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Dear Cyril,

I like you script a lot as it made it easier to understand it more. May I
ask if you have a similar script for plotting the dispersion derivative and
their different meaning with the canonical (i.e. similar to the temporal
plots)?

Many thanks

Aser

On Thu, Oct 13, 2016 at 11:49 AM, cyril pernet <[log in to unmask]>
wrote:

> Hi Jiang :
>
>> Dear spm experts,
>>
>> I have some questions about the calculation of the latency of the BOLD
>> response and the explaination of  the temporal derivative of parametric
>> regressor.
>>
>> (1) The latency is estimated by the ratio of derivative parameter (beta2)
>> to canonical (beta1) parameter estimates and can be calculated by a
>> function latency=2C/(1 + exp(D*beta2/ beta1))- C, C = 1.78 and D = 3.10
>> (Henson et al., 2002). However, the beta1 can either a positive or a
>> negative value that lead to a response later than the canonical when the
>> beta2 is positive and the beta1 is negative.
>>
> yes Henson is correct, the modelled hrf is simply obtained by summing the
> double gamma + derivative
>
> beta2 + / beta1 + = early response (latency is negative)
> beta2 - / beta1 - = early response (latency is negative)
> beta2 - / beta1 + = delayed response (latency is positive)
> beta2 + / beta1 - = delayed response (latency is positive)
> -- see bottom for a simple script showing this
>
> Therefore, is it right to use the abosolute value of beta1 in this
>> function to calculate the latency and the earlier or later of the BOLD
>> response only depends on whether the derivative parameter is positive or
>> negative rather than the canonical parameter.
>>
> no
>
>> (2) When we get a significant effect in the temporal derivative of
>> parametric regressor (reaction time – mean(reaction time)), is the
>> explaination right that for a region with deactivation, when we only put
>> “1” on the “paraRT_TD” regressors, the significant regions means that the
>> in the regions, the larger the reaction time, the larger the temporal
>> derivative, and the earlier the BOLD response appear in the region.
>>
>
> for a region with deactivation = you are already in an area where the hrf
> regressor is negative
>
> when we only put “1” = I would never do that - always add an inclusive
> mask (with lenient threshold) for the hrf regressor
>
> paraRT_TD” regressors = voxels that change trial to trial as a function of
> RT
>
> interpretation = hrf peaks (earlier/latter, depends beta value) than
> expected by trial to trial variations
>
> for be able to say 'the larger the reaction time,  the earlier the BOLD
> response appear ' you need to show a systematic change in the timing of the
> peak, the temporal derivative doesn't do that - it only 'moves' earlier or
> latter your RT regressor
>
> Cyril
>
>
> ------------------------------------------------------------
> ---------------------------
> For question 1, you can convince yourself running that simple example
>
> xBF.dt = 0.5;
> xBF.name = 'hrf (with time derivative)';
> xBF.length = 20;
> [xBF] = spm_get_bf(xBF)
>
> beta1=2; beta2=3;
> latency=2*1.78/(1 + exp(3.1*beta2/beta1))- 1.78;
> figure; subplot(2,2,1); plot(beta1*xBF.bf(:,1),'--','LineWidth',2);
> hold on; plot(beta2*xBF.bf(:,2),'g--','LineWidth',2);
> plot(beta1*xBF.bf(:,1)+beta2*xBF.bf(:,2),'r','LineWidth',2);
> title(['Beta1 +, Beta2 +, latency=' num2str(latency)],'FontSize',13');
> axis tight; box on; grid on
>
> beta1=2; beta2=-3;
> latency=2*1.78/(1 + exp(3.1*beta2/beta1))- 1.78;
> subplot(2,2,2); plot(beta1*xBF.bf(:,1),'--','LineWidth',2);
> hold on; plot(beta2*xBF.bf(:,2),'g--','LineWidth',2);
> plot(beta1*xBF.bf(:,1)+beta2*xBF.bf(:,2),'r','LineWidth',2);
> title(['Beta1 +, Beta2 -, latency=' num2str(latency)],'FontSize',13');
> axis tight; box on; grid on
>
> beta1=-2; beta2=3;
> latency=2*1.78/(1 + exp(3.1*beta2/beta1))- 1.78;
> subplot(2,2,3); plot(beta1*xBF.bf(:,1),'--','LineWidth',2);
> hold on; plot(beta2*xBF.bf(:,2),'g--','LineWidth',2);
> plot(beta1*xBF.bf(:,1)+beta2*xBF.bf(:,2),'r','LineWidth',2);
> title(['Beta1 -, Beta2 +, latency=' num2str(latency)],'FontSize',13');
> axis tight; box on; grid on
>
> beta1=-2; beta2=-3;
> latency=2*1.78/(1 + exp(3.1*beta2/beta1))- 1.78;
> subplot(2,2,4); plot(beta1*xBF.bf(:,1),'--','LineWidth',2);
> hold on; plot(beta2*xBF.bf(:,2),'g--','LineWidth',2);
> plot(beta1*xBF.bf(:,1)+beta2*xBF.bf(:,2),'r','LineWidth',2);
> title(['Beta1 -, Beta2 -, latency=' num2str(latency)],'FontSize',13');
> axis tight; box on; grid on
>
> [log in to unmask]
> tel:  +44 (0)131 465 9530
> http://www.sbirc.ed.ac.uk/cyril
> http://www.ed.ac.uk/edinburgh-imaging
>
>
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