The brain’s capacity to re-allocate resources and to deal with its attentional capacities is relevant for survival and serves adaptive functioning 
. How limited processing resources are managed between sensory modalities which are implicated simultaneously via two or more different tasks is however not fully understood. Cross-modal processing has been subject to several experimental investigations 
. The results can be subsumed under different theoretical frameworks: The ‘automaticity theory’ 
states automatic processing to be present in the unattended secondary task and immunity to cross-modal influences 
. Several studies have found evidence for an absence of crossmodal effects on secondary task processing 
. In contrast, the ‘gain-load theory’ 
suggests that the primarily engaged modality uses the limited capacities which causes inhibition and thereby decreased processing of secondary input. This was also supported by others 
and moderated by the assumption of differential effects on undistractable and distractable components of crossmodal attention (e.g. reduced distraction effect but intact automatic change-detection mechanisms, 
Recently, Haroush and colleagues 
have reported evidence for yet another alternative. In a perceptually demanding visual attentional blink paradigm healthy young participants showed cross-modal augmentation processing of unattended sounds. This was interpreted as a consequence of executive control due to cognitive overload resulting from the attended task. The decrease in executive control challenged the otherwise effective suppression of irrelevant input 
. In contrast to the gain-load theory, the effects expected here on secondary task processing are beneficial rather than detrimental.
Another alternative explanation for advantageous crossmodal effects may include generalized attention, a concept attributed to a spread of cognitive alertness 
. This may be caused by the challenging task in the primary modality, which supports the notion of attention being a general, modality-independent cognitive resource serving beneficial purposes for other modalities.
One family of crossmodal effects are primary visual load effects on secondary auditor processing. Most studies focused on the auditory change effects 
. Results show inconsistencies regarding the directionality of crossmodal effects. Some report decreased MMN amplitudes in the secondary task 
, others find the opposite 
and there also exist null-findings on potential crossmodal influences 
). While the MMN reflects active sensory memory processing 
, the N1 as its prerequisite contributes to encoding the sensory memory trace. It acts out stimulus perception as well as feature-detection mechanisms and represents fundamental auditory processing 
. However, it was usually not distinguished whether standard or deviant processing was affected and which of the two was responsible for the decrease in auditory change detection 
. It remained open whether the observable effects would already be present during basic tone processing. SanMiguel and colleagues 
made an exception to this reporting an effect of visual working memory (WM) on the auditory N1. However, memory load was manipulated only on one level and the directionality of this effect (decreasing/increasing) could not be determined. Haroush and colleagues 
also reported auditory evoked responses (AEPs), however, they also focused on the MMN and the significance of the effect specifically of N1 or P2 amplitudes could not be evaluated.
The aim of the present study was to investigate how stepwise increases in a four-level visual WM design would influence basic auditory processing. Rather than audiotry change effects we wanted to specifically analyze standard tones, representing sensory encoding for the memory trace which is the prerequisite for further higher-level processes such as the auditory change effect.
We used FMRI in order to assess WM manipulation and concurrently recorded event-related potentials (ERP) to measure auditory processing. Although a simultaneous recording of both modalities is not strictly required, it has several advantages: It enables disentangling modality-specific effects but guarantees inferring direct relations due to the measurement simultaneity and the time-point stable task manipulation of both modalities.
Often-replicated fronto-parietal network activations are well-established fMRI correlates of visual WM 
. Electrophysiological tone responses are characterized by the auditory N1-P2 vertex potential. These ERP components can also be reliably obtained when recorded in the MR scanner and the potential coupling between both measures is a matter of ongoing research 
Our hypotheses were based on a successful manipulation of visual WM load, which would result in uni-modally enhanced fMRI activation patterns in WM-related areas. Cross-modal effects in fundamental auditory processing were investigated via AEPs simultaneously measured, as well as measured outside the scanner in a different sample. Our simultaneous measurement setup would further help us to provide a more refined answer to how the spatial and temporal correlates of potential crossmodal load effects would manifest themselves by reciprocally informing one measurement modality by the results of the other