Signal-detection analysis of hemispheric differences in visual recognition memory.

In the present experiment, subjects decided on each trial whether or not a unilaterally presented probe digit was a member of a previously memorized set of two, three, or four digits. The probe was presented at a near-threshold duration and followed by a visual pattern mask. Signal-detection estimates of detectability and response bias were obtained from subjects' confidence ratings regarding their decisions. The detectability of the probe in memory was significantly better when the probe was presented to the right visual field-left hemisphere than when presented to the left visual field-right hemisphere. The response criterion became significantly more lax as memory-set size increased, but only for probes presented to the left visual field-right hemisphere. The present results are consistent with reaction-time studies using verbal stimuli that indicate a left hemisphere advantage in the efficiency of memory comparison.