The spread σ in the final settings of repeated adjustment processes is often taken equal to (or at any rate proportional to) the difference limen d as found by a method of forced choice. A detailed investigation into the adjustment process shows that this is not necessarily correct. In principle, σ = (ξd)12, where ξ is the (average) move length in the adjustment process. This implies that σ is proportional to the square root of the difference limen if σ is constant. Normally, however, the subject intuitively chooses ξ roughly equal to 13d, so that σ∼d holds in most practical cases. These ideas are applied to binaural frequency discrimination of sinusoids, the duration of which is variable.

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