Dear Freesurfers,
We intend to implement a probabilistic reversal learning task (Hampton et al, 2006) in an ER-design. Each of its 120 trials matches the following pattern:
|<---- Response ---->|<-- Fixation -->|<-- Feedback -->|
The phases of Response and Feedback take 2 sec and 1 sec, respectively. We are wondering how to setup the durations of Fixation and the ITI in an optimal way, which means trading task-duration off against efficiency. We would like to estimate these values by some software rather than by rule of thumb. Do you know whether there is such a tool anyway?
In Freesurfer there is a tool included that is called optseq2. It is described as follows:
“optseq2 is a tool for automatically scheduling events for rapid-presentation event-related (RPER) fMRI experiments (the schedule is the order and timing of events). Events in RPER are presented closely enough in time that their hemodynamic responses will overlap. This requires that the onset times of the events be jittered in order to remove the overlap from the estimate of the hemodynamic response. RPER is highly resistant to habituation, expectation, and set because the subject does not know when the next stimulus will appear or which stimulus type it will be. RPER is also more efficient than fixed-interval event related (FIER) because more stimuli can be presented within a given scanning interval at the cost of assuming that the overlap in the hemodynamic responses will be linear. In SPM parlance, RPER is referred to as 'stochastic design'. The flexibility of RPER means that there are a huge number of possible schedules, and they are not equal. optseq2 randomly samples the space of possible schedules and returns the 'best' one, where the user can control the definition of 'best'. Cost functions include: average efficiency, average variance reduction factor (VRF), and a weighted combination of average and stddev of the VRF. The user can also specify that the first order counter-balancing of the sequence of event-types be pre-optimized.”
Will it do the job? After a first try, I guess that optseq2 may not allow constraints such that Response is always followed by Feedback.
Could you please give me a hint how to setup durations of Fixation and the ITI in an optimal way?
Best wishes from Dresden, Daniel
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Dipl.-Inf. Daniel Geisler Wissenschaftlicher Mitarbeiter Bereich Angewandte Entwicklungsneurowissenschaften Klinik und Poliklinik für Kinder- und Jugendpsychiatrie und -psychotherapie Tel. +49 (0)351 458-7071 Fax +49 (0)351 458-7206
Universitätsklinikum Carl Gustav Carus an der Technischen Universität Dresden Anstalt des öffentlichen Rechts des Freistaates Sachsen Fetscherstraße 74 (Haus 25, Raum 233A), 01307 Dresden http://www.uniklinikum-dresden.de Vorstand: Prof. Dr. med. D. M. Albrecht (Sprecher), Wilfried E. B. Winzer Vorsitzender des Aufsichtsrates: Prof. Dr. med. Peter C. Scriba USt.-IDNr.: DE 140 135 217, St.-Nr.: 201 145 00020