4 – Divided Attention

divided attention trying to do two things at the same time

Some dual tasks cause no interference.

Example

Walk and chew gum

Some dual tasks cause interference.

Example

Drive and talk on cell phone.

Question

What kinds of tasks can be done concurrently without interference?

Demo Task A = Rotate right arm clockwise.

Task B = Rotate left arm counterclockwise

A & B no interference

Demo Task A = Rotate right arm clockwise.

Task B = Rotate right leg counterclockwise

A & B interference

Typical Divided Attention Experiment

3 conditions: A only

B only

dual-task (A and B at the same time)

dual task interference occurs if

Performance on A is better during A-only condition than during dual-task.

or Performance on B is better during B-only condition than in dual-task.

Laws prohibiting cell phone use while driving (as of 2013)

For experienced drivers, hands-free phone banned in 0 states.

Handheld phones banned in 10 states (but not Florida).

Texting while driving is banned in 41 states, including Florida.

In Florida, texting is “secondary offense”

(Source - Insurance Institute for Highway Safety)

www.iihs.org/laws/cellphonelaws.aspx

 

Left blank

 

Driver Distraction

Common belief: Driving is unaffected by driver’s use of hands-free phone

Typical explanation. The two tasks are very dissimilar.

driving car visual, spatial, manual

talking on hands-free phone oral, verbal, auditory

Laws conform to this belief.

Use of handheld phones prohibited in many states.

Use of hands-free phones allowed in every state (as of 2011).

Does this make sense? Or do hands-free phones also cause interference?

Driver Distraction experiments

Task

Ss drive in simulators

Ss must avoid cars, pedestrians.

Typical Measures

Braking time

Number of collisions

Common Conditions

driving while talking on handheld phone

driving while talking on hands-free phone

driving while talking to passenger

driving while reading text

driving while composing text

driving intoxicated

Experiment: Effect of hands-free phone

Ss drove in simulator. During dense traffic, car in front stopped unexpectedly.

Sample result Brake Time (ms)

no distraction 933

talking on hands-free phone 1112

Conclusion

Interference is attentional – not just manual.

(Strayer et al., 2003)

Experiment: Hands-free phone vs. Intoxication

Ss drove in simulator. Car in front suddenly stopped.

One result:

Brake time (ms)

intoxicated (BAC 0.08%) 779

hands-free phone 849

(Strayer et al., 2011)

Experiment: Is hands-free phone worse than talking to passenger?

“… Passengers tend to adjust their conversation based on driving difficulty; often helping the driver to navigate and identify hazards on the roadway and pausing the conversations during difficult sections of the drive. By contrast, this real-time adjustment based upon traffic demands is not possible with cell phone conversations.”

Strayer and Drews (2006, p. 130)

Experiment

S drove in simulator; was asked to exit the highway at rest stop “about 8 miles away”

S listened to friend tell story

Result: Drivers who Missed the Exit

driving alone 4%

passenger conversation 12%

hands-free cell phone conversation 50%

(Drews et al., 2008)

Other findings from driver distraction studies:

Most Ss overestimate their ability to drive while using a hands-free phone.

Hands-free phone as bad as handheld phone

Four 1-minute videos (bottom of webpage)

www.psych.utah.edu/lab/appliedcognition/news.html

Strayer and his colleagues (2001, 2003, 2006, 2009)

Bottleneck Experiments

Driving and talking are hard tasks.

Can interference occur if tasks are dissimilar and easy?

Procedure

Task 1 S1 Hear high or low tone R1 say “high” or “low”

Task 2 S2 See “A” or “B” R2 press left or right key

RT1

RT2

Ss practiced task 1 alone, task 2 alone, and dual task.

Practice trial data were excluded from final analysis.

Results: RT2

Task 2 alone ~ 500 ms

Task 2 in dual task ~ 700 ms

Conclusion

Even two easy, dissimilar tasks can yield massive dual-task interference.

(Pashler, 1984; Welford, 1941)

Why does Task 2 take so long? That is, in which stage does interference arise?

Perception Response Selection Response Production

Perceive high tone Since tone is high, say “high” Say “high”

Perceive “A” Since letter is A, press left key Press left key.

Hypothesis: The mind can perform only one “response selection” at a time.

