The overall goal of the following experiment is to independently measure the neurophysiological signals of two attentional processes attending and ignoring during sustained attention. This is achieved by designing a computerized task in which participants press buttons in response to two concurrently presented sensory inputs in order to elicit the conditions necessary for engaging the attending, ignoring, or neither process. As a second step, participants perform the task combined with electroencephalography or EEG, which detects and records electrical brain activity while they engage the attending and ignoring processes.
Next, the EEG data are analyzed using computer software in order to extract average responses to sensory inputs under conditions of attending or ignoring, and in the passive reference condition when no attention is deployed. The results based on the event related potential or ERP analysis show differences in the temporal evolution of the average neurophysiological response to a single sensory input when it is either ignored or attended relative to the passive reference condition. The main advantage of this technique over existing measures like the attention modulation effect, is that it allows us to test new hypotheses about whether attending and ignoring processes are implemented by the same or different brain mechanisms.
The implications of this technique also extend toward therapy or diagnosis of attentional deficits because impairments of attending and ignoring processes can produce similar symptoms such as distractibility making treatment choice difficult. This method assesses the integrity of each process separately and is therefore able to more accurately detect the true source of the symptom. Begin by creating two gray scale sinusoid gradings approximately 5.7 inches in diameter, and with any frequency, the images will have an onscreen duration of 100 milliseconds.
Tilt one of the gradings 10 visual degrees to the right off the median, tilt the other grading 10 visual degrees to the left off the median. Next, generate two pure auditory tones, one with a pitch of 750 hertz and the other at 900 hertz. With each having a duration of 100 milliseconds, ensure that the degree of tilt in the visual stimuli and difference in pitch in the auditory stimuli are sufficiently distinct, such that the participant can distinguish between them without relying on guessing.
Then create computer code that will control the presentation of auditory and visual stimuli during the experiment using presentation software. Present visual stimuli centered on a gray background and present auditory stimuli through speakers positioned on either side of the screen. Select the number of stimuli to be presented.
Present at least 150 of each of the visual and auditory stimuli per experimental condition to ensure that there are enough repetitions for a reliable neurophysiological response. Next, select the timing for each of the auditory and visual stimuli. Use an inter stimulus interval or ISI of 750 to 1000 milliseconds between sequential presentations of stimuli from the same modality, interleave the auditory and visual stimuli.
Finally, divide the stimuli into segments of 25. Each segment will be proceeded by one of three randomly selected task instructions. Inform the participant about the task prior to collecting neurophysiological measures of brain activity.
Instruct the participant to attend and respond only to auditory tones and to ignore visual stimuli. When the instruction is listen, ask the participant to press the left arrow if the tone is high and the right arrow if the tone is low. Similarly, instruct the participant to attend and respond only to visual gradings and to ignore auditory stimuli.
When the instruction is look, ask the participant to press the left arrow if the grading is tilted to the left and the right arrow if the grading is tilted to the right. Finally, instruct the participant to make no responses when the instruction is passive, ensure that the participant is still keeping their eyes open and is focused on the screen. During the experiment, alternate the instructions for listen and look between segments in order to make the previously attended modality irrelevant, thus making it a potent distractor.
Once the participant is well versed on the task, begin collection of neurophysiological responses to the attended and ignored signals. During the Im A prepare the electroencephalography or EEG cap and recording equipment according to the manufacturer's instructions. Apply the cap to the participant's scalp and verify signal, impedance, and quality at each of the sensors.
Next, synchronize the neurophysiological recordings with the stimulus presentation software and neurophysiological recording software according to the manufacturer instructions. Finally, record the neurophysiological signals while the participant performs the task. To ensure that the software has a precise record of the timing of each stimulus and response, prepare the neurophysiological data for statistical analysis by using analysis software.
Begin by removing non neural signal components that will contribute variability to the recordings of brain responses. Use a high pass filter of 0.1 to one hertz to remove slow drifts such as those caused by changes in impedance of the sensors. Then use a low pass filter of 30 to 50 hertz to remove high frequency components such as those introduced by electrical noise, exclude or interpolate sensors that show unreliable data following removal of major non neural components.
Re-reference the data at each electrode by taking the mean across all sensors and subtracting that value from each sensor. Next, extract. Temporal epics of approximately 1000 milliseconds surrounding each auditory and visual event.
Include 100 milliseconds preceding the stimulus onset and 600 milliseconds following the stimulus onset. Subtract the mean of the data in the pre stimulus baseline to re-express the ERP amplitudes as changes relative to the pre stimulus signal. Then compute the average ERP by averaging the data from all epics that fall into the same condition, which are either attended, ignored, or passively perceived stimuli.
Finally, to identify the time course of attending processes, compare the amplitude and timing, as well as the spatial distribution of the ERP response after attended stimuli against those during the passive condition. Similarly, to identify the time course of ignoring, compare the amplitude and timing, as well as the spatial distribution of the ERP response after ignored stimuli against those during the passive condition. The IMAT protocol uncovered unique temporal and spatial profiles of attending and ignoring processes with respect to the attention modulation effect, defined as the difference in neurophysiological response for attended versus ignored condition.
In the auditory sensory modality, attending and ignoring processes contributed at different time points to the attention modulation effect following tone onset. This suggests that both processes are required during auditory sensory processing and also that they involve different brain dynamics in the visual sensory modality. The visual sensory ERP indicated a significant effect of attending but not ignoring, which suggested that only attending processes are required in visual sensory processing and account for 100%of the attention modulation effect.
After watching this video, you should have a good understanding of how to independently measure the physiological responses of attending and ignoring processes of attention control. Following this procedure, other methods like source imaging can be performed in order to better understand which brain regions are involved in generating the neurophysiological signals.
