key was hit/released StimTracker Support for Cedrus StimTracker devices is now included. On StimTracker devices, there are the following methods: set_pulse_duration() activate_line() clear_line() See the docstring for activate_line() for documentation on how to use it. These methods are not available if the device is a response pad. StimTracker is used in software such as SuperLab, Presentation and ePrime for sending event markers. Timers Each Cedrus XID device has an internal timer a Base Timer and a Response Time Timer. The Base Timer should be reset at the start of an experiment. The Response Time timer should be reset whenever a stimulus is presented. At the time of this library release, there is a known issue with clock drift in XID devices. Our hardware/firmware developer is currently looking into the issue. Given the issue, use of the response timer built into the response pads is optional. If you wish to use the time reported from the response pads, do the following after importing the pyxid library: import pyxid pyxid.use_response_pad_timer = True This will return the time in the 'time' field of the dict returned by XidDevice.get_next_response(), otherwise, the 'time' field will contain 0. IMPORTANT: Even if you choose *not* to enable the optional timer, you still *must* call reset_base_timer() and reset_rt_timer() at the start of an experiment. This is necessary because pyxid uses the fourth and final byte of the keypress timestamp as a boundary, and pyxid expects the byte to always be null. This will succeed as long as the timer is reset at least once every 4.66 hours. Windows Specific Issues Sometimes, windows fails at detecting XID devices. Running detect_xid_devices() a second time should result in finding the devices.