Memory for pictures and sounds: independence of auditory and visual codes

Three experiments examined the mnemonic independence of auditory and visual nonverbal stimuli in free recall. Stimulus lists consisted of (1) pictures, (2) the corresponding environmental sounds, or (3) picture-sound pairs. In Experiment 1, free recall was tested under three learning conditions: standard intentional, intentional with a rehearsal-inhibiting distracter task, or incidental with the distracter task. In all three groups, recall was best for the picture-sound items. In addition, recall for the picture-sound stimuli appeared to be additive relative to pictures or sounds alone when the distracter task was used. Experiment 2 included two additional groups: In one, two copies of the same picture were shown simultaneously; in the other, two different pictures of the same concept were shown. There was no difference in recall among any of the picture groups; in contrast, recall in the picture-sound condition was greater than recall in either single-modality condition. However, doubling the exposure time in a third experiment resulted in additively higher recall for repeated pictures with different exemplars than ones with identical exemplars. The results are discussed in terms of dual coding theory and alternative conceptions of the memory trace.