We studied two patients with impaired visual perception and imagery caused by bilateral posterior cerebral lesions. The first had prosopagnosia and achromatopsia, and the imagery disorder involved the description of objects from memory, especially faces and animals, and colors of objects. The second had visual disorientation; the imagery problem involved the description of spatial relations from memory. Impairments of visual imagery, like disorders of visual perception, can be dissociated. Object and color imagery may be dissociated from imagery for spatial relations. A given imagery deficit tends to be associated with the corresponding type of perceptual deficit.

We measured the severity of left spatial neglect in 29 patients, 2 to 4 weeks after right cerebral infarction. The severity of neglect increased with both the size of the lesion and the degree of premorbid diffuse cortical atrophy. Recovery over 3 to 5 months from an initially moderate to severe neglect was less complete in patients with cortical atrophy. The importance of lesion size shows that spared areas of the right hemisphere limit the severity and duration of left neglect. The importance of premorbid atrophy suggests that the integrity of the left hemisphere is also essential.

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Quantitative measurements of delta activity were made in 10 healthy elderly controls and 31 subjects with Alzheimer's disease. Delta activity did not discriminate between the healthy elderly controls and the early mild Alzheimer's disease subjects. However, delta activity was a significantly greater percentage of total EEG power in the moderate-to-advanced Alzheimer's subjects when compared to either the healthy controls or mild Alzheimer subjects. In the T3 and T4 electrodes, delta activity in the moderate-to-advanced Alzheimer subjects was 78.3% and 47.6% higher, respectively, than in control subjects. Furthermore, delta activity was an excellent predictor of dementia severity within the 31 subjects with Alzheimer's disease.

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