Two findings showing bottleneck during Response Selection

Manipulation Effect on RT1 Effect on RT2

----------------- ------------------ ------------------

Task 2 Perception made harder none none(e.g., “A” appeared blurry)

Task 2 Response-Selection made harder none increased(e.g., if “A” then press B key)

(Pashler, 1984)

RT2

lag wait

RT1

Bottleneck Practice Questions

Predict the effect of each manipulation on RT1 and RT2

Manipulation RT1 RT2

Harder P1 increase increase

Harder P2 none none

Harder RS1 increase increase

Harder RS2 none increase

Harder RP1 increase none

Harder RP2 none increase

RT2

lag wait

RT1

Another Prediction: Increasing lag by 1 ms should shorten RT2 by 1 ms (up to a point)

100 100

RT2 = 550

lag wait

50 150

RT2 = 600

lag wait

Another Bottleneck Experiment

Same Basic Procedure

Task 1 S1 Hear high or low tone R1 say “high” or “low”

Task 2 S2 See “A” or “B” R2 press left or right key

Lag between S1 and S2 varied from 50 to 900 ms

(continued)

RT1

RT2

Prediction of bottleneck theory

Actual data

(Pashler, 1984)

RT2

Lag between S1 and S2

Slope = -1

RT2

Lag between S1 and S2

What dual-tasks can be done without interference?

Distinction

choice-RT task

Examples Tasks used in bottleneck studies

simple-RT task

Examples

hit key as soon as light appears

catch ruler dropped between your fingers

Two choice tasks interference

Two simple tasks no interference

One simple, one choice no interference

Perception Response Selection Response Production

Perception Response Production

Summary of Bottleneck Studies

Many easy tasks require “response selection.”

If people try to do two such tasks concurrently, one task must wait (bottleneck).

The bottleneck occurs if both tasks need “response selection”

Task Switching

If we cannot do two things at once, can we at least switch back and forth?

Yes, but switch is costly

task 1 alone --------------------------

task 2 alone --------------------------

Switch without cost1 --------

--------- ---------2 ---------

--------- --------

Switch with cost1 ---------

------------------

2--------------------------

Data show that switch cost is high.

Experiment

Ss shown two category names (e.g., Insect, Vegetable)

Ss immediately say 4 examples of each category as quickly as possible

Ss told in advance that responses should be:

blocked A AA A BB B B

antgnat moth fly bean corn

pea yam or

alternating A BA B AB A B

antbean gnat corn moth pea

fly yam

Result

Alternating is almost twice as slow!

Conclusion

Switching is costly.

demo

Reversed Normal

 

Mental Rotation demo

Indicate whether F is mirror-reversed or normal

 

Mental Rotation

Letter Rotation Experiment

Indicate whether letter can be rotated so that it looks normal.

no yes

IV = amount of rotation 135° 30°

Results

Interpretation Ss “mentally rotated” object at constant rate

800

RT(ms)

500

0 180 rotation (degrees)

 

Demo: For each pair, indicate whether two images depict same object.

yes

yes

no

 

More examples

yes

yes

no

3D mental rotation experiment

Ss saw pairs of images depicting 3D objects.

For each pair, Ss indicated whether two images depict same object or different objects.

When images depicted the same object, it was rotated.

within the plane or in depth

(continued)

Results

Interpretation

Object is mentally rotated

(Shepard & Meltzer, 1971)

Demo –digit span forward

3 8 7 2

4 6 1 9 4

5 3 7 8 6 9

6 6 9 4 5 2 8

 7 4 2 6 9 8 5 7

 8 8 1 6 3 7 2 4 9

 9 6 2 5 7 3 4 9 8 1

 10 9 3 8 2 4 7 1 5 3 6

 11 5 8 1 4 7 9 3 2 6 1 7

 12 6 9 5 1 7 2 8 5 3 7 2 4

 

Demo –digit span backward

2 7 3

3 6 9 4

4 3 8 5 2

5 5 3 9 8 1

6 7 5 9 8 3 4

7 9 8 4 1 3 6 8

8 5 1 7 3 6 7 9 2

 

Span Task

S hears 3 – 10 items (digits or words), typically at a rate of item per second

Immediately afterwards, S tries to repeats items aloud in same order

DV = span = number of items S can report in the correct order

Digit span task used on many IQ tests.

(e.g., Baddeley, 2003; Cowan, 2005)

How do people perform the span task?

rehearsal loop

Mental mechanism that is used to rehearse verbal info (silently or aloud)

Examples

Rehearsing a phone number until you have a chance to jot it down

Rehearsing someone’s name so you’ll remember it later.

Mental arithmetic

23 x 15

= (20 x 15) + (3 x 15)

= 300 + 45

= 345

 

 

Does span increase if items rhyme?

 

whoblueviewdocoupyoutrue

 

booklovetrapwaitbirdheadwall

 

rakebakemakelaketakecakefake

 

ropedarkhandmoonsoftfearedge

Word Span Experiment

Each list included 7 words.

