OPM-MEG Speaker Artifact Detection

Empty room PsychoPy experiment for characterizing audio speaker artifacts in OPM-MEG recordings.

Design

Sound and no-sound trials are randomly interleaved in a single continuous recording using a permuted block design (block size = 6): within every 6 consecutive trials there are exactly 3 sound and 3 no-sound trials in random order. This ensures tight temporal balance between conditions throughout the recording, preventing slow environmental drift from being confounded with condition.

Each sound trial plays a unique pink noise waveform (pre-generated before the experiment starts) to prevent phase-locked averaging artifacts.

Screen color changes in the blue channel encode trial type for PixelMode B hardware triggering into the MEG acquisition system. PixelMode B is enabled automatically at startup via pypixxlib and disabled cleanly on exit.

State	RGB (0–255)	Description
Sound ON	(0, 0, 32)	Pink noise playing
No-sound ON	(0, 0, 64)	Screen only, no audio
ISI	(0, 0, 0)	Inter-stimulus interval

Parameters

Edit the PARAMETERS block at the top of Speakertest.py:

• N_PER_CONDITION — trials per condition (default 200; 400 total)
• BLOCK_SIZE — trials per permuted block, must be even (default 6)
• BLOCK_DURATION — ON period duration in seconds (default 2.0)
• ISI_MIN / ISI_MAX — jittered ISI range in seconds (default 1.5–3.5s)
• NOISE_VOLUME — speaker volume 0–1 (default 0.8)

Output

• opm_speaker_artifact.log — full PsychoPy log
• opm_speaker_artifact_events.tsv — trial-by-trial onset times, block numbers, and ISI durations

Requirements

• PsychoPy
• pypixxlib
• NumPy