Subject: Re: identification task...negative d' values. From: John Culling <CullingJ@xxxxxxxx> Date: Wed, 3 May 2006 17:02:04 +0100Negative d's that occur consistently can be meaningful in that:- 1) the absolute value gives the discriminability of pairs of stimuli 2) the sign indicates the ordering of the stimuli along the perceptual dimension that the listeners were instructed to use for their decisions. However, for the task described, which does not employ a single perceptual dimension, it does imply that the labels used by the participants simply did not conform to those the experimenter expected when designing the data collation. Presumably there are more than 3 stimuli in the described continuum. How has the experimenter decided where the phoneme boundaries between one vowel label and the next "should" be? John.