Wednesday, February 07, 2007

Objective measurement of awareness.

Studying consciousness is difficult because asking subjects to report their awareness of a stimulus perturbs that awareness. A new paper by Persaud and Cowey shows that asking subjects to wager on whether their response is correct can solve this problem.

From their paper: "The performance of any cognitive task, from recognizing a face to running a business, is an amalgam of many decisions. Some are made consciously and some are not. There is no agreed-upon way of determining which decisions are conscious. Simply asking people might seem a straightforward method, but they may deny awareness if the question asked does not relate to the method they think they used to reach the decision. Numerical confidence ratings have been suggested as an alternative to verbal report but participants may underrate their confidence or withhold conscious knowledge, as they are given no motivation to reveal it. Here we demonstrate that a newly created measure, post-decision wagering, in which people are offered cash rewards for revealing conscious knowledge, can be used to determine which decisions are made without awareness. We asked participants performing three very different tasks—visual discrimination in blindsight, string selection in an artificial grammar task and pack selection in the Iowa gambling task—to place wagers on the outcomes of their decisions. We found above chance performance in the tasks, but the wagers indicated a lack of awareness that the decisions were correct. By making it clear when awareness is absent, this method may help to answer one of the central questions of contemporary neuroscience: how does neural activity give rise to conscious experience?"

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