Subject: Re: identification task...negative d' values. From: Erick Gallun <gallun@xxxxxxxx> Date: Tue, 2 May 2006 23:15:18 -0400Negative values simply mean that the listener consistently used the wrong label. Quite reasonable in an identification task, I suppose. If the values are small (less than the variability of the measure) I would chalk it up to random variability. If they are large, then it is a meaningful result that should be interpreted. I wonder, though, how are you calculating d' from three phoneme labels? Feel free to contact me off-list. Erick Gallun Postdoctoral Fellow Hearing Research Center Boston University At 01:22 PM 5/2/2006, silvadmr wrote: >Dear list, > >I have some few small negative values of d' obtained from an >identification task in witch subjects label vowel sounds from a >continuum with tree phoneme labels. Generally, the graphs and tables >in the literature never show negative values of d' ( i think >it occurs here and there). >The interpretation of such values from an identification task of >that kind must not be the same as the interpretation of negative >values obtained in a yes-no experiment...cause in the case of >indentification we have "different sounds" rather then a "signal >stimulus" and a "signal plus noise stimulus". > >What is the usually adopted procedure? >Should I take the absolute values (given the nature of the >identification task)?...should I convert them to 0? should I keep >them as negative values? > >Thanks!