Priority Maps in Cognitive Neuroscience

Lecture 16: Where are the priority maps?

Priority maps are cognitive/neural mechanisms for determining the sequential allocation of attention to the visual world.
Multiple priority maps exist in the brain, with subtle differences in how they code information.
To qualify as a priority map, cells should respond to:
- Saliency information (stimulus-driven information).
- Top-down goal-directed information (goal-driven information).
- Both.
They should not respond to particular feature values (like discriminating between colors).
Examples include:
- Superior Colliculus (SC).
- Lateral Intraparietal Area (LIP).
- Frontal Eye Fields (FEF).

The diagram illustrates the flow of information related to attention and priority processing across different brain areas:

Bottom-up Processing: Starts with the retina, moves through the LGN (Lateral Geniculate Nucleus), and then to V1 (primary visual cortex).
Saliency-driven Pathway: Involves the Superior Colliculus (SC).
Top-down Processing: Originates in the DLPFC (Dorsolateral Prefrontal Cortex) and influences areas like the Frontal Eye Fields (FEF).
Other Structures: The Basal Ganglia, Pulvinar, and Mediodorsal Nucleus (MD) of the thalamus are also involved.

The superior colliculus is located in the midbrain.
It plays a crucial role in processing visual salience.
SC cells respond preferentially to the salience of the visual stimulus; the more salient, the greater the response.
Firing rate of SC neurons correlates with model-predicted saliency.
SC cells respond preferentially to a salient stimulus (goal-irrelevant) around ~60 ms after stimulus onset, when the stimulus is in the receptive field (RF).

Question: Cells in the Superior Colliculus (SC) code for the salience of the visual input across the visual field. What type of stimulus would an SC respond to?
Answer: A stimulus that is physically distinctive from its surroundings (e.g., a bright flash, sudden movement, or high-contrast object).

The frontal eye fields are located in the frontal cortex and are involved in the voluntary control of eye movements.
To generate an anti-saccade, the brain must:
- Inhibit the unwanted reflexive saccade to the target.
- Trigger an intentional correct anti-saccade made in the direction opposite to the stimulus.
FEF responds more for antisaccades (goal-driven) than for prosaccades (stimulus-driven), reflecting goal-directed priority.

The longer it takes for FEF to discriminate between target and distractor (goal-directed), the longer it takes to complete the search.

Question: Cells in Frontal Eye Fields (FEF) code for the goal-directed priority of the visual input across the visual field. What type of stimulus would an FEF neuron respond to?
Answer: A stimulus that matches what the person is intentionally searching for (e.g., a red circle when they're looking for red circles).

Neurons in LIP respond preferentially to:
- The saliency of a stimulus, not its content (salience-driven priority).
- The target of a search (goal-driven priority).
Thus, LIP integrates/sums attentional priorities from different sources.

Question: Cells in LIP code for both the salience of the visual input and their goal-directed priority across the visual field. What type of stimulus would LIP respond to?
Answer: A stimulus that integrates both its physical distinctiveness and its relevance to current goals.

Priority maps likely exist in complicated, multi-peak forms, but this is hard to test.
The differences between these areas are generally more of degree, not kind.
- FEF is also sensitive to saliency.
- SC can be sensitive to the observer’s goals.
This is due to the interconnectedness of these brain areas.
- The saliency signal begins in SC and is carried through to FEF through forward connectivity.
- The goal signal begins in FEF and is carried to SC by backward connectivity.