Rod and frame tests were administered before and after a single electroconvulsive shock treatment (ECT) delivered either to the left or right cerebral hemisphere of neurologically normal patients being treated for depression. A third group was also tested twice but with no intervening ECT. All 12 left-ECT patients showed more field-dependence (larger errors) on the second test; all 12 right ECT patients showed less field-dependence. The findings were discussed in terms of a model in which two cognitive control processes, field articulation and scanning, are localized in the left and right brain hemispheres, respectively. Also, implications were drawn regarding the possibly special role of shock to the right hemisphere in the treatment of depression.