TEMPORAL CHARACTERISTICS OF PRIMARY-SECONDARY MESSAGE INTERFERENCE IN A DICHOTIC-LISTENING TASK

During [human] performance of a shadowing task the unattended message had been shown to be processed at a semantic level. Four experiments were reported that dealt with the question of how processing of the unattended message influenced the difficulty of shadowing the attended message. Experiment 1 demonstrated that pupil dilation measured the difficulty associated with a shadowing task. In Experiment 2 it was shown that during shadowing of 20-item lists pupil dilation decreased as shadowing continued when either words or white noise were in the unattended channel. The idea that it takes time for the attentional mechanism to focus on the attended message was supported. In Experiments 3 and 4 it was found that decrease in difficulty of shadowing was much less when the attended and unattended messages came from the same stimulus category (letter-letter, digit-digit). When the unattended message was from the same stimulus category as the attended message, it may interfere with the ability of the attentional system to focus on the attended message.