Left unilateral neglect is greater for non-namable than for namable objects in recognition memory

Abstract

Patients with right hemisphere damage often fail to notice, respond to, and report on left-sided stimuli, a condition termed unilateral spatial neglect (USN). In a previous study, we found that USN patients showed a significant contralesional disadvantage both in immediate recall and in delayed recognition of presented visual objects. However, successful verbal recall of an object immediately after its presentation eliminated to a large extent the effect of the spatial position on delayed recognition. Our aim in the present study was to assess whether the formation of a verbal memory trace is responsible for the attenuation of the lateralized bias in recognition of objects that have been verbally recalled. To this end, we compared the immediate recognition performance of 16 USN patients and 16 control subjects for two categories of pictures: namable objects (fruits, furniture, etc.) vs. abstract colorful non-namable pictures. Both healthy controls and USN patients showed a better mean general performance for objects than for abstract pictures (controls: discrimination rate d’namable objects: mean ± standard deviation 3.20 ± 0.86, d’non-namable 2.05 ± 0.73; USN patients d’namable 1.61 ± 0.68; d’non-namable 0.98 ± 0.58). Laterality index [LI = (d’Left- d’Right)/(d’Left+ d’Right)] revealed a greater lateralized bias for abstract pictures than for object pictures in USN patients (USN patients: mean LInamable: −0.14 ± 0.15; mean LI non-namable: −0.42 ± 0.27; controls: mean LInamable: −0.01 ± 0.06; mean LI non-namable: 0.06 ± 0.11). Semantic processing modulates the spatial biases exhibited by USN patients in recognition memory, even in the lack of an explicit verbal recall task; left-sided information is partially perceived and might be more accessible when coded dually - both verbally and visually. The use of verbalization as a rehabilitation technique in USN deserves further investigation.