The Crossmodal Congruency Task as a Means to Obtain an Objective Behavioral Measure in the Rubber Hand Illusion Paradigm

The overall goal of this procedure is to use the cross modal congruency task as an objective measure in the rubber hand delusion paradigm. First, the rubber hand delusion is induced using synchronous brush stroking of a viewed rubber hand while the participant's own hand is hidden from view. The participants are then asked to discriminate tactile targets while viewing light distractors in the so-called crossmodal congruency task.

Brush stroking is repeated before every trial, and this is repeated at least 60 times. The final step is to run a control condition where the illusion is not induced using asynchronous brush stroking. Ultimately, the crossmodal congruency task is used to show changes in multisensory processing that are critical for modulations of body representations, as in the rubber hand illusion.

The main advantage of this technique of existing methods like rating scales, prop perceptive drift, and physiological measurements, is that the crossmodal concurrency tasks can be used as an objective measure, one which is less susceptible to observe and experimental biases and adaptive physiological processes. Our participant today will be Marina Ko, The rubber hand delusion, or RHI uses a box that covers the participant's own hand while presenting a view of an artificial hand. The artificial hand does not have to be made out of rubber.

Here a prosthesis is used. Two soft brushes are used to stroke the hands. Experimental software provides timing signals via headphones for delivering the brush strokes for the cross modal congruency.

Task tact Tours, such as an electromagnetic solenoid type stimulator or a small speaker are used to deliver tactile stimuli. Here, tactile stimuli are delivered by small speakers placed inside the box. A dummy tector should also be put in place for the rubber hand.

Next LEDs are put into position to deliver visual stimuli. Once everything is in place, use experimental software to program the stimulus presentation. To begin, instruct the participant to be seated in a comfortable position.

After they place their hand in the box, be sure that they can see the rubber hand and not their own. Use a gown to cover their shoulder and arm as well as the part of the rubber hand, which goes up to the wrist. Once in place, instruct the participant to respond and discriminate the location of the tactile targets as fast and as accurately as possible.

Next, show the participant how to use the computer mouse to mark responses during testing. It is useful to include training blocks so that the participant becomes familiar with the Crossmodal congruency task. First, use practice trials without visual stimuli in order to custom participants to the tactile targets.

Then use practice trials including the LED stimuli. Before testing, provide the participant with headphones playing white noise to block any potential sound which could arise during stimulus delivery. The experimenter should then get into a position where they can comfortably deliver both brush strokes.

Place a fixation point between the lights and instruct the participant to fixate on it throughout the experiment. When ready, induce the rubber hand illusion with synchronous brush stroking. Both hands should be touched at the same time and in the same location.

Deliver the strokes one to three minutes before the crossmodal congruency task. And once more before every trial, use asynchronous stroking as a control condition where both hands should be stroked with a temporal offset. To begin the task present one tactile stimulus and one visual stimulus to either a spatially congruent or incongruent location.

Present, congruent and incongruent trials in different locations and in a randomized sequence. Use no-go trials in order to ensure that participants are looking at the stimuli. For example, ask participants to withhold the response.

If the lights in both locations turn on at the same time. When participants regularly press a button during these trials, then this can indicate that they are not looking at the lights. You can also use rating scales to monitor subjective experiences during the RHI paradigm Rating responses from the questionnaire seen here may be compared to those collected earlier.

After testing, obtain the average of performance measures for each participant and each condition. Trials in which participants responded too soon or too slow are automatically discarded from the analysis. The number of false alarms in no-go trials should be checked to determine if any significant differences exist between conditions.

Only response times for correct trials are used to calculate the crossmodal congruency effect. Both the response time and response error differed significantly between different RHI conditions. The CCE was significantly increased when the RHI was induced with synchronous stroking as compared to asynchronous stroking when brush stroking was not delivered prior to every crossmodal congruency task, the CCE was not significantly modulated.

Once mastered, this technique can be done in approximately 15 minutes per condition.