Our research aims to investigate and understand the neural mechanisms that underlie various process.
Using EEG, we are able to monitor and record the brain's electrical activity while human volunteers participate in various perceptual and cognitive tasks.
Using EEG, we are able to monitor and record the brain's electrical activity while human volunteers participate in various perceptual and cognitive tasks.
What is EEG? Why do we record it?
EEG (electroencephalography) is a electrophysiological monitoring method that uses scalp electrodes to record the brain's electrical activity. It is a noninvasive procedure that enables us to see changes in the brain activity with millisecond precision that are associated with mental operations underlying seeing, hearing, attending, remembering, and responding (among other things). The high temporal precision of EEG complements the high spatial resolution of blood-flow-based neuroimaging methods, which tell us where in the brain things happen but not when they happen (because blood flow to the brain lags behind the actual brain activity). We record EEG primarily to help figure out answers to questions that cannot be answered on the basis of behavioural and blood-flow-based neuroimaging studies. |
Control of Visual Attention
In everyday life, people must often search cluttered and continually changing visual environments for objects of interest (targets). The search for a target is particularly challenging when other highly salient objects (distractors) are also present in our field of view. We can deal with the surplus of information and attempt to avoid distraction by focusing our attention on specific items or at specific locations in the visual field. We use event-related brain potentials (ERPs) to track people’s attention while they search for visual targets and try to ignore other, potentially distracting stimuli. When an observer pays attention to one of many items in the visual field, the selection processes taking place in the brain give rise to an ERP component called the posterior contralateral N2, or N2pc. If you focus your attention covertly (that is, without moving your eyes) on an item on the left side of the visual field the ERP recorded over the posterior scalp becomes more negative on the right side of the head than on the left side of the head. If you shift your focus of attention over to an item on the right side of the visual field, the posterior ERP becomes more negative on the left side of the head than on the right side of the head. We use the N2pc to learn how people extract information from the visual environment, and we do other studies to figure out what specific process gives rise to the N2pc. Select publications for Control of Visual Attention
1. Tay, Harms, Hillyard, & McDonald (2019). Psychophysiology 2. Christie, Livingstone, & McDonald (2015). J Cogn Neuroscience 3. McDonald, Green, Jannati, & Di Lollo (2013). J Exper Psychol Hum Percept Perform 4. Green, Doesburg, Ward & McDonald (2011). J Neuroscience |
Figure from Christie, Livingstone & McDonald (2015)
|
An example of the task from Gaspar & McDonald (2014)
|
Distractors in the Visual Field
Experimenters have long debated whether salient-but-irrelevant visual distractors capture attention "automatically". Using ERPs, we discovered that a colour-singleton distractor (the red disk in the search arrays to the left) sometimes elicits the N2pc component described above (Hickey, McDonald, & Theeuwes, 2006). Although this distractor-elicited N2pc was initially interpreted as evidence for the automatic capture of attention, we later learned that this capture can be prevented (Jannati et al., 2013; McDonald et al., 2013). For example, when the features of the visual search stimuli remain fixed across trials, the distractor no longer elicits the N2pc but instead elicits an ERP component called the distractor positivity, or PD, which is believed to reflect attentional suppression (Hickey, Di Lollo, & McDonald, 2009). More specifically, this PD appears to reflect a suppression-based process that reduces salience-driven distraction (Gaspar & McDonald, 2014). While the PD indicates that individuals can ignore some distractors, plenty of research has shown that it's difficult for people to ignore distractors that possess a relevant feature or otherwise resemble the target. We have recently shown that in those cases, the distractor captures attention (i.e., elicits an N2pc) and boosts the processing of subsequent stimuli appearing nearby (Livingstone, Christie, Wright, & McDonald, 2017). Enhancing the perceptual representation of an irrelevant object impairs search for the target, whereas enhancing the perceptual representation of the target itself facilitates search. Select publications about Distraction and Suppression
1. Smit, Michalik, Livingstone, Mistlberger, & McDonald (in press). Psychophysiology 2. Gaspar & McDonald (2018). Psychol Sci 3. Livingstone, Christie, Wright & McDonald (2017). J Exper Psychol Hum Percept Perform 4. Gaspar & McDonald (2014). J Neuroscience |
Multisensory Processes
To perceive real-world objects and events, humans (and other animals) need to integrate several stimulus features belonging to different sensory modalities. The processes that enable us to pay attention to multimodal objects are still poorly understood. An important question is whether a stimulus in one sensory modality automatically attracts attention to spatially coincident stimuli that appear subsequently in other modalities, thereby enhancing their perceptual salience. In the lab, we have provided evidence that the sudden appearance of a salient sound affects the way we see a subsequent visual stimulus appearing nearby (for a recent review, see McDonald et al., 2012). Recently, we discovered that a lateral sound actually activates visual brain areas in the occipital lobe. This auditory-evoked occipital activation can be picked up with EEG over the posterior scalp, as shown in the figure to the right. This finding highlights the important interactions between sensory modalities that were once considered completely separate. Select publications for Multisensory Processes
1. McDonald, Störmer, Martinez, Feng, & Hillyard, (2013). J Neuroscience 2. McDonald, Teder-Sälejärvi, Di Russo, & Hillyard (2005). Nature Neuroscience 3. McDonald, Teder-Sälejärvi, & Hillyard (2000). Nature |
Figures from McDonald et al. (2013)
|
Figure from Jannati, McDonald & Di Lollo (2015)
|
Visual Working Memory
Humans can remember the features of three or four visual objects for short periods of time. Individual differences in this working memory capacity, which accurately predict fluid intelligence and performance in numerous cognitive tasks, have been hypothesized to reflect variations in attentional processes that govern access to the memory system. However, the specific attention mechanism that differentiates high- and low-capacity individuals is not yet fully understood. In the lab, we have shown that differences in working memory capacity are specifically related to distractor-suppression activity in visual cortex. Our EEG measures reveal that although high-capacity individuals are able to actively suppress distractors (as evidenced by a PD component), low-capacity individuals cannot suppress them in time to prevent distractors from capturing attention. Select publications for Visual Working Memory
1. Gaspar, Christie, Prime, Jolicœur, & McDonald, (2016). PNAS 2. Jannati, McDonald, & Di Lollo, (2015). Canadian J Exper Psychol |