About the task
The Marker 1 sound is played to signal the start of a trial. An object is shown in the centre of the screen (Phase 1). (Optionally, the subject has to touch this object; optionally, it can be rewarded for doing so.) The object vanishes, and a delay ensues. After this delay, the object is re-presented together with another object (Phase 2), heralded by the Marker 2 sound.
In delayed matching to sample (DMTS), the subject must touch the object that was shown first. In delayed non-matching to sample (DNMTS), it must touch the new object. (Both test the subject's ability to remember information about the first object during the delay; the matching/nonmatching option is typically used to account for or overcome a subject's species-specific natural tendency to select either familiar or novel stimuli.)
Correct responses are rewarded; incorrect responses are punished. Optional correction procedure: if correction is switched on, failed trials are repeated until the subject gets them right. RNC: I've implemented a one-off correction phase as used in DMTL (Sidse's PAL request); ask if she wants consistency across tasks or to repeat entire trials again and again.
Choice of objects
| • | In primate testing, unique objects are normally used for each trial, so a D(N)MTS task requires a large library of pictures. |
| • | Pigs are poorer at visual discrimination; therefore, Sidse wants to ensure that the test only uses objects known to be discriminable by pigs. She suggests (1) that the objects are combinations of one of 6 colours and one of 6 patterns; (2) that the target object is selected pseudorandomly, such that it is never an object that has been presented in the last 5 trials, unless the correction procedure is on; (3) that the distractor object is similarly selected, such that the distractor has not been presented in the last 5 trials, either as a target object or as a distractor. |
| • | This constraint is implemented - but note that if you don't have enough stimuli for this purpose, this constraint will be violated (what else could the task do, after all?). |
Levels
Levels are defined by the delay (option to enter these; typically, level 1 has a zero delay). The task can be run either:
| • | with the level chosen at random for each trial (the possible levels to be used are specified in a list); |
| • | with a fixed level; |
| • | with a level specified at the start, but that increases when a criterion is met (the criterion being that X of the last 20 trials were performed correctly). |
Configuring the task
| • | Maximum number of trials. When the subject has performed this number of trials, the task ends. (You may specify 0 for no limit, though you must specify a limit on the number of trials, the time, or both.) |
| • | Maximum time. When this time elapses, the task is terminated as soon as the current trial has finished. (You may specify 0 for no limit, though you must specify a limit on the number of trials, the time, or both.) |
| • | Maximum time to wait for a response. If the subject fails to make a response within this time, the subject fails the trial. (This time limit applies to Phase 1, if you require your subjects to touch the Phase 1 stimulus, and Phase 2, and the correction procedure if one is used.) |
| • | Time between trials. Specify a minimum and a maximum intertrial time (they may be the same). The actual time is chosen with a rectangular probability distribution within these values. |
| • | Must touch phase 1 stimulus. If this is selected, then the subject must respond to the Phase 1 stimulus in order to proceed to phase 2. If you choose this option, you may also choose whether or not the subject should be rewarded for touching the Phase 1 stimulus. If you do not want your subject to have to touch the stimulus, you must specify the Phase 1 stimulus duration instead. |
| • | Matching. If this is ticked, the task is delayed matching to sample. Otherwise, it's delayed non-matching to sample. |
| • | Correction phase if subject fails Phase 2. Optionally, phase 2 can be repeated immediately (once) if the subject fails it the first time. |
| • | Stimuli. This shows the list of available stimuli. You cannot put a stimulus into the list more than once. Click Add and Remove to add/remove stimuli. |
| • | Levels. On the right-hand side of the screen is the list of memory delays (delays between phase 1 and phase 2) that correspond to levels in the task. You may add, remove, or re-order the levels with the buttons next to the list. You may then choose the starting level, and the method by which the task chooses a level for each trial. (You can have the level fixed, or chosen randomly for each trial, or you can increase the level by one every X trials, or you can increase the level by one when X of the last 20 trials have been performed correctly. Set your chosen value of X in the box.) |
Options for reward and punishment are set in the General Parameters section; visual objects are defined in the Visual Object Library.
Screenshots from the task
Phase 1
Phase 2. Which one was it? (Or, which one wasn't it?)
