PSYC 330 Chapter Notes - Chapter 6: Ellipse, Posterior Parietal Cortex, Bilevel Rail Car
4 Jun 2018
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CH6 Visual Search
Intro
Most visual activity involves search
We’ve learned a lot about attention from search experience
- Searching for objects that are difficult to find can be attentionally demanding
- Theme: capable to shift attention independently of eye movements
Targets with unique features are easier to find
- Eg Waldo
Camouflage & safety clothing
- When people want to kill people/ animals
- Opposite → wearing something distinct → distinct color, eg orange (safety color)
- “Look for the orange object”
- When you are picking up someone in the airport
- Safety gear
Serial and Parallel Search
- Search for a target defined by a combination (conjunction) of 2 features can be difficult
Neisser’s search experiments (1964)
- Search for certain target letters positioned
in arrays of non-target letters (distractors)
■ Preattentive stage (parallel)
- preattentive processing is carried out
in parallel on all search items at
the same time—> a target with
unique feature pops out—>
immediate target detection
- Eg hard to find Z on the right side,
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2
as it is surrounded by angular objects (vs circular)
■ Attentional processing (serial)
- alignments of focused attention to different items in the search array in order to
locate a target
- Slow detection
‘Odd-man out’ task
Search for texture boundaries
- Texture segregation: when objects
differ in terms of shape, orientation, size,
the process of determining boundaries
between the regions of object
- It is possible for entire regions of
objects that share a common
unique feature to pop out
- A boundary between
distinct regions is
immediately apparent
- Increasing number of items
within the region does not affect the time required for the boundary to pop out
- Increasing number of objects in different regions of an array that share the same
features increases the time to find the boundaries
- The search for boundary between regions of objects requires serial
attentional analysis
Targets with unique combination
- Doesn’t have a unique feature, but just a unique color/shape combination
- Features module associated with each item would have to be assessed in a serial
manner
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- Red shape target: attention is involved in accessing information from the color
module and shape module to verify that it has the unique combination
Set-size effect
- For the hard-to-find items, the more
items surrounded (search set items), the
longer it takes to find the target
- Implies that items are serially
inspected (one by one)
- When the target doesn’t pop out
from the distractors by virtue of
possessing a unique feature
Exhaustive & serial self-terminating search
- Exhaustive search: serial inspection of
entire array occurs on target-absent trials
- If target is not present →
searching the entire array to determine this and search for conclusion
- Serial Self-terminating search: Serial inspection of array terminated when target
found
- Over the course of many search trials on which target is present, only half of the
items will need to be inspected before it is found
- Even though not all of the distractor items have been inspected, the search ends
when the target is located and a response is made
Feature Integration Theory
- When the spotlight is directed at an object → it carries a gluing operation
- posterior parietal cortex is responsible for that
Spatial maps in brain areas
Feature maps & master map
■ Feature maps with different properties of an object → combine to makes master map
- The feature map provides a signal that allows focused attention to be directed
to the same location within the master map → the observer will immediately
detect the target’s presence
■ Parallel search: find yellow bar, among red/green short/
long bars
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Document Summary
We"ve learned a lot about attention from search experience. Searching for objects that are difficult to find can be attentionally demanding. Theme: capable to shift attention independently of eye movements. Targets with unique features are easier to find. When people want to kill people/ animals. Opposite wearing something distinct distinct color, eg orange (safety color) When you are picking up someone in the airport. Search for a target defined by a combination (conjunction) of 2 features can be difficult. Search for certain target letters positioned in arrays of non-target letters (distractors) Preattentive processing is carried out in parallel on all search items at the same time > a target with unique feature pops out > immediate target detection. Eg hard to find z on the right side, 2 as it is surrounded by angular objects (vs circular) Attentional processing (serial) alignments of focused attention to different items in the search array in order to locate a target.