Two kinds of lists: rhyme and non-rhyme

Results rhyme span < non-rhyme span

This is the phonological similarity effect

Effect occurs even if rhyming words are spelled very differently

crew, who, moo, through

Thus, when using rehearsal loop, information is stored as sound, not image.

(e.g., Baddeley, 1986)

How many items can you hold in your rehearsal loop?

7 ± 2 ?

Demo

6 words on each list

 

associationopportunityrepresentativeorganizationconsiderableimmediately  

 

sumhatewitbondyieldtwice

 

Another Word Span Experiment

Ss perform word span task

Each list included 6 words.

Two kinds of lists: short words (1 syllable each) and long words (5 syllables each)

Results

long-word span < short-word span

This is the word length effect

Conclusion

span = amount of info that can be said in about 2 s

The magic number 7 is wrong

 (Baddeley et al., 1975)

If magic number is wrong, why does digit span equal about 7?

Observation

IQ tests reveal that English kids had greater digit span than Welsh kids

Experiment

Welsh-English bilinguals tested in both languages

Results: English digit span > Welsh digit span

Why? English digit words are shorter than Welsh digit words

(Ellis & Hennelly, 1980)

Arabic Digits1. wahed2. ithnan3. thalatha4. arba5. khamse6. sitta7. seba8. thamanya9. tesa10. ashara 

 

Cantonese Digits1. yat2. yih3. saam4. sei5. ngh6. luhk7. chat8. baat9. gau10. sahp

 

Prediction

If digit span = 2 sec, then digit span should vary by language so that

digit span = number of

digits that can be said in 2 s

Cross-Language Digit Span Experiment

E measured how fast Ss could read digits in their native language

E measured Ss’ digit span in their native language

 

ResultsLanguage syllables per digit words read in 2

s digit span

Arabic 2.3

5.4

5.8

Spanish 1.6

7.0

6.4

English 1.2

7.6

7.2

Thus, digit span = number of digits that can be said in about 2 seconds.

Conclusion

Magic number 7 is merely an artifact of the English language.

(Naveh-Benjamin & Ayres, 1986; see also Stigler, Lee, & Stevenson, 1986)

Sign Language

In ASL, some words take longer to sign

Long signs include PIANO, BICYCLE, CROSS

Short signs include TYPEWRITER, MILK, CHURCH

Word span is shorter if signs are long.

(Wilson & Emmorey, 1998)

The End

Sometimes, we need to “work with” or “hold information” that is visual

Questions

How many windows are on the front of your house? 

If you’re traveling south, and you must turn east, do you turn left or right?

Demo

1 7 7 6 1 4 9 2 1 9 4 1 1 7 7 6 1 4 9 2 1 9 4 1

 

chunking increases span by reducing number of items  

 

 

visuospatial scratchpad

Used for temporary storage and manipulation of spatial and visual information

Examples

Visualizing the campus layout in order to give someone directions.

If you’re traveling south, and you must turn east, do you turn left or right?

 

Sample Task

 

1 2 3 4 5 6 7 8 9 10 11 1213 14 15 16

Are visual-spatial scratchpad and rehearsal loop truly different mechanisms?

Experiment

Dual-task

Results

Both verbal hard

Both visual hard

One of each easier

(Baddeley & Hitch, 1974; Brooks Cocchini et al., 2002; Fougnie & Marois, 2006)

 

Demo Verbal Task As the woman chased her poodle, her poodle chased a cat 

Spatial Task        

Spatial Response point to “yes” or “no” Verbal Response say “yes” or “no”

(Brooks, 1968)

 

What is meant by analog?

Example

On hard drive, similar images have dissimilar representations (digital)

12:59:59 and 1:00:00 look similar on analog clock (but not on digital clock)

 

Implications of mental rotation studies…

1. Mental imagery can be studied objectively and quantitatively (without relying on introspection).

2. Linear RT growth suggests that images are mentally rotated.

 

demo

How many left turns as you

drive from ● to ▲ ?

… right turns?

 

Subtraction method has untenable assumptions.

1. Stages are non-overlapping.

For example, RP might begin before RS complete.

2. Stage durations are independent.

  Duration of RP might depend on duration of RS.

Still, in some cases, subtraction method has utility.

 

Demo

How fast does sensory info (e.g., ankle twist) move from ankle to brain?

Compare ankle and shoulder: E taps S’s ankle or shoulder; S raises finger  

 Since d = r t d

r = ------ t

1.5 m = -------- = 150 m/s 0.01 s

Fact from textbook

Impulse along myelinated axon can move as fast as 120 m/s = 260 mph

Demo – semantic similarity

Same task as before.

