Figure 1.

Modifications of Delay-Match-to-Sample (DMS) task. (I) In the original DMS task, the first stimulus is the cue and the second is either a match or a non-match to the cue. Participant remembers the cue and responds differently for match or non-match. (II) DMS with multiple samples again requires memory of the first, cue stimulus and waiting for its match, which may appear following multiple non-match stimuli. (III) Same as (II), but there may appear matches to non-cue (not first) stimuli, which should be ignored. (IV) DMS with multiple samples, any one of which may be the cue. Participant remembers all previous stimuli of the trial, and responds to a match to any one of them. In the examples shown for (II–IV), there are three samples presented besides the cue and match, but this number is variable and unknown to the participant. Symbols schematically represent images presented as sample, cue and match. Dash represents delay between image presentations, in our case always 1 s.