Place, U. T. (1974-03-20). Lecture 20: Mental events, mental acts and imageless thoughts.(20/3/1974). Section 5
[Abstract]Mental events as the interface between a process and a state. Imageless thoughts. Our knowledge of our own mental events. The symbolic nature of thought
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Download: Amsterdam lecture 20

Place, U. T. (1997h). Wundt's theory of imageless thought as a possible key to the role of slow-wave sleep in depressive ruminations [Conference presentation, presented at the Sixth Annual Meeting of the European Society for Philosophy and Psychology (ESPP), Padova, 28th August 1997]. European Society for Philosophy and Psychology
[Abstract]Sleep contributes in two ways to the aetiology of clinical depression. The dream imagery of REM sleep stamps in associations between current environmental events and other emotionally charged incidents in the past, only some of which are depressive in nature. The imageless ruminations of slow-wave sleep have a more specific depressive effect in that they keep alive, often indefinitely, problems for which no solution is to be found.
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Download: 1997h Wundt's Theory of Imageless Thought as Possible Key to the Role of Slow-Wave Sleep in Depressive Ruminations.pdf