Re: identification task...negative d' values.

[Massimo Grassi <massimo.grassi@xxxxxxxx>]

Dear ... (what's your name?)

> 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).

how are you calculating d'? If you use excel the formula is the following:

d' = normsinv(H) - normsinv(FA)

where H and FA are, respectively, Hits and False Alarms probabilities.  
If you were simply inverting H and FA...

However, I don't understand one thing. You write "subjects label vowel  
sounds from a continuum with tree phoneme labels". So you present me a  
sound that is between /a/ and /i/ and I have to decide whether I  
perceive /a/ or /i/. Is d' the appropriate analysis?

Ciao,
m
********************
Massimo Grassi - PhD
Laboratorio di Psicologia
Via Petracco 8 - 33100 Udine - Italy
http://www.psy.unipd.it/~grassi
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