Use of short intertrial intervals in single-trial experiments: A 3T fMRI-study

Stefan Pollmann*, Christopher J. Wiggins, David G. Norris, D. Yves Von Cramon, Torsten Schubert

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

31 Citations (Scopus)


We investigated the detectability of task-related changes in the fMRI- signal in an averaged single trial design under systematic variation of intertrial intervals (ITI) in the range between 4 and 12 s. Investigation of the signal timecourses showed a shortening of the baseline period and subsequently a reduction in signal amplitude with decreasing ITI. The main finding is that effect size, i.e., the ratio of task-related signal changes and error variance remained approximately constant from ITI of 12 s down to 6 s. At ITI = 4 s, the effect size was reduced by about 50%. The effects of ITI reduction were comparable in all six cortical ROI which were analyzed. In two subcortical ROI, effect size was already reduced at longer ITI. At ITI = 4 s, the rising flank of the BOLD response was delayed compared to longer ITI. When the data were corrected for the temporal overlap of successive BOLD- responses, the signal amplitudes at ITI = 4 s were comparable to the amplitudes measured at an interval of 12 s. This indicated that the amplitude reduction was mainly due to a linear superposition of the contiguous BOLD- responses.

Original languageEnglish
Pages (from-to)327-339
Number of pages13
Issue number4
Publication statusPublished - Nov 1998
Externally publishedYes


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