Visual Selective Attention

The space based view is that visual attention is directed to and on the basis of regions of space in a visual scene. These consists of models such as:

• The spotlight model of visual attention - Posner (1980)
• Zoom-lens model - Eriksen and St James (1986)
• Multiple spotlights - Awh and Pashler (2000)

The basic idea is the same for all types: Objects that fall under the 'beam' of attention are subject to further processing with priority.

The object-based view expresses the idea that attention selects from objects themselves, rather than potentially empty regions of space. Duncan (1984) adopts this view and states that objects/groups are parsed in accordance with Gestalt laws, and are then subject to further processing.

• Overt - You look at what you are attending to.
• Covert - Attention moves independently of eyes (a mental shift).

• Participants responded to presence of target - added a cue (either valid/invalid), used to attract attention to the area of space.
• Target performance faster at the cued location compared to when the target appeared in the invalid location.
• 80% of trials were valid (to build up expectation). Remaining 20% would be invalid. Neutral trials were also included.

Time costs were accounted for by a three part process:

1) Disengaging attention.

2) Moving attention to the location.

3) Engaging attention at new location.

Eriksen and co's model was the zoom-lens - we can increase/decrease the area of focal attention at will, just like a zoom lens.

Methods

• Laberge reported findings supporting the zoom lens model.
• In this study, five letter words were presented, and a probe requiring a rapid response was occasionally presented instead of the word. There were two conditions: 1) Focused - categorize the middle letter / 2) Unfocussed - categorize the whole word (leading them to adopt a broader attentional beam).

Results

• Focused: Reactions fastest at central letter.
• Unfocussed: Detecting the probe was equal for all locations.
• This shows that the attentional spotlight/zoom lens can have a very narrow (letter task) or fairly broad (whole word) beam.

• This study also supports the zoom-lens claim.
• 4 squares were presented in a semi-circle. 
• Participants cued to focus attention on one specific square/two specific squares/all 4 squares.
• Afterwards, 4 objects were presented and participants decided whether a target was among them.
• When a target was present, it was always in one the cued squares. Used fMRI to assess brain function:
• 1) Targets detected fastest at small attended region.
• 2) Activation in early visual areas was most wide-spread when attended region was large and most limited when the attended region was small.
• This supports the notion of the attentional beam being able to be made wide/narrow.

View created by Awh and Pashler (2000). 

• It is a superior account of visual attention.
• Attention is more flexible - can conserve resources by avoiding attending to irrelevant regions of space that fall between relevant areas.

• Study used a 5 x 5 grid containing 23 letters and 2 numbers. 
• Asked to find 2 digits. 2 spatial cues presented before the display.
• 80% predicting location of numbers / 20% invalid.
• 1) Z-L prediction: Prediction covers both locations - easier to detect A than B
• 2) M-S: Select cued location at the same time

Found:

• No difference in detection speed of digits at A + B.

• Stimuli: Showed participants a box and a line superimposed at the same location.
• Box and line each had two properties: Box - Short/tall with gap on left/right. Line - Dotted/dashed and oriented to left/right.
• Task: To report two object properties.
• Found: Participants slower to report two properties that belonged to belonged to different objects, compared to two properties of the same object.
• The two object cost is the idea that attention selects objects - if it selected space the two-objects would be selected (as they appear at the same location). 

O'Craven, Downing and Kanwisher (1999) studied object-based selection. 

• 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:

• 1) If attention is location-based it should select both stimuli (both at the same location)
• 2) If attention is object-based, one or the other image should be selected.

Found

• Selective activations: When the face moved, it was slected resulting in activation of the FFA. When the house moved there was more activity in the parahippocampal place area - compelling evidence that attention can select multiple objects.

• Attention can operate in both ways.
• Purely object based selection might arise when the task object requires object-centred representations of shape.
• Attention is space-based when the task can be solved by detecting visual features in an array format by the visual cortex.

• Tested both types of attention in one study, using an adaptation of the cueing paradigm.
• Presented rectangles at either side of fixation. 
• One end of a rectangle was cued (to draw attention).
• Then a target appeared at one end of the rectangle. Task was to detect the target.
• Conditions:
• 1) Valid - cue indicated the location of the target.
• 2) Invalid same object - the cue appeared in the same object as the target, but at a different end of it.
• 3) Invalid different object - The cue appeared in a different object to the target.

Found:

• Target detection faster on valid trials. Also faster in invalid same object trials compared to invalid different object trials.
• Suggests that when cued to the wrong end of the object, the whole rectange was still selected (as predicted by object-based attention). 
• Demonstrates both types selection in the same study.