Visual Selective Attention Flashcards
What does Visual Selective Attention Actually Select?
Two camps:
•Those that propose visual attention selects from regions of space
•Those that propose visual attention selects instead on the basis of object
What are the two camps?
The Space-Based View: Visual attention is directed toward and selects on the basis of, regions of space within a visual scene.
•The Object-Based View: Visual attention is directed towards objects rather than potentially empty regions of space
What is Space-Based Selection
Visual attention is directed to, and selects on the basis of, regions of space in a visual scene
- Many analogies have been proposed over the years
- Spotlight (Posner, 1980)
- Zoom-lens (Eriksen & St. James, 1986)
- Multiple spotlights (Awh & Pashler, 2000)
•The idea is the same for all of them: objects that fall under the “beam” of attention are subject to further processing with priority.
Whats Object-Based Selection
Attention selects from objects themselves, rather than potentially empty regions of space
- Makes intuitive sense as visual attention is mainly concerned with objects of interest to us:
- Observers eye movements as they view natural scenes are directed almost exclusively to objects (Henderson & Hollingworth, 1999)
- Duncan (1984) suggests that objects, or groups of objects are parsed in accordance with Gestalt laws and are then subjected to further processing
•Which is the best characterization?
Space-Based Selection: Overt vs. Covert attention
What’s the difference?
Overt attention: you look at what you are attending to
Covert attention: attention moves independently of eyes (a mental shift)
Space-Based Selection: The Spatial Cueing Paradigm
important tool: Participants respond quickly to the onset of a target (light or other simple visual stimulus).
- Target is preceded by cue whose function is to draw attention to the occurrence of a target in spaces
- Cues come in different forms (arrows, a flashing up shape)
- As a rule, target detection is fastest when it is presented at the cued location
Posner (1980): The Spatial Cueing Paradigm - what did they do/ and findings
Participant’s task: To respond to the presence of a target (button press)
- Presented them with a pre-cue (arrow) before the target appears
- Purpose of the cue: to attract attention to the area of space
- Two conditions are compared:
- Valid cues: indicate the location the target will appear in
- Invalid cues: indicate a location the target will not appear
•Typical finding: target performance is faster at the cued location compared to when the target appears in the un-cued location
Posner (1980): The Spatial Cueing Paradigm - what type of attention does it make use of?
Makes use of covert attention
Participants fixate a central cross, then are shown a directional cue (arrow
And then a target
tTheir task is to respond as soon as they see the target
Space-Based Selection: The Cueing Paradigm
On 80% of trials the arrow pointed to the direction where the target would appear (valid trials)
- On the remaining 20% of trials the cue was invalid – it pointed to the wrong side
- Neutral trials presented a double headed arrow and no direction cues
Space-Based Selection: The Cueing Paradigm - results
When attention was shifted to the correct area (valid 80% of trials) response times to target faster
When the cue was invalid (20% of trials) responses were slowed
.The cost was attributed to a three part process
1) disengaging attention
2) moving attention to the true location
3) engaging attention at the new location
Space-Based Selection: Posner (1980) – Spatial Cueing Paradigm - interpretation
interpretation: moving attention is a cognitive phenomenon not tied to physical eye movements but instead, an internal mechanism
“Attention can be likened to a spotlight that enhances the efficiency of detection of events within its beam’
The mental mechanism that prepares you to encode stimulus information.
The Spotlight vs. Other Metaphors of Space-Based Attention
Metaphors of Space-Based Selection
Posner (1980) suggests that space-based selection operates like a spotlight, illuminating a very small area for processing priority.
Others (e.g., Eriksen & St. James, 1986) claim it is more flexibly than this and can zoom (increase or decrease in size) to alter the area covered like a zoom lens.
A third approach is that attention can split (e.g., Awh & Pashler, 2000) (multiple spotlights)
Which is the best characterization of space-based selection
Metaphors of Space-Based Selection: The Zoom Lens
Eriksen and St James 1986
likened visual attention to a zoom lens
- They argued that the window of attention can be increased or decreased with task demands
- This may make sense – when driving a car, you attend to as much as possible. But if rabbit runs out your attention focuses in on that event.
- Can we find empirical evidence for this claim?
The Zoom Lens: LaBerge (1983)
LaBerge (1983) presented participants with 5 letter words
Occasionally, a probe requiring a rapid response was presented instead of, or after the word.
The probe could appear in any of the locations of the 5 letters
.There were two conditions:
Focused condition: participants were asked to categorize the middle letter (to focus attention on a narrow space)
Unfocussed condition: participants were asked to categorize the whole word (spreading attention wider)
The Zoom Lens: LaBerge (1983) - procedure and conditions?
+LaBerge (1983) presented participants with 5 letter words
Occasionally, a probe requiring a rapid response was presented instead of, or after the word
.The probe could appear in any of the locations of the 5 letters.There were two conditions
:Focused condition: participants were asked to categorize the middle letter (to focus attention on a narrow space)
Unfocussed condition: participants were asked to categorize the whole word (spreading attention wider)
The Zoom Lens: LaBerge (1983) - findings
in the focused condition, detecting the probe was fastest when it appeared at the central letter (the one they were told to focus on
)In the unfocussed condition, detecting the probe was equal for all 5 letter locations!
