VIEWS: 0 PAGES: 6 POSTED ON: 9/29/2012
Control of (some) External Devices using MatLab/Cogent Steffan Kennett, Topics covered Parallel Ports (see Stimuluscheck.m): Set-up procedure Implementation in code Problems (addresses, timing) Eye-tracking (see Eyetracker_demo.m): Acquiring data. Meaning from data (calibration) Vocal Reaction Time (see voiceRT.m): Acquiring data Calculating reaction time Calibration Parallel Ports • Digital Signal • Up to 8 lines independently controlled • Use signal to switch on stimuli (lights, taps, TMS etc.) – This requires some form of switch box to transfer signal and power to the external stimuli (e.g., LEDs or tappers) • Use signal to trigger EEG, fMRI, TMS. – Requires the parallel port cable is appropriately wired for your specific device Installation: Excellent documentation at point 3.12 of cogmanv125.pdf Extract UserPort.zip follow instructions. Use function “outportb(port_address,value)”. See Stimuluscheck.m Parallel Ports Address: usually 888, could be 632, 956. Refers to specific parallel port. Value: any integer from 1 to 255 Value is actually the decimal version of an 8-bit binary number (1 1 1 1 1 1 1 = 255). Line Binary value Decimal value 1 00000001 1 2 00000010 2 3 00000100 4 4 00001000 8 5 00010000 16 6 00100000 32 7 01000000 64 8 10000000 128 Lines 3 and 5 would be value = 4 + 16 = 20 Eye-tracking • Cogent only supports the ASL 5-series (e.g., ASL 5000), which is the eye-tracker currently installed in the MRI scanners at 12, Queen Square. • Good documentation is in G2UsrManv124.pdf. See pages D10, E5, F21 and section I. • See also sample m-file Tracker.m (Samples folder) and Eyetracker_demo.m (Matlab course download) Calibration tip: Once you’ve set-up the eye-tracker you will have to carry out the tracker- software’s own calibration procedure. Even having done this, start each experiment, or better, each block of trials with a mini-calibration of your own. Use jumping crosses of known visual angle (see . Choose these visual angles to be relevent to your experiment (e.g., close to fixation point if you do not want saccades in your experiment). See jumping_cross.m. Vocal Reaction Time • Uses built-in microphone or one plugged into the sound card of your PC. • Employs “config_sound” prior to “start_cogent” • Commands used (input/output variables in italics): – preparerecording(duration_in_ms) – recordsound – waitrecord – sound_vector = getrecording • See voiceRT.m for a fully commented, working script – RT is calculated by measuring the first sample which exceeds a threshold level (user sets this) and working out the time since the stimulus was presented.
Pages to are hidden for
"No Slide Title"Please download to view full document