Hemispatial neglect, a condition that emerges most frequently following a lateralized brain injury, is characterized by a deficit in awareness or attention to one side of space (typically the left side of space is ignored after right hemispheric damage). Patients with spatial neglect behave as if half of their world has ceased to exist. Our lab works extensively with these patients to understand the nature of this deficit and to explore methods for correcting their attentional bias.
Findings from our lab:
- While viewing pairs of chimaeric faces (composed of "smiling" and "neutral" half-faces), Neglect patients typically select the face in which the right half is depicted as smiling as the "happy" one. After employing prism adaptation to shift the patient’s visual field to the left, we found that the patient made increased eye movements to the faces on the left side of space, but still chose the right side as ‘happier’ and was completely unaware of the chimaeric nature of the stimuli. It seems that prism adaptation modulates functions of the parietal lobe, such as the control of eye movements, but fails to influence the underlying mechanisms of neglect.
- In a recent study, we demonstrated that short periods of lateralized pointing could induce attentional biases in healthy participants on a Navon hierarchical letter task (left pointing led to more global interference and right pointing resulted in less). Since global features are preferentially processed in the right hemisphere(RH), we hypothesized that periods of leftward lateralized pointing should increase RH activation and increase the hemisphere’s propensity for global information, thereby causing an impairment in detecting local features on the Navon task. This study has important implications for Neglect patient rehabilitation, since it suggests that lateralized pointing could possibly be used in conjunction with prism adaptation to ameliorate the low and high level attentional biases normally observed in Neglect patients.
Visual Working Memory
Visual working memory (VWM) is a crucial cognitive faculty that supports many different behaviors such as driving a car or remembering a phone number. Our lab seeks to understand the relationship between VWM, attention and object perception. We have conducted a number of studies looking at the neuroanatomical substrate and electrophysiological markers of VWM, as well as how this memory system is influenced by environmental factors.
Findings from our lab:
- In a combined object recognition and change detection task, our lab found that high VWM load impaired object recognition performance specifically on the left side of space. This transient induced left neglect correlated with increased activity in traditional VWM networks (particularly along the intraparietal sulcus), suggesting that VWM and object recognition may share the same neural substrate.
- The electrophysiological marker of VWM is known as the contralateral delay activity (CDA) and is characterized by increased negative amplitude in the channels contralateral to the attended side during VWM maintenance. Our lab found that the CDA was present during a visual search task and also correlated with VWM capacity and search efficiency. This suggests that VWM resources are often deployed in tasks without explicit memory instructions and may serve to inhibit the searching of previously viewed items.
Cognition and Aging
The aging process is a game that everyone must take part in, and the past years have seen a marked increase in research in cognitive aging. Our lab is specifically interested in looking at how attention and VWM resources decline with age and what strategies can be implemented to improve these faculties. The lab recruits older adult participants via the University of Toronto Adult Volunteer Pool, and collaborates with research scientists at Sunnybrook Hospital and The Rotman Research Institute.
Findings from the Lab:
- Collaborating with our colleagues in the Barense Lab, we conducted a study looking at the electrophysiological biomarkers of age related cognitive deficits. Older adults with mild cognitive impairment (MCI), a preclinical impairment defined by low scores on a standardized neuropsychological test and thought to represent a precursor to Alzheimer’s Disease, showed a distinct electrophysiological profile compared with an age matched control group. The MCI group showed impaired performance on tasks of VWM and attention, and showed corresponding reductions in the CDA and P300 component (the latter representing an electrophysiological hallmark of attention). These results suggest that these components might be sensitive to early stages of neurodegenerative diseases and could be used as biomarkers for detecting Alzheimer’s Disease.
Since the visual system processes different object features (for example, colour and shape) in disparate regions, how does the brain effectively bind these different characters together to create a coherent object percept? We have conducted a number of studies investigating this so called ‘binding problem’ and continue to explore the factors that influence feature binding and how it is represented in the brain.
Findings from the Lab:
- In our lab, Ryan Stevenson is currently investigating how multisensory binding deficits may be at core of the more typical symptoms of Autism Spectrum Disorder (ASD). Clinical trials are currently underway to assess how training in sensory binding may affect the course of ASD in children.
- A study from our lab employed a basic change detection VSTM task and found that the CDA (the marker of VWM, mentioned above) may reflect object individuation as well as within-object feature binding, providing support for a dual-system model of VSTM.