This shows that the attentional spotlight does appear to be able to zoom in and out
The Zoom Lens: Muller et al. (2013)
Each trial consisted of four squares in a semi-circle arrangement.
- Participants were cued to attend to one, two or all four.
- Four objects were then presented (one in each square) and the observers decided whether a target (e.g., a white circle) was among them.
- FOUND: Brain activation in early visual areas was most wide-spread when the attended region was large (attend to all four squares) and most limited when small (attend to one square).
- Behavioral performance was best with the smallest attended region and worse with the largest one
. •This provides converging evidence for the zoom lens view
Metaphors of Space-Based Selection: Multiple Spotlights (AKA Split Attention) - Awh and Pashler 2000
propose that we may use multiple spotlights of attention.
Could conserve resources by avoiding attending to irrelevant regions of visual space that fall between relevant areas
suppose you had to identify two digits that would be presented a little way apart at cued locations.
Suppose also that on some trials a digit was presented between the two cued locations.
Zoom-lens theory would predict the area of maximal attention should include the two cued locations and the space in between so detection of digits in the middle should be good.
Multiple spotlights would predict detection of the middle digit would be poor.
What would an experiment like this find?
Metaphors of Space-Based Selection: Multiple Spotlights (AKA Split Attention) - Awh and Pashler 2000 method
5x5 grid containing 23 letters and two numbers
Task: Find the two digits
Two spatial cues presented before the display
80% trials: Predicted locations of numbers (valid trials)
20% trials: Not predictive (invalid trials)
Mulltiple Spotlights: Morawetz et al. (2007
presented letters and digits at five locations at the same time (one in each quadrant of the visual field and one in the center).
- In one condition, observers attended to the visual stimulus at the upper left and bottom right locations and ignored the rest.
- Found two peaks of brain activation corresponding to the attended areas but less activation corresponding to the region in between.
- This pattern strongly supports the notion of split attention.
Object-Based Selection: Duncan (1984
- sfimuli and task
Stimuli: Showed participants a box and a line superimposed at the same location.
Box and line each had two properties
.Box: short/tall with a gap on left/right.
Line: dotted/dashed oriented to left/right
.Task:to report two object properties
Object-Based Selection: Duncan (1984
- findings
Participants slower to report two properties that belonged to different objects, compared to two properties of the same object:
Two-object cost
Suggests attention selects objects.
If it selected space the two-object cost would not arise as both objects would be selected (as they appear at same location).
object-Based Selection: O’Craven, Downing & Kanwisher (1999) - what they did and predictions
Stimuli:two stimuli (a face and a house) transparently overlapping at the same location, with one object moving slightly
Task: Attend to the direction of motion of one of the objects, or to the position of the stationary target
Predictions:
If attention is location-based, it should select both stimuli (both at the same location)
If attention is object based, one or the other image should be selected
object-Based Selection: O’Craven, Downing & Kanwisher (1999) - findings
fMRI showed selective activations:
when the face moved, it was selected resulting in more activation in the fusiform face area
when the house moved, there was more activity in the parahipocampal place area
Compelling evidence that attention can select individual object
attention Seems to be able to Select from Objects and Space
General consensus now is that attention can select on the basis of regions of space and objects.
Compelling evidence of this would be to show both types of attention operating within a single paradigm.
Can we find any evidence like this`/
object-Based & Space-Based Selection: Egly, Driver & Rafal (1994
- Devised a clever adaptation of the cueing paradigm
- Presented rectangles at either side of fixation
- Then one end of a rectangle was cued (to draw attention)
- Then a target appeared at one end of the rectangle
- Task: To detect the target
object-Based & Space-Based Selection: Egly, Driver & Rafal (1994 conditions
Valid: the cue indicated the location of the target
- Invalid same object: the cue appeared in the same object as the target, but at a different end of it
- Invalid different object: the cue appeared in a different object to the target
object-Based & Space-Based Selection: Egly, Driver & Rafal (1994 Findings
: Target detection fastest on valid trials (as expected by space-based selection)
- Detection faster on invalid same object trials compared to invalid different object trials
- Suggests that when cued to the wrong end of the object, the whole rectangle was still selected (as predicted by object-based selection)
- Demonstrates both types of selection in the same study
object-Based and Space-Based Selection: Hollingworth et al. (2012
Adapted Egly et al.’s (1994) study.
- There were three types of within-object cues varying in the distance between the cue and subsequent target.
- There was evidence for object-based attention: when the target was far from the cue, performance was worse when the cue was in a different object rather than the same one.
- There was also evidence for space-based selection: When the target was in the same object as the cue, performance declined the greater the distance between target and cue.
- Conclusion: The two types of selection are not mutually exclusive
