Fixate Task¶

HED task ID: hedtsk_fixate

Family: Pseudo tasks: rest, fixation and self-report blocks

Note

Pseudo task. A block that establishes or holds a state, or collects a self-report, rather than eliciting a cognitive process through a trial structure. It is in the catalog so that such blocks can be labelled with the same vocabulary as the tasks around them. See Pseudo tasks in the task criteria.

Also known as: Fixation Block, Fixation Baseline, Central Fixation

Participant holds gaze on a fixation target for a block with nothing else to process or do; used as a baseline or control block and to limit eye movement.

Description¶

A fixation target, usually a cross or dot at the centre of the screen, is shown and the participant is instructed to keep looking at it for the duration of the block. Nothing else is presented and no response is made. Fixation blocks serve as the implicit baseline in block-design fMRI, as the inter-block interval in many EEG designs, and as the control condition for localizers. Gaze may be monitored with an eye tracker, but that is a matter of measurement and does not make a different task. The distinction from an eyes-open Rest Task is the instruction: here fixation is the required activity, not a convenience. Fixate is a pseudo task: it holds a state rather than eliciting a process, so it carries no process links.

Inclusion test¶

An experiment is an instance of this task when its procedure matches, it manipulates at least one of the listed variables, and it records at least one of the listed measures.

Procedure	Participant maintains gaze on a fixation target for the block, with no other stimulus to process and no response to make.
Manipulation	Block duration; target form and size; background (blank, static scene); whether gaze is monitored and fed back.
Measurement	Baseline neural activity for contrast with task blocks; fixation stability (gaze dispersion, saccade and blink counts) when eye-tracked.

Cognitive processes¶

None by design. A pseudo task sets up or holds a state rather than probing a process; the processes engaged during the block are whatever the participant brings to it.

Further references¶

Stark, C. E. L., & Squire, L. R. (2001). When zero is not zero: The problem of ambiguous baseline conditions in fMRI. Proceedings of the National Academy of Sciences, 98(22), 12760-12766. (DOI)