At HVEM, Canada (Masters and RA at UBC)

I had the amazing opportunity to work on several different projects while at Vancouver, addressing several key questions. The main areas I worked on were:

Decision making

Patient studies

Saccadic system

Face categorization

Decision making

How people make decisions about money – by evaluating value, probability and risk, was one of the projects I worked on during and after my Masters. I was interested in how we as humans individually perceive reward, probabilities and how biases affect these decisions.

Quantifying decision parameters:

I was interested in quantifying differences in individual tendencies and biases while making decisions under different conditions such as risk, ambiguity etc. To this end, we have developed several tasks such as the Vancouver Gambling task and the Vancouver roulette task. In these tasks, subjects participated in behavioral/eye tracking studies where they make decisions about money in a gambling/game type setting.

Mathematical modelling and prospect theory:

The prospect theory is a mathematical model that we have used to understand how our subjects quantified value and probability. This is an emperical model that seems to accurately predict the under-weighting of increasing magnitude (law of diminishing returns) and over-weighting of smaller probabilities. This theory thus explains why people buy lottery tickets and get insurance (lower probability). We have used this model to understand the “amount driven” and “probability driven” decisions of our subjects. Using the same tasks and modelling on patient populations would help scientists to understand exactly what process is disrupted.

Pupil size changes in decision making:

Under constant illumination, pupil size changes are a result of the sympathetic nervous system activity, specifically, activity in the Locus Coeruleus which releases nor epinephrine. We can thus use pupil size as an indirect measure of nor epinephrine release. Behaviorally, pupil size changes in response to cognitive load and arousal, and one study has even time-locked the exact time of decision to the maximum pupil size.

I was interested in pupil size as they vary with decision making in different settings. Components such as arousal, anticipation of reward and cognitive load interact to result in a “net” activity of the sympathetic system, and this can be measured using the eye tracker while people are making decisions. This, to me, is very cool since in humans, we are in a sense able to (indirectly) probe the activity of a single pathway and its role in decision making. I measured and analysed pupil dilation in subjects making decisions in our eye-tracking tasks.

Game theory and social neuroscience:

In order to gain a better understanding of individual differences in attitudes to decision making, I used game theory paradigms. These are “games” that assess an individual’s level of trust and reciprocal trust, altruistic tendencies etc. I used these tests in conjunction with our behavioral tests, when it was of interest.

Patient studies

Working with patients was an inspiring and insightful experience. I had the opportunity to work on projects investigating eye movements in patients with Prosopagnosia (face blindness), Internuclear opthalmoplegia (INO), Parkinson’s disease, Neimann Pick Type C disorder (NPC), Gaucher’s disease, visual field defects and Hemineglect.

Disorders of oculomotor system : INO  and visual field defects.

For the INO project , we tried to quantify the changes in fast eye movement – saccade – parameters (like amplitude, velocity etc) in patients when eye movements are not conjugated between the eyes (as is the case in INO patients).

In the presence of a visual field defect, patients modify their eye movements and we wanted to investigate if this behavior is a consequence of the brain damage or the field defect itself. Using gaze contingent display paradigms, we ran experiments to test this for different tasks such as visual search, line bisection etc.

Disorders of higher cognition: Hemineglect.

For this project we simulated Hemineglect as an attentional gradient in healthy controls and assessed performance on the line bisection task. Our goal was to test if healthy participants behave like hemineglect patients when there is an attentional gradient.

I was also involved in a project investigating scene viewing by pure neglect patients, using gaze contingent displays.

Metabolic disorders: NPC, Gaucher’s disease

I have run eye movement assessments on patients with NPC and Gaucher’s to assess the change/decline in oculomotor behavior for horizontal and vertical saccades.

Disorders of visual cognition: Prosopagnosia

In collaboration with a fellow graduate student in our laboratory, I was involved in a project assessing oculomotor behavior of healthy controls when compared to prosopagnosics while viewing faces under different conditions.

Disorders of decision making: Parkinson’s

In a collaborative project, we were interested in investigating the gambling problems that are observed in some Parkinson patients due to Dopamine (DA) imbalance in the brain. Dopamine is a neuro-modulator that plays an important role in motor actions as well as in reward driven behavior. Parkinson’s is believed to arise from DA depletion in areas such as the Ventral Tegmental Area (VTA) and Nucleus Accumbens (NA). Patients on medication (L-DOPA) also modify (normative) risk-averse behavior. In patients with and without medication, there is an imbalance in DA, albeit in different areas in the brain.

Are these deviations in behavior a result of changing probability evaluation or disruption in magnitude assessment? The subjective perception of value – and its shift –  in this patient group is what we focused our hypothesis around.

The saccadic system

Contextual effects on saccade programming:

While working on this project I was primarily interested in the contextual effects on saccade programming. Saccades are fast eye movements that foveate (bring into focus) regions of interest in the visual world. I used an Eyelink 1000 system (it tracks eye position and movement information) to answer questions about the temporal processing time, spatial averaging properties and biases in the oculomotor control system.

Some of the questions we have investigated are:

1) What is the effect of temporally displacing a target and distractor’s appearance on the saccade metrics?

2) How does the spatial averaging (of a target and distractor information when they are close to each other, called the global effect) change when subjects are instructed to make saccades towards the target as opposed to away from it (antisaccades)? This was the topic of my Master’s thesis.

3) How is spatial attention modulated in the presence of a relevant and irrelevant cue?

Some of the related studies that I was involved in investigated questions about saccadic adaptation, attentional modulation effects of different cues, inter-hemispheric contributions to averaging effects etc.

The superior colliculus has a visual map of the world in polar coordinates and several contextual effects such as the global effect is believed to arise from this region. It seems to be a an important node where top down information converges before the command to execute the eye movement is sent to motor neurons. In addition, the superior colliculus is believed to play a role in blindsight (when people without the striate/ primary visual cortex can still see). I was interested in pursuing studies that investigate the structure-function relationship of this region in the brain.

Face categorization

I was investigating a series of hypotheses relating to how faces are recognized and categorized. These experiments arose from several lunchtime conversations with various colleagues when we were discussing how (almost) instant judgements are made about faces. I was interested in questions such as

1) How quickly are faces categorized in terms of gender, race, and age?

2) How do low and high level properties contribute to judgements about race, gender and age?

3) What effects do these attributes have on a viewer’s performance on a task, spatial attention etc?

I have used behavioral and Ideal Observer techniques to probe our hypotheses.

If you’d like to discuss any of the above, please feel free to contact me!

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