Setup overview

Our experimental setup contains several commercially available hardware components, and revolves around a custom-developed standalone software solution, “DataStreamer,” that we make freely available here:

<<https://osf.io/h6b8v/>>

The downloadable materials include, along with our DataStreamer software, example, and template files for creating stimulus protocols and a comprehensive user guide. The authors can be contacted for support.

Figure ​Figure1A1A illustrates the design of our setup. Its general working principle is as follows: The experimenter designs per participant and per experimental run a stimulus protocol in the form of a digital file. The stimulus protocol file contains all the tACS information and stimulus information, including their relative timing, in the form of multiple time series (representing the tACS signal, stimulus triggers, and other stimuli; see inset in Figure ​Figure1A).1A). The protocol is loaded into DataStreamer, which allocates the different time series to separate channels of a National Instruments digital-to-analog converter (NI DAQ). The NI DAQ feeds these signals to relevant connected devices serving stimulus presentation (tCS machines, stimulus computers, or other stimulation devices). In the following sections, we provide more details on the setup and procedures, as well as the Section Materials and Methods for our validation experiments reported under Section Results.

Set-up. (A) The main set-up consists of a PC running our custom software (“Data Streamer”). This computer is connected to a multi-channel NI DAQ that converts the digital time series into analog/digital output signals and keeps all output streams synchronized. NI DAQ channel output is sent to a tCS device, to an auditory amplifier (in the case of auditory experiments), and/or as an LPT trigger to present visual, somatosensory, or magnetic stimuli through preferred stimulation devices. Example stimulus protocols for the Data Streamer in an auditory experiment are given in the inset (two auditory streams in channels 1/2, tACS stream in channel 3, LPT triggers connected to stimulus presentation PC in channel 4). The auditory amplifier could be any other stimulation device accepting analog signals as input. Panels (B,C) display the setup for experiment 1 and 2, respectively. Experiment 1 assessed the validity of the setup up to and including the stage of the NI DAQ. Experiment 2 added a tCS device and a head model (a melon), enabling to assess the validity of the complete setup.