Attention protects the fidelity of visual memory: behavioral and electrophysiological evidence

Recall from visual memory is vulnerable to the influence of task-irrelevant information, including the remembered, prototypical value of stimuli seen previously. Wilken and Ma (2004) proposed that this distortion of recall was actually adaptive, with the task-irrelevant information compensating for imperfections of memory. We tested their proposal by using trial-by-trial oscillations in the electroencephalogram's alpha band (8-14 Hz) collected from human subjects as a marker for the strength of visual attention. Subjects' recall of stimulus spatial frequency showed a systematic error, namely a shift toward the prototypical value of previously seen stimuli. The magnitude of this prototype effect was strongly related to the amplitude of alpha band oscillations recorded at posterior sensor locations during the first 100 ms after stimulus onset. Our results support the hypothesis that the prototype effect is compensatory for imprecision in memory. Moreover, the attentional modulation of alpha activity during the encoding of the target stimulus is consistent with the view that attention sharpens the neural responses that are elicited by the task-relevant stimulus.