 

catdogpighorsegoatsheepcowhen

 

skynailnurseboxlightnoiseshirtgrass

 

Some details from study by Naveh-Benjamin and Ayres (1986)

Syllables Digit Reading Aloud rate

Language Per Digit Span (in digits / 2 sec)

English 1.1 7.3 8.0

Spanish 1.5 6.5 6.2

Arabic 2.5 5.5 5.2

 

 

Mental Rotation Experiment

Ss first became familiar with several irregular polygons.

On each trial, Ss saw one of the polygons or its mirror image.

Task It is the same or mirror-reversed?

(continued)

Alternative version: stimuli = irregular polygons

(

 

rotation

 

What about 3-D mental rotation?

(

 

Visual tasks and verbal tasks are controlled by different mechanisms.

Evidence

dual-task studies

Both verbal very hard

Both visual very hard

One of each easier

KF (motorcycle accident)

visual storage okay, verbal storage imparied

(Baddeley & Hitch, 1974; Brooks Cocchini et al., 2002; Fougnie & Marois, 2006)

latent bottleneck (Lien et al., 2006)

RT2

0 200 400 600 800 S1 - S2 Lag

Why exactly does this dual-task interference occur?

Traditional Explanation

Resources are limited, so progress on at least one task is slowed.

Task 1 alone |------------------------------|

Task 2 alone |------------------------------|

500

Dual-Task

Task 1 |------------------------------|

Task 2 |---------------------------------------------|

700

(continued)

Bottleneck Theory

During certain stage in completion of Task 2, progress completely stops.

Task 1 alone |------------------------------|

Task 2 alone |------------------------------|

500

Dual-Task

Task 1 |------------------------------|

Task 2 |------- wait -----------------------|

700

In other words, at some point, Task 2 must wait for Task 1.

Experiment

Ss saw between 1 - 6 “study letters” at rate of one per sThen Ss saw target letter.Ss hit yes or no key, depending on whether target was a study letter.

For target-absent trials, task included :

Perceive TargetMentally scan study letters, one at a timeSelect response (“no”)Produce response

Results: Each additional study letter increased RT by 38 ms

Conclusion : Ss “mentally scanned” letters at rate of one per 38 ms

(For complicated reasons, this interpretation is no longer popular.)

(Sternberg, 1966)

 

Bottleneck finding conflicts with traditional view of dual-task interference:

limited resource theory

tasks can be done concurrently and without interference if demand < supply.

(e.g., Kahneman, 1973; Pashler, 1984; Welford, 1941)

 

 

Everyone knows what attention is.

(James, 1890)

A formal definition of the term “attention” is not presently available…

(Pashler & Johnston, 1998)

Demo Even two easy tasks can cause dual-task interference  Easy: Pat head and stomachHarder: Pat head, rub stomach  Easy: R hand CW, R foot CW. Harder: R hand CW, R foot CCW.

 

Sample Experiment 

Ss shadowed 10 words presented to one ear.

At same time, S tried to remember 10 other items simultaneously.

1) seen as pictures

2) seen as words

3) heard as words (in other ear)

Then Ss tried to recall the 10 non-shadowed items.

Results

(3) was hardest; (1) was easiest.

Conclusion

Task similarity increases dual task interference.

(Allport, Antonis, & Reynolds, 1972)

Statistic

In 2009, cell phone use was a factor in 995 driving fatalities in US (NHTSA).

3 possible locations of bottleneck

Perception Bottleneck

| ------ P1 ------- | ------------- RS1 ---------- | -- RP1 -- |

lag |--wait--| ------ P2 ------- | ------------- RS2 ---------- | -- RP2 -- |

Response-Selection Bottleneck

| ------ P1 ------- | ------------- RS1 ---------- | -- RP1 -- |

lag | ------ P2 ------- | ------ wait -------| ------------- RS2 ---------- | -- RP2 -- |

Response-Production Bottleneck

| ------ P1 ------- | -------------- RS1 ---------- | ------ RP1 ----- |

lag | ------ P2 ------- | ------------- RS2 ---------- |-- wait--| ------ RP2 ------- |

 

 

Bottleneck Experiment 1

Ss did two choice-RT tasks described in previous study (see/press & hear/say).E varied difficulty of P2

Hypothesis Predicted Effect on RT2

Bottleneck during Perception increase

Bottleneck in Response Selection no change

Results no change

Conclusion no bottleneck during Perception

(Pashler, 1984)

 

 

Bottleneck Experiment 2

Ss performed the two choice-RT tasks described in previous study.E varied difficulty of RS2

