Re: identification test procedure

["Timothy C. Justus" <Timothy.C.Justus@xxxxxxxxxxxxx>]

Hello -

In response to James Beauchamp's message, I would suggest that a signal
detection analysis be applied to determine if subjects can tell the difference
between the real and synthesized tones.   The problem with only knowing the
subject's correct answers (hit rate) is that it doesn't allow you to separate
sensitivity (the ability to discriminate) from decision criteria.  By knowing
both the hit rate and the false alarm rate (or the miss and correct rejection
rates, since these are 1 minus the other two, respectively) you can plot a
receiver operating characteristic (ROC) which can separate effects of
sensitivity and decision criterion.  The probability of hits is plotted against
the probability of false alarms.  A point falling near the diagonal would
represent chance performance - they can't tell the difference - whereas points
away from this line show discrimination.  You can draw ROC curves on these
figures representing a given level of discrimination, with points along the
same curve represent different decision criteria.

I'm sure there are individuals out there who could explain this much better
than I.  I hope this is helpful.

Timothy Justus
Dartmouth College

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