Attributes of Attention:

David Crundall Rm 315

Quantal or analogue?

Spatial or object-based?

"attention can be likened to a spotlight that enhances the efficiency of the detection of events within it's beam"

(Posner, 1980)

A zoom lens model of attention(Eriksen & Yeh, 1985;

Eriksen & St James, 1986; Eriksen & Murphy, 1987)

Two current issues in the psychology of attention and evaluation of the spotlight metaphor :

1. Is attention analogue or quantal? (Does it move around the visual scene, or jump from place to place?)

2. Is attention spatial or object oriented? (Do we have a spotlight of attention that covers an area, or does attention just focus on objects in the visual scene).

Tsal (1983):

Tsal used a 33 ms precue at either 4, 8, or 12 degrees followed by a 33 ms target (either X or O) at varying SOAs

+... ... X XXX XX OOOOOO

+.X

+ .X

+.X

Long SOA – Far target

+.X

Short SOA – Far target

+... ...

Through linear regression he found asymptotes of 83, 116 and 150 ms SOAs for the three eccentricities of 4˚, 8˚ and 12˚. He even estimated the velocity of attention at 1˚ per 8 ms.

400

450

500

550

600

650

50 ms 83 ms 116 ms 150 ms 183 ms

SOA (ms)

RT

(m

s) Far (12º)

Mid (8º)

Near (4º)

Shulman, Remington and McLean (1979):

+O O O O<O

250

270

290

310

330

350

100 200 300 400 500

Near- Expected

Near - Unexpected

Far - Expected

Far - Unexpected

The conclusion from these two experiments:

Not only does attention seem to move in an analogue fashion, but it also seems to process items that it passes over.

Criticisms of Tsal:

1) The time to asymptote is not just taken up with movement of attention. There is also

• time needed to react to the cue and perceive it's location• time needed to disengage from the centre and program a movement of

attention• a time benefit due to the warning nature of the cue

We can not say that retinal eccentricity just relates to travel time of attention, as the eccentricity factor is likely to affect one or more of these factors. Therefore we cannot infer linear movement times from the asymptotes.

Erikson and Murphy (1987)

2) Eccentricity may increase discrimination difficulty: attention may suddenly appear at the target but the further out it is, the longer it make take attention to work out what it is. This would give the same results as Tsal.

Yantis (1988)

Criticisms of Shulman et al.:

The difference between near and far targets on the cued side is maximum at an intermediate SOA suggesting that particular SOA caught attention while passing over the near target. However the same interaction occurs on the unexpected side suggesting a warning effect may account for some of the results.

Eriksen and Murphy (1987)

PRO QUANTAL

Sagi & Julesz (1985):

They found the distance between the two letters on the circle didn't affect RTs on a similarity decision.

Other experiments showed that this processing was serial rather than parallel.

x

letter distance

+

TT

Criticisms of Sagi and Julesz:

Their experimental distinction between parallel and serial processing was inadequate.

They used a post-stimuli mask when testing parallel and serial theories which may have interfered with any attentional movement.

They only used two subjects.

Kwak et al. (1991)

Kwak, Dagenbach & Egeth (1991):

They repeated Sagi and Julesz' experiment with both straight and rotated Ts and Ls and again found little affect of distance upon subject performance.

In order to prove quantal movement rather than analogue they still had to demonstrate that the processing was serial rather than parallel.

They used a "within-trial, visual quality manipulation diagnostic of subadditive effects".

Three types of trial:

• High (H-H)• Mixed (H-L)• Low (L-L)

A serial system:

High = 100 ms (50 + 50)Mixed = 120 ms (50 + 70)Low = 140 ms (70 + 70)

A parallel system (a two horse race):

High = 100 ms (100 vs 100)Mixed = 120 ms (100 vs 120)Low = 120 ms (120 vs 120)

640

660

680

700

720

740

760

High Mixed Low

Visual quality

Re

act

ion

Tim

e (

ms)

Different

Same

They found an increase in RTs from both the high to mixed contrast trials, and the mixed to low contrast trials. This suggests serial processing.The lack of significant differences led them to accept that the trials were being processed serially.

Coupled with the lack of distance effects, they concluded that the two stimuli were processed one before the other, though as the distance between the two stimuli didn't have an effect on slowing RTs, the jump must have been instantaneous (quantal not analogue).

Sperling and Weischelgartner (1995):

They likened attention not to one spotlight that moves, but to many fixed spotlights.

2 assumptions:that all spotlights are fixed;only one spotlight can be fully on.

(Though Castiello & Umiltà have shown that focal attention can be split, 1992)

They found no influence of distance upon attentional processing times and therefore concluded that either attention was quantal or, if analogue, it moved too fast to be detected by their paradigm.

In conclusion:

• Initial evidence of analogue shifts of attention have been criticised

• Current evidence supports quantal movement of attention

• Quantal attention does not mean that the spotlight has be rejected. According to Sperling and Weichselgartner, we just have more.