'That McDougall had arrived at his conclusions following a close engagement with German physiological psychological research practices was no coincidence. By the middle decades of the nineteenth century, the influence of Kant on German scholarship had encouraged an intimate relation to emerge there between the study of the senses through the generation of illusion, and debates surrounding physical and vital explanations of physiological function (Schickore 2006, esp. 385-391; Galaty 1974). [note: 'I would like to thank Fabio de Sio for impressing on me the importance of Kant for mid-nineteenth-century physical physiology.']'