Changing places

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This article is about the thought experiment called "changing places". To read about the novel by David Lodge, see Changing Places.

The changing places thought experiment was conceived of by Max Velmans, Professor of Psychology at Goldsmith's College, University of London, and was discussed in his 2000 work, Understanding Consciousness. The experiment was designed to demonstrate the difficulties in distinguishing phenomenologically between a first-person experience of an event (a subjective experience of an object) and a third-person experience of the same (that is, the observation of such an experience in a subject).

[edit] The Experiment

Velmans conceives of a situation in which an experimenter ("E") is observing the subject ("S") exposed to a light stimulus. The differences between the two viewpoints, Velmans argues, is primarily derived from a difference in interest, reflected in a difference in their required activities. To explain, during the experiment S is required only to report on his experiences of the light, which he needs to communicate to E in an appropriate manner. E, on the other hand, is interested primarily in S's experience of the light, and thus E's focus is not just on the light (which she now thinks of as a "stimulus") but also on the observable events in S's brain, and on S's reports concerning what he experiences. Thus, E is interested first and foremost in the subject's experience, and how these relate to the light stimulus and brain states of S that she can observe. In such a case, E's experience of events would be considered "objective" or "public", while S's experiences are "subjective" and "private"; while E's focus is in recording the neural causes and correlates of visual experiences, S is interested only in reporting about such experiences.

However, Velmans points out that all that would be required for S and E to exchange roles is for them to change their respective foci (as he puts it "S and E merely have to turn their heads"), so that E focuses exclusively on the light and reports her experiences, while S focuses her attention not just on the light, but on the events of E's brain and his reports of the experience. In such an event, S becomes the experimenter and E becomes the subject; thus, following current conventions, "S would now be entitled to think of her observations (of the light and E's brain) as 'public and objective' and to regard E's experiences of light as 'private and subjective'" (Velmans, Understanding Consciousness, 175).

Velmans points out that this outcome is patently absurd, as the phenomenology of the light (that is, the way that it is experienced) remains the same from the perspective of S or E, whether it is thought of as being an observed stimulus or a subjective experience. Nothing has changed in the nature of the light that either party can observe save in the contextualising focus of their interests. That is, Velmans concludes, there is no phenomenological difference between publicly observed phenomena and private, subjective experiences.