Högskolan i Skövde

The level-of-processing (LoP) hypothesis postulates that transition from unaware to aware visualstimuli is either graded or dichotomous depending on the depth of stimulus processing. Humanscan be progressively aware of the low-level features, such as colors or shapes, while the high-levelfeatures, such as semantic category, enter consciousness in an all-or none fashion. Unlike invision, sounds always unfold in time, which might require mechanisms dissimilar from visualprocessing. We tested the LoP hypothesis in hearing for the first time by presenting participantswith words of different categories, spoken in different pitches near the perceptual threshold. Wealso assessed whether different electrophysiological correlates of consciousness, the auditoryawareness negativity (AAN) and late positivity (LP), were associated with LoP. Our findingsindicate that LoP also applies to the auditory modality. AAN is an early correlate of awarenessindependent of LoP, while LP was modulated by awareness, performance accuracy and the levelof processing.