What is meant by “top-down” and “bottom-up” processing? Give examples of both. Bottom up processes are evoked by the visual stimulus. Top down processes are operations that reflect the subject’s current cognitive goals.
What is meant by “top-down” and “bottom-up” processing? Give examples of both.
Bottom up processes are evoked by the visual stimulus.
Top down processes are operations that reflect the subject’s current cognitive goals.
In the case of eye movements, fixations that are for the purpose of getting specific
information to accomplish a task are said to reflect top down control.
Fixations that are evoked automatically by the occurrence of a stimulus are said to
be under bottom up control.
What is “Neuroeconomics”? Explain how the saccadic eye movement
circuitry is influenced by reward.
Humans/primates exhibit behaviors that lead to expected reward. Reward is
provided by the release of dopamine.
Neurons at all levels of saccadic eye movement circuitry are sensitive to reward.
Neurons in substantia nigra pc in basal ganglia release dopamine.
These neurons signal expected reward.
This provides the neural substrate for learning gaze patterns in natural behavior, and for modeling these processes using Reinforcement Learning.
Dopaminergic neurons in basal ganglia signal expected reward. (Schultz, 2000)
Expected reward is absent.
Response to unexpected reward
Increased firing for earlier or later reward
Conditioned stimulus predicts reward
Neural Circuitry for Saccades
Substantia nigra pc
signals to muscles
Substantia nigra pc modulates caudate
Neurons at all levels of saccadic eye movement circuitry
are sensitive to reward.
LIP: lateral intra-parietal cortex. Neurons involved in initiating a
saccade to a particular location have a bigger response if reward is
bigger or more likely
SEF: supplementary eye fields
FEF: frontal eye fields
Caudate nucleus in basal ganglia
Cells in caudate signal both saccade direction and expected reward.
Hikosaka et al, 2000
Monkey makes a saccade to a stimulus - some directions are rewarded.
This provides the neural substrate for learning gaze patterns in natural behavior, and for modeling these processes using Reinforcement Learning. (eg Sprague, Ballard, Robinson, 2007)
Give some examples that eye movements are learned.
Jovancevic & Hayhoe 2009 Real Walking
Experimental Design (ctd)
Trial 1: Rogue pedestrian - always collides
Safe pedestrian - never collides
Unpredictable pedestrian - collides 50% of time
Trail 2: Rogue Safe
Unpredictable - remains same
Top Down strategies: Learn where to look
Shinoda et al. (2001)
“Follow the car.”
“Follow the car and obey
Give some examples that reveal attentional limitations in visual processing
Difficult to detect color change in one of 8 colored squares.
Color-changing card trick
What are these examples called?
What conclusions has been drawn from these experiments.
Briefly summarize the experiment by Jovancevic, Hayhoe, & Sullivan.
What did they find?
How sensitive are subjects to unexpected salient events (looming)?
Subjects walked along a footpath in a virtual environment while avoiding pedestrians.
Do subjects detect unexpected potential collisions?
Colliding pedestrian path
Does a potential collision (looming) attract gaze?
Colliding pedestrian path
More fixations on colliders in normal walking.
No effect in Leader condition
Why are colliders fixated?
Small increase in probability of fixating the collider.
Failure of collider to attract attention with an added task (following) suggests that detections result from top-down monitoring.
Time fixating normal pedestrians following
detection of a collider
Longer fixation on pedestrians following a detection of a collider
Subjects rely on active search to detect potentially
hazardous events like collisions, rather than reacting
to bottom-up, looming signals.
To make a top-down system work, Subjects need to
learn statistics of environmental events and distribute
gaze/attention based on these expectations.