The role of attention in visual and auditory suffix effects

The auditory suffix effect (SE), in which recall of the terminal items of a sequence is impaired by presenting a redundant item at the end of the sequence, has been attributed to the displacement of information from auditory sensory storage. However, the SE may result entirely from unnecessary processing of the redundant item due to a failure of attentional control. Two studies examined this possibility using visual presentation to minimize the importance of sensory storage as a source of information. Experiment I first demonstrated a visual SE and showed that its magnitude did not vary when background illumination was altered, a factor which affects the duration of sensory storage. Experiment II used auditory as well as visual presentation and tested the hypothesis that training subjects to ignore the suffix would reduce the SE. Training was achieved by interpolating redundant items identical to the suffix within sequences. It abolished the visual SE but left the auditory SE unaffected. The visual SE, therefore, is not solely determined by the physical characteristics of the suffix, and cannot be based on erasure in sensory storage. The auditory data, on the other hand, were consistent with the erasure hypothesis. It was concluded that an SE does not of itself demonstrate the involvement of sensory storage, and, in particular, the visual SE appears to reflect the degree to which the redundant item can be excluded from focal attention.