Hypothesis Effect on RT2

Bottleneck during Response Selection increase

Bottleneck during Response Production no change

Results increased

Conclusion Bottleneck does not occur during Response Production

(Pashler, 1984)

 

 

Practice Questions

Assume bottleneck in Perception stage. Indicate effect on RT1 and RT2

Manipulation RT1 RT2

Slightly harder P1 increase increase

Slightly harder P2 ---- increase

Slightly harder RS1 increase ----

Slightly harder RS2 ---- increase

Perception Bottleneck

| ------ P1 ------- | ------------- RS1 ---------- | -- RP1 -- |

lag |--wait--| ------ P2 ------- | ------------- RS2 ---------- | -- RP2 -- |

Assume bottleneck in Response Production stage.

Indicate effect on RT1 and RT2

Manipulation RT1 RT2

Slightly harder P1 increase increase

Slightly harder RS1 increase increase

Slightly harder RS2 ---- ----

Slightly harder RP1 increase increase

Response-Production Bottleneck

| ------ P1 ------- | -------------- RS1 ---------- | ------ RP1 ----- |

lag | ------ P2 ------- | ------------- RS2 ---------- |-- wait--| ------ RP2 ------- |

 

 

An analogy showing why initial slope of -1 supports bottleneck

Suppose two customers visit ATM and each requires exactly 1 minute

ATM can handle only 1 customer at a time, so bottleneck occurs

RT2 equals the time Customer 2 is at the ATM

Lag between their arrival Customer 2 time at ATM (including wait)

0:15 1:45  

0:30 1:30

0:45 1:15

1:00 1:00

1:15 1:00

1:30 1:00

Thus, adding 15 s to lag simply adds 15 s to RT2 unless Customer 1 has already left

 

A diagram showing why initial slope of -1 supports bottleneck

S1 R1

Task 1 |----------------------------------- |

S2 R2

Task 2 |….lag….|- - - - -wait - - - - -|---------------------------------- |

S2 R2

|………lag………. |- -wait - |---------------------------------- |

Remember: RT2 = time between S1 and R2

So, add 1 ms to lag shorten wait by 1 ms reduce RT2 by 1 ms

 

Actual Data:

(Pashler, 1984)

RT2 (ms)

Lag (ms)

Optional: Results of last two studies inconsistent with P or RS bottleneck

Perception Bottleneck

| ------ P1 ------- | ------------- RS1 ---------- | -- RP1 -- |

lag |--wait--| ------ P2 ------- | ------------- RS2 ---------- | -- RP2 -- |

Response-Selection Bottleneck

| ------ P1 ------- | ------------- RS1 ---------- | -- RP1 -- |

lag | ------ P2 ------- | ------ wait -------| ------------- RS2 ---------- | -- RP2 -- |

Response-Production Bottleneck

| ------ P1 ------- | -------------- RS1 ---------- | ------ RP1 ----- |

lag | ------ P2 ------- | ------------- RS2 ---------- |-- wait--| ------ RP2 ------- |

 

 

Illustration of CEO 

Dual-task X hear/say one passage & read/type another  Dual-task Y hear/type one passage & read/say another

Which dual-task creates more dual-task interference? Y

 

  Example

For both tasks in X, stimulus = response Hear “iz”, say “iz”

For both tasks in Y, stimulus response Hear “iz”, type “is”

Thus, both tasks in Y require a more difficult “response selection”

(Shaffer, 1975)

Results

Data are linear.

intercept = 1 s

slope = 1 s / 60°

Every additional 60° of stimulus rotation increased RT by 1 s

Interpretation Ss “mentally rotated” mental image at rate of 60° per sec

Claim Mental rotation data are observable measure of “mental imagery”

(Shepard & Meltzer, 1971)

4

RT(s) 1

0 180 rotation (degrees)

Demo

rectangle trapezoid parallelogram

 

Demo

pentagram pentagram within pentagon hexagram

 

Mental Imagery

Many people believe that they can form mental image of familiar object.

Experiment

Ss were asked question about simple shape

Example

Does this include a rectangle?”

Two Conditions Performance

Answer question while looking at shape. Perfect

See shape. Form mental image. Answer question. Poor

ConclusionPeople overestimate their ability to form mental image

(Reisberg, 1993)

However, “mental imagery” does appear to have a visual component.

Experiment

Ss told to “think about” a cat OR “form mental image” of a cat

While they did that, Ss were asked:

Does the cat have a head?

or

Does the cat have claws? 

Results Question Answered More Quickly

-----------------------------------------------

Thinkers claws

Imagers head

 (Kosslyn, 1976)