Conditioning experiments.

Conditioning experiments may easily be configured in PsychLab. Classic conditioning, with CS+, CS- and UCS stimuli can be designed, or any variation on this method. Measures taken in the experiment are not limited to those commonly used: Skin Conductance and Heart Rate, derived from EKG.

A typical Classic Conditioning experiment involves three phases: habituation, acquisition and extinction. Any stimulus may be used, but commonly pictures are shown. This is achieved by placing a second screen (connected to the same computer running PsychLab software) in front of the subject. All that will be seen on this screen is the stimulus pictures, as detailed in this link. Typically during habituation, CS+ and CS- stimuli are presented without UCS. Any number of stimuli may be presented (the current limit to total number of pictures or sound files is 199, but this could easily be extended).

Pseudo randomisation or true random stimulus selection is possible, as is the Inter Trial Interval (ITI). Typical ITI range might be mean = 12.5 seconds, variation = +/- 5 seconds. There is always a compromise in experiment design when considering ITI. With measures such as SC and HR, at least 10 seconds minimum ITI is desirable, because responses with these slow changing varaibles take a long time to complete. These measures are different to measures like startle or EEG ERP, where less than a second is sufficient to capture the response. However, the longer the ITI, the more likely the subject is to get bored and lose attention, therefore a compromise is generally reached of perhaps 10-15 seconds.

The number of trials in habituation, acquisition and extinction is entirely selectable. Typically 8 habituation trials might be used. In the acquisition phase, CS+ and CS- stimuli are presented, but this time CS+ is accomapnied by UCS in some or all of the trials. Typically loud unpleasant noise or electric shock may be used. The level of such UCS can be established earlier using a ‘workup’ when the increasing levels are presented until the subject reports tolerance level.

The workup is performed using the Stimulator test panel in Psychlab Acquire program. The ‘Increase by:’ box is set to determine incremental level increase, and the appropriate button is repeatedly clicked so that the subject receives stimuli of increasing severity. The ‘Level’ slider goes up with each stimulus, and the Level indicator on top of the slider shows the value reached. When tolerance level is reached, this valuel is noted and entered into the ‘parameter’ field of the Subject Details panel. This level will then be used for all UCS stimuli in the procedure, when data acquisition for the Conditioning experiment is started.

In the extinction phase, the CS+ and CS- stimuli are similarly presented, but as with the habituation phase the UCS is absent. Each stimulus type might be presented 10 times, allowing adequate opportunity for response to the UCS to extinguish.Pseudo or true randomisation is used throughout.

Method

The PsychLabAcquire program is started with physiology waveforms in Idle mode. The Conditioning PCC script file is laoded at the time when SAM1 is started.

The subject is seated; electrodes and transducers are attached. If shock UCS is used, particular care is taken to ensure that the electrodes connected to the shock generator are situated on a part of the body where electrical stimulation cannot cause harm, such as the inside of the lower arm, well away from the heart and with the two electrodes positioned closely together so that no current can flow beyond the local shock site

The shock generator is then armed by pressing the button. The UCS workup is performed as described above, and the level transferred to the ‘Parameters' field of the Subject Details window..

If picture stimuli are used, the subject is asked to watch the Stimulus screen, told that a number of pictures will be shown, and told that UCS may or may not occur. Data acquisition is then started, using File, Open data acquisition. When the subject is settled, the 'Start recording' button in PsychLabAcquire program is clicked.

The program selects between the CS+ and CS- pictures, presenting them for the required presentation time and with the defined inter-stimulus-intervals. The time and category of each stimulus is registered in an event channel recorded at the same rate as physiology measures. UCS shocks are separately registered in the event channel. This event channel is used when data are analysed off-line after the recording has been made, to allow trials to be identified by CS+, CS- or CS+UCS category.

Stimuli are delivered for all three phases of the experiment, habituation, acquisition and extinction. Typically a total of 42 stimuli might be used in all. After the last stimulus (long enough to allow analysis of any response), measurement is automatically terminated, with data stored on hard disk ready for subsequent analysis.

Electrodes are removed and cleaned ready for the next experiment.