This chapter begins with the intellectual disorder produced by focal brain lesions with the assessment of impaired problem solving caused by injuries to the parietal-occipital areas of the left hemisphere. It describes a possible type of intellectual disturbance which will later be contrasted to intellectual disorders caused by injuries to the frontal lobes. Patients with injured parietal-occipital brain areas often fail to perceive simultaneously a complex set of figures presented to them, since their attention is usually confined to one of the perceived elements. A review of the material proves, however, that these are not the only defects patients with parietal-occipital brain lesions have since, after overcoming the difficulties decoding the problem's logico-grammatical constructions, patients encounter serious difficulty identifying the correct arithmetical operations necessary to solve the problem correctly. The experiments with programmed training confirmed that in the case of parietal-occipital lesions, intellectual activity is impaired only in its operational element.