Subject: Re: Interpreting a negative d' From: "Versfeld, N.J." <n.versfeld@xxxxxxxx> Date: Fri, 13 Mar 2009 22:47:13 +0100 List-Archive:<http://lists.mcgill.ca/scripts/wa.exe?LIST=AUDITORY>This is a multi-part message in MIME format. ------_=_NextPart_001_01C9A425.A48C01C5 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable =20 Even in the case of a 3IFC, it is important to give feedback after each = trial. Otherwise the subject may adopt a non-optimal strategy, such as = -for example- only considering the last two intervals, discarding the = first interval, which he may consider as a reference (anchor) interval. = Such a strategy indeed can result in a (statistically significant) = negative d'. =20 Niek ________________________________ Van: AUDITORY - Research in Auditory Perception namens Landsberger, = David Verzonden: do 12-3-2009 19:04 Aan: AUDITORY@xxxxxxxx Onderwerp: [AUDITORY] Interpreting a negative d' I have conducted an experiment where I have obtained for one subject in = one condition a negative d' which I cannot explain. I was hoping that = someone here might be able to offer me some insight. The experiment is a 3 interval forced choice task where a sound is = presented in each of the three intervals. In two of the intervals, the sounds are identical. In the third interval, the sound is different. (Obviously = the order of stimuli is randomized.) The patient's task is simply to tell = me which of the three sounds is different. In a 2IFC task, a negative d' might indicate that the subject has misunderstood the task. For example, if two sounds were played and the subject were asked to pick the sound that was higher pitched, a negative = d' would mean that the subject reliably picked the lower pitched sound as having a higher pitched. However, for a negative d' in a 3IFC task where two stimuli are the = same, the subject would have to reliably not pick the different one as being different. What would that suggest about their perception? I don't = think its a misunderstanding of the task as the same subject was able to = perform fine in the same task using a different set of stimuli. Any advice would be greatly appreciated. Thanks, David ------_=_NextPart_001_01C9A425.A48C01C5 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable <HTML dir=3Dltr><HEAD><TITLE>[AUDITORY] Interpreting a negative = d'</TITLE>=0A= <META http-equiv=3DContent-Type content=3D"text/html; charset=3Dunicode">=0A= <META content=3D"MSHTML 6.00.6000.16809" name=3DGENERATOR></HEAD>=0A= <BODY>=0A= <DIV id=3DidOWAReplyText5218 dir=3Dltr>=0A= <DIV dir=3Dltr> </DIV></DIV>=0A= <DIV dir=3Dltr>=0A= <DIV id=3DidOWAReplyText82215 dir=3Dltr>=0A= <DIV dir=3Dltr><FONT face=3DArial color=3D#000000 size=3D2>Even in the = case of a 3IFC, it is important to give feedback after each trial. = Otherwise the subject may adopt a non-optimal strategy, such as -for = example- only considering the last two intervals, discarding the first = interval, which he may consider as a reference (anchor) interval. Such a = strategy indeed can result in a (statistically significant) negative = d'.</FONT></DIV>=0A= <DIV dir=3Dltr><FONT face=3DArial size=3D2></FONT> </DIV>=0A= <DIV dir=3Dltr><FONT face=3DArial size=3D2>Niek</FONT></DIV></DIV>=0A= <DIV dir=3Dltr><BR>=0A= <HR tabIndex=3D-1>=0A= <FONT face=3DTahoma size=3D2><B>Van:</B> AUDITORY - Research in Auditory = Perception namens Landsberger, David<BR><B>Verzonden:</B> do 12-3-2009 = 19:04<BR><B>Aan:</B> AUDITORY@xxxxxxxx<BR><B>Onderwerp:</B> = [AUDITORY] Interpreting a negative d'<BR></FONT><BR></DIV>=0A= <DIV>=0A= <P><FONT size=3D2>I have conducted an experiment where I have obtained = for one subject in one<BR>condition a negative d' which I cannot = explain. I was hoping that someone<BR>here might be able to offer me = some insight.<BR><BR>The experiment is a 3 interval forced choice task = where a sound is presented<BR>in each of the three intervals. In = two of the intervals, the sounds are<BR>identical. In the third = interval, the sound is different. (Obviously the<BR>order of stimuli is = randomized.) The patient's task is simply to tell me<BR>which of = the three sounds is different.<BR><BR>In a 2IFC task, a negative d' = might indicate that the subject has<BR>misunderstood the task. For = example, if two sounds were played and the<BR>subject were asked to pick = the sound that was higher pitched, a negative d'<BR>would mean that the = subject reliably picked the lower pitched sound as<BR>having a higher = pitched.<BR><BR>However, for a negative d' in a 3IFC task where two = stimuli are the same,<BR>the subject would have to reliably not pick the = different one as being<BR>different. What would that suggest about their = perception? I don't think<BR>its a misunderstanding of the task as = the same subject was able to perform<BR>fine in the same task using a = different set of stimuli.<BR><BR>Any advice would be greatly = appreciated.<BR><BR>Thanks,<BR>David<BR></FONT></P></DIV></DIV></BODY></H= TML> ------_=_NextPart_001_01C9A425.A48C01C5--