Dupoux, E., Kouider, S. & Mehler, J. (2003). Unattended Lexical Activation? 
Explorations using Dichotic Priming, Journal of Experimental Psychology: 
Human Perception and Performance, 29(1):172-84.

We use lexical decision in a dichotic listening situation and we measure 
identity priming across channels to explore whether unattended stimuli can be 
processed lexically. In a series of 6 experiments, we vary the temporal 
synchronization of the prime and target word, as well as the acoustic saliency
of the unattended prime by embedding it in a carrier sentence, or in babble
speech. When the prime is acoustically salient, a cross-channel priming effect
emerges, and participants are aware of the prime. In contrast, when the prime is
less salient, we find no identity priming, and participants fail to notice the
prime. Saliency is manipulated in ways that do not degrade the prime itself, as
shown in control experiments. These results are inconsistent with models of late
filtering which predict equal priming irrespective of prime saliency. We conclude
that lexical access cannot occur outside the focus of attention.