Visual Selective Attention

Question 1

What does Visual Selective Attention Actually Select?

Answer 1

Two camps:
•Those that propose visual attention selects from regions of space
•Those that propose visual attention selects instead on the basis of object

Question 2

What are the two camps?

Answer 2

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

Question 3

What is Space-Based Selection

Answer 3

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.

Question 4

Whats Object-Based Selection

Answer 4

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?

Question 5

Space-Based Selection: Overt vs. Covert attention

What’s the difference?

Answer 5

Overt attention: you look at what you are attending to

Covert attention: attention moves independently of eyes (a mental shift)

Question 6

Space-Based Selection: The Spatial Cueing Paradigm

Answer 6

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

Question 7

Posner (1980): The Spatial Cueing Paradigm - what did they do/ and findings

Answer 7

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

Question 8

Posner (1980): The Spatial Cueing Paradigm - what type of attention does it make use of?

Answer 8

Makes use of covert attention

Participants fixate a central cross, then are shown a directional cue (arrow

And then a target

tTheir task is to respond as soon as they see the target

Question 9

Space-Based Selection: The Cueing Paradigm

Answer 9

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

Question 10

Space-Based Selection: The Cueing Paradigm - results

Answer 10

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

Question 11

Space-Based Selection: Posner (1980) – Spatial Cueing Paradigm - interpretation

Answer 11

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.

Question 12

The Spotlight vs. Other Metaphors of Space-Based Attention

Metaphors of Space-Based Selection

Answer 12

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

Question 13

Metaphors of Space-Based Selection: The Zoom Lens

Eriksen and St James 1986

Answer 13

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?

Question 14

The Zoom Lens: LaBerge (1983)

Answer 14

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)

Question 15

The Zoom Lens: LaBerge (1983) - procedure and conditions?

Answer 15

+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)

Question 16

The Zoom Lens: LaBerge (1983) - findings

Answer 16

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

Question 17

The Zoom Lens: Muller et al. (2013)

Answer 17

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

Question 18

Metaphors of Space-Based Selection: Multiple Spotlights (AKA Split Attention) - Awh and Pashler 2000

Answer 18

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?

Question 19

Metaphors of Space-Based Selection: Multiple Spotlights (AKA Split Attention) - Awh and Pashler 2000 method

Answer 19

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)

Question 20

Mulltiple Spotlights: Morawetz et al. (2007

Answer 20

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.

Question 21

Object-Based Selection: Duncan (1984

- sfimuli and task

Answer 21

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

Question 22

Object-Based Selection: Duncan (1984

- findings

Answer 22

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).

Question 23

object-Based Selection: O’Craven, Downing & Kanwisher (1999) - what they did and predictions

Answer 23

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

Question 24

object-Based Selection: O’Craven, Downing & Kanwisher (1999) - findings

Answer 24

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

Question 25

attention Seems to be able to Select from Objects and Space

Answer 25

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`/

Question 26

object-Based & Space-Based Selection: Egly, Driver & Rafal (1994

Answer 26

• 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

Question 27

object-Based & Space-Based Selection: Egly, Driver & Rafal (1994 conditions

Answer 27

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

Question 28

object-Based & Space-Based Selection: Egly, Driver & Rafal (1994 Findings

Answer 28

: 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

Question 29

object-Based and Space-Based Selection: Hollingworth et al. (2012

Answer 29

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