A Two-interval Forced-choice Task for Multisensory Comparisons

Psychophysics is essential for studying perception phenomena through sensory information. Here we present a protocol to perform a two-interval forced-choice task as implemented in a previous report on human psychophysics where participants estimated the duration of visual, auditory, or audiovisual intervals of aperiodic trains of pulses.

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This method can help answer critical questions in the field of perception neuroscience. Such as how time intervals are estimated by different sensory modalities. The main advantage of this technique is that it provides measurements of accuracy and reaction times which are perceptual outcomes of behavioral processes.

Though this method can provide insight into human perception, it can also be applied to other animal models, such as trained or human primates. Begin by opening the experimental software. Click on the Set Path option in the Menu tab.

Then select the Add Folder button, select the stimuli GUI folder, and press the Save button. Then click on the Close button. Open the stimuli GUI M file using the open option under the Main Menu tab, then press F5 on the keyboard to display the GUI.

Next, click on the condition pop-up menu to select the preferred distribution of pulses. Select the desired number of pulses in the number of pulses pop-up menu. Next, click on the generate IPI button to display the IPI's values at the IPI values box, and to see a plot of the resultant distribution of the pulses.

Then, click on the generate video button and wait for the pop-up window displaying gray, four degree circles to close. Click on the Play button to see the created V stimulus. Finally, click on the Generate Audio button to observe a plot of the created audio and click on the Play button to listen to the new audio.

Begin by creating sets of P and AP VA and AV trials by listing the names of the created stimuli in a spreadsheet. Use different columns to include all the information required during the task, such as the modality of the reference and comparison stimuli, the number of repetitions per trial, the stimuli durations, and the expected response. Next, open the tasks file and load the created stimuli by selecting the stimulus folder from the control panel.

Use the Up and Down buttons on the dialog box to display a zero. Then, press the folder icon to select the stimulus folder. Next, press the white noise button located on the control panel to activate the background noise.

Then, place the decibel meter as near as possible to the headphones and set the volume control to 65 dB SPL. Adjust the background volume control located on the control panel to 55 dB SPL. Test the task by clicking on the run, right arrow icon under the Tools tab and perform some test trials.

Lastly, hold down the Spacebar to begin each trial after the appearance of the visual queue at the center of the screen. Release the Spacebar after the delivery of a pair of stimuli and press the Upward or Downward arrow key to finalize the trial. Begin by asking the participant to fill out a questionnaire regarding their age, gender, handedness, and physical or psychological conditions.

Tell the participant about the aim, procedures, and duration of the experiment. Be careful no bias is induced, then ask the participants to sign an informed consent form to participate in the experiment. Next, escort the participant to the testing room and have them sit comfortably in front of the monitor.

Situated at a distance of 60 centimeters away. Place the keyboard at a reachable distance and adjust the headphones to the participant's head. Calibrate the decibel meter as previously described.

Then, run the software to begin the training trials. Instruct the participant to start a trial after the appearance of the visual queue by pressing and holding down the Spacebar for the entire trial. Signal to the participant to release the Spacebar after the presentation of two sequential stimuli and to press the Upward arrow key if the second stimulus lasted longer than the first or to press the Downward arrow key if it lasted for a shorter period of time.

Signal to the participant to take the headphones off and tell them to use only the right index finger to complete the task and comment on the possibility of taking a five minute break in case the participant feels tired or distracted during the experiment. Turn on the noise blocking feature of the headphones and let the participant practice 10 to 15 trials. Finally, have the participant complete the task.

Non overlapping confidence intervals of the parameters obtained from the tanh function fit indicated statistical differences. This result is apparent at the visual aperiodic sigmoid shifting downward. Suggesting that the participants perceived the intervals longer than the reference as shorter.

The acoustic and audio visual performances were similar during periodic and aperiodic conditions, indicating an A dominance over V in AV discriminations. Further, in the visual condition, the transition from shorter to longer occurred faster in the aperiodic condition. This result suggests that the participants were confident of their decisions as evidenced by the reaction times.

In contrast, reaction times of periodic and aperiodic audio visual resemble those of the acoustic conditions, also suggesting an acoustic dominance. Simultaneously with this procedure, methods like EEG, FMRI, or neurophysiological recordings in trained animals can be implemented in order to answer additional questions like where and how different brain areas produce the perception of time intervals.

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Journal (Behavior)

Journal (Behavior)

A Two-interval Forced-choice Task for Multisensory Comparisons

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