Attentional deficits have long been regarded as central in schizophrenic patients' cognitive functioning. Kraepelin already regarded an attentional deficit as a common finding in schizophrenic patients (Kraepelin 1919). Of course this is not surprising, because attention is a function central to any cognitive operation, be it perception, the recall of information, or the planning of motor acts. Theories of schizophrenic cognition that have seemingly nothing to do with attention, such as Bleuler's formulation of the "loss of associative threads", or Shakov's "loss of major set", to name but two, can also be interpreted from the view point of an attentional deficit.