Hi Jason,

Have you considered a mental arithmetic task? The difficulty of serial subtractions can be varied by adjusting the length of numbers in the subtrahend and/or minuend. Difficulty might also be manipulated by adjusting the the time allowed to provide an answer, but this could introduce unwanted emotional activation.

Best,

Mal

Hello Mal,

That is a great idea, I will look into it. Do you remember me from the EO VA? I hope you are well. Thank you for the response.

Jason

Another thought would be to do a memory encoding/retrieval paradigm where you ask if an item is old or new and vary the number of intermediate stimuli. This can create a wide-range of difficulties. However, you might still want to use discrete delays to boost the power of each difficulty range. 

Reference:

Huijbers W, Pennartz CM, Daselaar SM. Dissociating the "retrieval success" regions of the brain: effects of retrieval delay. Neuropsychologia. 2010 Jan;48(2):491-7. doi: 10.1016/j.neuropsychologia.2009.10.006. Epub 2009 Oct 14.

Check out the MIST:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1197276/

I use the N-back task for this purpose, and it works really, really well. It's well controlled (in that the same motor response happens on every trial) and all that varies is the cognitive load. Subjects have to say if the currently presented item matches a defined target (0-back), the previous item (1-back), the presented item 2 back in the sequence (2-back), and so on. Most subjects really struggle with the 3-back. The version I use is based on:

Ragland, J. D., Turetsky, B. I., Gur, R. C., Gunning-Dixon, F., Turner, T., Schroeder, L., … Gur, R. E. (2002). Working memory for complex figures: An fMRI comparison of letter and fractal n-back tasks. Neuropsychology, 16(3), 370–379. doi:10.1037//0894-4105.16.3.370

I just use a 0-back and 2-back condition mostly and it lights up the standard working memory/attention fronto-parietal network very nicely. I usually get good-looking results in a single subject. I have a version coded in PsychoPy that I can send you if you like - just drop me a line if you're interested. mbwall [at] gmail.

Hello Jason

I agree with Matthew's suggestion of using n-back task. However people improve on n-back task with practice which might be a confounding factor. Once people have a steady performance then only the cognitive load remains stable during the task. I implemented the task for my experiments according to the link mentioned below.

0-back is a good control condition that can serve as a baseline for subsequent tasks with higher difficulty level. This would allow to visualize cognitive load dependent activation. In my experiment 3-back task is already very difficult to execute, so a paradigm with 0-back, 1-back and 2-back would allow cognitive tasks with 2 difficulty levels considering 0-back serves as the baseline. 3-back task can be included provided participants are trained to execute this task and have a stable response accuracy.

I hope you find this useful.

Best

Bankim

http://www.sciencedirect.com/science/article/pii/S1053811910013820

I agree that the N-back is a great task for many reasons. However, it is very limited in the number of cognitive loads that you can use. Basically you can have between 0 and 3. My aim is to have a task with many small increments of load. The mental arithmetic tasks seem to be able to do this. I just wonder if each participant will perceive each trial to have the same cognitive load, is cognitive load perception subjective.

Maybe you would like to have a look at our paper that just came out:

Lemche, E., Sierra, M., David, A.S., Phillips, M.L., Gasston, D., Williams, S.C.R., Giampietro, V.P. (2015). Cognitive load and autonomic response patterns under negative priming demand in Depersonalization-Derealization Disorder. European Journal of Neuroscience doi:10.1111/ejn.13183 (West Sussex, U.K., John Wiley)

Not sure if you will consider face recognition sufficiently cognitive but since no one has mentioned it what about degraded faces. I guess it shows close to continuous levels of increasing cognitive load with increasing degradation, and the level of degradation can be manipulated in whatever increments you want. Most recent use I am aware of is D. D. Garrett, A. R. McIntosh, and C. L. Grady, "Brain signal variability is parametrically modifiable," Cereb Cortex, vol. 24, pp. 2931-40, Nov 2014. Has the interesting perspective of signal variability instead of mean signal level.