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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Hi all,
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<div><font size="2">A question about the centre head bias.</font></div>
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<div><font size="2">Does computing a contrast of conditions remove the issue of the centre head bias? Read below.</font></div>
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<div><font size="2">The </font><a name="localizing_oscillatory_sources_using_beamformer_techniques" id="localizing_oscillatory_sources_using_beamformer_techniques" title="" style="line-height: 1.5em; font-size: 10pt; padding: 0px; margin: 0px; color: rgb(51, 51, 51);"><font size="2">Localizing
oscillatory sources tutorial talks about the possibility of a </font></a><a name="localizing_oscillatory_sources_using_beamformer_techniques" id="localizing_oscillatory_sources_using_beamformer_techniques" title="" style="padding: 0px; margin: 0px;"><font size="2"><font color="#333333" size="2"><span style="line-height: 1.5em;">beamformer
over estimating power in the centre of the head, and suggests </span></font><font color="#333333"><span style="line-height: 20px;">several</span></font><font color="#333333" size="2"><span style="line-height: 1.5em;"> methods of </span><span style="line-height: 19px;">counteracting
this.</span></font></font></a></div>
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<div><font color="#333333" size="2"><span style="line-height: 19px;">After suggestion use of the NAI to counter this bias, the tutorial goes on to show this beamformer method using contrasting conditions and says that using this approach we can "a</span></font><span style="font-family: Calibri, Geneva, Arial, Verdana, sans-serif; line-height: 22px; text-align: justify; background-color: rgb(255, 255, 255);"><font size="2">ssume
that the noise bias is the same for the pre- and post-stimulus interval and it will thus be removed."</font></span></div>
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<div style="text-align: justify; "><font face="Calibri, Geneva, Arial, Verdana, sans-serif"><span style="font-size: 15px; line-height: 22px;">The tutorial uses the following code to do this:</span></font></div>
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<pre class="code" style="padding: 0.5em; margin-top: 0px; margin-left: -10px; font-size: 12px; border: 1px dashed rgb(204, 204, 204); overflow: hidden; font-family: Consolas, 'Andale Mono', Menlo, Monaco, monospace; background-color: rgb(247, 249, 250); white-space: pre-wrap; width: 640px;">sourceDiff = sourcePost_con;
sourceDiff.avg.pow = (sourcePost_con.avg.pow - sourcePre_con.avg.pow) ./ sourcePre_con.avg.pow;</pre>
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<div style="text-align: justify;"><span style="font-family: Calibri, Geneva, Arial, Verdana, sans-serif; font-size: 15px; line-height: 22px; background-color: rgb(255, 255, 255);">My question again: Does using this </span><span style="font-family: Calibri, Geneva, Arial, Verdana, sans-serif; font-size: 15px; line-height: 22px;">approach
and computing the contrast condition remove the centre of head bias for this contrasted condition?</span></div>
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<div style="text-align: justify;"><span style="font-family: Calibri, Geneva, Arial, Verdana, sans-serif; font-size: 15px; line-height: 22px;">Thanks!</span></div>
<div style="text-align: justify;"><span style="font-family: Calibri, Geneva, Arial, Verdana, sans-serif; font-size: 15px; line-height: 22px;">Kaelasha</span></div>
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<p class="MsoNormal" style="margin: 0cm 0cm 0.0001pt;"><font size="2">PhD Candidate</font></p>
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<span style="font-size:10pt; font-family:Tahoma,sans-serif">Brain and Psychological Sciences Research Centre</span></p>
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<span style="font-size:10pt; font-family:Tahoma,sans-serif">Swinburne University of Technology</span></p>
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<span style="font-size:10pt; font-family:Tahoma,sans-serif">Melbourne</span></p>
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<span style="font-size:10pt; font-family:Tahoma,sans-serif">Australia</span></p>
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