B. Milner, “Effects of Different Brain Lesions on Card Sorting: The Role of the Frontal Lobes,” Archives of Neurology 9 (1963): 90–100; A. M. Owen, A. C. Roberts, J. R. Hodges, B. A. Summers, C. E. Polkey, and T. W. Robbins, “Contrasting Mechanisms of Impaired Attentional Set-Shifting in Patients with Frontal Lobe Damage or Parkinson’s Disease,” Brain 116 (1993): 1159–1175.