Multimodal Spatial Perception Experiment

Participants sat in a quiet, dark room, 180 cm away from the center of a 24 modules custom-made array (Fig 1A) spanning ± 36° of visual angle (with 0° being the center of the array, negative and positive values indicating leftward and rightward position, respectively). All testing procedures took place in total darkness so that the array was not visible to the participants, excluding the possibility that responses were influenced by contextual cues (such as the array’s silhouette). Each module could deliver either visual or auditory stimulation. Visual stimuli were red flashes with a diameter of 3° of visual angle at participant’s viewing position, while auditory stimuli were 2 kHz sine wave pulses with 60 dB Sound Pressure Level (SPL). Every module could deliver only one stimulus at a time, i.e., a module could produce either a sound or a flash, never both simultaneously (even though participants were unaware of that). The array was linked to the computer used to run the experiment through a USB cable. The connection between the array and the laptop was also powered via a dedicated host. The experiment was developed and run using MATLAB (v. 2013b).