Sugar ingestion and dichotic listening: Increased perceptual capacity is more than motivation

Participants ingested a sugar drink or a sugar-free drink and then engaged in apair of dichotic listening tasks. Tasks presented category labels then played aseries of word pairs, one in the left ear and one in the right. Participantsattempted to identify pairs containing a target category member. Target categorywords were homonyms. For example, arms appeared as a target inthe “body parts” category. Nontargets that played along with targets wererelated to a category-appropriate version of the target (e.g.,sleeves), a category-inappropriate version (e.g.,weapons), or were unrelated to either version of the target(e.g., plant). Hence, an effect of nontarget type on number oftargets missed was evidence that participants processed nontargets for meaning.In the divided attention task, participants monitored both ears. In the focusedattention task, participants monitored the left ear. Half the participants ineach group had the divided attention task before the focused attention task; theother half had the focused attention task before the divided attention task. Weset task lengths to about 12 min so working on the first task would givesufficient time for metabolizing sugar from the drink before the start of thesecond task. Nontarget word type significantly affected targets missed in bothtasks. Drink type affected performance in the divided attention task only aftersufficient time for converting sugar into blood glucose. The result supports anenergy model for the effect of sugar ingestion on perceptual tasks rather than amotivational model.