|Voice keys for vocal responses in psychology experiments
In certain psychology experiments voice keys are used for recording responses and measuring reaction times. These operate on the basis of "crossing thresholds" or the number of times an auditory signal reaches or crosses a certain set threshold. The trigger threshold for a voice key is also susceptible to whether fricatives, plosives, voiced or unvoiced sounds are made in order to trigger it.
Often the researcher is unaware of what this threshold actually is and whether the setting is the same as one used previously. As with other response devices the electronics and the interface used can vary considerably from device to device which can add 10's if not 100's of milliseconds to actual response times.
Without independently checking trigger thresholds it is often hard to determine exactly what is happening. Poorly calibrated voice keys can account for a significant amount of variation within your experiment. The highly sensitive Black Box ToolKit v2 digital microphone can help you calibrate you own voice keys for use in your own experiments.
Typical timing error in standard voice keys (STVK) versus hand coding the recorded
waveform (adapted from Tyler et al, 2005)
For a more in-depth discussion on voice keys and the magnitude of error they can introduce consult:
Kessler et al (2002), "Phonetic Biases in VoiceKey Response Time Measurements".
Tyler et al (2005), "The delayed trigger voice key: An improved analogue voice key for psycholinguistic research".