Attributes of Attention:

David Crundall Rm 315

Is attention spatial or object based?

The spatial debate

• “Until [1981] attention was viewed (implicitly or explicitly) as similar to a spotlight directed toward regions of space, 'illuminating' the objects located there...”

• “The evidence consisted primarily of demonstrations that the spatial separation between elements modulated attentional effects...”

Egeth & Yantis, 1997

• Now some researchers suggest that attention is directed to objects or perceptual groups according to Gestalt principles.

Evidence for spatial attentionEriksen & Eriksen (1974) - The Flanker Compatibility Effect

Subjects' task: to read the centre letter of a five letter string and if the centre letter was H or K they were to push a lever one way. If it was S they were to push the lever the other way

The FCE only works when the flankers are very near to the target (<1˚). From such evidence evolved the theory of a minimum width spotlight of attention.

Response Compatible

Response Incompatible

KKHKK SSHSS

RTs < RTs

Evidence for spatial attention

Other evidence for spatial attention came from studies which showed that attention fell off with increasing eccentricity:

Hoffman & Nelson (1981) - identify a target and a secondary shape nearby. As distance increased between the target and the secondary shape so accuracy was reduced.

Downing and Pinker (1985) used a cueing experiment with 10 potential target sites:

Reaction times slowed as the invalid cues appeared further away from the cued location.

Arguments for object-based attention arise

Kahneman & Henik (1981):

Occlusion of objects renders them visually incomplete and fragmented in the raw retinal image.

Yet we perceive a coherent world and perceive complete objects rather than parts of objects.

Therefore we must have some form of early visual mechanism which can construct representations of objects.

Early Evidence for object-based attention?

Rock & Gutman (1981):

Subjects were presented with two overlapping images of different colours. They were asked to make an ascetic judgment on one of them.

Later they were asked to recall one of the images (either the one they previously attended to, or the other one).

Subjects couldn't remember the unattended images. Therefore attention is object-based as otherwise the unreported object would have also been processed within the beam of attention.

Driver & Bayliss (1989), Bayliss & Driver (1992):

Eriksen & Eriksen (1974) found response compatibility effects for distracters that were close together (<1˚).

But spatial separation between a distracter and a central target may decrease the effect of the distracter due to the breakdown of the target/distracter perceptual group.

They did two experiments (1989, 1992) using the Flanker Compatibility Effect to distinguish spatial attention and object-based attention.

K S H S K

S K H K S

K S KSH

S K SKH

Driver & Baylis, 1989

K S H S K

S K H K S

Baylis & Driver, 1992

400

410

420

430

440

near far

Incong

Cong

Kahneman (1992)

S

+

P

S

The task: The initial letters disappear, the shapes move around an invisible circle and another letter pops up in one of the shapes. Subjects had to respond to this letter as fast as possible.

+

Egly, Driver & Rafal, 1999

+

+

Watson & Kramer, 1999

+

Lamy & Tsal, 2000

Lavie & Driver, 1996

They believed that object-based attention did occur, but only within the spatial spotlight.

Results –

Object trials better than both near and far trials. Distance didn't affect the object bias.

Conclusion - Object based attention works over large distances...but what if the spotlight was so large that this object bias was still occurring within it?

One way to test this is by forcibly reducing the spotlight before showing subjects the two lines using a precuing paradigm.

Lavie & Driver, 1996Using a precue…

The precue removed the obect bias.

They concluded that object-based attention does exist but only at a second level of selection. The first selection is based on the spatial spotlight and anything within it can then be attended to on the basis of objects.

To summarise:

• Initial research suggested that attention is a spotlight which is directed to areas of space, illuminating all within it's boundaries.

• Later evidence suggested that objects were more important than space.

• Recent research suggests a two tier system wherein the spotlight makes a rough selection of space to attend to, though selection between things in the spotlight occurs due to the perceptual grouping of objects.

• BUT…

Avrahimi, 1999