Active and Cognitive Vision

Our laboratory is interested in elucidating the neural bases of the natural behavior associated with the processing of visual information. Vision is an active process that requires intermittent shifts of gaze – saccadic eye movements – interrupting periods of fixation during which perceptual processing analyzes both the foveal image (to identify local singularities) and the peripheral image (to select the next detail to analyze).

The selection of a particular visual object among many potential targets for a saccade and the precise control of each saccade are two important processing stages underlying this natural visual behavior. In addition, the strategy involved in searching a visual image depends on knowledge about the target being searched and memory of the images details already examined.

Multiple projects are undertaken in four lines of research: the neural basis of visual selection, visual working memory,
audiovisual communication, and action control. Related projects are also being investigated in collaborations with other groups.

Our laboratory studies visual behavior by training animals to perform tractable behavioral paradigms that are grounded in solid theoretical frameworks. The experimental approaches range from the recording of the extracellular activity of individual neurons to the manipulation of neuronal activity with pharmacological agent and electrical microstimulation. Data are analyzed with sophisticated analytical techniques and quantitative modeling.

Research Projects:

Visual Attention

The posterior parietal cortex is the final destination of a visual processing stream dedicated to action, and we investigate neural substrates of saccade target selection in a particular area of this cerebral cortex, along with its projection to the superior colliculus, a brainstem structure providing the motor command to the saccade generation circuit. The activity of neurons is recorded in animals performing tasks that probe the perceptual decisions that guide actions and the motor decisions that regulate when actions are produced.

A series of experiments examines visual image processing by presenting visual search displays that promote natural visual behavior, as in finding the hero of “Where's Waldo?” cartoon book. We have found evidence that neurons in the posterior parietal cortex and the superior colliculus participate in the process of selecting a visual object from several others by reflecting its identity, the knowledge of the observer about this object, and the visual context. This work is expected to provide new insights into the neural circuit and process signaling the goal of actions.

This research is currently supported by an Operating Grant from the Canadian Institutes of Health Research and by funding from the Harry Botterell Foundation and the Chancellor's Research Award of Queen's University.

Visual Working Memory

Our ability to maintain information temporarily is critical for goal-driven behavior. The neural circuit associated with visual working memory includes the posterior parietal cortex, and we investigate the characteristics of the neuronal activity in this cortical that persists following the disappearance of a visual stimulus. This persistent activity is considered a signature of working memory and the underlying mechanism is thought to involve the slow kinetics of the NMDA synaptic current.
A definitive aspect of working memory is that it is capacity limited: only a small number of items can be stored at one time. Our experiments aim to estimate the capacity limitation of the visual working memory of our animal model using a sequential comparison task and to identify its neural correlates. This work is expected to provide new insights into the neural processes underlying mnemonic representations.

This research is currently supported by a Discovery Grant & Accelerator Supplement from the Natural Science & Engineering Research Council.

Action Control

The control of action – such as saccades – entails not only signals that can initiate and execute movements but also signals that can cancel already commanded movements. Such stopping behavior is studied by manipulating the control exerted by a subject over its actions with a countermanding paradigm, a test of the ability to stop a response once the go stimulus has been presented. This race between STOP and GO signals provides a powerful method to study the temporal dynamics underlying movement processing: being interruptible during an initial controlled phase before exceeding some criterion value, after which a ballistic phase inexorably leads to movement execution.

A series of experiments examines movement processing in posterior parietal cortex, basal ganglia, and superior colliculus by determining whether neurons carry the necessary neural signals to be directly involved in the decision process that regulates whether and when saccades are produced. The underlying analytical approach is based on the principle that for neurons to influence behavior they must change their activity early enough when a prepared movement is countermanded instead of executed.

The executive system that gives us the ability to countermand actions is found to be dysfunctional in several brain disorders such as schizophrenia and Parkinson’s disease. One research goal is to identify the functional and dysfunctional processes underlying inhibitory control of action in humans. By comparing the stopping performance of healthy and schizophrenic subjects during a countermanding saccade task, we wish to determine whether and how the inhibitory control of action of these patients is impaired.

This research is currently supported by a Group Grant from the Canadian Institutes of Health Research and was previously supported by the EJLB Foundation Research Programme and an Early Researcher Award from the Ontario Ministry of Research & Innovation.

Audiovisual Communication

The general goal of our research program is to understand natural vision and the focus of a series of experiments consists of investigating the processing of the most biologically relevant stimulus, the human face. Experiments examining the perception of audiovisual speech and the gathering of visual information from dynamically animated faces are ongoing in collaboration with Dr. K.G. Munhall and the Speech Perception and Production Laboratory in the Department of Psychology at Queen's University.

Verbal communication maybe unique to humans, but this capability evolved from predispositions that can be traced within our evolutionary past. An animal model of audiovisual communication is being developed to study the neural circuit and processes responsible for the integration of audiovisual communicative signals.

This research is currently supported by an Operating Grant from the Canadian Institutes of Health Research and was initiated by a Grant from the National Institutes of Health.