The images were presented centrally and appeared black on a white background. On initial presentations these visual stimuli could (50%) or could not be paired with a meaningless sound (created with Adobe Audition 1.0). These sounds differed in their spectral composition, ranging from 100 Hz to 4700 Hz and were sometimes modulated in terms of amplitude envelopes and/or waveform types (triangular and sinusoid). All sounds were 500 ms duration (10 ms rise/fall, in order to avoid clicks; 16bit stereo; 44100 Hz digitization).