Phonemic and category encoding of unattended words in dichotic listening

Abstract

The claim that unattended items in dichotic listening are categorized (Smith & Groen, 1974) was examined in three experiments using dichotic presentation and probe reaction time. Negative probe words from the unattended list were more difficult to reject when the dichotic lists shared a semantic category than when they differed in category, whether or not the attended list was precued, thereby replicating and extending Smith and Groen’s findings. The difficulty with intralist probes following dichotic lists of a homogeneous category was found to be a special case of the probe similarity effect, since extralist probes of the same category as the attended input were rejected more slowly (and with more errors) than different category probes. The effects of category homogeneity were evident on the attended, but not on the unattended, inputs (Experiment 2). The third experiment compared focused and divided attention with dichotic lists of unrelated items. Phonemically similar probes were more difficult to reject when related to items on the attended channel in the focused condition than either channel in divided attention, and easiest to reject when similar to an unattended item. Linear regression confirmed that the unattended input was processed only at a precategorical (acoustic) level.