Conditional Visual Discrimination

Stimuli appear one by one; some require the subject to respond LEFT to win, and some require the subject to respond RIGHT.

•	A stimulus appears on the screen, along with two response manipulanda (left and right). It is possible to obtain reward for any stimulus, but some stimuli require a Left response, and some stimuli require a Right response.

•	The first response to a stimulus is registered, and the subject receives reward/punishment accordingly (or, if it fails to respond, an omission occurs and is punished).

The stimulus can appear briefly or for as long as the subject is allowed to respond.

The stimulus (like any in MonkeyCantab) can be a blank stimulus. This allows the task to be used as a two-choice vigilance task, as follows:

- the subject must respond (e.g.) left for the visible stimulus, and right for the "non-stimulus"

Examples of a conventional CVD configuration, and this kind of vigilance configuration, are shown below.

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Trial initiation. Specify the initiation method (spontaneous, requiring a lever response, requiring a response to a stimulus on a touchscreen, requiring a magazine response). For stimulus initiation, you can set its appearance and location. For magazine initiation, you can have the magazine light illuminated to indicate the need for a response. For initiation methods other than "spontaneous", specify also the initiation limited hold time (after which failure to respond causes the trial to be abandoned; use 0 for no limit). See also Use with Dogs.

•	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.)

•	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. The time between trials starts after any reward or punishment from the previous trial has finished.

•	Maximum time to wait for a response. Once the response manipulanda have been presented, this is the time that the program will wait for a response before abandoning the trial as an omission.

•	Locations. Click to choose the Locations used for the stimuli. The three locations are considered, in order: LEFT (for the left manipulandum), CENTRE (for the stimulus), and RIGHT (for the right manipulandum).

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Pick stimuli... This can be (a) completely at random, in which a stimulus is drawn at random from the combined "go-left" and "go-right" lists (with replacement); (b) draw-without-replacement (DWOR). In DWOR, the task creates a combined 'pool' of "go-left" and "go-right" stimuli, created by taking the go-left and go-right lists and making as many copies of them as the DWOR multiplier, which you specify. On each trial, a stimulus is drawn without replacement from this pool. The pool is re-created when it is empty. See also randomness, pseudorandomness, and drawing without replacement.

•	"Go-left" and "go-right" stimuli. Specify your list of "go-left" and "go-right" stimuli. There is a button to swap the sets.

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Leave successful stimulus/manipulandum on during reward? (etc.) When the subject responds successfully, the stimulus and/or manipulandum can be left on the screen during reward. When the subject responds unsuccessfully, the stimulus and/or manipulandum can be left on the screen during punishment. These things can either be left on for the duration of the reward/punishment (as specified in the General Parameters), or you can specify how long to leave them on the screen for.

•	Stimulus duration. The stimulus begins when the trial starts (immediately upon trial initiation, as defined above). Specify the stimulus duration, or zero to have the stimulus remain on-screen for as long as the response manipulanda do.

•	Delay from trial start to manipulanda appearing. A delay can be added between the trial start (when the stimulus appears) and the response manipulanda appearing. (The manipulanda then remain on screen for the "maximum time to wait for a response", as above.)

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Reverse within a session. Optionally, the contingencies (whether a stimulus is "go-left" or "go-right") can be reversed (for all stimuli simultaneously) during the session, whenever the subject performs X of the last Y trials correctly. Specify the X and Y. (When a reversal occurs, the requirement is reset.)

•	Correction procedure. A correction procedure can be applied if desired. In the "harsh" technique, the correction procedure begins whenever a trial is performed incorrectly; the trial is re-presented up to A times or until the subjects responds correctly. Specify the parameter A.

The screenshot above shows the CVD set up in conventional fashion. Here's an example of the CVD set up as a vigilance task; in this example, the trials begin spontaneously, the stimulus (or "non-stimulus") appears for 1 second, and then the respond manipulanda appear for up to 5 seconds. Note also that you can vary the proportion of stimulus and non-stimulus trials; for example, to have a 3:2 ratio of stimuli to non-stimuli, enter 3 copies of the stimulus in one list and 2 copies of the non-stimulus in the other list.