L23 - Visual Attention (TV) Flashcards
How can selectivity of attention be demonstrated?
1) Inattentional blindness
Paying attention to A so you do not notice B
2) Change blindness
Perceptual phenomenon that occurs when a change in a visual stimulus is introduced and the observer does not notice it. For example, observers often fail to notice major differences introduced into an image while it flickers off and on again.
3) Attentional Blink
The phenomenon that the second of two targets cannot be detected or identified when it appears close in time to the first.
E.g. When you a presented a series of letters and suddenly a number, then more letters and a number, you will only see both numbers if the time between the numbers are at least 500 msec apart, otherwise you miss it
4 types of attention
1) Exogenous
Bottom-up - when something suddenly happen. It is effortlesss e.g. red balloon
among a sea of blue balloons
2) Endogenous
Top-down - requires effort (e.g. Finding Waldo)
3) Spatial
Helps to confine processing to a particular location/object
4) Feature-based
Helps to process all objects sharing a common feature (e.g. all red cars in a car park)
Visual search experiments can test for
- Colour (PARALLEL search)
- Orientation (PARALLEL search)
- Feature conjunction: colour AND orientation search (SERIAL search)
Visual search experiments can test for
- Colour (PARALLEL search)
- Orientation (PARALLEL search)
- Feature conjunction: colour AND orientation search (SERIAL search)
What takes longer, parallel or serial search?
Serial
*This is because parallel search is pre-attentive (pop-out)
Treisman’s feature integration theory
When perceiving a stimulus, features are “registered early, automatically, and in parallel, while objects are identified separately” and at a later stage in processing.
OR
Postulates an attentional spotlight (covert attention) acting on a visual area or areas early along the visual pathway that aids in early selection of visual field location for further processing
Which cortical area is the most likely source of attentional spotlight? Site of gating - controlling what you process?
PPC, V1
During spatial attention tasks, in which 2 cortical areas are enhanced responses observed in? Which precedes the visual stimulus?
MT and LIP
LIP precedes the visual stimulus
What is coherence? Is LIP and MT coherent?
Coherence is a measure of the degree of synchronicity between the two neuronal activities
Not only are the two areas in sync with each other in the range of 25-45 Hz (low gamma freq) but further analysis shows that it is LIP that drives MT to sync with it
Which pathway is faster - magno or parvo?
Magno
*It travels to area MT and because it is so fast, there is enough time for feedback from MT to be sent to V1 to select one location to focus on.
So there is a neural substrate for dorsal areas to gate what goes into the ventral areas
What is the binding problem in perception?
Receptive field sizes progressively increase along the ventral stream as different stimulus attributes are processed in different cortical areas. How do you bind all this info together?
However, position invariance is an important property of any system of object recognition - which means certain neurons responds to specific things e.g. faces
How is the binding problem solved?
The spotlight of attention acting on an early visual area aids in the selection of a visual field location for further processing. Thus binding errors do happen in PPC lesions.
OR
Synchronisation between neurons that code for features that belong to the same object.
Conditions where visual attentional mechanisms may be impaired
Hemispatial neglect, developmental dsylexia, acquired dsylexia, ADHD, schiz, accidents, sleep disorders
