Anne Treisman proposed the 'Attenuation Theory' as a model of selective attention. Her model is a revision of Donald Broadbent's filter model. Where Broadbent thought that a filter was responsible for the selective attention, Treisman believed it was instead a process of attenuation that resulted in selective attention. Both Broadbent and Treisman believed in an early selection process for attention. Treisman's model of attenuation elaborates Broadbent's orginal filter model. Treisman's theory accounts for words like 'fire' that seem to bypass the filter model. Attenuated words have different levels of importance. A word like 'fire' has a higher importance then the word 'red' for example. The word fire would make it through the selective attention process because of it's importance. Broadbent's filter model did not account for this. Here is Treisman's attenuation model:
This model is mentioned in the Cocktail Party Effect, go check it out!