The majority of my research has focused on our ability to voluntarily shift our attention to specific locations in space in order to enhance processing of items that appear at that location.
- Are there reliable electrophysiological markers of attentional control processes? (e.g., Green et al., 2008, Psychophysiology)
- What underlying neural mechanisms enable us to control our spatial shifts of attention? (e.g., Green & McDonald, 2008, PLoS Biology))
- Do all sensory modalities utilize the same neural system for shifting attention? (e.g., Green et al., 2011, J Neurosci)
Although most of my previous work has focused on examining attentional control using scalp-recorded electrophysiological signals, I am currently working on projects that use fMRI (e.g., Green et al., Poster presented at Neuroscience 2010) and integrate fMRI and EEG to explore the neural substrates of voluntary attention.
Attentional Processes in Dyslexia
Using my work on attentional control in neurologically healthy individuals as a jumping-off point, I have been examining the electrophysiological indices of attentional control in individuals with reading difficulties. Although this project is still in progress, results indicate that the attentional control network may be functioning in a similar way in individuals with and without reading difficulties, but that for those with reading difficulties it takes longer for the necessary sequence of neural activities to be initiated due to a reduction in early sensory and perceptual processing. A number of follow-up studies investigating the relationship between various attention processes and reading difficulties are now underway.
Inhibition of Return
I have a number of current projects that invlove a phenomenon known as Inhibition of Return, or IOR. IOR is a counter-intuitive effect, wherein responses are slower when an object appears at a recently attended location than when it appears at a novel location. My projects have used electrophysiological indices of attention to provide evidence that:
- Attention is biased away from previously attended locations and toward novel locations (McDonald et al., 2009, J Cogn Neurosci)
- This perceptual bias towards a particular location builds up over successive trials and can be modulated by the sequence of previous events (Green et al., Poster presented at Psychonomics 2008; manuscript in preparation)
- Attentional biasing can occur both within and between sensory modalities. (Green & McDonald, Poster presented at CNS 2009; manuscript in preparation)
EEG Source Imaging
Any discussion about the use of EEG to investigate human cognition inevitably includes a statement about EEG being excellent for determining when a cognitive process took place but not necessarily where the activity was generated in the brain. Although it is true that it is difficult to determine where EEG activity recorded at the scalp is generated, in recent years much progress has been made in improving methods of estimating these neuroelectric sources.
One of my major research aims is to use, and further the development of, new and innovative measures and analysis techniques that can deepen our understanding of neurocognitive processes. Electrical neuroimaging techniques have the potential to provide accurate estimates of the sources of neural activity while retaining information about the timing and sequence of activities, and can be performed at a fraction of the cost of fMRI.
I have collaborated/consulted on a number of projects on topics such as binocular rivalry, visual masking, category learning, inhibition of return, visual search, attentional blink, and neural plasticity in congenitally blind individuals, so that other researchers can utilize these cutting-edge techniques (e.g., Doesburg et al., 2009, Brian Res; Doesburg et al., 2009, PLoS ONE). I also contributed a chapter on the use of beamformer spatial filtering of EEG for a book on advanced analysis techniques (Green & McDonald, 2009, in T.C. Handy, Brain signal analysis: Advances in neuroelectric and neuromagnetic methods).
My current methodological undertaking has been to assist in setting up a new system for simultaneously recording EEG and fMRI and explore ways of examining the single-trial covariation between these two signals. Currently I am using this relatively new approach to examine the trial-to-trial covariation between EEG oscillatory activity and the hemodynamic response during visuo-spatial shifts of attention.