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?