Detailed Long-Term Memory for Unattended, Irrelevant, and Incidentally Encoded Auditory Information

At any moment, a myriad of information reaches our senses, of which only a small fraction is attentively processed. A long-held belief is that unattended information is only weakly processed if attentional demands are high and the unattended information is irrelevant, leaving no recognizable trace in long-term memory. The present study challenges this assumption. Participants (N = 51) were simultaneously presented with a rapid visual stream of words and an auditory stream of everyday sounds, with the instruction to attend to the visual stream and detect word repetitions, and to avoid distraction by the irrelevant sounds. No mention was made that their memory would be tested later. Memory for the sounds was tested in a surprise two-alternative forced choice recognition test with similar foil sounds. Half of the sounds were tested immediately after encoding, the other half after a delay of 24 hr. Memory performance was substantially above chance in both the immediate and the 24-hr delayed test, without significant forgetting across time. These results demonstrate that detailed and durable long-term memory representations are formed for unattended and irrelevant information that is incidentally encoded in a different sensory modality than the attended information.