"[F]or though, when we are solicitously engaged in any action, deeply involved in any thought, or strongly hurried away by any passion, we may often be unconscious of the impressions made by material causes on the organs of sense; yet we cannot but be sensible of the ideas formed within us by the internal operation of our minds, because their very existence depends upon our being conscious of them, and is at an end, as soon as either we attend not to, or forget them."
— Whytt, Robert (1714-1766)
(Sect XI, pp. 286-7)
Robert Whytt, An Essay on the Vital and Other Involuntary Motions of Animals (Edinburgh: Printed by Hamilton, Balfour, and Neill, 1751). <Link to Google Books>